yea. I am wondering why that happen? I was think about that if the exhaust pressure is low it wound take more force to compress the exhaust valve spring, therefore the drive train will lose some of the torque. But my friend said that the for the to compress exhaust valve spring shouldn't matter that much.

 

do you mean replacing the catalytic converter with a striaght piece, or the whole exhaust?

 

well I know both way should lose low rpm torque, of course the whole exhaust should be more significant. it would be good if someone explain both. thx

 

you lose back pressure when its a straight pipe, so it flows alot better at the high rpms, but you lose the pressure at the low, so you lose some power.

 

that depends on the size of the piping... and whether it's turbo, or n/a...

 

well. lose what kind of pressure at the low? like the pressure in the combusting cyclinder? or the exhaust header?

 

backpressure is for carbe'd cars, not ours.
you'd run outtal torque b/c there would be too much air. essentially you'd be leaning out the engine.
If you advanced your timing and increased fuel, you could compensate to a point.

 

oh I thought the MAF will take care of the fuel mixture problem. anyway thanks for the input

 

Backpressure is to help in evacuating the cyclinder of exhaust gases IIRC.