Headers too big??
 

I'm wrapping up my 509 build and one of the last things I needed was headers. I found a great deal on some older style CMI split top big tube headers. My HP level will be about 600 n/a. Are these headers going to be too big for this application? If so is there a muffler or anything else I could use to restrict overall flow a tad until I need these monsters? Am I over thinking this?

"my headers are just too big, all this flow is just too much!".. Said no one ever.
:D

I thought too little back pressure will hurt torque. I believe they are 2 1/4 primaries

LOL.

But....where is my dislike button.

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What are the dimensions of said first post headers ?

You don't adjust exhaust performance by restricting it. You do by the dimensions of the inner id primaries / length of said primaries / and ID and length of the collectors.

It's not 'too much flow' that kills an engine, it's incorrect dimensions.

Before someone says anything - SC'd are less effected. But, that's not then engine we have here.

Yeah not sure of all of those demensions. These are just off the shelf CMI split top headers for Big Block.

A large header will definitely effect how a engine performs , some back pressure may help an engine at lower rpms. My last motor 598 had sweepers on it , it was a turd down low , system was dry to tip way too loud , so I put a pair of cmi sound eliminations muffs on and my low end grunt seemed like twice as strong , the boat would plane off like I had dropped two to pitch sizes of prop frikken blew my mind , food for thought good luck

KR252Boss - it's simple, actually. Just find out what the primary ID is and report back. We'll let you know if they are 'too big.'

I doubt they are 2 1/4 ID primarys.

OP

Great question and I think there is a lot to learn here.

Thanks for posting

Just one of those things people should know.

Somewhere back about ten years ago I get a call from a engine / dyno shop to help tune a motor they have. Motor made good power on the dyno but seems lazy in the boat. 502 with blah, blah, blah parts. Okay, not blah, but your typical 550-575hp parts. Custom carb was being blamed and they where chasing there tails. That's why i was called (not a hero call....I know them and they figured another brain would be good.)

once looking at it and all the normal stuff, i ask about the headers. "i don't know was the answer." Which like in this thread is the answer I get almost 100% of the time. "used Stellings" was all they knew.

They where double walled (water cooled of course) and looked big anyway.

So, they fought and thought, fought and thought, about pulling them off.

I left.

Get a call some days later.

2 1/2" ID headers.

Wholly schit !!!!!!!!!

Found some used KE's and they said they got the carb tuned in easy (back to original paramters) and boat ran " the Nuts !"

That's exhaust for you.

If you don't know what you have, then you can't diagnose or understand what you have.

Plain and simple.

This is great news since Im getting rid of my headers and going to manifolds looks like I`ll probably be doing 100mph next year with all the extra power I`ll pick up with more backpressure.
I gotta call all those catback companies and tell em they`ve been doing it all wrong.. more back pressure = more power, not the other way around!!!
Now Im thinking forget the big 5" manifolds, I can get the bravo 4" version for about 1/2 the cost and have more power to boot.
Maybe I`ll have my guy weld up some 2" restrictors.

Cheap way.
Smush in some Idaho Potatoes. maine potatoes work for the SBC's.

Poke a 3/4" straight hole thru the Potatoe. 1/2" for the Small Blocks.

If you can, stick a kid's handheld multicolored pin wheel in it. You'll get a slight Vortex effect with it.

It Works !

Edit in: Friday PM, doing paperwork at work, so I get real weird. No one take offense. Maybe worry for me a lil. LOL.

:bong::bong::bong::signs069:

I can't recall every witnessing a scenerio, where on a big block chevy making in the area of 1HP per cubic inch or more, where a smaller diameter header primary made more power than a larger diameter, over 5000RPM.

I really doubt the CMI split tops are larger than a 1 7/8'' ID primary tube.

We can get into all kinds of header runner lengths and diameters, that would be ideal. But whats the runner length in a GIL manifold? Stainless marine manifold? EMI manifold? Like almost nothing. Heck merc manifolds are just a common log.

