Hi all,

I've been thinking of uprating the turbo on my MY98UK for some time now to compliment the existing mods (exhaust/downpipe/filter/boost controller) as it feels a little asthmatic after 5000rpm or so. I have been recommended the Sti's IHI VF23 Turbo. My question is, does any one know if running a standard turbo at 1.2bar, and running one of these at 1.2bar produce different flow rates. ie. does more charge enter the piston chamber. Some people I have spoken to are adamant that 1.2bar is 1.2bar regardless of what size turbo you are running. So if a tiny turbo is running at 1.2bar there is the same amount of air entering the piston chamber as if a huge turbo is running 1.2bar. BUT, others say that a larger turbo will flow more air at the same pressure.

Can anyone shed any light on this??
Thanks,
Nito

A larger turbo will be working less hard to pressurise the air to the fixed pressure... so the resulting air will be cooler than a more highly stressed smaller turbo.

Hey peeps. long time no see http://bbs.scoobynet.co.uk/smile.gif

Larger turbo equates to more air, its elementary my dear Watson.

million dollar question :

Take a 5cm diameter pipe and a 10cm diameter pipe, pressurise it at 1bar which pipe will get more air mass flow? bearing in mind that you have the same pressure.....

If you're an atheist, use water instead of air then you can actually SEE the volume of water flowing :/

no, I didnt fail physics in uni.


max

*former village idiot now upgraded to kitchen chimp.*

"But we are not talking about a larger pipe"

The plenum and intake system is still the same size, so at 1.2bar you will have exactly the same amount of air

Moray is right, in that the turbo is less stressed and the pressurised air will be cooler, and at high revs and WOT the larger turbo will be capable of moving enough air to maintain the maximum boost, when the engine is eefectively a larger pipe because it is removing the air from the intake more often.

Paul

pnebbs,
I think the analogy was that the bigger turbo was the larger pipe....

But surely the size of the turbo is irrelevant (heat efficiency excepted) if the smaller turbo can move enough air to pressurize the system at 1.2bar (at lowish revs)

The turbo is only part of the system, and if you have a 5cm pipe with a 10cm bulge partway down it would make no difference

Paul

Malique, (and Mike?)

Changeing the turbocharger will not affect the volume of air on the pressurised side of the engine.

Cooler air will be more dense, containing more oxygen per unit of volume, giving more efficient burn and slightly reducing the chance of "dieseling".

Moray
(Who didn't do physics at uni in the first place. http://bbs.scoobynet.co.uk/rolleyes.gif )
(Oh, someone's going to point how wrong I am now! http://bbs.scoobynet.co.uk/wink.gif )

I did do physics at uni, I have to agree with Moray.

I never studied fluid dynamics, quatum mechanics and thermmodynamics yes, but these will not help here.

Aside from this,

Go for a massive turbo, like an 05H. These flow much more than engine can take, take longer to spool up, but punch you much harder in the back when they kick in.


Moray, will not like this comment.

I tell you what Adam, if you make it to the RR day at PS on the 27th, I'll take you for a ride in my car and you can decide if you prefer a short punch in the back or being pushed back into your seat all the way to the redline... http://bbs.scoobynet.co.uk/wink.gif

Torque Developments reckon that a larger turbo will flow more air at the same pressure than a smaller one. He used the drainpipe/windmill example!!

On another note, I've found my Turbo to be leaking some oil as my boost controller uses a filter which has been swamped with some oil. I think the bearings may be on their way out. Any ideas how much longer the Turbo should last, it's only just started to lose some oil. Does the oil damage the engine! Moray, can you remember what you paid for your hybrid?

Thanks,
Nito

Wont the larger turbo be able to hold the boost pressure at higher engine rpm?

I have a matched larger turbo on my RS and it will pull 16psi at max engine rpm whereas the standard turbo would only hold 12psi at the max rpm of the turbo. Even if I had a 32psi actuator on the original turbo it would not pull over 12psi at max rpm since the turbo just could not pressurise the volume of air required at max engine rpm to 16psi.

If I now have a 32psi actuator on the turbo the new turbo will pull over 22psi until the over boost comes in. Hence it has a 19psi actuator and pulls 20psi on pickup and holds 16psi at max engine rpm, 7000rpm.

This was explained to me by Ahmed Bayjoo the guy who built the engine.

jon