I was told once that for the M20 motors a single pipe is better for it, and with the the M50/M52 it is better to go dual.
So when i had my M20 in I had a single 3" from a high flow cat back to a brullen. Now with my M52 i have headers and dual
2 2/4" all the way back. I did feel with my M20 a diffrents with the exhust, chip, and intake.
I ran my car at Cayuga stock (i'm not the greatest drag racer) my best was a 15.1 and with my mods the next year my best was a 14.6. Not great but a little better.