In shopping through the classifieds section every set of headers I see listed states that they don’t leak, have been pressure checked, or have been repaired. Logically I would take this to mean they are prone to leaking. I never see nor have heard of manifolds leaking. I’m sure it can happen but would assume it’s much less common. So what is the appeal of headers other then they look much cooler? Is there a point in hp manifolds are just maxed out and above that you have to go headers? All the new engines run them so I assume they are superior but why? I would have hard time spending that much money if there is a more reliable product available for similar cost.

CMI made some headers that leaked, frankly marine or auto, headers are nearly always hand made by some "dude". Not exactly a science, however development is. If you ever watched "how its made" you can see the hedman header company production line and you will see those "dude's"

Headers are awesome and always are a benefit. Marine headers are complicated and expensive. But they work.

For 95% of those with tubular headers you correct. Weird huh ?

SO, yeh, with NA the more cam overlap one has the more headers are effective. Effective headers need primary tubes that are not smaller than / or obstruct the exh port opening. Proper length does help, but collector size and length is most important. Most 502/640's with the Crane 741 / 525EFI cam/ or slightly larger like 18-20" collectors. A wrong length can really fuk things up, but most people don't care. They want bling/bling.

Diamond Marine's Thunder + Lightnings are cast headers. Best of both worlds, and luckily they have the dimensions most 502/540's will like. Just try to end up with the 18-20" total length on your collector to end of tailpipe dimensions.

This reminds me of the thread ( Why are TS Guns so much more than flat decks ) all marine exhaust is expensive, it boils down to application and how much you want to spend. A lot of what you're reading is 10-15 year old headers that people are trying to get the last mile out of, Ive not read about a failure of the CMI Gen X header and they've been out about 10 yrs ?

I have a set of Lightning tubular headers that are 21 years old that are still mint. Wouldn't ever consider anything else. Longest runner length I can find with a long collector that has a nice downward pitch so water won't run back. I have a pretty big cam and no issues with reversion.

Stellings seem to last great in freshwater applications, mine are 20 years old and look new at all welds and collectors, a must for huge cams and yes depending power level there is more power, over 600HP you need the headers in a N/A application to benefit the build to the max, this was tested a few years ago, Stainless marine vs headers was 38 Hp. None I have heard sound as good as the long stellings, I love them. The CMI split tops are next best thing in my opinion.