exaust reversion

[rightytighty]

I'm having a motor built with a fairly stout HR cam. 572 chevy, single carb. Not setting the world on fire. Appx 750 HP. My only request to engine builder is that I want to run Log style exaust for noise reasons (little kids) as well as makes a nice sleeper. I know it'll cost some power. I'm o.k. with the compromise. He says 20-30 HP loss.

Builder is worried about Cam over lap drawing water back into engine (reversion). He wants me to make water jacketed tail pipe section that attaches to the log, so exaust will in effect be dry, but log and tail pipe are water jacketed. He says no biggee, any muffler shop can help build this. I have my doubts.

Anyone done anything like this?? Got any pics? Pointers? Suggestions?
I don't want over transom exaust.

Thanks

 

[steveo143]

You'd be better off with some aftermarket i/o type water manifolds. Used imcos etc. Go over to offshoreonly.com, some good stuff of this type shows up quite regularly. I've seen old sets of Drake/Eickhert cast header and pipes, all water cooled for less than 800.00. I've got a set of Drakes, 21/4" individual equal length runners probably worth an extra 50-70 hp.


:beer:drnkfr:drnkfr:monkeypee

 

[rightytighty]

Thanks. Will take a look. Any other suggestions are appreciated!

 

[jockorace]

Neil,
Your engine builder is incorrect in what he is advising you to do, or he just doesn't know what a fully jacketed log manifold with watertrap elbows looks like. The only time you need to really worry about reversion (at idle) is when you have water injected 2-3" from the exhaust port ( like most typical headers). Log manifolds and the elbows are dry INSIDE where the exhaust passes. The water is only in the double wall "jacket" and your block discharge line is only introduced into the elbow at the end where the 31/2" exhaust hose connects. Only THEN does it mix with the exhaust and out the transom tip. You do not need to do anything to the exhaust system on the boat.
In addition, if you do as others have suggested and put on offshore style exhaust (that's exactly what I just took off!), you will lose the use of the rear jump seats. Dave

 

[steveo143]

Neil,
Your engine builder is incorrect in what he is advising you to do, or he just doesn't know what a fully jacketed log manifold with watertrap elbows looks like.

What he said. My only concern is that the logs were restrictive on a 454 and he's going to a 572. What type did you remove? Are you trying to get this inside of an engine cover? Check out lilrick's thread below on the Spectra 20 build, the manifolds are only slightly wider that the stringers.


:drnkfr:drnkfr

 

[rightytighty]

Neil,
Your engine builder is incorrect in what he is advising you to do, or he just doesn't know what a fully jacketed log manifold with watertrap elbows looks like.

What he said. My only concern is that the logs were restrictive on a 454 and he's going to a 572. What type did you remove? Are you trying to get this inside of an engine cover? :drnkfr:drnkfr

Steveo,
Yeah, I don't have any room for the offshore style exaust. Took a good look at pics last night. I have a 1/2 covered engine w/ jump seats on the sides. There is no more room .
I don't want to lose the family space, so I have to make the logs work. I know it's going to cost me HP, but so be it. My goal is to only run mid/upper 70's, yet still not offend my wife and kids...I grew up with flatties, but we've had a wakeboard boat for last 6 years and I'm trying to get back to my roots while still maintaining some of the civility and useability of the wake boat. My wife is humoring me, but there are limits...

 

[steveo143]

I'd build what you described in your first post and not use elbows or turn downs. Andy Herbert on here as "The Bandit" could build what you need out of stainless easily. Elbows and turn downs are restrictive, just put Salisbury flaps on the ends and be done. Any chance you going to CFW New Years?
If I remember right you just bought a Sanger cruiser, great boat.:drnkfr:drnkfr:drnkfr

 

[rightytighty]

I'd build what you described in your first post and not use elbows or turn downs. Andy Herbert on here as "The Bandit" could build what you need out of stainless easily. Elbows and turn downs are restrictive, just put Salisbury flaps on the ends and be done. Any chance you going to CFW New Years?
If I remember right you just bought a Sanger cruiser, great boat.:drnkfr:drnkfr:drnkfr

Yeah, I just bought the black/red Sanger ski race boat out of Clearlake.
PM sent to Andy. Thanks for the suggestion. Will look at seriously. Would love to go watch at CFW, but can't work out family schedule. Looks like LL has turned out to be not an old timer but one of the board jokers. Good entertainment all the same.. Sounds like "mouth" spent big trying to get ready for "the race".. Hope he's not too bummed.

Am going to try and coordinate a little get together at our lake (pine flat) in Spring. We've got a real nice set up that can accomadate a pretty good group, plus there's campgrounds directly below us w/ a launch ramp. There is no sheriff patrol until Memorial, so that should be fun. I look forward to meeting a bunch of cool people with some amazing boats. Also look forward to doing a little hot lap videoing from the top deck of the houseboat. Think those will be pretty cool video posts!!!!

 

[BDMar]

Neil,
Your engine builder is incorrect in what he is advising you to do, or he just doesn't know what a fully jacketed log manifold with watertrap elbows looks like. The only time you need to really worry about reversion (at idle) is when you have water injected 2-3" from the exhaust port ( like most typical headers). Log manifolds and the elbows are dry INSIDE where the exhaust passes. The water is only in the double wall "jacket" and your block discharge line is only introduced into the elbow at the end where the 31/2" exhaust hose connects. Only THEN does it mix with the exhaust and out the transom tip. You do not need to do anything to the exhaust system on the boat.
In addition, if you do as others have suggested and put on offshore style exhaust (that's exactly what I just took off!), you will lose the use of the rear jump seats. Dave

I wish I would have seen this before. His engine builder is correct. Those water trap elbows were designed to keep water from reaching the cylinders while the boat sat in the water without the engine running in a low profile jet boat or v-drive. Log manifolds with those "snail water trap elbows" will absolutely allow reversion on the engine you are describing. We have seen it dozens of times. Engine with camshafts with a fair amount of overlap (which I'm sure his 572 has) will pull water in past those elbows. Exhaust pulses don't care about that little hump. If you look at the bottom of the exhaust port through the snail over the hump it is nothing. The distance from the rear cylinder to where the water mixes with the exhaust is very short. We have seen reversion with Imco manifolds and dry pipes all the way to the tips before the water mixes with the exhaust on a Bravo application. It took removing the tips and making tail pipes that extend through the transom before mixing water and exhaust to eliminate reversion....easily three times the distance those snails give you.