okay this is probably very stupid question but amuse me anyway.

If you have 2 identical car with same mods except the turbo. Does the car with bigger turbo make more power with the same psi than the smaller turbo or does it matter if the smaller turbo can keep the boost pressure at high rpm?

 

Generally speaking, a smaller turbo makes good torque down low, but chokes the engine up high. Conversely, a big turbo doesn't generate much torque down low, but really opens up in the higher rpms. Yes, there is some over lap. A slightly bigger turbo at low boost can make the same power as a smaller turbo at high boost. However, you need to decide what's more important: turbo spool up, or reliability? Big power up top, or a more broad power band? Running a smaller turbo at higher PSI is more taxing on the motor than a larger turbo at a lower PSI. So if spool up isn't of concern to you, then running a smaller turbo at high boost is not a good route. Like wise, if you want to make big power(350+), you're going to want a bigger turbo to make that power safely. Make sense?

Steve

 

So if both turbos run at same psi level lets say 14psi bigger turbo makes more power?

 

I would say it makes the same at the same psi. it's just where that psi is on the rpm is the factor.

but then again I dont know that much a bout turbo's.


Mage

 

No question. The difference between a small turbo and a big turbo is the "amount" of air moved. We measure this in Cubic Feet per Minute(CFM). A big turbo will move a lot more CFM at 15 psi than a small turbo. I suppose this is the tricky part to understand. It is possible to move MORE air at the SAME PSI by using a larger turbo. More air, of course, means more oxygen into the engine, and hence, more power.

Steve

 

15 psi is 15 psi no matter what size your turbo is. Some turbos (small ones) can produce 15 psi of pressure from 2.3k to 4k rpms where after 4k it starts to run out of its "efficiancy range" and than your just blowing really hot air(bad) and you haven't maxed out your engine. A big turbo will spool up and create 15psi of boost at say 4k all the way to red line, efficiantly(meaning not really hot air) or even 20 psi of boost because bigger turbos need more exhaust power to spin a bigger compressor. bigger compressor, bigger pump capaple of producing higher boost.

If you put to big a turbo on a rotary you may never even spool it up(no boost), if you put to small a turbo you'll get a cute little boost and than your turbo will max its self out and your smile goes bye,bye.

 

its like blowing through a coffee straw and a drinking straw. if you blow with the same force, the coffee straw will be harder to blow through, which means that it has to be at a higher psi to move the same volume of air.

 

Straws......

 

Turbocharger efficiency also plays a role of course.

A small turbo that has to work hard at 15psi will produce a hotter intake charge than a larger turbo that isn't even breaking a sweat at 15psi.

Hotter air is less dense, which means less power.