MG Ashley/Bonneville Midget.

...Or Useful Stuff for Spridget owners.
Looking around the web, there seem to be a lot of "Here's my Midget" sites, many of which are great but very few seem to deal in interesting and useful data which isn't available from Haynes or Practical Classics. As one rusty sill looks very much like another and most of us don't need to go further than the garage to view a car in pieces I'll try and concentrate on the variations from standard spec. which I've made.
Health and Safety Disclaimer:  Much of what follows contains descriptions of modifications to the car which are non- standard and not approved by the manufacturers. While every effort has been made to ensure accuracy and point out safety implications on the way, it is UP TO YOU to determine whether any of this work is safe to do and within the capabilities of the person carrying out the work. They may also be illegal in your country or state. So don't sue us if you end up in the ditch!...

  • History of the car
  • More Legroom
  • Strengthening and stiffening the bodyshell
  • Fibreglass bonnet
  • 'Adding Lightness'
  • Suspension mods
  • Gearboxes
  • Wheels and Tyres
  • Engine mods - normally aspirated 
  • Supercharging
  • Other modifications
  • Bookshelf



    History of the Car:
    I bought the car in 1985 with just over 100,000 miles on it and six previous owners. A typical well used Midget of the time it was in pretty good shape, shiny and mechanically sound. I bought it from a specialist dealer in Guildford and paid a very hard- saved £1750 for it- towards the top end of the market at the time but worthwhile as it was solid, usable and reliable. - Important when you're an 18 year old student with limited mechanical experience  using it as everyday transport.
    I spent that summer of '85 just playing with my new toy. both driving it around and tinkering with the niggly little things. I learned a huge amount just by looking and checking things in the Haynes manual, tweaking and tightening things which were wrongly adjusted or loose and cleaning and repainting dirty or rusty fittings.
    Over the years I repaired or replaced most things, except the engine, which was always pretty strong.  When it needed a rebuild I had the head reworked- ported, skimmed etc. by Oselli Engineering of Oxford. I also fitted a Kent 266 cam, freer flowing exhaust system and manifold and modified the inlet manifold and carbs to help the airflow. (see the engine section below for more details). In 1994 I acquired a "barn state" Frogeye, which I restored and still own. I am also on my second Jaguar XJ6 which I use most days. However I've never felt the slightest urge to get rid of my Midget. - I love driving it too much. In 2001 I finally started the "proper" restoration, stripping every single nut and bolt off, getting the body dry stripped back to bare metal and welding in new floorpans, sills etc. etc. plus various modifications and improvements, all listed below. The car was back on the road in July 2002 (after far too long in the paint shop!) and was well worth the wait.

    What's an "Ashley Bonneville Replica" then?
    after a truly memorable  trip to the Utah Salt Flats in 2001, (see features)  I happened to be reading John Sprinzel's book "Spritely Years" where I found a reference to Tommy Wisdom's 1960 Alpine rally car. Supercharged and painted metallic Ice Blue (the colour I'd always wanted to paint mine) Sprinzel's later called this a 'Bonneville' Sprite after the 1959 Shorrock -equipped MG record car. Obviously this was what I was building without even knowing it.
    Modifications for those of us who aren't midgets!

    As the 6'4" John Sprinzel said to me, "all very tall people should own one". Actually I suspect that very few shorties own them as if you are sensitive about your small stature you don't buy a car called "Midget", do you?
    I am 6 feet 6 inches tall. People queue up to watch me climb in and out of my car yet I am perfectly comfortable when driving it even for long distances. I don't think I could sleep in it (as I did once or twice as a much more flexible 19 year old!) but I'm happy with the driving position now. I have modified things slightly to make myself more comfortable.

    Seats:  These make the biggest difference. The bucket type seats on the Frogeye and early Midgets are the worst for the long-legged as they have very thick cushions and the back angle isn't easily adjustable. I drive my Frogeye with a much thinner cushion in the drivers' seat and replace it with the original one for show only.
    There have been a surprising number of seat types fitted over the years. As all the models from MK1 through to rubber bumper have the same interior dimensions, try sitting in different models at shows. There is a huge difference between new and old seat foams, especially on the earliest seats.
    On my car the best seats I have found are Midget Mk 2 / early MGB ones as the backs and cushions are the thinnest while still remaining comfortable. Raising the seat up on wooden spacers can give you more legroom (see the note below on floorpan mods) provided you don't then bang your head on the roof. Alternatively, putting wedge shaped spacers under the seats tips the angle of the seat back, giving more arm room and better thigh support. play around with wood blocks and see what works for the shape you are.

    Body modifications:The first mod is so worthwhile I can't believe I didn't do it years ago!  I have made an approx. 2" (50mm) deep trough in the driver's footwell about 320mm square. My heels rest on this lowered floor which alters the angle of the legs and gives a couple more inches of effective legroom, stopping my knee from hitting the dash. The difference in comfort this makes for the long-legged is just fantastic. Pictures and diagram below reproduced in the interests of reducing human suffering.

    The trough is made of 20 gauge/ 1mm steel sheet, spot welded together and then welded into a hole cut into the floor pan. the drain holes have deflector plates welded to the undersides so the water doesn't come back up!  There is still enough original floor on the right to enable the original throttle pedal to be retained but I find the pendant type shown here to be more comfortable. The 2" depth is arrived at as being about the deepest trough practical without reducing the ground clearance. The underside of the trough is now level with the exhaust height, so provided you can get over the speed bumps without dinging the pipe, the floor should also be safe.
    If you are long in the torso rather than the leg you could lower the seat area in the same way.
    NB:  This won't work if you have a left-hand drive car as the exhaust runs right under the floor.  I think the 1500 exhaust runs under the left side of the car too for most of its run (I've never been underneath one to look) but check.  The only way to run a footwell trough on a LHD car would be to re- route the pipe.

