Internal Combustion Engine Supercharger

[martyn nutlandParticipant @martynnutland79495]

[martyn nutlandParticipant @martynnutland79495]

My modest machining skills no way measure up to this at the moment – and may never. But my ultimate goal is to make a mechanically driven supercharger for an Austin Seven. (It would need to 'blow' at no more than 7 psi)

Do members think this would be feasible for a non-professional i.e. someone who, unlike many of our distinguished forum participants, hasn't served a formal engineering training?

Has anyone done it!

Has anyone ever seen a drawing?

Is the amount of material (e.g. for the body) so great as to make it financially unviable, or, might a steam engine cylinder casting be an economical start point.

Any views appreciated to help me start thinking rationally.

Martyn

[JasonBModerator @jasonb]

Certainly seen quite a few made for large models eg 1/4 and 1/3rd scale V8 and V10 so not a lot smaller than an A7 engine. Probably better off starting with a block of aluminium and carving it from that. Have a search around some of the forums where more engines are made like MEM MEM and HMEM.

Edited By JasonB on 29/11/2015 17:02:31

[Tim StevensParticipant @timstevens64731]

The answer must depend (at least) on what your skills level is, and what equipment you have. There are various designs of supercharger, all of which include relatively complex machining, and which rely on fairly tight dimensional control (as well as knowing exactly what materials work best together). Only you can decide how far from 'modest' you a) need, and b) can achieve.

You may do better to start with (if you insist on going forward with this) by looking at the various devices already in use for hill-climbing and similar cars – although most of them have bigger engines. We know that the A7 engine can produce much more power than standard without supercharging, relying on higher revs and more sophisticated head and cam designs. We also know that Austin themselves produced a supercharged A7 before WW2 but they started with quite a different block, crank, head, valve gear, etc. And, we know that there have been supercharged versions of smaller engines, too. But not many …

Your decision must also depend on what you hope to do with the finished product. If it is for a sprint or hill-climb, then the life of the product need not be long, so you can get away with things which would not do for a longer distance or time (whether we are looking at wear, or heat capacity, etc). And, the rules for period racing (competing against engines or cars of a similar age) may well not allow for completely new or home-build designs.

And of course, you need to know that when your first try fails (perhaps taking your A7 engine with it) you can call up the necessary time, cash, and parts to make what you hope is an improvement.

I hope this helps towards a sensible decision

Regards, Tim

Edited By Tim Stevens on 29/11/2015 17:07:45

[mike TParticipant @miket56243]

Hello Martyn

I am currently building a 1/3 scale working model of a two stage supercharged Mercedes Benz W165 Grand Prix engine, from 1939. I have almost completed the two stage Roots type supercharges. I am sure a single stage Roots blower is all you will require for your Austin.

For my 1/3 scale model, I machined the casings and rotor from a solid billet. A large casting would be a better starting point for a full size blower. You should be aware that the synchronising gears must be made to a very high precision with minimum backlash, as their function is to prevent the two rotors from crashing together.

You can see some of what is involved at http://www.modelenginemaker.com/index.php/topic,5142.0.html

Hope this helps

Mike

[egaParticipant @ega]

I no longer have my copy of Bill Williams' book on Austin Seven Specials but I seem to recall he had something to say about supercharging.

[Gordon WParticipant @gordonw]

Good luck with your project. It can be done , but is it worth it? A7 engines are getting scarce. We used to supercharge m/bike engines when I was young, belt drive cabin blowers ( ex MOD ) were common. maybe get something similar today, engine shrapnel was also common. Have to decide which side of the blower to put the carb. both need some plumbing mods and jet sizing. Don't want to put you off, just things to the think about.

[JAParticipant @ja]

Before the War the Army had Austin 12 (I think that was the model) radio vans and they were slow. The Mechanised Warfare Experimental Establishment decided a supercharger was required and one was fit to a van. It went even slower.

A supercharger absorbs a lot of power and if the engine's breathing is very poor……..

[martyn nutlandParticipant @martynnutland79495]

Thanks all. Much wisdom. Consensus: 'Don't try it'. Conclusion: I now won't.

Thanks again, everybody.

Martyn

[Chris Evans 6Participant @chrisevans6]

Having a life long desire to compete in various forms of motorsport I have "Blown" a few of my cars. Always by buying the blower and making up the bits to fit and get it to work. Is your wallet big enough for a steel crank? I would be reluctant to add a blower to an original Seven. Maybe get hold of a reliant engine to play around with. If you do go ahead I suggest casting the main casing. A good aluminium foundry local to me (20 miles) here in the Midlands if you require castings. Chris.

[martyn nutlandParticipant @martynnutland79495]

Thanks Chris.

No way will I be going ahead with this. I've been sufficiently put down and put off.

By the way, the Seven crank is steel. I'm not that daft after 50 years around them.

