cmi headers
 

my buddy has a 27 awesome cat we just put his new engine in and the water jacketed tails on his CMI stainless headers dont have enough drop to fit the transom cut outs for the exhaust. they are about an inch and a half to high.

the questions are:

1) do the tails have to be water jacketed or can i make my own stainless tails and run em dry with the water going over board from the header outlet? or if i make my own tails do i need to weld in a bung for water to enter them?

2) where and how much should he expect to pay for a set of tails that will fit his application. also how do you measure and make sure you get the right ones when he does find some or decide to buy new ones?

Yes they absolutely have to be water jacketed. If not they will start the transom on fire.

Order custom tails from CMI.

Never Run A Dry Non-jacketed Exhaust In A Boat!
 

+ a million what Griff said. Get the right parts for the job! Fires on the water is no joke.

lol thats all i need to hear to convince me. lol

i was sure there had to be some kind of hazard running them totally dry.


Question: what about injecting the water into a stainless tail?? hence a water injected tail rather than a water jacketed tail????

i know water injected headers stay really cool and dont have much problems.......


thanks for the info guys!

Just send the stock tails into CMI and have them modified.

They must be water jacketed in a closed engine compartment. Even dry tails are water jacketed.

If you need new tail pipes you can mock it up with pvc pipe and then send that to cmi and they will make the new pipe exactly the way it needs to be. Just and idea :coolcowboy:

It is a lot easier to cut new holes in the transom and patch the old ones. Faster, cheaper.

ok.

forgive my questioning, but if all tails must be water jacketed then whats the difference in the the stock exhaust that Mercruiser uses, in most cases either a straight stainless pipe clamped on both ends by rubber boots or simply a rubber hose, that goes from the manifold riser where the water is injected to the exhaust tips at the transom. hence a "water injsected" wet tail pipe and not a water jacketed tail pipe.

just wondering......im gnna do what is right...but at the same time i understand that there is often more than one way to skin a cat and still be safe and functional at the same time.

reversion wont be a problem.....so why couldnt i run "wet" tails with the water being injected into the tial pipe at the joint where they meet the riser......just like stock merc stuff???

the point being that i have the material and can make my own tails for almost no money if this idea will work.

Merc stock exhaust dumps it at top of the 90 in the riser so tail or rubber boot is cool. Cmi runs a jumper and dumps at end of tail, but the water runs in the whole tail so it keeps it cool. No real way around this. Many have tried to think or try a way around it and char grilled their transoms. You can bend the cmi tails to a point.

I guess you could do it that way, but its a good waste of a pair headers and defeats part of the purpose of having them. Anybody that sees it will think its a cobbled together system. It may even revert water on a stock engine. On stock Merc cast stuff, at least the water is directed toward the stern under pressure and into the exhaust fumes.
Also, that is not "water injected" per se. That is just wet exhaust. Water injected is like what is used on jet boats.

im going to try to have my tails modified first...i think they can be tweaked pretty easily to work with what i have. and they are such nice pieces i hate not to use them.

and my CMI tails have the water inlet going into the jacket on the tail right at the joint where they meet the header, not at the end of the tail. it then exits into the exhaust stream through a 5/8 hole inside the tail pipe about an inch from the end of the jacket where the rubber boot connects to the exhaust tip.

the only problem i see as poker-n-run pointed out would possibly be the header-to-tail joint cuppler getting too hot.

whats wrong with runing wet tail pipes? i see alot of boats that have nothing but a 4 foot rubber exhaust hose ruinning from the riser to the transom and it works.....idk...im just thinkinout loud here. and thanks to everyone for the feedback, sometimes what i start with sounding like a great idea gets smacked down because of something i didnt consider.

running the pipes with water being injeted into them (wet tail pipes) should be no different than stock mercruiser or merc 496 exhaust when it comes to water reversion.

and as far as it looking cobbled together.....that depends on who is doing the welding. and yes im sure there are many who would turn their nose up at it no matter how good of a job you did because its not the "right" way to do it.

The reason they dump at end of tail pipe is to reduce any chance of reversion inherent in a true header set up. The ones with the long rubber boots use an anti reversion piece cast into the riser.
You are not the first to try. The coupler would get crazy hot and probably melt the rubber hose were it joins. Not to mention if you put water in at coupler you will have reversion issues. Farther down and tube would be too hot.

2 ton...
Not sure if you understand what reversion is.....you can actually draw water back into engine due to valve timing and overlap and a reverse pulse in the exhaust. The reason the tails don't introduce water sooner is keeping it as far from exhaust valves as possible before adding water to exhaust stream. What engine did he install? The camshaft specs will determine if you should even consider a wet exhaust introduced farther forward.

reversion shouldnt be a problem with the cam thats in the engine. its a 502 bored to 4.5. edelbrock aluminium heads, 112 LS on cam. 850 demon...etc....500-550 hp.

this is not a radical motor at all....not even close. we could run stock merc manifolds if we wanted to.

i understand the point of injecting water into the stream farther down the exhaust pipe.

why does the need to inject the water further down the exhaust stream only apply to headers and not the stock merc exhaust as some are suggesting??? if the same engine and cam doesnt show water reversion using stock merc 496 manifolds then it shouldnt show water reversion running headers. right?

Nobody does what you are suggesting to do. There must be a reason why.........one way is right and one way is not.

If you want to risk your engine, boat and safety, then its up to you.

lol very true.

ive already conceded that i was def going to go the "right" way....but i just wanted to hear some others take on my thought process.