Larger turbo = more air flow?

[argetni]

Can someone please explain this to me?

Let's say there are two identical cars, but car #1 has a larger turbo, boost level is at 8 psi. Car #2 has a smaller turbo, boost level is also at 8 psi. Car #1 has more turbo lag due to the larger turbo while car #2 has a better throttle response.

I always heard people say larger turbo create more top end horsepower because it has more air flow. So if car #2 blows 10 units (I don't know the correct unit of air flow volume, so I just make it simple here) of air into the combustion chamber in each combustion, how many units of air does the car #1 's turbo blow?

If the answer is also 10 units, then why would a larger turbo produce more horsepower?

If the answer is greater then 10 units, does that mean car #1's engine has more tears and wears than car #2 (even their boost level is 8 psi)? Or does car #1 has a greater chance of blowing up a motor?

[plumvtec]

It's all about lag. Turbo lag.

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'96 JR6 GSR Sedan (black currant pearl) FOR SALE !
'93 Honda CBR 900RR
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[Holden]

I'll take a partial stab at this.

The smaller blower is going to have to spin faster to produce the same amount of boost. This will heat the air up more.

So...

Small Turbo ==> 8psi hotter air
Big Turbo ====> 8psi cooler air

The cooler air is more dense. So even though the two turbos are blowing the same volume of air, the bigger turbo is blowing more mass (more oxygen to burn).

Some turbo dude will likely answer this better.

What you need to remember is that the "units" you were talking about are really two seperate things. Mass and Volume. Boost psi is related to volume (cubic feet), but power is related to mass (pounds).

Greg

[Civic TSI]

Right on Holden and I should add that a bigger turbo is less restrictive for the exhaust gas which mean less heat again. Also, a bigger turbo doesn't necessarily mean more lag. I went from 505cfm to 660cfm and reduce my lag at the same time. Choose the right turbo for your engine.

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To 24 PSI, and beyond !
HS Le Club

[MDA]

Just to add a little to Holden & Civic TSi information, remember that your absolute max air flow at top RPM will be restricted if you're running high boost with a little turbo. Ex. a small t3/t3 wont push over 15 lbs at the top... so you're boost will drop.. However a t3/4 can keep over 15lbs right up to redline... My figures may be off ... but it's the general idea...

[argetni]

Holden: So even the volume is same (coz the boost psi is same), the larger turbo blows cooler air, which is more dense and has more amount of oxygen. More oxgyen need more fuel, and the combustion is greater so that it produces more power, right? If yes, in other words, it puts more tears and wears to the engine. Is that true?

[Holden]

If detonation and heat are ignored as factors, yes, the larger turbo will stress the engine more.

However, heat and detonation cannot be ignored. These are what kill engines, not excessive power (to a point... obviously too much power will break things too).

Engines handle extra power fed "normally" to the pistons through a slow, even burn much better than they handle the doubling or tripling of cylinder pressures that can occur with detonation.

I can't tell you which setup would be better for engine health. I would guess the larger turbo, but there are too many unknowns here.

Greg