civic4982

I'm trying to get a physics understanding of why a smaller turbo running at 5PSI will make less power than a larger turbo at 5PSI running on the same engine.

Can anyone help explain it?

at 5PSI, shouldn't the same amount of air be going into both setups? therefore shouldn't the power be the same?

civic4982

ok, so boviously more heat is lost with the larger trubo since PSI is the same and volume is the same...

where's the heat lost on the larger turbo as opposed to the smaller one?

scalbert

You also have to consider where the power is being made.

A smaller turbo will spool up quicker giving larger gains down low. However, it will run out of breathe up high; possibly dropping the boost and over heating the air. So while it gives you 5 PSI down low it may only supply 4 PSI near redline. Couple that with less efficiency, greater heating of the air thus less dense of a charge, and you have a lower peak power output.

civic4982

how does it heat teh air more?

CLSmike

Larger turbos are "larger" they carry more air and so they might be pushing 5 psi but its lets just say 1 cubic feet of air compressed at 5 psi whuke they smaller turbo is 1/2 a foot of cubic air at 5 psi.

scalbert

There are several reason but the biggest contributor is becasue it has to turn faster to create the same boost. Since it is moving faster the air is sliced into faster and creates more friction. This heats the air even further. Remember, it is not unheard of for a turbo to be spinning 80,000+ RPM.

civic4982

I think that's a misjudgement of the place where PSI is measured. PSI is measured as air going into the intake manifold. the amount of air stored in the turbo is less important. Keep in mind that their container is still the same, being the container that the put the pressurized air into. The 5PSI in two of the same containers at the same temperature is still the same amount of air. What you're saying is incorrect.

However, scalbert you're helping me understand how the air gets cooled more quickly. thanks.

suXor

It's all relative. A larger turbo is only usefull if the intake and engine can handle the larger volume of air. Putting a T04/5 on a 4 cylinder with stock intake manifold is a waste since your spooling is longer and the greater air volume can't be used effectively by the engine.