    The ideal solution to the whole legroom problem would be to move the seat further back. However the rear bulkhead is a complex structure and vital to the car's structure, so cutting and modifying its shape needs skill and high standards of workmanship to retain the strength of the car. I have seen it done, on the Huffaker racing Midget in California and can confirm it made a huge difference. Ed Huffaker is a fellow 'bean-pole' and reckons it was worth the considerable effort involved to get him sitting where he can control the car properly.

    Moving The Controls.
    The brake master cylinder is spaced off the pedal box by about 1/4" (6mm) using thick washers (or a spacer plate for the engineering purist). This has the effect of dropping the position of the pedal by about 1.5" (37mm) further away from the driver. This has no effect on the way the pedal works except that the total pedal travel is reduced. The pedal is in the solid full on position  well before getting near the floor. If the pedal is going to within 2" of the floor you have serious brake problems already!  There is still plenty of pedal travel for things like bleeding the brakes.
    This brings the brake pedal pad in line with the throttle which makes driving easier. My feet are far too big to manage any serious heel-and-toeing in this car, but I can change pedals faster and therefore drive more smoothly. Obviously I can't modify the clutch pedal this way as the full pedal travel is needed

    I've modified the throttle pedal from the standard 'organ stop' type  as  my foot only touched the top corner of it anyway.  The aluminium pad is curved slightly to allow the foot move smoothly and spaced up from the lever bar to sit at a comfortable height. (see the picture above)

    The steering wheel is about 1" smaller in diameter than the original '72 MG one. This gives me 1/2" more knee room on both sides and makes climbing in and out easier. I would hesitate to fit anything much smaller as the steering effort goes up surprisingly quickly (especially on wide tyres) and makes the car feel a bit twitchy at least until you get used to it. The standard Frogeye wheel is huge which makes the cockpit very cramped but it makes the steering is beautifully light and precise.
    It is possible to move the steering wheel away from you a little (as was done on some of the works and Sprinzel rally cars) but it is already pretty close to the dash and you soon run out of knuckle room.  You need to modify the wheel boss by machining it- difficult with any of the standard wheels as the boss is a hollow casting but simpler if you have an aftermarket one like a moto-lita etc. with a nice, solid boss which can be machined down. Alternatively just fit a wheel with less "dish" to the spokes.
    Moving the wheel towards you will give extra knee room, but at the expense of elbow clearance. as it is so close already it is unlikely to help much but if you are exceptionally long in the leg like me it may work. you can easily experiment by spacing the wheel away from the boss with washers and longer bolts (although be sure to use something completely solid and safe like a properly machined spacer ring before driving the car.

    Notice I have made no mention of altering the length of the steering column by cutting, re-welding etc. If you have the necessary skills to do this then go ahead if you are ABSOLUTELY confident you know what you are doing. Just bear in mind that this is allegedly what killed Ayrton Senna, and that was done by Formula One engineers...

    Stiffening and strengthening:
    The Sprite/Midget body tub is essentially a miniature version of a D-type Jaguar's. This made for a very light, stiff structure by the standards of the day, and one which stood up well as little changed in over twenty years of production.  However there are a couple of tweaks which can be done.
    Firstly though. The whole of the car's structure must be 100 per cent sound. This is a true monocoque and almost every part is a load bearing structure. Therefore if your car needs any welding at all, get it done absolutely right first. The ideal method is during a full restoration, to blast clean the whole structure and having cut out and replaced rotten areas (patches are a stopgap measure at best and downright dangerous at worst!) then strengthen many of the spot welded seams by mig-welding a seam along them. 
    Areas to strengthen by this method are:
    Sills (top and bottom edges), edges of rear wheel arches (where they join the box sections inside the boot and behind the seats) , rear bulkhead joints (especially around spring hangers), the panels on the outer sides of the footwells (inside the front wings), the rear spring mounts (inside the boot on half elliptic sprung cars) and the front chassis rails either side of the engine. 
    You can beef up the front structure by welding a piece of thick 1"x1" angle under the triangular box sections (see picture) joining the suspension mounting area down to the front footwell. Tim Fenna of Frontline Developments recommends this to make the front end structure more rigid. 
    The front lower crossmember is in front of the sump, -where tyre fitters always put their trolley jacks, denting the plate underneath. As many people do, I cut this lower plate out as it was seriously concave. Before replacing it,  I  added three pieces of 1" square tube running fore and aft, inside the box so the new plate wouldn't get bent by jacks. Drain holes in the lower surface allow water to escape.

    Spridgets generally don't suffer from scuttle shake unless they are seriously corroded. However it is worth adding a bracing bar of 1/2" (13mm) tubing at the centre and two small fillets between the bonnet hinge boxes and the scuttle top. These make the whole of the scuttle totally rigid and don't interfere with the positions of the wiper rack or wiring etc. under the dash. Similarly, seam welding along the back of the horizontal bulkhead joint reinforces the spot welds and helps prevent the moisture getting in. Some early competition cars had a welded- on tube running all along this joint.

    If you are running an electric fan and have space in front of the engine,  a bracing rod can be fitted between the front dampers or their mountings although it needs to be made removable so you can get the engine in and out past it! A similar rod, joining both rear wheel arches, or linking up to the rear edge of the cockpit  can also be fitted, although at some cost to boot space.

    Lastly don't underestimate the strength of the front inner wings. These tend to rot or crack at the rear corner where they join the very tip of the sill. As the joint here is generally fiddly to do and can involve an awkward looking lump of weld, people tend to ignore it. However if this area isn't firmly attached to the sill the inner arch is not triangulated and will flex about. You should be able to stand on the inner wheelarch easily even without the mud shields etc. in place. When they are, they form an extra line of bracing, through the radiator uprights (and the radiator!) all round the front of the car. Making this area strong may not do much to the car's actual stiffness but it will feel much more solid.

    Adding Lightness:
     This is quite tricky in terms of the actual structure. If you look at race cars you will see lots of butchery- inner wheel arches and boot floors removed, footwell panels replaced in aluminium, fibreglass rear ends etc. etc. This is fine for the track as the cars are running on  a very smooth surface and for small mileages. I would tread very carefully for a road going car though. You can replace the rear wings or the whole rear end by bonding in fibreglass parts but they will need to be much thicker and heavier than the racing versions if you are to avoid the gel coat and paintwork cracking the first time you go over a bumpy road.

