Hey everyone!

I just blew my exhaust manifold apart last weeks. Well, a modification to the manifold blew apart. Got me wondering about back pressure…

for example sake, let’s just say that I am running 10 psi boost and my exhaust manifold sees 10 psi between the head and turbine. If I increase my boost to 20 psi, does the back pressure rise at the same rate?

 

Short answer, no.

Does it go up with boost? Yes, but not linearly like your example.

 

Would back pressure increase at a higher rate?

 

Depends on the turbine stage of the turbo and where the compressor and turbine efficiencies are at.

 

Normally it's a non linear relationship. Given the same size turbo usually the drive pressure will rise faster than boost pressure.

It's not just the turbine, or the drive ratio that becomes more restrictive, everything in the exhaust contributes, so if you are marginal at 10psi the drive pressure will come up a lot faster than if you have a bunch of room for growth.

Pressure drop on the compressor side increases as boost increases, so depending on if you have things like intercooler or convoluted charge piping before the manifold you will have more loss before the intake manifold as you turn up the boost.