I've got a 21' Donzi that I'm putting a 502 in. original was Merc 454, Borg warner and TRS drive. I'm currently using the stock 454 exhaust manifolds but looking for an upgrade. The 502 has been mildly built, I'm told it will run around 425 hp.


What are the pros and cons of headers vs manifolds? what should I be looking for to replace the manifolds?

I’ll start with this chart.
Engine is Merc Racings HP500 (carbed 502) that all came with Gill Exhaust .

Several more here:
https://www.offshoreonly.com/forums/...xhaustdyno.pdf

you run in salt or fresh water ?

Fresh water,

I have used almost all of them.
The KE headers are bad ass they sound great had them on my Powerplay and Baja
The SM are ok for stock applications and the gen III are better but the sound is not there.
CMI look great and sound great , price is more than all the above. Have them on my Nortech

Pictures of boat please.

CMI’s look badass, but as a guy who spent 800 bucks last week having one of my CMI headers repaired I can understand people wanting to go with a different more reliable product.

I have a set of brand new Gil manifolds with used dry pipes with mufflers inside them $2500 for everything, new gaskets and all.

Does anyone still make the KE manifolds?

Yup. Diamond Performance has them made.
https://www.diamondperformanceparts....ducts/755-8935

They are called Thunder and Lightnings now.
Not sure if covid supply chains effected them ir not.