75 separator rebuild

SneakyPete wrote: Did you figure out what exhaust manifold you are going to use? I would really caution you on the ones you posted before. Cam choiuce will be extremely critical. You want the water from the riseres to be injected as far down stream as possible. You really need to shoot for cam with a wide LSA, at least 112*. I would hate for you to grenade a motor due to reversion. I initially used aluminum manifolds from GIL (massive weight saving over the merc cast iron, with the stock Merc SS risers. When I whent to a much lumpier cams and the AFR heads, I used Stainless Marine manifolds and custom risers (the risers alone where in neighborhood of $2000). The reason mine were so expensive was because they were "S" shaped to match the low opening in the stern, and they were fully dry. If you go with a milder cam, you should be able to use the Gils with a stock merc riser. But that also depends on your hatch clearance. Another thing to be wary of is older cast iron manifolds can leak, especially at the junction with the riser. When I pulled the original motor apart, a couple of cylinders were full of water becuae the corroded manifold was leaking at the riser junction and water was going back into the motor. You dont want $500 in exhaust parts killing a motor that cost 5-15k to assemble.

Been looking into Imco,s all aluminum any advice on a good manifolds? my cam is 222 230 at 50 with 530 lift. the exhaust is thru transom above water. also looked into hi teks very nice but pricey.

I would still run flappers on the exhaust as well, if you are sitting in the middle of the lake dealing with alot of boat waves from traffic, they find their way up the pipes pretty easy with the good angle.

The pipes on my barefoot are above the platform, a straight shot form the rear of the manifolds and a definite on the flappers. Im not sure of Jeffs pipe configuration, if its a straight shot or not?

Ok here is the motor specs didnt want to tell just yet but here we go! 1990 1 piece rear main roller block {marine] scat 383 stroker bottom end, 30 over ballanced, forged pistons. [hyperutectic] pro comp custom built heads 202s 160s 74cc chambers running 10.5 to 1, air flow intake, cam is bullet racing 222& 230 at 50 with 530 lift altradyne grind running hyd rollers with roller rockers, 1 50 on exh and 160 on int. dui dizzy holly 750 doudle pumper. running throu a alpha gen 2, with shower, mated to a 26 pitch custom built prop as stated earlier! we are shooting for 6000 to 6200 rpm,s all day long. this boat only weighed 2200lbs new so with all the lighter parts we are hoping to lose 200 lbs but thats just a guess on are brain food [BEER] when i spoke earlier about the motor i wanted [Blueprint] the specs and quality of part were not up to par for what we have in mind. thanks for keeping this thread alive. I have alot more pics I will post shortly.

Brian,
I was joking when I mentioned the tubers producing big wakes/waves!!
You're concerned or have actual experience with getting water over the top of the swim platform, into the high through transom exhausts and into the engine? Sorry but you must have foam that's so wet (and rotten stringers) that your boat must sit a foot below the normal from factory water line? What about the pre around mid 70's boats that didn't have flappers on them? They didn't even have "risers" on the exhaust manifolds - just elbows!!! Please expound on your logic.

Pete are you familiar with how the 91 and up barefoots sit idle in the water? If I remember correctly it takes about 42" to float this terd. I dont doubt there could be a triaxle load of wet foam in there but planting that pig block in the rear doesnt help either ! I cant remember the idle stance of the seperators, its been years since the only one on our lake left although I hope to have one someday unless Jeff buys them all lol. At some point I will try to snap a pic of the inside, maybe that will help explain but the ones you are talking about I believe have pretty long pipes compared to my footlongs.

What they're talking about is the engine potentially inhaling it's own exhaust manifold cooling water.

Really radical cams can leave the exhaust valves still open while the piston is at the start of it's intake stroke. This causes a little bit of suction on the exhaust side at idle. Not so much an issue when the engine is revving high and blowing hard out the exhaust.

That's why the mention of "dry" exhausts, which are not truly dry but have a dry inner tube for the exhaust with an outside tube to create a jacket for the cooling water.

^^ Cool.

Yeah, I figured I'd explain it a bit. There was a lot of technical info laid out above, which I wouldn't have understood myself, except my brother had explained it to me in person.

remember, it could be porpoising turd too lol

Reversion can tak on many forms, from enough water to fill the cylinders to a slight mist. The major reversion problems is that water doesnt compress (as most people know), and therefore bends parts.The second is that the slight mist, spraying onto 1200* (or more) exhaust valves can literally cause them to shatter. Super hot valve meets cold mist, rapid contraction of metal, cracks, then shattering. Picture this, you run it at 5k rpm for 5-10 minutes, then come off plane and let it idle, the idle allows for reversion, cool water mist meets super hot exhaust valve and theres your problem. If you plan to run this bad boy at high rpm for any length of time, I hope you are running inconel exhaust valves. They use that(very expensive btw) allow in nascar and off shore boat motors, and I ran them in mine. It comes down to do you want $200 in valves scattering a $5000+ motor. This crap adds up, but with boat motors, they are at 100% load 100% of the time and they must be built right if you plan to run it hard. I used Ferea inconel valves (AFR was able to set the heads up with them, so I didnt have to add them later). If you plan to run this boat like a skit boat, but have some extra power on tap, a high quality SS exhaust valve "should" be ok, but if you are gonna hammer it, then spend the extra coin now instead of a lot of extra coin later. One more thing, my buddy was running a full dry exhaust on his 540 bbc and the water was ejecting at the tails. His cam was so hairy (even with a 114 lsa), that he was getting reversion. He had to get custom tails that re routed the cooling water thru a fitting in the hull, keeping the water far away from the exhaust opening. 111 lsa seems tight to me, but I am far from an expert, just somewhat knowledgeable. Every motor is different. Is that cam specifically fore marine use? Hopefully the power band is where you need it. One more thing, pushing a lot of power thru and alpha can make it break. Does your dizzy have a rev limiter? The reason I asked is becuase if you scatter the drive while running at 5500rpm, you dont want to break the motor too. I ran a Crane (not sure if they are still in business) HI-6m. It had a built in rev limiter, as well as multiple ignition curves and the ability to lock the timing with no need for added modules (unlike MSD). Also they have great reliabilty. My buddy carries a spare MSD box with him becuase they have been known to fail with no rhyme or reason, even units that are fairly new (from what I've heard, not personal experience).

after a couple fast runs, he will figure out that the gas gauge will move as fast as the tach, its easy to burn up a hundy in gas in a couple hours...that has a tendency to keep you out of the second set of barrels

Your on the home stretch. Looking good!

Hay Eric! whats the skiny on the alinment of the out drive to the motor thx for any advice on this issue? PS if its entailed will you please call and explain, I do better talking with some one than reading on the matter. 269 506 1249 Jeff

if you dont understand you can call me 330-273-8291

just snaked a guy for 2 hydro's, 22's, usually 750.00 apiece, got the pair for 4 hundies, the guy you talked to over at hydro has been buzzing the lake again, he has a merc hopped up like Ive never heard before