SoCal Jet Boats
Tech Talk => Projects => Topic started by: ralph on July 05, 2012, 07:43:50 PM
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I know most of you guys get rid of the Logs and install headers, but I'm going the other way. I've got a 700hp blown chevy 468 in a Mariah 18ft jet, and with over transom Basset headers it's so loud my wife and kids don't want to ride in it. I figured the Logs n' snails through the hull would quiet it down considerably, and since it's just a play boat, even with the more restrictive logs, I'll still have "enough" power. Problem is, the fittings for the snails want to be where the stringers already are! I've seen lots of pics of Jets with this combination. Is my motor lower than the rest? How do the rest of them fit?
Ralph
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Pics would help.
A couple turbos would help quiet it down ;D
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I know most of you guys get rid of the Logs and install headers, but I'm going the other way. I've got a 700hp blown chevy 468 in a Mariah 18ft jet, and with over transom Basset headers it's so loud my wife and kids don't want to ride in it. I figured the Logs n' snails through the hull would quiet it down considerably, and since it's just a play boat, even with the more restrictive logs, I'll still have "enough" power. Problem is, the fittings for the snails want to be where the stringers already are! I've seen lots of pics of Jets with this combination. Is my motor lower than the rest? How do the rest of them fit?
Ralph
I ran into this problem when I built my day cruiser years ago. The stringers were too tall to clear the exhaust manifolds and the snails when the engine was in the proper position. Apparently the stringer spacing was set up for center-rise exhaust manifolds. And aluminum center-rise manifolds were not available for the Olds that I was running (and installed) at the time. And I didn't want to cut down the stringers.
I didn't want to cut down the stringers. So I flipped the logs end-for-end, so the log exits point towards the bow. I then welded up some water-jacketed 180 deg stainless steel elbows to bolt onto the logs. These perform the function of the riser, as well as turn the exhaust back to the transom. The inner tube of the 180 is 3" OD SS tube, with a flange welded on to bolt to the logs. The water jacket is 4" OD SS tube/elbow, sectioned and welded so it fits over the 3" tube, and positioned to allow a close-out flange where I dump the exhaust and water jacket cooling water into a long 4" SS tube via 4" ID silicone hose. From there it goes out the transom through another piece of 4" tube, and flappers/silencers of your choice.
The system works pretty well. I only see about 2 psi of back-pressure at WOT with a 496 Chevy and Shotgun silencers. I've never measured backpressure on a standard log/snail system, but I'm guessing that my set-up is a little less restrictive. It runs way cold too, since I'm drawing water off a dedicated fitting from the pump for the elbows/exhaust pipes.
A lot of work, and nice winter project, if you're so inclined. Just need a mig welder, a band saw, and a grinder. But a pair of performance center-rise manifolds would be much easier to bolt on (but more expensive).
Reply if you want to see a pic or two.
Matt
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Reply if you want to see a pic or two.
Matt
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YES!PLEASE
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The center rise manifolds would do the trick, but I think they look too modern for me. Are there logs that sit higher than my Hardin's? I only need about an inch more clearance if I use the rear fitting on the snail, so I'm considering notching the stringers. Smooth, radiused notch, though.
I love the Turbos idea, but I've already got the 6-71. Next boat maybe!
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Here ya go. Don't make fun of my hack job. The elbows have some surface rust as a result of an annealing process that I did a few years ago to help ensure that the weld joints didn't crack. Took the temp too high in my wife's ceramic kiln......
Note that the right side has a straight 4" pipe. The left side has a 4" marine "muffler". A noise reduction experiment. The marine muffler robs some RPM's.
Matt
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http://www.performanceboats.com/parts-sale/105683-bbc-center-ride-manifolds.html (http://www.performanceboats.com/parts-sale/105683-bbc-center-ride-manifolds.html)
Scroll down on this one the second set of logs have a bitchn snail that might work for ya...
http://www.performanceboats.com/parts-sale/104680-lots-parts.html (http://www.performanceboats.com/parts-sale/104680-lots-parts.html)
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I have those same ones on the first listing. Looks like his leaked the way mine did. They're great units, have them surfaced and make some lead gaskets and good to go.
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Thanks, Mom. Haven't seen snails like that before. I figured out that if I cut my rail kit shorter, and use the rear inlet on the snails, the snail fittings will almost clear. Just a little trimming required. So, I tried to get the plugs out of the rear fitting hole in the snails. Big allen key, same size as a 3/8 bolt head. Been there 40 years, and they're NOT moving. I tried to knock "em loose with my air impact gun. No dice. Might have to machine them out - any ideas?
Ralph
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Give them a good soak of PB blaster. Or try some heat with a mapp gass or propane torch. That may free it up.
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Im planning on doing the same thing with a 8-71 blown 502. did you make the switch yet? Im worried about the logs n snails being able to handle all that. what problem did you encounter with running the engine aside from getting them to fit?
Thanks,
Jason
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go center rise... if u look enough you can come across a set of em for 200-400 bucks. you probably have that in metal alone trying to fab up your own.
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I gave up and still run the OT Bassets. I think Kaotik's right for jbess - go 4"center rise. That's way too much air to shove thu logs and snails. I haven't had any problems with the engine other than the noise. I LOVE the blower!
Ralph
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Finished product.
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https://youtu.be/qRAfCWhM2-k
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Hey guy seen these on cl inland empire only asking 100$ and I thought of this post type in BBC under auto parts
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Thanks for the heads up placecraft Jess.
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No problem glad it worked out
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