Hi there, I was wondering, if I would put on 2 mandrell bent exhaust manifolds on my VQ30DE, and run complete exhausts from both manifolds to the back of the car (so every cilinder bank has it's own exhaust, no Y pipe anymore), would that make up some more HP? Or do the banks need eachothers backpressure to operate properly?

 

When designing performance exhaust systems, special attention needs to be given to maintaining the mean gas velocity within a certain range.

If it is too high, your flow losses become excessive and the increased backpressure will prevent your cylinders from fully emptying the products of combustion.

If it is too low, the suction (low pressure area) at the exhaust port will be reduced and will not be as effective in helping to draw out (scavenge) the exhaust gases from the cylinders.

Both scenarios serve to reduce the amount of the intake charge that flows into the cylinders. Smaller charge, means lower combustion pressure and the result is reduced engine torque.

The above comments are for NA engines. Tuning exhausts for FI is a different story.