    The opening panels are another story. Fibreglass boot lids and doors offer a decent saving in weight although you may find it difficult to fit all the window winder mechanisms etc. as most of these parts are sold for racing and are therefore fairly basic.  Standard bonnets can be had with all the necessary fittings and internal bracing to bolt straight in place. The 'one piece" front ends, i.e. bonnet plus wings offer a big saving in weight as you are replacing these panels plus the front valance assembly too.
    Fibreglass isn't easy to work with though. Getting a good fit is difficult and with some panels may be impossible (see the account of my restoration!) as you can't bend it and bash it like steel. Older panels with cracked gel coats need a huge amount of work to prevent the cracks reappearing and most of the race weight panels will need extra layers to make them stiff enough for road use. Think carefully just how much weight you will be saving and whether the time and money would be better spent on another area. The majority of the weight of the doors for example is in the quarterlight and window equipment, not in the steel shell.
    Lastly it is hard to get a perfect paint finish on fibreglass as it flexes and is easily damaged when rubbing down or polishing. Having said all that, every time I look at my Ashley front end I'm sure it was worth all the considerable grief required!

    The Fibreglass Bonnet:
    For the record- since everyone asks, this is an early Ashley Laminates one. Made in the very early 'sixties for the Frogeye it is obviously heavily influenced by Italian design (it as been likened to a baby Ferrari!) and of course the Jaguar E-type. The central rib is essentially a strengthening device, similar to the pressing on the VW Beetle, but it looks good, and provides a raised area above the scuttle line. There are air vent holes here, added by me but apparently original as the period ad says they supply warm air to the screen..
    The hinging arrangement is very neat with a steel tube bonded into the structure at the front. This takes two short tubes with brackets which bolt onto the front subframe using the holes previously used by the bumper supports.  Two V grooves in the rear edge engage with nylon blocks in the scuttle channel to stop it shaking. Similar  nylon blocks on the sill tops hold the bottom edges in position.
    If you look at the air intake opening you can see it was originally intended to take a Frogeye grille, with the winged Austin Healey badge above. I left it off as the car is schizophrenic enough already. The MG badge is from  a pre-war car  (PB, TF etc,) and the grille mesh is the expanded aluminium stuff beloved of the boy racers. The number plate letters are fixed directly to it. - an idea pinched from the Lotus Elan. The lights are transferred straight from the original car if a Frogeye, albeit with extra earth return wires as the current won't find its way home through fibreglass.

    The hard top isn't Ashley as these look rather unfortunate! Although an unknown type it sets off the front shape very well. As with the other GRP panels it has had extra layers of glass bonded to the inside to strengthen it.

    Lightening parts:
    Depending how obsessive you get (I'm second only to Rob in my habit of weighing parts all the time) you can save a good deal of weight by attention to detail. Drilling non- structural parts can make them 10% (or more) lighter fairly easily and replacing things in a lighter material often helps. Aluminium is approximately 40% the density of steel and many parts can be re made or bought. Here are some examples:
    The engine backplate can  be replaced with an alloy one, available off the shelf at Moss etc., this will save about  2.5kg (NB: this is not allowed in some classes of racing)
    Aluminium cylinder heads are available, although fearsomely expensive and not always legal on race cars they offer better cooling properties and replace that big ol' lump of cast iron with something about 8 kg lighter.
    I rebuilt my heater box in aluminium. Although rather extreme in terms of the work (!)  involved this does save a bit of weight. You may find them for sale from places like Cambridge Motorsport or Ashley Hinton.
    Aluminium radiators and fuel tanks are also available. It depends on how rich and/ or obsessed you are.
    Lightweight racing batteries are a possibility. -expensive though. Most racers reposition the battery lower in the car to help the handling.
    Lighter road wheels have multiple benefits as they reduce not only the overall but the unsprung weight. The rotational inertia is also reduced, improving braking and acceleration. Wire wheels are a little lighter than Rostyles and the hubs are smaller and lighter too.
    Side windows can be replaced with Acrylic / Plexiglass material which is roughly half the weight. It's generally illegal to do the windscreen though and you need to be careful to avoid scratches.
    If you dare, remove the spare wheel entirely and carry an aerosol of "instant spare" type foam. This is actually standard on some new cars, including Lotus  though not such a good idea for long trips. The foam may not work on wire wheels if the inner tube gets seriously shredded. 
    Take a good look at what else you carry in the boot. A well- thought out set of breakdown tools is useful and can be fairly small.  Don't be tempted to lighten the jack!

    Uprating the car:
    Ever since the first Frogeye came out in 1958, people have been modifying their cars to make them go faster. The A series engine can be tuned to produce over 200bhp, with varying degrees of reliability. First port of call is the A series Bible: "Tuning BL's A Series Engine" by David Vizard. This covers virtually every size, type and configuration of the engine ever built and explains in no- nonsense terms what will and won't work. He also stresses the need to set engines up on a rolling road. This is the one step which separates serious tuners from the dreamers and bullsh***ers, and real horsepower from pub horsepower  ( Pub hp = approx 1.5 x True hp)
    Also think carefully about what you want from the car as there are different sorts of "fast" . A  race-spec engine will produce a nice impressive number at the top of the rev range but is likely to be off-cam and virtually undriveable in traffic.  A millder state of tune which gives a fatter torque curve at the expense of top- end power is likely to make for faster times and a more enjoyable car on roads rather than tracks.

    Brakes:  While an uprated engine is always great, a lot of driving enjoyment can be gained from more powerful lights, horns (!) and brakes. Halogen headlights are a must in modern traffic, plus you can actually see things at night when it's raining!  A decent air horn (although please, not the tune-playing variety!)  gets the attention of Volvos etc. who tend to overlook such a tiny car however fast it is approaching.  Brakes are usually mentioned alongside engine tuning with the maxim "don't start what you can't stop" and this is absolutely right.  However, really good brakes make any car more rewarding to drive as well as reassuring for emergencies. I have Frontline Developments' 9" Supersport disc kit on my car. This uses great big cross-drilled discs, larger callipers and uprated (EBC greenstuff) pads, really hauling the car down from speed in a well controlled progressive way. Fantastic modification, highly recommended for road and track.

