Opinions on best shift point for Bracket racing and converter stall for below, 421 SBC, glide 1.80 first, 3050lb race weight w/driver. Suspect that peak torque may be at slightly lower 5800ish.
RPM STPTrq (Clb-ft) STPPwr (CHp)
6000 625.4 714.5
6100 622 722.4
6200 619.5 731.3
6300 618.2 741.5
6400 616.7 751.6
6500 615.3 763.3
6600 614.2 773.2
6700 613.4 785.2
6800 614.2 795.2
6900 613.3 805.7
7000 608.6 811.2
7100 607.4 821.2
7200 604.2 828.1
7300 599.6 833.4
7400 596.2 840
7500 589.7 842
7600 582.2 842.4
7700 576.3 844.9
7800 565.6 840
Appreciate input in advance

That's a nice 421, must have some good cylinder heads on that sbc!

2BKING

This message has been edited. Last edited by: B KING,

7800

I like to shift about 200 RPM higher than peak power and run converter on loose side. Keeps it in the powerband better.

I'd be interested in what's in that build to make power like that.

Thank you, 13 degree brodix heads by Eric Weingarter, edelbrock 2844 previously converted to 4500 and ported with heads by eric, Chris Cobb designed comp cams 55mm core ~.800 lift, pac 1225s, je shelf 13° pistons 14.8 to 1, 1150 get em carburetor, callies billet crank, and x rods, 4.155 x 3.875, T&D rockers, BAM 0.904 lifters, billet melling shark tooth wet sump, professionally assembled, dyno and tuned by Nesbitt's Performance, very happy with results.

This message has been edited. Last edited by: BG7X77,

quote:

Originally posted by BG7X77:
Thank you, 13 degree brodix heads by Eric Weingarten, edelbrock 2844 previously converted to 4500 and ported with heads by eric, Chris Cobb designed comp cams 55mm core ~.800 lift, pac 1225s, je shelf 13° pistons 14.8 to 1, 1150 get em carburetor, callies billet crank, and x rods, 4.155 x 3.875, T&D rockers, BAM 0.904 lifters, billet melling shark tooth wet sump, professionally assembled, dyno and tuned by Nesbitt's Performance, very happy with results.

That's a bad ass build! thanks for the info

Flash 7000, shift 7600

Shift before peak hp? I have seen information that says pick a spot over peak by 100 to 400 rpm thr flatter the curve the lower the amount over peak. I appreciate your input, im guessing your close on flash.

That is a stout 421 and with that cam and lifters should be relatively durable. Good motor.

If you was to shift before peak HP I think it would not be nearly as consistent or as fast. Even lugging motor for just a split second is costly. It makes 50 more HP at 7000 than it does at 6500 RPM. The difference between 7000 and 7500 is only 29 HP. The difference between 7700 and 7200 is only 14 Hp. The difference between 7200 and 6200 is almost 100 HP! Now 6500 may not really be "lugging" motor but it is not at peak power and you can see further it drops down more it will hurt it. I think that thing needs to be 6800 and up all way down the track.

This relates to my 421 engine, With AFR245 heads and a 950 alky carb, dyno peaked about 7000-7100. I had shift point set at 7400 till I looked at the G force graph on Racepak and saw it was laying over after 7000. Obvious decision to change the shift point.

quote:

Originally posted by BG7X77:
Shift before peak hp? I have seen information that says pick a spot over peak by 100 to 400 rpm thr flatter the curve the lower the amount over peak. I appreciate your input, im guessing your close on flash.

Gives you a little in the bank if the shift is slow....it's only 2 HP from 7600 to peak.
I like the keep the entire run in a 600 RPM or less window.