Superchargers

Evening to you all does anyone know how to size a supercharger to an engine and where do you get them from, I am talking about the big ones you see poking out of the bonnet of custom cars.

Rich

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Reply to
Rich
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Do you want it to work, be the right size/setup for a road car or just to "poke up out the bonnet and look big?

They are positive displacement pumps. So if you have one that has a capacity of say 1000cc then it pumps 1000cc per revolution. A car thats

1000cc actually only pumps half that since its only on its induction stroke every 2nd revolution per cylinder. So it would if geared 1 to 1, double the engines air throughput and power roughly.

Or on a 2 litre engine you would gear it 2 to one for the same effect. etc...

Reply to
Burgerman

Yes to all questions, what's the point of having one just poking through the bonnet !!!!! :)))))) Can you tell me more about them?? Rich

Reply to
Rich

I could but I am not about to randomly write a book! What do you WANT to know?

Reply to
Burgerman

Perhaps I'm missing something but isn't he more likely to have a 4 = stroke car?

Paul

Reply to
Paul Laidlaw

4 strokes = 2 revolutions
Reply to
scott

Exactly! You are missing the fact that a two litre car only pumps every other revolution so it is 1 litre per revolution...

It inducts nothing during the compression and power strokes, that a full revolution.

Reply to
Burgerman

THe only ones that'll poke out of a bonnet are those fitted to a V6/8 engine. They sit on top of the inlet manifold.

Reply to
Conor

well I'm still missing something then cos sure it only inducts anything = every fourth stroke, not 2nd. so a 2 litre car pumps 0.5 litre pre revolution surely?

Reply to
Paul Laidlaw

I've thought about it a bit more and now all is clear

Paul

Reply to
Paul Laidlaw

4 stroke = induction, compression, combustion, exhaust. Or down, up, down, up - a stroke is an up or a down, not an up AND a down. If you had a one cylinder two stroke, it would fire on every revolution, four stroke every other.
Reply to
Doki

one revolution (crank all way round) = two strokes (one up, one down) per piston.

HTH

Reply to
Tim S Kemp

As a four stoke only sucks and blows on alternate revs shouldn't it's capacity really be 1/2 of what is normally claimed. Due to being minorities the 2 stroke and wankel get victimised and have often been forced to be rated at twice their actual capacity. While it should be the piston 4 stroke that gets rated at half.

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Reply to
Peter Hill

That's just doing the same thing using different words.

Reply to
SteveH

I realised this after my post, I wasn't applying enough brain.

Cheers

Paul

Reply to
Paul Laidlaw

"> I could but I am not about to randomly write a book!

Ok here we go :

1 how is the size of a supercharger worked out. 2 where can you get BIG ones from in the UK !!!!!! max 1432 CFM for my engine !!!!!!!!! 3 how do you work out the pully sizes, belt size 4 what power would be consumed for this type of blower? 5 what boost press do you decide on is there a right or wrong pressure. 6 what about back firing pressure relief valve. 7 what sort of HP increase would you expect on a 5 to 1 CR and 650 HP And any thing else you might think of for a start point......

Rich

Reply to
Rich

Not relevant. There IS no max, and positive displacement pumps do not care about "maximums" they just pump x cc's of air (per revolution) as does your engine.

Very easily if you know a) engine capacity per revolution b) supercharger (or pump if you prefer) capacity per revolution...

Lots. No Idea how much - far too many variables!

No.

There is the pressure you decide on! Based on fuel octane rating, main use, compression ratio, reliability, specific engine or transmission weaknesses etc.

Yep, what about one? You WILL need one! Because the air cannot go "backwards" as its a positive displacement pump... Just a plate with springs that can hold in 1.5 times your required pressure will be fine.

Too many variables. Fuel? RPM? Normal volumetric efficiency? Temperature of intake air increase? etc etc.........

A big, sorry a VERY BIG book on engines and physics????????

You are trying to run before you can crawl!

Reply to
Burgerman

In article , snipped-for-privacy@ntlworld.com spouted forth into uk.rec.cars.modifications...

ISTR that with this engine, it might already be the case.

I think it was a RR Meteor, or something similar.

Reply to
MeatballTurbo

A blower pumps air, each turn it will displace some air into the output tube. This will increase the pressure in the plenum / tubes. Higher pressure will mean more air in the cylinders when they open.

Now, you have a pump pushing air into the plenum and the engine itself is essentially acting as an air pump too, so you need to work out the pressure you want at the airflow you will be expecting to get with that pressure. This is non-trivial as the pressure differential will affect how much air stays in the plenum and how much it tries to pass back through the pump.

You also have a question of the size of the impeller, and the speed at which you will spin it relative to the engine speed. This also needs to be balanced.

Reply to
Questions

It will mean EXACTLY the capacity of the supercharger since its a positive displacement pump. Its why supercharged engines have flat featureless torque curves... Nothing else much mattters anymore!

Its not relevant. The engine is force fed the air so no longer has to "pull" (yes I know its wrong but its easier to understand this way) its own air in. It gets the VOLUME that the supercharger gives it.

If your engine is runs about 100 percent volumetric efficiency (some less some actually more due to ram/resonace effects) and makes say 100 bhp from 1 litre then it keeps numbers simple. If you feed it twice this air it will always have twice the air/fuel in the cylinders and make twice the power. And it will be if measured running at 1 bar boost all the way through the rpm range.

Things are not quite this simple but that about covers it...

If you want twice the power pump twice the air that the engine did normally. Or twice its capacity over the full 4 cycles (2 revs)...

You will not actually get twice the power because you lose some compressing, you lose some due to lower compression, and some through other losses though. And its an ever decreasing gain as the boost rises.

But there are so many variables that you can't calculate it... Its why manufacturers spend millions on developent work.

so you need to work out the pressure you

Reply to
Burgerman

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