    Pretty much everyone agrees that the standard Spridget front suspension is pretty terrible. In perfect condition it works well, but the antiquated design means that even with regular greasing it will wear pretty rapidly. The main problem is the use of the lever arm damper as the suspension top link. This is subject to a lot of twisting loads (you can feel it moving under  really heavy braking) and as soon as the top trunnion bush starts to wear, so does the lower fulcrum pin,  the kingpin bushes, the inner fulcrum rubbers etc. etc. until it fails the MOT. The Armstrong/ Girling lever arm type damper is hardly cutting edge technology either and the internal parts wear fairly quickly (very quickly on exchange- refurbished units) necessitating changing, or the time-honoured bodge of adding heavier oil like EP90 to the reservoirs. 
    At the risk of sounding like 'Advertorial' for the company, Frontline's front suspension kit is truly excellent. The top damper is replaced with a fabricated upper wishbone assembly which resists the twisting motion of the kingpin far better. A Koni telescopic damper is fitted, which is adjustable for rate. The coil spring, wishbone and kingpin assembly are all retained but these have a much easier life now they are held in position by the new top wishbone. 
    I also fit 'Superflex' Polyurethane bushes to the inner fulcrum pins and top trunnion bushes. Other brands are available and possibly cheaper but check two things: Don't buy any bushes with bubbles or holes in the material (inferior quality) and check the metal sleeves used are stainless. Mild steel bushes rust solid to the fulcrum pins, making their removal one of the all-time nightmare jobs.
    Polyurethane is better than the original rubber because it "tightens up" the feel of the suspension steering without transmitting lots of vibration. It doesn't soften with age like rubber or wear quickly like the Nylon /Nylatron stuff we used to use. 
    An alternative to the Frontline kit is to modify the damper so it has a longer pivot shaft and a second arm coming from the body, rather like an MGB damper. This is the method favoured by racers for years, especially in classes which demand the use of the original dampers.  Another method is a rose-jointed connecting link from a bracket on the body to the top trunnion, which works well but requires very careful positioning to retain the proper suspension geometry.

    Front anti-roll bars: If your car hasn't got one, go out and buy one immediately! it will make probably the biggest single difference to the handling and feel of the car, it is relatively cheap and you can fit it inside an hour without dismantling anything.  The idea is to pull down the unloaded inside wheel in a corner, keeping it in contact with the track and increasing front end grip.
    Anti roll bars come in a number of different thicknesses. The standard one fitted as a factory option is 9/16" . Uprated ones of 5/8" and 11/16" are available from the likes of Moss, all of which are suitable for road use. Competition cars can go up to 3/4" or even 7/8"  but this would be too much for a road car, increasing the understeer instead of reducing it.
    The bar mounts  in a pair of blocks, rubber as standard, neoprene for uprated. Competition cars run solid aluminium mountings which make the bar effectively stiffer but they are dreadfully noisy and counter-productive on normal bumpy roads.

    Increasing the amount of negative camber to 2 degrees neg. helps the turn-in on road cars (this amount is designed-in to the Frontline kit) without making it too 'darty' or nervous. Adjustable offset trunnions are available which allow you to play with varying amounts.

    Rear suspension:
    The standard setup uses leaf springs and a solid "live" axle, the problem being that the axle is avery heavy piece of unsprung weight, located only by the springs. In cornering, the body tries to move laterally over the axle, while rolling due to the weight transfer to the outside of the bend. The springs tend to twist, allowing the body to move laterally, but they also alter in length as they bend, causing the axle to move out of alignment. All of this is A Bad Thing as far as handling is concerned as the back end of the car is trying to steer and the movement of the axle sideways upsets the geometry of the car. What is required is an axle which moves freely up and down in relation to the body but not from side to side. It should also remain square to the body, i.e. not trying to steer the back end of the car.
    Early cars with quarter -elliptic springs have better sideways axle location as the short springs are very thick, resisting the twisting force and holding the axle in line fairly well. They also have radius arms which further control the location. However, the very short, multi- leafed springs have a lot of internal friction and a small radius of travel resulting a rather bumpy ride and less than subtle control.
    The later cars' half-elliptics improve the ride with  slightly smoother control of the axle. However, they twist much more and change in length as they bend, allowing the axle to move sideways and steer more. The absence of radius arms doesn't help either.
    Much of the unwanted motion can be removed by improving the bushes which locate the springs but first check all the mounting hardware is secure.  I once worked on a car with an undersized bolt replacing one of the rear shackle pins, allowing the spring to move ever so slightly sideways. The poor car shimmied along like a nervous duck and actually swapped motorway lanes under hard braking. Lethal...
    Fit polyurethane bushes to the rear spring shackles and the U-bolt locating pads. I have been unable so far to find a poly replacement for the 'Metalastik' bush which goes in the front spring eye but so long as the standard one and its pivot bolt are in perfect condition they should be OK.
    Frontline (yes, them again) do a very simple conversion which replaces the lever arm dampers with adjustable telescopic ones. This controls the axle motion better and is more comfortable. They have also developed their r "RTL" or rear Traction Link which is a very clever double-Watts linkage device which prevents sideways axle movement and lowers the rear roll centre by an adjustable amount. Result, more grip and less tendency to snap oversteer on the limit.

    A word about spring and damper adjustment.  The basic set up for the road should be "Stiff at the Front, Soft at the Back".  I experiment at track days with different damper settings.  By progressively firming up the rear shocks I made the car understeer a little less (by increasing the tendency to oversteer) until I over did it. - I knew I'd over done it when I spun!  - That was the limit for a smooth, fast track where the suspension can be set much harder. Keep the rear nice and soft for the road or you'll spin out on the first bumpy roundabout.

