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
