This has came up before on here when people have came out with bollocks about a bigger engine means more power on the same size turbo.

Thats obviously bollocks if you know how turbos work, but i always thought itd be the SAME power, but accrding to this, if they right, a SMALLER engine can potentially give MORE power for the size of the turbo...

It goes on in great detail, on, and on, and on, and makes my head hurt, lol

They right? Wrong? I dont care, but interesting anyhow...

 

Steve,
I concur with what they have put and although more cc's will give better response, it can mean that the engine will consume more air than the turbo can provide and so the boost will tail off (like a T3/4 does on a 2.0 litre), as well as the issue with the "choke" point.

 

Consuming more air than the turbo can give is irrelavent surely? Isnt that just when the engine has maxed out the turbos potential? Thats happen regardless of cc if the engine is capable of that power?

The rest, i dunno

 

Steve,
Just think of an engine as an air handling unit, the bigger the engine the more air it can process - 2litres of air is less than 5.7 litres of air .

A T3/4 can barely give a 2 litre engine enough air for 400bhp. Putting a T4 on an engine that goes up in air flow capabilities the same as the turbo does will result in the same boost drop off, as the bigger engine will be able to consume more air.

The thing that most influences the power with a turbo is the VE of the engine. The Cosworth has a pretty good VE when compared to others .

 

Steve,

The really simply way to think about it, is if you look at the compressor map you can see the efficiency areas for given air flow and pressure differentials. If you for sake of arguament could increase the engine capacity by 50% with no other engine changes, the pressure ratio would be lower for the same power at the same rpm due to the increase in swept volume. If you look back at the compressor map for this same amount of compressor flow as before, but now at a lower pressure ratio you may well find you are now in a zone much less efficient.

Ultimately all these means is choose your turbo correctly for your engine, don't just go increasing capacity without considering all other factors.

 

But surely a 400bhp capable T34 is capable of that 400bhp on a 2litre or a 10litre, itd be at lower revs when it maxes it out on the 10litre, but itd max it out all the same.

 

Oh, now karl explains it, i think i get it, possibly

 

All irrelavent to my car, but was interested none the less

 

No, the turbocharger flows depending on the pressure. Too high of a pressure can either mean more air flow or less air flow, depending on the compressor efficiency map.

Now, the engine must be able to draw enough air in to make the power. A smaller engine will need more psi to make the same power than the larger engine with the same turbocharger, but it could even make less power as higher psi usually leads to hotter air.