    Wheels and Tyres: Unless you are building an out-and-out racer don't go too mad on big wide wheels and tyres. The fact is that  the original designers did know what they were doing when they specified the standard sizes. Big changes to the diameter or width will affect the suspension geometry and apart from looking a bit silly on a Spridget, mega-wheels can also put a huge strain on things like wheel studs and bearings. Make sure you know what you are doing!

    165 x 13 tyres are about the widest that will go onto most standard wheels meant for 145s although check with your local specialist if you are in any doubt.  Remember to order 165s in 70 profile (145s are 80 profile) so the tyre diameter stays the same, or you will have a "Bigfoot" Spridget and seriously muck up the handling.
    Tyre makes are a matter of preference, although DON'T buy remoulds, budget brand tyres or anything with a lower speed rating than required for your state of tune.
    I have had various things over the years and my favourite are Michelins - very good dry grip with a nice progressive breakaway and excellent in the wet.
    Tyre Pressures.
    The  factory  manual states 22 psi front 24 psi rear for 145/80 section radials. 
    By all means try increasing these pressures but  don't  just assume that 'more is better' . After all, the factory would have specified higher pressures if the car performed better on them, wouldn't it ? . The only argument against this is that modern tyre compounds are very different from those available in 1958, or even 1980 so experimenting with a few psi may pay dividends. For the record, when I ran 145s I used to run them at 24 psi front /26 psi rear. 
    Wider tyres are a lot more difficult. I have found very little information or consensus on what pressures to run for my 165/70s.  I tried 24 psi front /26 psi rear and my (lightened) car hopped about like a ping pong ball!  At present I am running 23 psi front /25 psi rear which is much better although I am continuing to experiment. It does illustrate how sensitive these cars are to tyre pressures. 

    The early so-called '"smooth case" 'boxes are a bit dodgy. They use baulk-ring synchromesh which wears rapidly and doesn't result in the nicest changes even when perfect. Many of the parts are unobtainable so if yours needs major bits in overhaul you may be in trouble. A much better bet is the later box which has a ribbed case and much better synchro rings. A well- maintained one is an absolute delight to use. The problem comes when you increase the engine's power. Anything much above 80bhp and unless your gearbox is really perfect, it will start to complain. Reconditioned ones aren't necessarily good enough - I'd rather go to a specialist with a really good reputation and get them to rebuild my 'box or do it myself, rather than swap it for one done by a reconditioner.
    I got fed up with my car spitting out reconditioned 'boxes and anticipating huge amounts of lovely torque from the supercharger decided to put another make of box in. This would be much stronger plus having the benefit of FIVE Speeds.

    The basic choice is between a Toyota (Supra?) gearbox and a Ford Type 9 (or N) Sierra one. Since I did my conversion there is now a third option in a Nissan -based kit (available from the USA) The Toyota box is apparently very good and smooth but the problem is in finding one as they have all been snapped up by kit car builders and MG modifiers etc.! This, plus I knew I'd never live down the ribbing I'd get given my views on Japanese cars :-) meant I decided on a Ford unit. 
    The advantage is that the Ford Sierra box is fairly easy to find, although stocks are diminishing as everyone else has switched to using them. A scrapyard one with a couple of months guarantee should cost around £50-60. The bellhousing unbolts in a couple of minutes  and you are left with a reasonably neat and small transmission unit.  The gear ratios are identical except first which is very slightly lower, plus a lovely long- legged fifth which makes very high speed motorway cruising a pleasure.
    Now all which is needed is a conversion kit.
    Frontline (yes, I know, I really should get a T shirt or something for all these plugs but I keep buying their stuff because it works!) do a kit which consists of an alloy bellhousing which fits the standard engine backplate and bolts straight on, and a modified propshaft to cope with the different size and position of the output shaft. Also included in the kit are a suitable clutch plate (different splines on the Ford input shaft) available in normal or extra large size, a rear mounting/crossmember piece and a new speedo cable which is over 6 feet long!
    The mounting plate is needed because to make the thing fit you have to cut out the chunk of centre cross member which goes through the transmission tunnel to give enough clearance. As just removing this would weaken the car, a replacement bridging piece bolts on below the floor line to restore the rigidity. This is the only part of the kit I an not 100% happy with as it doesn't really look strong enough. I boxed mine in with additional plates and added two more bracing bolts to be on the safe side. With a little ingenuity you could weld it in but Frontline's Tim Fenna assures me there is no need. 
    The mammoth speedo cable exits the side of the gearbox, comes through a hole drilled in the tunnel and then runs inside the car, under the front of the drivers' seat and up behind the trim panel in the footwell before turning back towards the speedo head.  Once installed this is actually much neater than it sounds but you do need to route the cable smoothly. You also have to have the speedo re-calibrated which is a nasty sting in the tail as it isn't mentioned particularly prominently in the Frontline literature. Frontline will handle this or it is £60 from Speedograph Richfield (recommended as they rebuilt my whole unit and recalibrated it in less than a week)
    The other major mod required is cutting a hole about 3.5 inches square in the transmission tunnel, just behind the original gearlever hole. The fact that the lever sits further back can be compensated by bending the Sierra lever forwards so the gearknob top sits exactly where it used to. If you pick up a Sierra gear lever with the 'box it it is fairly straightforward to modify it to fit the car- you can cut it to any length you like and then re- thread the top to take the knob of your choice or simply Araldite it on. Alternatively you can buy a ready- modified one with the kit. 
    "Quickshift" kits for this box are very simple. Demon Tweeks sell a set of spacing pieces which alter the pivot point of the lever giving a shorter throw. I recommend using the car a bit first though, until you get used to the gate pattern.

    So what's it like?  The gearchange is very good indeed -almost but maybe not quite as good as a really nice crisp MG/ Morris 'box. It is however, a great improvement to have synchromesh on first, and the fifth gear is just lovely. 70 mph equals about 2750 rpm which makes the motorway a much less hectic place! Plus it means the car is potentially geared for up to about 150mph+ if the engine can manage it!

