My project is getting closer, scheduled for the Muffler shop in two days trying to figure out what is best for tail pipe size, it has headers with 3" collectors with 3" cut outs right behind the collector, am thinking 3" from their to Mufflers, (mufflers are Raptor with 2 1/2 openings) and then 2 1/2 on out the back, is this ok, or should I scrap all the 2 1/2 stuff. Car is a 3200 lb. with a 30 over 440, 9.97 CR, with max wedge heads and intake with 750 carbs, and a RB .510 lift 242 dur. cam. any guesses on HP

scrap the 2&1/2" stuff & use 3". Any dia reduction/bend/twist or turn from the collectors on back(with the exception of an X pipe) will cost you power. Then you only have to deal with the increased noise that a 3" system brings to the table. I would suggest dynomax muffs & some resonators downstream from them.

I would go either mandrel bent 2.5" from the cut-outs back or go 3" the whole way and scrap the cut-outs. Going 3" to the muffler then 2.5" the rest of the way it pointless.

3 inch aint nothing but a bunch of noise and no back pressure. Unless you making 500 hp or better its a waste of $. Back pressure helps in the torque factor.

Mandrel bent 2-1/2" would probbly be the best option, and it would probbably flow as good or better than crimp bent 3". The 2-1/2" is easier to fit too.
If you had 3" mufflers then I would say use 3" tube.

Just for comparison info, my Charger 451 stroker originally used 3.5" crimp bent tubing with Dynomax race bullet mufflers that dumped under the car before the rear axle. The car was just way too loud for the street, so I installed the TTI 3" mandrel bent exhaust system (used my old Hooker headers) with the Dynomax SuperTurbo mufflers, and tail pipes over the axle and out the back like stock. The quieter and smaller diameter TTI system did not make a difference in the cars performance at all.