[454cutlass86]

im goin to get a sets of headw and the exhaust ports are like round rectangle and the headers i have are round with this be an issue

[techinspector1]

Which is larger, the ports or the pipes?

[Guy Hiltz]

I havent seen any headers with a round rectangular shape,but a 2 inch primary tube,(round),header is probably as close as you will get.My old combo had the 188 cast iron GM rectangular port heads and BlackJack 1 7/8 headers and there was quite a mismatch,but it didnt seem to hurt performance any.
Guy

[cobalt327]

I've spent hours filling and grinding header tubes/flanges to get a decent transition from the head into the header, to avoid using a header that was larger than optimum.

I've not done before/after dyno tests but think that anything that can be done (within reason) to avoid or correct mismatched ports in the induction and exhaust will be of some benefit.

Others might say that a small mismatch at the exhaust can be beneficial due to reduced reversion. My thoughts on this is that for the small gains made at the point where reversion may be reduced is more than offset by the larger gains seen with a freer flowing exhaust.

"Porting" headers will probably net only small gains unless the mismatch is pronounced. But when you have many small gains that work together there will be a worthwhile improvement overall, IMHO.

EDIT- I would think that a correctly sized header w/some mismatch (like Guy, above) would be better than a too-large header w/o a mismatch, as long as it wasn't too bad. In any event, my comments are not directed at Guy's post- just my thoughts on the deal.

[454cutlass86]

http://store.summitracing.com/partde...5&autoview=sku


those are the headers i have the tubes are 1 -7/8 into a 3.5 collector and im goin with the procomp heads

[Guy Hiltz]

What size engine are you building ??
If you are going bigger than a 454,I would suggest using a header with 2 inch primary tube.
Guy

[454cutlass86]

496 with around 9.5-1 CR lol this is bad news for me since there is no way i can afford another set of hedders and i paid 500 for those damnint lol

[cobalt327]

Hedman Super Comps vary from 1-7/8" to 2-1/8"- but lump all BBC's together from 396 to 502.

I've used 1-3/4" headers twice on 468ci BBC's, seemed to work well but w/o a back-to-back comparison, who knows how much (if any) I left on the table.

I tend to be conservative when it comes to sizing carbs and headers- I choose to tune for the range I use the most on the street as opposed to what'll produce the most HP at peak.

If new headers aren't in your budget, I'd think 1-7/8" would be all right for a mildly cammed 500ci range BBC. Those heads would prob. really want 2"-ers if you have a bigger cam, though. You will be giving up power upstairs with them, no doubt unless the cam is real mild.

You can use free-flowing mufflers and an "X" or "H" pipe to help things some.

I see you paid $500 for yours. I hope they are ceramic coated and came w/a dozen roses!

[454cutlass86]

no they wasnt coated, thats was an extra 200 and couldnt afford it then either lol

the engine will be a 100% street engine so pry wont see top end

the cam im thinkin about is the comp cams xr274r dru@.50 is 236/242 lift 639/646

[cobalt327]

Until you see that the cam you have is going into a 496, it would seem pretty healthy. But in that large of an engine, I think you will be OK.

That said, I would be interested in seeing what a dyno simulation makes of this combination.

What's "known":
496CI
9.5:1 CR
Procomp heads (I have no clue on these)
Headers 1-7/8" into a 3.5" collector
Comp Cams XR274R duration @ 0.050 is 236*/242* lift .639" In./.646" Ex.
Edelbrock RPM
Holley 850 CFM

You might persuade some kind soul to dyno it for you to see what effect the small headers have at what point in the power band compared to the 2"-er's.

EDIT- Cam and induction details.

[454cutlass86]

the intake will be an edelbrock airgap, carb is not sure around 850cfm

i talked to hedman and they said it wont be that much of a lost with that big of an engine

part number i think is 11-770

[techinspector1]

Originally Posted by 454cutlass86

http://store.summitracing.com/partde...5&autoview=sku


those are the headers i have the tubes are 1 -7/8 into a 3.5 collector and im goin with the procomp heads

Do yourself a favor and read the first 4 posts in this thread. After that it gets political, but the first 4 are informative.
http://www.camaros.net/forums/showthread.php?t=89117

[454cutlass86]

thanks alot tech I took a look at it ....ive talked to few poepl who like the procomp and who dont I heard good thing and bad I wish I could afford dart,merlin but cant .... and its hard to find aluminum oval port heads

[cobalt327]

Those headers you linked are a little high at $800, IMO.

Other than the "ball and socket flange" and the small primaries to the 3-1/2" collector, they're much like THESE. But they cost $620 and have 2" primaries and a standard collector flange- otherwise the same.

That's comparing Hedman Huslers to each other- I'm sure there are headers w/comparable specs out there for well under $300 if you were to look.

[techinspector1]

Originally Posted by 454cutlass86

thanks alot tech I took a look at it ....ive talked to few poepl who like the procomp and who dont I heard good thing and bad I wish I could afford dart,merlin but cant .... and its hard to find aluminum oval port heads

Ummmm....here's a ton of 'em...
http://www.superchevy.com/technical/...rock_gmpp.html

Is there some compelling reason to use oval ports?