After posting a pic of my new exhaust, cheater_5 brought up a valid point. Because the exhaust is so large there will be no backpressure.

From my understanding backpressure is only needed to help scavange exhaust gasses. Now that I have fitted tuned length extractors, which are better at scavaging do I really need backpressure??

I am not too fusses cause I only fitted the exhaust of this size for the SR20DE when it arrives so I didnt have to do it twice but what is this backpressure all about.

A mate of mine has a kp starlet with rally 4k and when it first went in he had 2 1/4 exhaust but run half of it at 2" becuase thats just what he had and he hadnt got around to putting it all in.
He drove it like for that. keep in mind this engine isnt really road friendly. Anyway he drove it like this for ages then got put the rest of the 2 1/4" exhaust in. He didnt like it much as the cam was a lumpy bugger for rally it made driving under its power band a dick so he went back to full 2".
For this reason, im running 2" through the whole car with the race a15 in now.
Thats just for more low end torque and drivability tho.

No, you don't need backpressure, the less the better. But you might need to re-jet the carburetor to make it run well.

See Wikipedia: Backpressure

The backpressure argument in exhaust tuning will never be settled because its not really a question of "need", but more of "want",
what do you want more of, bottom end torque or top end hp?
when u get rid of backpressure altogether u can find it too unresponsive at low revs and need to stir the gearbox more in city driving,

but it will LOVE to REV

Its the same as runner lengths and unsprung weight... internet discussions that amount to ####all of none in the real world for most of us :P

City driving and low torque, I think yes it's needed.
For high revving race conditions, no.

Have you looked at the F1 cars and GP bikes exhaust? I can't imagine any back preasure from their exhausts.But remember, they see high revs all the time.

Well that just about settles it. I dont need back pressure cause I wanna rev the piss out of it. Its got a big cam anyway so its already a pig around town. Thanks for the input lads