You want the least resistance possible. The shortest & biggest exhaust that is practical for you would be best.

 

5inch straight out of the hood.

 

the dyno results were pretty spot on car feels like it gained the extra 20hp, regardless doesnt matter i just slapped a 60-1 on earlier and seeing how much power i can get out of open 2.5inch dp

 

More or less to an extent. Too large will stop air flow to a crawl. Too small and air velocity will accelerate too fast and revert on it's self. It has to be a balance of fast enough velocity to keep the air moving rapidly versus power made. The manifold design AND turbine arrangement play huge roles in this amongst other things like the tune, cams, head design....

Smaller turbine A/Rs will see greater gains from larger diameter exhausts because they ramp speed so quick on the velocity side then peak out soon. A larger exhaust does not allow it to peak out as soon, which changes the breathing of the turbo hence creating more power.

Larger turbine A/Rs will see less gains from larger diameters because they move air very linearly and not so ram p-in-peak-like with small turbine A/Rs. That linear fashion allows smaller diameter exhausts to be more efficient and moving air at volumes because velocity stays up.

Last thing you want is excessive air hanging in the exhaust. This is what back-pressure is. Turbos don't like back pressure and cause almost a cardiac arrest of sorts when there is too much air volume in the exhaust and the turbine wheel can't inch in anymore.

Remember, you will meet plenty of exhaust restrictions OTHER than exhaust size including turbine A/R, manifold, head and cams. Exhaust is the last thing on the menu for flow out of the engine.

 

so this could also explain my slight boost creep at higher rpms...poopy manifold design...lol

 

What would you recommend with your s1 kit with the .63 AR Turbonetic turbo Paul?


I know i have to go bigger then 60mm im just unsure on what to go to...

 

Boost creep comes from manifold design, wastegate size, wastegate plumb out, size gate, turbo size and boost ran. It's yet another delicate balance.

 

.63 is one of those middle road A/Rs. 3" will still do you justice in all honesty.