Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
(OP)
Should turbo (boost) manifold pressure be equal to exhaust manifold pressure to maximize horsepower and torque?
Application Drag Racing.
Engine V6 231 C.I
RPM Power Curve 2500- 6500
Application Drag Racing.
Engine V6 231 C.I
RPM Power Curve 2500- 6500





RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
I assume that you are trying to hop-up a Buick 231, in which case you will get much better, quicker and cheaper results by buying one of the many turbo kits available instead of trying to design your own. You may also be able to buy parts from someone who is upgrading to the next level. If you truly wish to learn to design your own I concur with pmrobert - get a book or two and get on some of the GN/GNX forums. If you want extreme talk to the tractor pulling folks - though they use alcohol or diesel for fuel.
ISZ
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
But, most of the time, it's going to be operating "off design", and then the reality is that the exhaust manifold pressure will be higher than boost pressure.
The lower you can get the exhaust manifold pressure, the better off you will be. Always.
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
"The lower you can get the exhaust manifold pressure, the better off you will be. Always."
For a given turbo output perhaps, but not in general.
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
"The lower you can get the exhaust manifold pressure, the better off you will be. Always."
For a given turbo output perhaps, but not in general.
Fabrico, care to justify why not in general?
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
"The lower you can get the exhaust manifold pressure, the better off you will be. Always."
I would say it's the always in that stand alone statement that needs to be justified. From a myriad of possible causes, both internal and external, low exhaust pressure could most easily emanate from doing below potential work. There are likely just as many inefficiencies that would cause low pressure as high. Optimum is the goal.
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
RE: Turbo (Boost) Manifold PSI vs. Exhaust Manifold PSI
But my expertise is the turbomachinery, so let me comment there. The inherent work balance between the turbocompressor stage and the turboexpander stage is not dirrectly related to pressure ratio or pressure change. It is directly related to enthalpy change (assuming mass flow is nearly identical between the two stages).
So, if you want to maximize the pressure drop across the reciprocator, minimize the compressor inlet temp and maximize the turbine inlet temp. Compressor work is related to enthalpy change so is therefore (assuming constant spec heat) related to delta T. But pressure ratio is related to Delta T divided by T1. Lower the compressor inlet gas temp and you will get much higher compressor pressure for a given shaft work.
Practically speaking, I have precooled the inlet charge with a LN2 cooled heat exchanger and achieved significantly lower turbine work demand for a given compressor pressure rise. I've never done this on a motor sports application (only aerospace), but it may have some real potential if the racing rules allow it.