Don Terrill’s Speed-Talk

I was told 15 years ago headers over 1 7/8 don't help. Alot has changed since then. What about now? Oldhead

sort of an open ended question.... on a 9:1 327, no. on a 12:1 434, probably!

A 2.5 inch header would "work". Might not make any power though. But, the exhaust gasses would certainly get out. But, yes, I have used 2 inch and even 2 1/8 inch header on small blocks. Its more about how much total power is being made. I had a road race 327 pick up 65 hp and 38 ft/lbs going from a 1 5/8 with 3 inch collector, to a 1 7/8 with a 3.5 collector, with a dual plane intake to boot. Totally bas akwards.

Frankshaft wrote: ↑Sat Nov 11, 2017 5:59 pm A 2.5 inch header would "work". Might not make any power though. But, the exhaust gasses would certainly get out. But, yes, I have used 2 inch and even 2 1/8 inch header on small blocks. Its more about how much total power is being made. I had a road race 327 pick up 65 hp and 38 ft/lbs going from a 1 5/8 with 3 inch collector, to a 1 7/8 with a 3.5 collector, with a dual plane intake to boot. Totally bas akwards.

Yet that same header combo on a restricted 2bb engine looses with larger header about that same amount.
The options for stepped or high velocity headers when going from 1 3/4' TO 1 7/8" builds more power then a straight tube set depending on the heads and cam choice. The extra scavenging of the stepped headers helps in a smaller carb as well as a big carb engine. Just depends on the RPM range you run.

Some guys find very good luck with a 1 3/4" header and while the info is available they never go bigger because of the work involved to fit them in the chassis thus loosing out on potential gains.

Frankshaft wrote: ↑Sat Nov 11, 2017 5:59 pm A 2.5 inch header would "work". Might not make any power though. But, the exhaust gasses would certainly get out. But, yes, I have used 2 inch and even 2 1/8 inch header on small blocks. Its more about how much total power is being made. I had a road race 327 pick up 65 hp and 38 ft/lbs going from a 1 5/8 with 3 inch collector, to a 1 7/8 with a 3.5 collector, with a dual plane intake to boot. Totally bas akwards.

I've found the same results.

A 900hp 410 sprint car uses 1 7/8 - 2
And on some tracks the wing cars run 1 3/4" headers.

I think the extra high compression has something to do with the small headers

englertracing wrote: ↑Sat Nov 11, 2017 8:48 pm A 900hp 410 sprint car uses 1 7/8 - 2
And on some tracks the wing cars run 1 3/4" headers.

I think the extra high compression has something to do with the small headers

850hp Cup motors run 1 7/8” off the head. Not really a compression thing, just that most people have waaayyyyyy too large of a header. Darin Morgan shared that the Cup cars like a little bigger exhaust port than you would find on a drag car at an equal power level due to the full exhaust requirement. Just another data point to suggest most headers are way too big.

The sky is the limit in header size for a SBC (literally). Lol

I am talking 1200 hp Oldhead

I think frankshaft had a point, total power is what matters. 1200 hp creates the same waste gas regardless of displacement. The rest of the system is part of the equation as well.

1200hp, run as big a header as will fit.

Is this supercharged?
Should be running port sized headers, then stepping from there.

hoffman900 wrote: ↑Sat Nov 11, 2017 9:32 pm

englertracing wrote: ↑Sat Nov 11, 2017 8:48 pm A 900hp 410 sprint car uses 1 7/8 - 2
And on some tracks the wing cars run 1 3/4" headers.

I think the extra high compression has something to do with the small headers

850hp Cup motors run 1 7/8” off the head. Not really a compression thing, just that most people have waaayyyyyy too large of a header. Darin Morgan shared that the Cup cars like a little bigger exhaust port than you would find on a drag car at an equal power level due to the full exhaust requirement. Just another data point to suggest most headers are way too big.

The sky is the limit in header size for a SBC (literally). Lol

I see a trend in higher cr and earlier evo engines with relatively smaller headers as of late
Like mentioned world of outlaws tuning a 1.75" header
And street cars with low cr late evo wanting relitavely larger headers
Like some 450hp thing wanting a 1.625 or 1.75" header.

englertracing wrote: ↑Sun Nov 12, 2017 2:20 am

hoffman900 wrote: ↑Sat Nov 11, 2017 9:32 pm

englertracing wrote: ↑Sat Nov 11, 2017 8:48 pm A 900hp 410 sprint car uses 1 7/8 - 2
And on some tracks the wing cars run 1 3/4" headers.

I think the extra high compression has something to do with the small headers

850hp Cup motors run 1 7/8” off the head. Not really a compression thing, just that most people have waaayyyyyy too large of a header. Darin Morgan shared that the Cup cars like a little bigger exhaust port than you would find on a drag car at an equal power level due to the full exhaust requirement. Just another data point to suggest most headers are way too big.

The sky is the limit in header size for a SBC (literally). Lol

I see a trend in higher cr and earlier evo engines with relatively smaller headers as of late
Like mentioned world of outlaws tuning a 1.75" header
And street cars with low cr late evo wanting relitavely larger headers
Like some 450hp thing wanting a 1.625 or 1.75" header.

Eh, still not sure. You see engines with that power in prep restricted classes running 1.5” tubing off the head. I’m talking 2bbl circle track engines and the “stock” type drag classes. Of course, this is a custom built header following everything Calvin preaches in terms of flow.

As Calvin has pretty much said here before, most headers are so bad, that bigger tubing works because you’re really just trying to minimize pumping losses at that point.

I’ve seen Calvin’s headers support ~60hp/cyl with 1 3/8” tubing off the head, and ~75hp/cyl with 1 5/8” tubing off the head.

hpetew wrote: ↑Sat Nov 11, 2017 10:57 pm I think frankshaft had a point, total power is what matters. 1200 hp creates the same waste gas regardless of displacement. <snip>

That’s true, but assuming the same VE in both cases, for the same hp a large capacity engine would turn proportionally lower revs and push out an inversely larger slug of exhaust each cycle.

Larger slug but more time to get rid of it

Bigger duration can use a smaller pipe just like with itb you can make more hp with smaller runner diameter if the cam duration is higher.

The higher the rpm the shorter the pipe the smaller it can be for the same losses.