    The gearbox does get quite hot - it is important to use the right  75/90 semi synthetic oil. Filling it is a pain as the filler/ level plug is on the side and you need some sort of funnel / tube device to get it in. Emptying is impossible! Ford, in their wisdom provide no drain plug of any kind.  You are supposed to remove the gearbox from the car while keeping it upright and level  (yeah, right..) then tip the oil out of the top after removing the cover. 
    Not being prepared to put up with this, I drilled a hole in the cast iron casing at the lowest point (there's a removable bits magnet inside here so line up with the hollow centre of that) and fitting a drain plug, lock wired for safety.  Similarly, I put another filler hole/ plug in the top cover. This is reached by removing the battery to reveal an access hole in the battery tray shelf directly above the filler.  Access is great with a forward hinging bonnet - a bit more fiddly with the standard set up but still much easier than using the side filler. The oil is expensive, viscous and really evil-smelling , all of which mean it's certain to be spilled!
    I would recommend replacing both the front and rear oil  seals on a secondhand 'box as you don't want to find out that they leak and you have to take the engine out again to change them!

    While on the subject of transmission, the half-shafts in the rear axle are susceptible to breaking under fierce acceleration. This affects all cars, even those with standard engines as a bumpy road surface can cause the axle to hop , putting big shock loads through the shafts. Power take-offs, wheel spin starts and other such hooligan antics are fun but you risk breaking the shafts. They invariably break at the splined end, leaving you with the unenviable task of extracting the broken bit from the diff.
    NB: this is also a reason why you can't use wire wheel half shafts in an axle meant for steel wheels. The shafts are shorter so they don't fit fully into the splines in the diff. Thus while the conversion seems to work, the first time you really put the power down they pop out or break... 
    There are two answers to the problem, either buy competition-grade half shafts which are stronger, or have your standard ones turned down in a lathe so they are the same thickness as the radius of the spline grooves. The reason for this apparent anomaly is that it allows the shaft to twist slightly under load along its whole length rather than shearing off at the weak point (the start of the splines).

    The best thing to do if you want to modify your standard A series engine is to buy David Vizard's book "Tuning BL's A Series engine" which is the absolute bible on the subject.  If you have a 1500 then I'm afraid I can't help you as I know almost nothing about these engines. - Triumph Spitfire people are the ones to talk to.
    Similarly, I won't go into detail of engine swaps such as the Fiat Twin-Cam and Rover K-series. There are plenty of specialists around who cover these conversions, and in terms of power-per pound they are a great way to go. However if you like to have at least a vaguely correct engine under the bonnet then stick with the A.

    Bolt-on modifications:
    Starting with the easiest in terms of mechanical complexity:

    Better Air filters.  If you are still using the standard "saucepan" air cleaners then throw them away and fit a proper pair of K&Ns or similar. NB: DON'T buy those shiny "pancake" chrome air filters which are an inch thick or less, however nice they look. They are worse than the standard items!  Fit ram pipes (sometimes called stub stacks) inside the filters to improve the air flow further. A decent tuner/ parts dealer will also sell you suitable carb needles and springs to match the increased air flow.

    Bigger carbs. - either  twin HS4's (Like an MGB) or a Weber . A single HIF6 or HS6 SU can also be used. All will need suitable manifolds.
    You can improve the standard inlet manifold with just a bit of amateur porting as it is a pretty terrible design.  Smooth out the corners around which the air flows, particularly the 'balance pipe' between the two main pipes as this flows a lot more air than you'd think.  You don't need (or want) mirror -smooth surfaces everywhere, but there must be no steps at the joints with the other components.

    Similarly, an SU carb. can be improved by slimming down the thickness of the throttle spindle and cutting off the ends of the throttle plate securing screws as they project into the air flow. Be sure to secure them properly with thread locking fluid so the engine doesn't swallow them! Also, radius off the leading edge of the dashpot piston where it protrudes into the carb bore on full lift to sharpen up the throttle response. - It is all in the Vizard book.

    Weber 40 / 45 settings.
    Although the Vintagent in me prefers the prehistoric SU, The Weber 45 is pretty much the standard carb used by racers.  For roadgoing applications though a 40 is fine. See Vizard for full chapter and verse on these but the following settings are quoted by Moss in their Special Tuning Manual:

    Road setting. Weber 40DCOE
    30mm Choke
    120 Main Jet
    45 Aux Vent
    F16 Emulsion Tube
    155 Air Jet
    35 Pump
    40F8 Idler Jet
    This is what is fitted to Andrew's green 1275 car (see garage page) so we know it works. It pulls as well if not better from all speeds. Significantly better than the standard twin SUs, especially on low-speed pickup. Sounds good too!

    Fast Road setting. Weber 40DCOE 
    32mm Choke
    145 Main Jet
    45 Aux Vent
    F16 Emulsion Tube
    180 Air Jet
    40/45 Pump
    50F8 Idler Jet
    This I have no direct experience of, but  I would guess loses some low revs tractability. You'll need a hotter cam and/or high lift rockers to exploit the difference, otherwise I doubt it will do any more than the Road setting except burn fuel.

    Race setting Weber 45DCOE 
    40mm Choke
    190 Main Jet
    45 Aux Vent
    F2 Emulsion Tube
    170 Air Jet
    60 Pump
    50F6 Idler Jet
    This is Moss recommendation and will, of course be a starting point as any race engine will have to be sorted out on a rolling road to optimise it for all the other variables in cam, ignition, exhaust etc.

    Lightening the flywheel. This doesn't actually increase the engine power at all but it does have a marked effect on acceleration as the engine first has to accelerate the mass of the flywheel before doing useful work on the transmission.  the work is best left to specialists who will balance the flywheel properly and will know how much weight to remove. Overdo it and the tickover will be horribly lumpy or worse, the flywheel could break, with lethal consequences.

    High ratio rockers can be exchanged for the standard items without removing the head. These improve the breathing by making the valves open further but take care! If they open too far they will hit the pistons (BIG bang!) so make sure there is clearance. - if you suspect your engine is non standard compression (skimmed head or altered pistons) then proceed with caution. High lift rockers can also change the effective cam timing as the valves will be opening at faster rates. Seek professional advice if not sure.

