Im going and picking up an 88 Turbo2 this weekend. The car has a full 2.5" RB turbo-back exhaust. I'm planning on a lot of upgrades, including hybrid turbo, FMIC, looking for close to 300RWHP. Will the 2.5" exhaust be a big restriction, as opposed to 3"? If so, I might just get a 3" DP, and have a midpipe going from 3" to 2.5", to bolt up to the cat-back (might sound kinda dumb..but I have a nice cat-back that is 2.5 and I really dont want to sell it) What do you think?

 

^- Amd yes I did search, but no one seemed to answer the question of whether or not a 2.5" DP and MP will be much worse than a 3"

https://www.rx7club.com/showthread.p...t&pagenumber=1

 

From what I've read, turbo's are not as sensitive to exhaust tune - as long as they breathe freely.
Your setup may not be perfect, but it should work well.
It's the NA's that are more fussy about smooth increasing pipe size.

 

The cross sectional area of a 2.5 inch pipe is 4.9 square inches, the cross sectional area of a 3 inch pipe is 7.06 inches thats roughy 31% more air volume that can travel through the 3inch pipe, therefore, the 3inch pipe is going to be MUCH less restrictive.. HOWEVER.. 300RWHP is totally opbtainable with a 2.5 inch system., you should have no problems from restriction with that goal. 350 HP + definately go with a 3" system.

HOWEVER.... I hope by hybrid turbo you are also planing on either having the wastegate ported or going with a new manifold and an external wastegate AND a Standa Alone ECU like a microtek or a Haltec... If you use the stock manifold.... you are going to have nasty problems with the wastegate and boost creep.