Mercury 496 Build- Exhaust/Camshaft Reversion

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01-28-2023 | 05:14 PM

#21

Jamescmei

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Quote:

Originally Posted by GPM

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)

No worries, yeah the 496 is the oddball. I really don't NEED manifolds I really need two things, reversion prevention and performance. If I can't get the performance right away that's not a big deal, then I need reversion prevention. If I go reversion prevention only, then I'd like it to be temporary until I can source the performance exhaust. Any and all help is appreciated though!

01-28-2023 | 06:31 PM

#22

TomZ

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From: Virginia Beach

They will bolt up but may be a little narrower that the 496 pipes. You should be able to make the tailpipes work with a hump hose (you’ll still need tailpipes… could have them made with the correct fit - contact CMI).

03-01-2023 | 12:04 PM

#23

Dragracer_Art

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From: Dawsonville, GA

Quote:

Originally Posted by Jamescmei

I have been all over Craigslist, Marketplace, and eBay. Only one nice CMI set around but they are +6 so that's not gunna work. The 496 E-Top CMI is what I'll need.

Can you point me to these +6 CMI headers ? I need exactly that for my boat.

03-28-2023 | 02:31 PM

#24

Jamescmei

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I don’t see them around for sale anymore, they were on marketplace and eBay by the same seller.

03-29-2023 | 11:41 AM

#25

cdail28590

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From: Windsor, NC

I dont know if its true or not but I was told regular 454/502 manifolds would bolt up fine to the 496. The only difference is that the 496 manifolds have a water provision on them and a manifold company could add that. Might be another option.

03-30-2023 | 09:37 AM

#26

87MirageIntruder

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From: Portland OR

Correct as stated above, the 496 OEM system is slightly wider in where the riser exit is than earlier BBC systems, and the manifolds have a spot for the temp sensor on each manifold to screw into.

03-31-2023 | 08:06 AM

#27

Joeyboost

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From: Cortlandt Manor NY

Im in sort of the same boat here, I am freshening up my 502 that popped a head gasket bored it out to a 509. want go with a little more cam so I have to lose the silent choice exhaust, I have EMI thunder manifolds and cast risers so Im to switching to SS risers that don't mix until it gets to the transom. Does it become a lot louder this way?

03-31-2023 | 09:28 AM

#28

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From: On A Dirt Floor

Quote:

Originally Posted by Joeyboost

Yes.
The further away from engine you mix the water, the louder it gets.

03-31-2023 | 09:41 AM

#29

Joeyboost

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From: Cortlandt Manor NY

Quote:

Originally Posted by Ryan00TJ

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?