[keoni1978]

I'm think about having custom exhaust made for my bike. Instead of 50mm I'm thinking about going up to 57mm. Since I dont know much about back pressure, ecu problems, etc.... How realistic is it to be able to run 57mm on a S4Rs engine?

 

[S4R4FUN]

not.

 

[Danimal]

You may end up lowering the exhaust gas velocity enough to really effect your low-RPM scavanging. You might gain a few upper-RPM HP at the expense of a lot of around-town driveability.

-Danimal

 

[Corse998]

I think since the intake manifolds are 50mm that will become your flow bottleneck if your exhaust grows over 50mm. Now, if you fit the Superbike intake system on there along with the big exhaust, you might gain some flow...