Thanks for the input.

Martyn

[WatfordParticipant @watford]

Martyn

Have a look at http://www.austinsevenfriends.com and go to the Forum. There is a pretty good index and you will probably find some helpful information there. Several guys have been down this path previously. Also, if you are an Austin Seven buff then you should probably be aware of this very friendly domain in any case.

Mike

[Russell EberhardtParticipant @russelleberhardt48058]

By far the easiest way of improving the Austin 7 engine performance is by improving the breathing and increasing the compression ratio from the original 4.9:1 ( or 5.8:1 for the Ruby) to about 7:1.

You can improve the breathing by replacing the zenith carburettor with a couple of SUs of 1" bore and by reprofiling the camshaft to give an extra 50 thou of inlet lift and a bit of overlap.

Of course extra performance requires a better crankshaft. If I remember I bought mine from a firm called Allen Crankshafts. (Now known as Midland Crankshaft Ltd and still making crankshafts for vintage cars and specials).

Russell.

[Gordon WParticipant @gordonw]

I was not trying to put you off, try it if you want. Supercharging , in it's self, actually helps the engine stress by balancing some of the mechanical stress. But you have to keep the revs. down, not much fun.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Gordon W on 30/11/2015 09:26:21:

I was not trying to put you off, try it if you want. Supercharging , in it's self, actually helps the engine stress by balancing some of the mechanical stress. But you have to keep the revs. down, not much fun.

. . . and the compression ratio. 5:1 max and 5 psi boost.

Russell

[Clive HartlandParticipant @clivehartland94829]

Just to give an indication of what supercharge means, I worked on Detroit Diesels and they were double supercharged with an exhaust blower and a Rootes blower over the plenum chamber and rated at 24 lb pressure.

This was a 2 stroke diesel V 6.. the same engine as on Greyhound buses in the USA.

Their trick was to break the first web of the crankshaft because the torque damper was stuck with paint.

Clive

[martyn nutlandParticipant @martynnutland79495]

Thanks again for all the input. Really appreciated.

Of course, I know about putting on an SU carburettor, opening up the ports, increasing the compression ration, fitting a Phoenix or some other species of non-original crankshaft and all the other bells and whistles like Honda pistons. The question was, could I make a supercharger.? The answer is clearly NO!

Best leave it there now methinks.

Thanks for the views.

Martyn.

[john carruthersParticipant @johncarruthers46255]

One of my teachers, the late Charlie 'Cog' Wheeler had several 7s, one of which had a tiny brass Shorrock blower.

He also tried using a minor 1000 air pump as used on US export models to help clean up the exhaust.

Then he settled on a modified Alpine conversion kit for a minor 1000, worked well for many years in daily use.

[martyn nutlandParticipant @martynnutland79495]

Thanks John.

Encouraging. Before I was put off, I thought of using something like 'Cog' Wheeler's air-pump as the body and adapting it.

Not sure, from your message whether he replicated the 'tiny Shorrock' or bought it. If it was brass I guess he made it himself to a Shorrock design as that make was very popular at one time. I seem to remember you used to see 'ads' for them in magazines like Motor Sport.

Austin, as I'm sure you know, supercharged one model of the Seven – the EA Sports commonly known as the 'Ulster'. They used the French make of 'blower' – Cozette. I think it was the Cozette number two, but I'm not sure of that and I've never actually seen one on the bench.

Thanks again for the comments.

Martyn

[Howard LewisParticipant @howardlewis46836]

New parts for Austin Seven engines are still available. There is a chap in south Lincolnshire who specialises in parts for racing Austin Sevens.

GOOGLE "Austin Seven Racing" for possible suppliers.

A Roots type supercharger would be difficult, but not impossible to make (and NOISY when in motion) but a sliding vane type would provide the extra air required. (Effectively it is a brake exhauster delivering to the carburettor rather than from a reservoir to the atmosphere)

The rotor is mounted eccentric to the bore in the body, and has three or four slots, in which vanes (often Tufnol type material) slide. Since a Clayton Dewandre exhauster could produce 20" Hg vacuum for brakes on a commercial vehicle, 5 psi boost should not be impossible to obtain with a suityable drive ratio.

Delivering to a carburettor, with the float chamber sealed and vented to the boost, the warmer air may well improve engine smoothness by vaporising the petrol and giving better mixture distribution.

It was usual to include a blow off valve in the induction system, in case of the engine spitting back; and possibly to limit the boost applied to the engine, (although that is a wasteful and thermally inefficient means of controlling boost)

But as already been said, the blower will absorb power, although a nett power increase should be available.

Howard

Edited By Howard Lewis on 07/12/2015 13:25:08

[martyn nutlandParticipant @martynnutland79495]

Howard

Many thanks for that.

Much food for thought and a lot to be studying before even considering whether such a thing could be made.

Thanks again.

Martyn

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