Don Terrill’s Speed-Talk

Had an 860 hp 505 in my nhra super st 70 chevelle with 2.125 by 4 inch headers with a merge collector with about 12 inches of collector measured at the pinch. I'm building a 532 this winter should make another 80 plus hp. This is a throttle stop deal. How much do you think these headers will kill this engine compared to 2.250 pri tubes?

i do not think they will kill it much if anything.

I had 2" x 3.5" headers on a 540 and i bought a set of lemons 2.25 x 4 and made no measurable difference at the track. Was a 750 hp motor.

410 Sprint Car engines and 358ci NASCAR engines (before being hampered a bit) run / ran 1 7/8” primaries (off the head) at the same power levels before stepping up.

The 2.125 headers would be my pick for the higjer hp engine, providing the port match is close.
Thats still a lot of pipe. There will be more in it with primary/secondary length.
How long do you run the throttle stop for, and how much throttle are you using on the stop?

gnicholson, about what max. RPM will the engine see ?? Mark H.

Max rpm will be about 7600 cruise rpm on the stop is 4200 and usually around 2.8 to 3 seconds.

We actually build headers specific for throttle racing..... the steps are in different places versus an all out power header...... consistency is important with throttle stop racing so knowing where the stop needs to be for say Great bend vs Earlville is a big deal. Then when the air changes, will it be consistent with the calculations for the stop...... went through this with Gary Stinnett years ago with Ryan Siffrings vette...... headers to make a huge difference when throttle stop racing...

I would bet that going bigger( 2.250") would not gain you anything, especially considering the RPM peak AND the throttle stop deal. Mark H.

I was thinking about building some step headers from 2.125 to 2.250 being how this is not a chassis car but still has the stock front frame of a 70 Chevelle the primary tubes are very hard to get equal although from everything I've read and experienced that's not that big of a deal but the trend is probably the shorter tubes especially with the diameter I have I guess a good exhaust program like pipe Max may help I'll probably just put on where I have and see what happens and then try some bigger headers on the dyno just to get an idea

Step from 2.125 to 2.250 would probably be a good choice, and pipe max should put you very close. Have you considered 4-2-1 type headers, or would they be impossible w/your chassis ?? Usually 4-2-1 's produce more steam BELOW peak torque number. Mark H.