[ta man]

Bump

[steve25]

If your bolting on a header tube that’s the same size as your ext port area at the flange you will pick up 3% more exh flow above .350” lift.

If that tube is 1/16” or more bigger then a added 4 to 5% will show up so don’t just go by the bare port cfm numbers.

Also on motors of under 9.5 compression low lift exh flow numbers when the piston has not yet reached BDC are very important in purging the cylinders.

Low comp motors hold onto a lot more hot gasses that did not get used to push the piston down on the power stroke.
If you don’t get a good head start on getting these gases out your VE numbers will never top 100%, in fact they may not even reach 95%.

[steve25]

Here’s the maximum horse power per cylinder per pipe diameter.

Reduce these hp numbers by 30% if you want to be well on the safe side of reaching your hp goals.

[78w72]

Originally Posted by ta man

Bump

Thanks for finding & bumping this old thread, you must have a really good memory to recall this from 8 years ago... but the new thread was more or also about if anyone has the dougs and how they fit compared to the O-port 2" HSC. This old thread has some good info on power vs tube size but no pics or much comparison on how the 1 7/8 dougs ground clearance is vs HSC.

[Stan Weiss]

Originally Posted by steve25

Here’s the maximum horse power per cylinder per pipe diameter.

Reduce these hp numbers by 30% if you want to be well on the safe side of reaching your hp goals.

Steve,
Do you know if pipe diameter is ID or OD?

This chart say pipe id.

Stan

[steve25]

ID Stan.

[Steve C.]

Inside diameter here

https://www.hotrod.com/uploads/sites...ound%7C875:492

Here the primary-tube diameter as a function of RPM and engine displacement.
From the origional article it was suggested If you're building a header set from scratch, the accompanying graph should serve as a rough guideline for primary tube diameter.


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[Dragncar]

I don't know about that Hot Rod chart. if you go by it, you can not even get the header size you need on a Pontiac with a aftermarket block. Even with a 2" header on a 461 it says you are only good for 6K.
Am I reading it right ?

[steve25]

For what it may be worth to some my flowbench testing has shown that for maxing out race motor power that when a pipe bend of over 40 degrees comes into play then if possible the pipe diameter needs to go up by 1/8” for ever 20 degree increase over 40.
Then the pipe ID can go back down to its starting ID that was at the exh flange.

[ta man]

Originally Posted by 78w72

Thanks for finding & bumping this old thread, you must have a really good memory to recall this from 8 years ago... but the new thread was more or also about if anyone has the dougs and how they fit compared to the O-port 2" HSC. This old thread has some good info on power vs tube size but no pics or much comparison on how the 1 7/8 dougs ground clearance is vs HSC.

My memory is good for some things...just don't ask my wife lol

[Steve C.]

Keep in mind when determining the inside pipe diameter you will need to know what guage material the header company uses .
A common choice is 16-guage and the thickness will vary slightly depending what specific material is used. So is 18-guage material

The formula below was published by David Vizard.
As many know much of his work has been centered around Chevy engines, especially the 350cid. Therefore I've often wondered if it might be biased in that direction.

That said I've taken note of it and worked the formula around my Edelbrock heads and with porting the exhaust port ended up towards 250 cfm at the upper lifts.
As noted David's formula is based on the INSIDE diameter. I run 2-inch headers (outside diameter) on my 505 that makes peak power at about 6000 rpm.

For conversation.... 16-gauge = .062" x 2 = .124" thus 2-inch headers = 1.876' inside pipe diameter


https://forums.maxperformanceinc.com...1&d=1516188310


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[PontiacHO]

All for a street engine? You guys are so technically advanced that us mere mortals can’t keep up here. Why not exhaust cut outs for the rare track days? In my opinion then the exhaust diameter really doesn’t factor in for extracting every ounce of horsepower for street driving.

[Steve C.]

Repeat from the origional post.....

"I have a question regarding header sizes for certain power levels. I currently have a ~525hp 400 based 467 pump gas stroker engine with 72cc round port e-heads & OF roller cam, runs low 11's. can provide more specs if needed. its mostly a street car but sees some frequent drag strip time at test & tunes."

Forgot to add....

I know it is old material but keeping in mind others search out and could be interested in similar material for interest.

.

[ta man]

Originally Posted by 78w72

Thanks for finding & bumping this old thread, you must have a really good memory to recall this from 8 years ago... but the new thread was more or also about if anyone has the dougs and how they fit compared to the O-port 2" HSC. This old thread has some good info on power vs tube size but no pics or much comparison on how the 1 7/8 dougs ground clearance is vs HSC.

I just spoke to my buddy Andy (Torquewar) he has ran the 1 7/8 Doug Roundport headers for years ..great fit and clearance. His car runs pretty decent too!

[steve25]

In reference to an earlier post about the KRE D ports the last set I did only got into the high 190s in terms of stock exh flow .

[Dragncar]

I don't know but all this stuff about headers, well from what I understand spending big money, talking 3K or so on a custom set of stepped multi piece headers is worth power. But not some huge amount . Talking 10 or so HP over some nice 2" inside dia Hookers with a good merge collector.
Kasse did win or almost win that contest with box stock Hookers after all.
These headers are a pretty good compromise for a lot of guys IMO. 1900$, SS, multi piece and have some nice merge collectors on them. I paid 500 $ for 2 mild steel merge collectors.
they are 1 7/8", wish they were 2" inside dia but you could make some good power and torque with these things.
https://butlerperformance.com/i-3164...tegory:1459705

[Skip Fix]

Those almost look like the old IA plain steel multi piece headers for early A body I have.

[Dragncar]

What makes them a good deal is they are SS and the collectors. Those things add torque.
You usually have to spend real money just for a collector like that.

[HWYSTR455]

I can say that I will never again run the Doug's 2" round ports, the bolts are a PITA. And the fit isn't that good either. I had to beat a couple spots.

I have to drop the starter to tighten 2 bolts as well.

Biggest issue I have with them is the collectors don't point straight back, they are slightly angled. By the time you get to the back of the car with a full exhaust, you will never get the tips to point right (thru the valance). Or even get it to exit behind the bumper.

That one funky tube that wraps over the filter sux too, I have to tip the filter to get it out when changing and dumps oil on the end of the tubes/collector.

I have a set of 1 7/8 that I'm trying to psych myself into installing, that part is taking the longest! I will have to rerun the X pipe and straight sections too. Not fun laying on your back.



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[Formulajones]

The biggest chassis header we run on our stuff is 2". Worked well on Dad's 571. They are just out of the box hooker super comps and used them on the dyno with an exhaust system and made 724ho 764 tq with them. They fit the car nicely, don't hang low. Exhaust is a custom 3 1/2" from headers into a dr gas X that changes to 3" from there.

My 598 also uses 2" hooker super comps and made 786hp 772 tq. Again just out of the box chassis headers that fit really well. Same exhaust system..

When you get into bigger header tubes, at least on our cars, they all seem to wrap one tube around the frame and the inner fender needs to be cut. No thanks. So we stick to 2" headers. They are just street cars and don't need anything fancier.

We run electric cutouts on everything including these 2 examples. Not for performance but mainly for fun. In fact my 598 on back to back passes ran exactly identical passes through the exhaust vs cutouts open. So the system seems to be working well enough on that setup.