headers vs manifolds
 

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 .


https://cimg4.ibsrv.net/gimg/www.off...f9be292022.jpg

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.

I will never go back to headers and headeraches.

Is the issue leaks or cracks? Are manifolds for reliable?

I ordered some in 2020, cancelled it after over a year. Checked back with him not long ago, hasnt had them in 3 years now. Customer was just planning a dyno session and said he was gonna buy some to try, I said good luck. Claims he was told they had them coming in june but thats NOT definitive whatsoever!

That’s sad. Those were supposed to be good.

I may have bought the last pair to come out of the foundry. June 2019

https://cimg8.ibsrv.net/gimg/www.off...f98717d8c.jpeg

At your power level , any decent manifold will do just fine. I would go with stainless marine myself as their customer service is excellent. I am running the Gen3 on my setup and am very happy. Imco powerflow is a pretty slick setup but I couldn’t fit it under my hatch. Like others , I initially wanted the Thunder and lightning setup but they seem to be nla. I certainly wouldn’t put a used exhaust on a new engine

I have Lightning headers that came with the boat in 1998. I've sent them in and had them tested and they are still like new. Of course I store my boat in a heated garage and don't leave it in the water overnight unless I'm staying on it. They are a bit loud, but I do have a pretty well built 524. When it starts to hit the power band it really sounds mean.