[78w72]

have a quuestion 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.

i'm currently running hooker super comp headers with 2" primaries & 3.5" collectors into a full 3" pypes x pipe system with race pros. for such big tube headers they actually installed nicely & fit pretty good, EXCEPT for ground clearance! they hang way too low for my ~2" lowered car on city streets. i have to run tall (27.5") front tires to get by & still have issues on big curbs, speed bumps etc. & when i get some 17"-18" wheels to swap around for a pro tour look i will probably have shorter tires & that wont work too well without scraping the header collector flanges or bottom of lowest tubes.

so my question is regarding header tube size for a 500+hp engine. ive read guys making upwards & above 600 with smaller tubes like 1 7/8, even 1 3/4. im considering changing the headers to get better ground clearance as opposed to changing the ride height or being stuck with taller than needed tires to just barely "scrape" by. would i loose any hp/tq going to a smaller header with better ground clearance? ive heard some say too big of tubes kills tq so maybe the hookers are too big for my application? i am considering having the heads ported by SD to their 315cfm to get closer to a real 550hp.

i didnt pay for the hookers, they came with a car i bought. they are expensive, ceramic coated ones are $800 & i dont really want to buy dougs for around the same price & ive heard they fit worse & arent tuned like the hookers. what i am considering is the tribal tubes tri-Y's. they make a 1 3/4 tube with 3" collector & a 2" with 3.5 collector. is 1 3/4 big enough for my power level? they say yes but they are also trying to sell headers... they are about $500 & supposed to have excellent ground clearance, they say they sit above the subframe rails. look like nice headers & for the most part people seem to love them.

does anyone here use the 1 3/4 tri y's at this power level? or another brand 1 3/4? just lookig for advice on if thats big enough for this power? i have a set of hedman 1 3/4 on a very mild 400 t/a & they fit great & have good clearance, just seems to small for 500+hp.

[Steve C.]

CFM flow on the exhaust ports ? At what rpm ?

For interest see posts 9 & 14 for some formulas here:

http://forums.maxperformanceinc.com/...t=David+Vizard


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[Steve C.]

Something else to consider. See my post #16 here for the two pictures showing before and after with my header modification.......

http://forums.maxperformanceinc.com/...custom+headers


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[78w72]

Originally Posted by Steve C.

CFM flow on the exhaust ports ? At what rpm ?

For interest see posts 9 & 14 for some formulas here:

http://forums.maxperformanceinc.com/...t=David+Vizard


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sorry i have no idea on exhaust cfm flow on my heads. they are out of the box stock round port 72cc e-heads & usualy shift points are around 5500-5800 rpm.

thanks for the links, i read those threads & saw the graph... but graphs are not always 100% accurate nor do they apply to every engine combo the same. also 1 or 2 posts down "taman" says he uses 1 3/4 headers & hes making a little more power than me but ran close to same times before his recent motor refresh. is he loosing hp or tq? i dont know, thats why im curious what others are using or suggest.

sounds like i would get by fine with 1 3/4, tribal tubes suggested a smaller tube header might increase torque due to better scavenging, but at what cost to HP, if any?

[Steve C.]

A FWIW, out of the box your exhaust ports according to Edelbrock flow 172 cfm at .500" lift and 185 cfm at .600" lift (28").


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[Navy Horn 16]

This is a really good watch for the 2.5 vs 3 inch exhaust questions:

https://www.youtube.com/watch?v=_PVXvHkr-Vs

It's fairly definitive proof that the whole "lack of back pressure kills torque" thing is a myth.

One option would be to run 2.5 inch exhaust for your "running around time" time, and have exhaust cutouts for your track time.

[78w72]

Originally Posted by Steve C.

A FWIW, out of the box your exhaust ports according to Edelbrock flow 172 cfm at .500" lift and 185 cfm at .600" lift (28").


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thanks again for the info on ex flow. im pretty sure SD doesnt touch the ex side on the porting so if thats what they will be at for cfm sounds like 1 3/4 are ok.

[78w72]

Originally Posted by Navy Horn 16

This is a really good watch for the 2.5 vs 3 inch exhaust questions:

https://www.youtube.com/watch?v=_PVXvHkr-Vs

It's fairly definitive proof that the whole "lack of back pressure kills torque" thing is a myth.

One option would be to run 2.5 inch exhaust for your "running around time" time, and have exhaust cutouts for your track time.

ive seen & read quite a few tests on exhaust pipe sizes & chose the 3" based on future power upgrades, but again ive heard guys say 2.5" supported their 600hp engines.

im not concerned with the ex pipe size or back pressure created by pipe size & mufflers etc, im more concerned about header primary tube size for my power level & secondary, the scavenging effect. the pypes exhaust system actually tucks up nicely & doesnt hang down too far so changing to 2.5" & dumps wont gain anything for my situation. its all in the headers & how far down the lowest tubes & the collector flange hangs with how low the car is.

guess i just need to decide between new headers or changing ride height.

[Steve C.]

Regarding the primary pipe diameter for your street/STRIP application your bias should be toward making more top end while sacrificing a LITTLE down low.

Also note if your cylinder heads are ported to 315 on the intake and the exhaust port is left untouched the exhaust-to-intake flow ratio will only be about 58 percent. This based at 0.600" lift. Due to the amount of energy (heat) lost during the combustion process, a basic ratio of 75 to 80% exhaust flow/size to intake flow/size is a viable target. And yet some suggest exhaust port flow numbers are about useless in the real world.

Also if left at 58 percent some will suggest adding additional exhaust duration on the cam choice.

