I know this had been discussed before, but I just couldn't find what I was looking for. Now, we have talked about how 10psi on a t3 is not going to be the same at 10psi on a t4, etc. One of the reason being efficiency. However, I am not getting the whole picture here.

1) so if I can consistently provide 10psi to a h22a using a smaller turbo, would upgrading to a bigger turbo and supplying 10psi yields the same result or not? Besides the different efficieny of the turbos ( which could heat up the air), is there any other factor I am not looking at?

2) If a bigger turbo can flow more cfm than a smaller turbo, say, a bigger one can flow twice as much as the smaller one, what does that mean? that I would be pushing more air at the same psi?

thanx

 

a good question.

 

... indeed

 

It's all abut cfm as opposed to psi. Once uyou get out of the efficiency range of a turbo then it starts heating the charge air which then doesn't make any more power or not as much. Put it this way I made 370whp @21psi with a small T3/T04B turbo then went to a T3/60-1 turbo and at 14psi made the same horsepower then 25psi 500whp. The old turbo I tried to make 400whp turning the boost up but didn't happen it was MAXED OUT! Granted I have increased my discplacement and had headwork done and some other changes but feel the biggest hp gain was from the turbo. Also check the Turbonetics site and will show all the compressor maps and show what each turbo's lbs/min is. I have an outdated Turbonetics Catalogue but the new ones have more info.

 

in terms of getting results...the one thing that might help you make more sense of it is this

a bigger turbo is going to make torque at higher rpm than a smaller turbo...torque at higher rpm = more horsepower

 

Anyone else has any inputs on it?

 

A bigger turbo will produce more airflow at X psi than a smaller turbo. The air produced by the bigger turbo might be heated up more, or it might be cooler than the air provided by the smaller turbo. This depends on the efficiency of the compressor the bigger turbo is using.

 

boost pressure is a measurement of the engine's resistance to the air being forced in by the turbo...a smaller turbo will have to work harder to achieve a given boost pressure...this harder work is accompained by more heat in the intake charge, which, as we all know, is no good when it comes to making power. i know also that a bigger turbo can flow more air at the same boost pressure...so there is more flow and cooler air, but i am not sure of the exact difference between flow, pressure, and all that.

ironically though, it is HEAT in the exhaust gases which helps our turbo's spool up and make their power!


[Modified by downpipe, 2:52 AM 11/10/2002]

 

No it wont be cooler air in all cases, because if the bigger turbo isn't spinning at the right speed to be in it's best efficiency area of the map, it will also heat up the air.

 

are you sayign that it will heat up the air even if it is spinning too slow? that doesn't make sense to me...i thought that it was the turbo wokring too hard that heats up the air...could you explain in more detail?

 

Yes, it will. If it's not at the right speed, either too fast or too slow, the turbo "thrashes" the air more (turbulence), which heats it up.

 

ahhhhh, i see. thanks.