    If you are rebuilding the engine then the first thing to improve is the cylinder head. If you need to have valve seat inserts put in for unleaded fuel then consider exchanging the head for a modified one. The ports and combustion chamber shapes are changed (see the Vizard book!) and bigger/ better valves can be put in. The head is the key to the way the engine 'breathes' and hence to horsepower. The truly dedicated modify their own heads while I'm happy to use the services of professionals who have all the necessary equipment, experience and skill. 
    Any decent engineering firm can "skim" the head for you. This involves machining metal off the flat lower surface which raises the compression ratio. Standard CR is usually around 8 to 1 or less. The engine will take at least 9 to 1 (mine ran 9.75 to 1 before the supercharger was fitted) and should not 'pink' on standard fuel, although 10 to 1 would be the real limit for ordinary pump fuel. 
    NB: If you have problems with pinking and retarding the ignition doesn't help. Shell Optimax is the highest octane (98) unleaded widely available in the UK- or you can use an octane booster type additive. 

    The Camshaft is the 'brain' of the engine. It controls the timing of the valves and hence the power characteristics. There are lots of different profiles available from tuning companies but remember they are all a compromise  between low end torque and top end power. A full race cam will have lots of valve lift and big overlap periods to generate lots of lovely BHP at high revs. however, those same qualities will mean the engine will be pretty gutless at  lower speeds. - indeed many race engines will barely run below 3000 rpm and spit and run rough until they come "On cam" at truly high speeds. Oh, - and only a plonker  thinks they can tell how "hot" a cam is by looking at the shape of the lobes.  Use the timing information supplied like all real engineers do.

    For more information try Companies like Moss etc. who sell tuning bits but don't forget that Minis use A series engines too, and the Mini world is teeming with extremely clever tuners.  For example, Minispares in north London have a catalogue full of trick heads, clever carbs etc. which can all be used on a Spridget. Also try Mini web sites, discussion groups etc. 

    An easy bolt-on way to lots of extra horsepower. - WRONG!  - If you just want to go fast, put a Rover K Series or Fiat Twin-Cam in. They require lots of cutting the car about, plus numerous modifications to make everything fit and work. However, supercharging is, if anything more complex still! 
    There is no really logical reason to go to a supercharger, but then when did logic ever have anything to do with classic car ownership? :-)  There is a historical precedent in that many early cars were supercharged - (see John Sprinzel's excellent "Spritely Years" for example.) Shorrock blower kits, often sold by Allards were available for many late 'fifties/ early 'sixties cars and home built specials using military surplus exotica like aircraft cabin blowers were also popular. The effect of forced induction on a small capacity engine like a 948cc Sprite's was dramatic, giving huge increases in power and especially torque for relatively little work.
    More recent versions of the A series are more efficient so the effect of the blower is not so marked. As a rule of thumb supercharging a mildly tuned 1275 won't result in enormous amounts of extra power, on the dyno but the torque increase will still be very noticeable.  The usable rev range is  widened, making the car more driveable and giving the appearance of a llot more power. This is where belt driven superchargers score over turbos. - you don't have to spool them up before they start to deliver. In Alan Allard's book "turbocharging and Supercharging" he makes this point  well: " Despite what the theoretical engineers and pro-turbocharger lobby may say, in sheer 'get up and go' and general all-round performance on the road, as opposed to the drawing board the supercharged engine compares very favourably with the turbocharged one."
    Be warned (again) though. This is NOT a cheap exercise! Unless you are very lucky indeed and find a complete kit for a bargain price, it will cost a huge amount in time and money if you are going to do it right and get the thing to actually work!

    Anyway, before going down this road,  First Catch Your Blower Kit. - Shorrock, Judson or Zoller blowers turn up at  autojumbles from time to time, but a word of caution. It is very hard to ascertain the condition of the compressor without stripping it down and rebuild costs are very high. I bought mine knowing it was in desperate but still saveable condition for £150. It cost me £850 to have it rebuilt making a cool £1000 on the blower alone. Yes, this is a huge sum but you can easily pay £500 for a blower which turns out to need just as much work! 
    The manifolds and pulleys are the most difficult part. If you find a complete kit with all the pipework etc. buy it. - Do your research so you know what all the bits look like and what can be adapted if necessary. The trouble is that the manifolding is designed to fit a particular application and tends to get lost in garage clearouts etc. You can easily spend £200 on a manifold, plus if you have to get pulleys etc. made the bill can quickly get into more hundreds.
    For the record, there are two basic inlet manifold designs for the A series engine, A short- intake one for the small capacity engine and one with longer, curved pipes for the bigger engines. The difference is there to allow clearance for the exhaust manifold. I have an early type (it was all I could find) which wouldn't clear my long centre branch tubular steel exhaust manifold.  I opted to have the exhaust manifold modified to clear the inlet as it is easier to do, but it required some very skilled fabrication and welding which cost another small fortune!

    The blower is driven off  a triple -V crankshaft pulley which replaces the standard single-V one. The two extra Vs take a pair of identical belts which drive the supercharger.
    If you can't find one of these you can have one made (fairly involved piece of lathe work - cost around £150) or you can try and find a US-spec engine. These have a triple pulley as standard; the extra belts being for the smog-control air pump equipment and they bolt straight on. The diameter  is almost the same. - adjust the blower pulley size to maintain the ratio if need be.

    Just to give a flavour of the scale of the work involved here is a  list of things which I have modified, moved or redesigned and built from scratch:

    Centre main bearing strap. - The bearing cap needs to be removed and machined off flat. The strengthening strap is a piece of steel which should be lapped flat against the  bearing cap so it  makes perfect contact all over for maximum strength. Then you need two new retaining bolts which are long enough to take the extra width of the strap.

    11-stud head. - If  you are using a Cooper S or aftermarket head it will almost certainly have 11 stud holes. The standard Midget one has only nine and will need accurate drilling for the extra two. The standard Midget block will then need to be drilled and tapped to take the new end studs (try not to break into the waterway at the front)
    The rocker cover and its gasket will need to be relieved to clear the new stud nuts when installed.

