ahhh yeeeah

 

Like momentum said in an earlier post, you can get backpressure from the exhaust not being large enough, which in turn, restricts the exhaust, or you can get backpressure from it being too large (too much volume in the pipes which reduces exhaust gas velocity and causes turbulence and backpressure that way). I think this is the reason why they say you CAN go too big....or else everyone would try to fit the biggest set of pipes under their cars.

Restrictions in the exhaust would limit horsepower AND torque? How about restrictions in the intake? It's known that, for rallying, there are restrictor plates on the intakes/throttle body to limit horsepower, but what this does it that it increases torque immensely (unless anti-lag is attributing to most of it).

From my experience with an exhaust cutout on my subaru(~350 crank hp), I felt that I lost torque once i opened up the exhaust cutout all the way. It could've been that the tune didn't fully compensate, but it was thoroughly tuned with it open and closed where the tuner found a happy median.

I say for the OP's case, a 4" would help, seeing that the 300whp car benefited from switching to a 4" from a 3". I say test it and find out

 

Yes exhaust restriction would lose both torque and horsepower...they are directly related. Lose torque and you lose HP....having a restriction in the exhaust will cause most of its losses up top where the torque will fall off hard and so will whp.

Intake restriction....doubtful because the TB and stock IM flow pretty well or else the power wouldnt be climbing to 9000rpm like it does. Although im sure if someone went larger TB and IM it would lose some midrange but once the engine is in the upper rpms I bet it would see some nice gains too.

 

The restrictors on the rally limit hp because you can only make x amount of power for x amount of airflow. You can however make an infinite amount of torque with the same airflow. The restrictors do nothing to gain torque it just happens that they make full power early in the powerband and hold it to redline so their torque/hp ratio seems high for their application. If you removed the restrictor you would gain both hp and torque.