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.

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.