    Exhaust manifold.  In order to get the tubular steel, long centre branch performance exhaust manifold to fit, it needed extensive modifications to the front and centre pipes. I just managed to cut , tweak and reposition the front pipe but the centre branch was beyond my talents. my local race preparation shop Barwell Motorsport fabricated a beautiful TIG welded section which cost an arm and a leg but works!  Of course you could just use a standard cast iron manifold which clears everything with no problems but that would rather defeat the object of tuning the engine. Supercharged engines need as free-flowing an exhaust system as they can get..

    Front bracket. This supports the blower  and needs to be accurately made to ensure perfect alignment. The blower is also supported at the rear from a lug on the inlet manifold and it is worth getting this positioned right so the blower outlet and manifold adaptor ports line up as perfectly as possible. That done, the front bracket can be made, together with two spacers which get it to stand off the timing cover by the correct distance so the pulleys line up. Ensure also that the bracket holds the supercharger square to the engine block or it will throw the belts.

    Carburettor bracket. - not an original part but well worth fitting as it helps support the considerable weight of the blower assembly as well as the carb itself. A piece of tube, flattened at each end runs from one of the carb fixing bolts down to one on the gearbox bellhousing.

    Belt tensioner. This was designed and made using a double V pulley as a jockey wheel on a moving plate attached to the front bracket.

    Carburettor. Original specs call for an SU type H4 to be used. However as these are rare, expensive and are technically inferior to the later models I used an HS4C, 
    This had to be fitted with an adaptor plate for the manifold (as the bolt centres are different) which also carries the throttle cable bracket. The Jet is specific to this model and no 100 thou sizes are available so it had to be reamed out from the 0.090" standard. A brass collar had to be made up with a tiny grub screw to allow the right type of needles to be used in place of the normal spring biased long needle setup.

    Heat shielding. The blower runs VERY close to the exhaust which is pretty much unavoidable. Custom made stainless shields placed between the exhaust pipework and the blower and its manifold. You can use glassfibre wrap, but it retains moisture and will rot a mild steel pipe very quickly.

    Boost gauge. There should be a suitable tapping in the manifolding between blower and head. A suitably threaded plug links a small bore tube off to the boost gauge. all connections need to be airtight.

    Big clutch. Needed for the big increase in torque, this caused clearance problems with the standard starter motor as the pinion would rub on the clutch cover (it's as big as possible so it is right out almost to the ring gear) and sometimes jam. Rather than relieve the cover or pinion I put in a reduction geared starter motor where the pinion engages from the front.

    Distributor. The Shorrock kit instructions require a limiting bush to be made fitting over the advance weight peg to restrict the amount of total mechanical advance. In practice, on the rolling road we found that this seriously restricted the power produced and the standard distributor was much better. The advance springs need to be modified however, to give an ideal curve. This work is still ongoing.

    Spark plugs. The aluminium head I'm using takes 12mm motorcycle type plugs. NGK's excellent web site led me to the right spec modern equivalent of the Champion N3/N5 quoted by Shorrock. However, they are resistor-type ones, so off with the resistive leads and on with straight copper cores ones. Now I still need the smaller plug boots to fit.

    Other modifications.
    Engine Steady Bar.  This will be familiar to Mini Cooper owners as they have a similar device fitted between the top of the engine and the bulkhead to counteract the engine's tendency to nod forward on its mountings under braking. On an inline engine such as the Midget's the bar prevents the engine from leaning over during heavy cornering, acceleration or braking, all of which twist it on its mountings. Racers use solid engine mounts but this is really unpleasant for the road.  Standard rubber mounts are fine if relatively new but they soften with age. If your exhaust starts to bang on the bodywork during hard cornering first change the mounts. 
    The steady bar is rubber mounted at both ends to stop it transmitting vibration and runs between a bracket on the top two bellhousing bolts and a convenient spot on the left hand bodywork. Result: the torque is used to drive the wheels, not twist the engine.

    Gearbox steady bar.   Not so much of a problem on the standard gearbox as the mounting is well designed, although it eventually goes soft and the three rubber blocks need replacing.  The Ford Sierra (Type 9) 'box  conversion relies on the tail sitting on a rubber block, which locates it but does almost nothing to hold it steady. Tuned engines or cars which see track use can suffer from the back end of the gearbox being pushed sideways by the torque or G loadings on it.  The solution is to make a steady bar similar in design to the engine one which stops the rear from twisting about its own axis or moving from side to side. This helps transmit the power better.

    The following are all recommended and should be available from specialists.

    Tuning BL's A-Series Engine David Vizard Haynes 1985/ numerous reprints
    Turbocharging and Supercharging Alan Allard Patrick Stephens Limited 1982
    Workshop Practice Clive Trickey Speed & Sports Publications Ltd. 1966
    Race and Rally Car Source Book Allan Staniforth Haynes 1986 (revised ed.)
    Modified Motoring
    John Sprinzel 1959 (reprinted 1961)

    Marque Histories:
    Austin Healey Sprite 1958 - 1971 R. M. Clark (ed) Brooklands Books 
    Original Sprite & Midget Terry Horler Bay View Books 1994
    Spridgets Chris Harvey Haynes 
    More Healeys. Frog-eyes, Sprites and Midgets Geoffrey Healey Gentry 1978
    Sprites and Midgets, The Eric Dymock Motor Racing Publications Ltd. 1981
    Sprites and Midgets. The Complete Story Anders Ditlev Clausager Crowood Press 1991

    The Works MGs,  Mike Allison & Peter Browning Haynes 2000
    Mighty Midgets and Special Sprites John Baggott Crowood 1998
    Spritely Years John Sprinzel & Tom Coulthard Patrick Stevens/ Haynes 1994

    Plus various other hand books and manuals of varying quality /usefulness for the completist collector.
    Lastly, I should recommend this site which has a number of the original BMC etc. handbooks available for free download as PDF files: