when people talk about exhausts back pressure always comes up eventually. do rotarys need back pressure?

 

no.

 

ok thank you

 

They run a better with no back pressure, then there's the NOISE.

 

lol. yea i experienced that NOISE first hand a couple times. it was bad, and yet................

 

so whats the diameter should it have?

 

Not one internal ombustion engine on the planet needs any type of back pressure. Back pressure is bad! velocity is good. You want an exhaust system that keeps velocity up. in the early days of tuning back pressure was confused with velocity and hense the parroted incorrect "knowlege" continues...

 

2.5" people have gone bigger, but the gains are small, and the noise is BIG

 

Not true. Are you familar with a two stroke?

But yeah everything else you said is right.

 

Two strokes are ESPECIALLY senstive to backpressure. They really really really do not like it.

It is critical to not confuse resonance tuning with backpressure. Resonance tuning *is* important for "closing the door" port wise but it couldn't work at all in the first place if there was backpressure in the system.

 

Think of it like a wood stove. You open the door wide open and the flames lick up, you close the door, but leave it cracked a little and the flames get even bigger.

A properly sized exhaust for your application will ALWAYS be the best option.

 

mines got a rb header 2.5 to a flowmaster 40 where the main cat used to be and it goes out to a long rice can sounds nice got warned bout the noise in town once it a 88 na not that it matters

 

what they all said

 

If I recall correctly Defined Autoworks made more power going from a 3" to a 2.5".

But size of the pipe also depends a lot on the specific engine build.

 

yep to both.

 

so if its a stock port motor would a 2.25 inner diameter pipe (5feet long) then a single exit to a 3in right under the diff to the muffler would it be good?