Another 2.5 inch vs 3.0 inch?

Kent mosby said

I am prepping the final installs and have a question on exhaust.
My 73 scamp will get its 512 RB installed in the coming weeks. The headers are TTI 440-200 with 2 inch primary tubes with 3.5 collector to 3 inch flange. Trans is 727 and 3.91 gears in an 8 3/4 rearend. Cam grind specs are 244/252 @ .050”, 282/290 adv, .516”/.537” lift(1.5:1 rocker), 112 sep, .016”/.018” lash. Future nitrous is an option but not certain. Holley Super sniper EFI will be installed with the motor.

The question I am debating is do I use 3 inch or 2.5 inch exhaust? I have read a bunch and am still confused.

Then I read this thread New 3" exhaust with 2.5" Tailpipes and yet I did not see any performance evaluation.

I have the 2.5 inch adapters on order but can change them if need be. Thanks for the wisdom.

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Your build is very very close to mine , I ran full 3 1/2'' dumped in front of the axle , w/ turn downs . Home brewed 12'' bullit (roundy round) mufflers w/ 3 1/2'' spiral inserts slid inside, and tack welded , A little loud on the gas , but doesnt bother me inside.
I f u look up engine size versus exhaust size , a 500'' engine should have 3 1/2'' . Dont remeber where I found that tho , already had it built before hand. Had some used old exhaust wrap and wrapped them completly/nasty stuff !
Had to pie cut a couple of pieces to twist around under the drivers side cross member , into the straight pipes leading to the muffs.
You pobly wouldnt need to do the pie cuts , I have raised port heads , that raise the whole mess up some . Easy to do w/ a mig welder .
DEFINITLY DONT USE 2 1/2 !! Unless u just gotta go over the rear end -------