My point, I wouldnt sweat it. Of course if you are installing this engine in your pickup truck to tow the boat, you may want to look into some TRI-Y headers for some low end GRUNT. :cartman:

Good read about marine exhaust

http://www.hardin-marine.com/instruc...comparison.pdf

I just measured 1 7/8 is the primary ID

Maybe you can find some info here, http://www.custommarine.com/pdf_docs/CMI-catalog-lo.pdf

Then you are all set. 2" would be better, but that's spliiting hairs.

My point is, if they where say 2 1/8", especially 2 1/4" or bigger, than it would not be splitting hairs.

Mild Thunder - you are mentioning mostly manifold system which have no tuning capabilities. They do offer low or no back pressure.

The more overlap your cam has (NA) (.050", .) the more tuned lengths and diameters help. On the flip side, the more 'wrong' lengths and dimaters can hurt.

I was witness to a 28hp gain on a SBC 450hp motor just over collector length.Why so big ? The lower hp length ended up being a 'wrong' length.

Yup, no schit.

Anyway - go run a 600hp 502 NA marine engine in a boat with Gill's or another free flowing manifold system. Then slap on the KE's. You'll see ! Serious.

God. damn. it. it's like I have esp.

It may affect your bottom end a tad but I don't believe you will see a difference in the top end. Unless you are looking to do hole shots all day I wouldn't bother changing your exhaust, you won't notice the difference while running. Bigger is better in my book not to mention a much nicer sound.

After Reading this I was curious as to what exactly I'm running. Mine are Stellings 4" dry to the tip with Stellings Dampers "not mufflers" and what seems to measure as 2" primary's. I'm running a 454 with huge cam and compression. I was told when I bought the Boat that he had to close the dampers to gain back pressure to take off. I quickly found out that wasn't the case. My boat is super loud and love it but this setup may be too big for what i'm running now but not for what I want to run later. 496 stroker. What you think?

Stellings made different size headers thru the years. They made some mammoth sized ones, but those were rare, and mainly for BIG power forced induction engines. As SB proved, they are not the header you want on a N/A combo. But, their normal headers, which are mostly 1 7/8 ID with good runner length and collector length, should be just fine. And prob a nice improvement over a set of GIL's or what have you.

I personally would be careful playing with changing out what you have. I mean if you were going to strap the engine to a dyno, then it may be worth trying a different header design.

Yup, 1 7/8" - 2" ID primaries good for most all 454-502's.

Anybody see my program printout and my remark on collector length ?

BTW: I've seen worse than the 28hp loss (I used as an example) just because of collector length being in 'worse length.'

Not only does power go down in those situations but the motor becomes lazy and less sensitive to tuning changes.

http://youtu.be/O1bXPNy1Yn4
Pretty good dyno test of different sized primary's

[QUOTE=SB;4219300]Cheap way.
Smush in some Idaho Potatoes. maine potatoes work for the SBC's.

Poke a 3/4" straight hole thru the Potatoe. 1/2" for the Small Blocks.

If you can, stick a kid's handheld multicolored pin wheel in it. You'll get a slight Vortex effect with it.

It Works !


Edit in: Friday PM, doing paperwork at work, so I get real weird. No one take offense. Maybe worry for me a lil. LOL.

http://www.youtube.com/watch?v=HktV2yGtLv8&sns=em

Yup, collector length was been used for years by the bracket drag racers, ad 18" then keep cutting it off in two " increments till you get ur best ET, if the ET drops off ad the 2 " back on LOL, Hell we could afford a dyno test nor were there any close, good stuff, I like the smell of Nitro in the morning :ernaehrung004:

We had a blown 509 on the dyno whit stellings when it made just under 750 hp don t know why but we swapped to a set KE and found almost 900 hp all on the same day same conditions we could not believe it just by swapping headers and adjust the carbs due to the better breathing

wow thats some power left on the table ... nice find

150 hp going to smaller headers, this is getting good!

that,s some powerful koolaid you have down there!:bong::bong:

Prob a good chance the stellings were leaking though fouling out a plug before the dyno pull!

like SB mentioned it s not only the smaller headers but also the collector is very important the KE have the inner pieces of the runners come together in a point and most of the others or all have the pipes stop equal and then even put a big elbow on it wich squeeze 2 pipes ,a friend of mine built a new collector on a pair older headers whit the point like the KE and it make about the same power as the KE so there is much to gain by other manufacturers if they put some better collectors on them .