exhaust exstensions
 

Was wanting everyones opinion on a exhaust question . I seem too be having a reversion problem. If I was too take the stock merc manifold and exstend the center exhaust area with tubing wouldint I be creating the same thing as a performence type manifold where the water is mixed much later down the system thus decreasing the chances for reversion. thanks

HAVE TOU TRYED THIS YET ? IM THINKING OF DOING THE SAME THING.

have you changed something in the motor to cause the reversion or is it an ongoing problem?

Yes the exhaust extensions did decrease the amount of reversion. Mine were about 8'' long muffler tubing brased too the stock manifolds. I was able to see a visable amount of reduction thru the pryometer hole that I have in the risers , you can actualy see a mist at low idle. Of coarse increasing the idle helps and eventualy stops the problem.

I have also done this. I was using Imco stainless short risers and had reversion with my stroker and larger cam. I welded on 22" 3" ID exhaust tube extensions onto the risers. They extend into the exhaust tip and water does not mix in until there also. Much louder and no more reversion. Should be some performance increase to boot. Just keep the extensions away from the exhaust hose to prevent them from burning.

383 small block video....

http://www.youtube.com/watch?v=gbnBNN3NjGY

http://www.youtube.com/watch?v=rxT0v...eature=channel

I did this to "Fastglass" stainless risers attached to stock cast manifolds. I wasn't looking to solve a problem per se', just wanting to eliminate the possibility. I bumped up my cam to something that is borderline, so figured it would be wise.

I simply bought 3" stainless tubing, cut 7" lengths, welded them solid to my existing riser outlet. This way, the mix is MUCH closer to the transom, further down hill and further away from my risers.

Somewhat noisy, but hey, it's a boat.

Oh, and what Ryan said, keep them good and centered up, or you'll be melting hoses......

This modification is bandaid. If you put in more cam to make more power, then it needs better exhaust to allow the engine to breath. Stock exhaust is marginal on even a stock 502mag.

If you put the very best exhaust you can on any motor doesent only increase hp about 40 50 over stock ? So If I spend the 1500 to 5k on other parts say like heads or big bore or stroke Would it not be the same ? Oh yea also hp improvments when small never show up on a boat ... unlike a car takes much more hp for 1 mph on a boat

......................or NONE.

I'll agree, once you get to a point, exhaust is absolutely necessary, up to said point, it can do from very very little to absolutely nothing.

Considering how ridiculously expensive exhaust is, I would spend the money elsewhere, unless, that is you are talking 500+ HP.

Totally agree with you

The more HP parts you add to an engine, the more critical good flowing exhaust is. Most published exhaust tests are done on stock engines and not on modified engines. The more an engine is modified, the greater the gains with good exhaust. This even more true with N/A engines that have bigger cams.

We had a guy with a 383 similar to mine. 234/240 hyd roller, AFR heads etc... Very similar exhaust setup, aluminum manifolds and short stainless risers with welded extensions into the tip. Poor man's dry exhaust esentially. With 1.75" dyno headers it made 491hp. With the boat exhaust 480hp. 11hp @ peak is all gained with dry auto headers vs dry boat manifolds. Other tests have showed on a relatively stock Merc 350, cam, carb, intake upgrades that a stock GLM manifold/riser setup was only down 3hp vs Revolution Marine/EMI setup. BBC might be a different story but at 450-550hp you can easily make it with exhaust extensions.

"Had a guy" - Ryan, I'm still here and ticking. Keep in mind it was not a stock manifold vs Kodiak test. And I am running Trickflow G1 heads (wishing they were AFRs).

Even stock riser's (merc) are on the borderline of reversion. So,
any improvement (mods) is a plus until you get to the 500 hp +.

:lolhit: Meant to say Had a guy from SW forum. But its kinda a no no around here to mention it.