Appreciate the input, Emilio. Have a like cat.

 

Must.... refrain... from...asking....emilio.... bench.... racer... question.... about.... not... using... 3"... exhausts.... on.... FI.....race....cars...

 

Turbo cars specifically: 3" weighs more, and if you can hit your targets with a powerband you're happy with with smaller, not a whole lot of point to a larger exhaust. Diminishing returns. Lowering the boost threshold not as important on a turbo car to a point. Small turbo on a 2.5" exhaust will spool plenty early, and transients are naturally much faster in the RPM range a race car lives in. Add in db limits at certain tracks (probably not a concern for 99% of turbo miatas), and you're squarely in "as big as necessary, as little as possible" territory.

Is 3" better for turbo car? Absolutely. Does it make or break a race car? No.

I don't want to sound like an askhole, but in the name of science i will eventually A/B 2.5" and 3" on an n/a car. Both on essentially stock longblock (where i expect 3" to have no improvement at all, and maybe lose torque) and on a Full-Swag-Ahead n/a built motor. I have an RB + Hytech 2.5" setup on the car right now, and i'll have a Maxim Works + 3" setup made. Not perfect science because of the different headers, but general consensus is that the Maxim Works don't perform any better or worse than the RB, so it's close enough to at least let me identify 3-5whp differences i'd imagine.

 

Any thoughts in the opposite direction? A lot to be lost by a 2.25 exhaust past header in the 180ish N/A range?