hi guys i just baught a 396bbc that has been fully rebuilt with bigger cam and lifters, head work mild port and polish, i beleave its been bored over, edelbrock performer intake, and this engine pull better than the old tired 427 lol i was wondering why does it seem like its running out of power around 4250rpm as it has a holley 650 double pumper converted to a 750 race carb with a kit from proform... the motor come with an old quadra jet and stock ignition and was in a heavier car 69 elcamino that was running low to mid 12s ive seen the slips and was there when it was runned a few times and was mostly consistant when i put the engine in place of my 427 it pull like hell till 4250rpm but i put the holley and an msd ignition the only othe difference i can see is exhaust as in the elcamino it had dual 2.5 inch exhaust and now its 2.5 inch to single 3 inch to a flowmaster so just need some advise on how to make it pull better in the upper rpm band id like for it to pull till 5000rpm and i have the limiter set at 5500rpm should i change exhaust ? intake manifold ? carb tunning + spacer ?

 

A single 3 doesn't flow quite as much as dual 2.5s. My own guess would be to try 3.5" if staying single. I think Mufflex makes a kit for our cars.

 

thats my thaught is starting with exhaust but was not sure if a 750 carb was big enough either cause most ppl run way larger like 850cfm.. so for exhaust i can go to dual from headers to a 4 inch single mandrel to dual again or true duals work just as good or better?