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MG Midget and Sprite Technical - SUPERCHARGERS

Has any menber experience of fitting and using a supercharger.My car is GAN4 1275 in standard trim- and
good condition. I have been looking at the options to increase performance and like the supercharger option.

I live in Spain and do not have the wealth of expert specalist services that exist in UK so I have do do most of my work myself. I know superchargers are expensive but maybe by the time you have modified the standard engine to give 90 plus bhp it would cost a similar amount.
I see them advertised around 2300 pounds. questions are.

What is the best spec of cylinder head ? I would imagine a gas flowed head with standard compression would be the way?

Would a standard gearbox,clutchand halfshafts be able to stand the increases power. The revs would presumably stay the same.

Where is the best source ?
Could I fit and tune it myself with a little help?
Any advise you could give would be highly valued. Its a big expense ,I do not want a mistake! Many thanks in advance, Bryan Gore N E Spain
B:J: Gore

Before considering a supercharger, you need to consider the existing configuration and condition of your engine. Any weakness will be made much worse by the supercharger. So if the engine is already tired, you will not gain much by adding a supercharger. I suggest doing a leak down test to evaluate the current condition of your engine.

I've been using the Moss supercharger for several years now and I've been very happy with it. I first used it on a "standard" engine, but later built an engine for use of force induction. I have not needed to upgrade the rest of the car.
Trevor Jessie

for £2300 you can buy an endurance-spec 120bhp race engine; the MOss blower kit is £2800 and I would hope at that price it's a fairly straightforward bolt-on kit althoguh I've not seen one myself. Moss claim a 40% increase in power - if you use that power then I would expect clutch and gearbox life to be almost halved, but as with a lot of things it will depend on how you use it and your driving style.
David Smith

Yes, you can build a naturally aspirated(NA) engine that makes more power for the same money. However, to make that sort of power on a NA engine requires you to sacrifice street drivability. How much are the Moss blower kits now?

And yes, it is an easy bolt on affair. It took me about eight hours from the time I pulled it in the garage until I was out for my first test drive.
Trevor Jessie

90-ishBHP is reasonably easy to attain without going over the top in expense, so I think the supercharger would be a more expensive route to achieve this. However, it will deliver way more torque than an NA engine of the same peak power - right from the word "go" at that - and leave you with a smile on your face so the money would be well spent.

As David says, it depends on your driving style how well things last. That's because the gearbox and halfshafts don't even have fantastic life expectancy with the standard engine. With care they will last reasonably well - Anthony Cutler has my admiration in how long his halfshafts have lasted with his K series midget, proving it can be done - but if you are a hopeless leadfoot like me it will be only a matter of time before something gives. So have a good honest look at your driving style and plan accordingly!

At the very least, get your existing halfshafts crack tested as they are the no 1 weakness in the drivetrain. If they are cracked they'll need replacing anyway so fit uprated ones at the same time. If you avoid excessive wheelspin, the diff should last quite well - it's lubrication failure in the centre gears during wheelspin which causes them to seize and then break which is the main problem there.

I would go for a gas flowed head with standard as you suggest. We have 9:1 on our K series with the supercharger on it and it handles it well. Flowing the head saves you from having to increase the boost to overcome a more restrictive inlet tract in order to achieve a given boost in the cylinder. The more boost, the more power required to drive the blower so you end up further behind.

Tuning for initial set-up is best checked on a rolling road, though a kit should include correct needles and ignition timing data if it's done properly. The cost of a rolling road is minor compared with the rest of the cost of the exercise, and usually delivers very good value in terms of BHP/pound. It also greatly reduces the chance of catastrophic failure from over-advanced timing or too-lean mixture.
Paul Walbran

what's the carb setup on the Moss kit, big single SU? Bet there aren't too many rolling roads in Spain with the ability, experience and spares to sort out and tune one of these. Remember the trouble Ben in Majorca had (wonder how he's doing) with just a Weber on his Midget.
David Smith

Moss Supercharger kit now ships with an HS6 ... I think. When I first bolted the kit(using HIF44) to my car I spent some money for some time on a chassis dyno. The mixture was good at most all revs and loads. The biggest issue is that it would go lean on tip in. I tried all sorts of ways to resolve the issue (damper oils, springs, etc). Ironically, the cure was simple ... an oversized air filter and a short stub stack. Still have a slight lean spot, but overall the car runs well.
Trevor Jessie

This thread was discussed between 19/04/2013 and 20/04/2013

MG Midget and Sprite Technical index

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