421 SBC - something holding it back at the track !

[steve cowan]

thanks for the replies guys,
if we start to set the cylinder head up in the right direction as far as avg CSA through the intake tract and work on cam timing events and the engine makes peak power at a higher rpm but we leave the rear gear the same would we expect the rpm across the stripe to be the same or higher due to the engine making more power?

[SBC-68-FIREBIRD]

Thanks for the replies boys.
I have not found out what correction factor they use. They are always busy as am I so rarely get out there to say hello.

[SBC-68-FIREBIRD]

Hey Boys, so I went out to a test n tune for a run last night.
Previous best was 10.92@122.
I changed the jets before heading out to 2 x sizes bigger in primaries & secondaries.
Had 2 runs -
10.92@122.04
10.92@121.88
Changed the jets again, up another two sizes so 4 sizes bigger that it was dyno'd with then had another two runs.
10.95@121.39
10.93@122.89
Changed the jets back to original size it was dyno'd with & had another two runs.
10.92@121.78
10.87@122.18
I did not have any smaller jets with me but I will try them next time. Also going to try dropping the pipes & see what happens. Wont be going back for a few months now, too hot this time of year.

[rocketracer380]

I did a 434 build with afr 235 eliminators 10:9.1 pump gas small.640 roller off the foot brake the car runs 10.1@135 @3400# the cam was speced by lsm it was on a 109 pro system carb 1000hp super Vic ported by cfm nuthing exotic and only 28 degrees timing total hi tens with a 421 is leaving alot on the table just for comparison my friends pump gas 355 with sportsman's went 11.1@ 119 all day engine is 20 + years old

[steve316]

Like was posted before You need a 1050 dom. & around 264-276 on 108 at .050 cam