I believe they will weld in a clam shape piece of metal just after curve of riser on bottom, creating a dam, if you will. They probably call it a reversion dam, now that i thinking if it. Make sure to ask’m.

CMI BB Chevy Marine Boat Headers Excellent Condition | eBay

I am running the HO525 203 cam. Think 731 specs. The HO600 206 cam think 741 spec. You definitely want the better exhaust with the 206 cam. Stock exhaust is likely to revert with the 206 cam. Hence Larry moving you toward the stock exhaust friendly 203 cam.

The Dana Marine exhaust made 553hp with 203 cam. Stock exhaust was 530hp.

Run the 206 cam. Modify your stock risers like mine. Upgrade in future.

Follow my recipe.....3" stainless extensions welded onto the stock 496 risers. Mine were 12.5" long. Water mixes with exhaust at transom. If you are running rubber exhaust hose make sure extensions do not touch the rubber.

More info on your setup. Heads? Intake?


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[QUOTE=compedgemarine;4857543]I have these Gil's. manifolds are new pipes are used but nice but are dry to the tip but do have mufflers welded in the pipes. 3K for all plus shipping

Thanks, I'll definitely keep this in mind. How well do the Gil manifolds flow compared to stock? From what I hear the stock do pretty well, I feel the Gil may be a "half step" and a bit more costly for something that isn't a big enough performance gain.

YESSSS! this is exactly what I need! Sent you a PM! Would love to talk to you about your Raylar experience as well!

The aftermarket options for exhaust on the 496HO that I know of are:
Dana Marine
Eddie Marine
Hardin Seaward
Stainless Marine
CMI
Lightning Headers
Hi-Tek of Australia

Keep in mind about half of these options don't perform any better HP wise as the stock system. Good luck to your project! I'm running a Raylar 800HO package myself, although I haven't upgraded the exhaust yet due to supply issues too.

Yeah it seems the CMIs and Danas are the way to go. Personally I'd like to do the Danas. The Stainless, Eddie and Hi-Tek seem to be very mildly performance oriented.

The 496’s exhaust is pretty good and lasts a long time. Remove the tubulators and extend the pipes like Ryan showed and they’ll work.

I appreciate the help, but typically "BBC" doesn't include GM's weirdo step brother the 496. 🤣

Sorry I didn't know that, thought they were the same bolt pattern. I did see this, Hardin Marine - Big Block Chevy Mercruiser 496 / 8.1L / 8.2L Exhaust Systems (hardin-marine.com)