Do your homework on the subject.
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[78w72]

good points. i did quite a bit of homework when building the engine/driveline so it would meet my goals with the parts i had or could afford. goals were basically just a street car that ran & drove good, didnt overheat or have problems with too big of a cam or too low of gears etc & be 500hp pump gas friendly & be respectable at the strip & be able to entry level auto-x. i met all those goals pretty well & for what the car is it runs faster than i expected at the track & excellent manners on the street.

porting the heads i thought would compliment the cam better & according to SD the 315 package would be worth 30-50 hp over stock e-heads. im not sure what he does for the ex ports but i recall him saying they dont need much work if any at this level. if the heads get ported i would go to 1.65 rockers for a little more lift & duration. i dont plan on changing any mahjor parts for more top end like cam or intake/carb for this car, head porting would be the most id be doing in the future.

just trying to improve ground clearance & considered the smaller tri-y's as an option... for what new headers cost i may stick with the hookers & just lift the car an inch or so.

[ta man]

Originally Posted by Steve C.

Regarding the primary pipe diameter for your street/STRIP application your bias should be toward making more top end while sacrificing a LITTLE down low.

Also note if your cylinder heads are ported to 315 on the intake and the exhaust port is left untouched the exhaust-to-intake flow ratio will only be about 58 percent. This based at 0.600" lift. Due to the amount of energy (heat) lost during the combustion process, a basic ratio of 75 to 80% exhaust flow/size to intake flow/size is a viable target. And yet some suggest exhaust port flow numbers are about useless in the real world.

Also if left at 58 percent some will suggest adding additional exhaust duration on the cam choice.

Do your homework on the subject.
.

Going from my flow numbers on my heads SD is right at 75% after port work. At .400 272.2/205.3 75.42% at .500 300.6/226 75.18%

[78w72]

Originally Posted by ta man

Going from my flow numbers on my heads SD is right at 75% after port work. At .400 272.2/205.3 75.42% at .500 300.6/226 75.18%

youre using 1 3/4 headers right?

[ta man]

Originally Posted by 78w72

youre using 1 3/4 headers right?

Yes Hooker Super Comps...

[Steve C.]

When they first came out the KRE d-port heads were reported to flow 226 at .500 lift on the exhaust right out of the box.

( High Performance Pontiac magazine / Feb 2004 )

As cast they had a 88 percent exhaust-to-intake flow ratio at .500" lift. With TA Man's intake port work and leaving the exhaust ports as is the ratio came down.



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[ta man]

Originally Posted by Steve C.

When they first came out the KRE d-port heads were reported flow 226 at .500 lift on the exhaust right out of the box.

( High Performance Pontiac magazine / Feb 2004 )

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That seems high..My 290 KRE SD's only flowed 203 cfm before at .500...I wonder when they stated 260/220 cfm in the magazine that was at .550....? Makes more sense? I never fully trust magazine articles..especially when they are pushing new products.

[Steve C.]

At .500" lift the magazine article reported 256 intake and 226 exhaust at 28". There has always been some controversy with the numbers.

calculating header design

http://garage.grumpysperformance.com...er-design.185/


And if you get a KRE product involved in the discussion be aware their flow bench is a Pitot Tube type. It does not correlate with a SuperFlow Edge Orifice type bench in any way. Thus for interest if you get looking at formulas they work on Edge Orifice Flow Benches.


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[Skip Fix]

Originally Posted by ta man

That seems high..My 290 KRE SD's only flowed 203 cfm before at .500...I wonder when they stated 260/220 cfm in the magazine that was at .550....? Makes more sense? I never fully trust magazine articles..especially when they are pushing new products.

Along those lines year ago Muscle Car Review had an article on a 455 SD my old machinist built. He had a very conservative dyno but cars "ran the numbers". Used an UD cam. Well the dyno numbers were too low it was taken to another shop for dynoing again(on the east coast so not Westech) and since Comp advertized in the magazine it became a Comp cam and not a Ultradyne.

Lots of articles about motors dynoed at Westech taken to the track that do not run the numbers.


I think Roger Bolinger in Germany has the Tribal tubes on his Butler road race motor.

I can tell you my Hedman step 1 3/4-1 7/8 lost HP on a friend's 462 roller motor SD Perf ported E heads that made 640 HP and runs mid 10s compared t the 2" headers.

I plan on dynoing my 0.060 455 ported round port E heads Stump Puller cam motor with the Tribals, my step Hedman's, and my Hooker 2" this spring. So more info then. Just got an associate so I might can have a day off for dynoing it now! Last year just me and working my butt off.

[bulletpruf]

Good question. I'm curious to hear what y'all think, too. My combo is a tad milder; should be making close to 500 hp with a moderately built pump gas 455, and hope to dip into the high 11's in a 68 convt. I have 1 5/8 headers now. I know they're too small, but I'm thinking 1 3/4 is about right for me.

One of the car magazines (Hot Rod, I think) recently published a graph about what header primary size is a good fit for what hp level, but my magazine is at home about 6,000 miles away at this point.

Anyway, I would say that 1 3/4" primaries would be a good size for your engine, but 1 7/8" might be a tad better. I think 2" is too big. If you Google "header primary size calculator" you'll find a few online calculators to help narrow it down.

Scott

[Skip Fix]

Pretty sure years ago Dave Sober(Torqujunki) had 1 3/4 header on his '69 Bird that dipped in the 9s on spray!

[Steve C.]

Hot Rod link:

http://www.hotrod.com/articles/heade...s-performance/

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