bucky

Repowered with a GM Goodwrench 350 (10067353) and since the heads needed to come off anyway to change the gaskets to marine spec we dropped in a Crane 270 cam. Duration both sides is 218 and lift both sides is 454. I can't find the card and don't remember what the lobe spec is (110,112 or whatever). Running T-bolt ignition and thru hub exhaust. Wellcraft Nova 23 with Alpha and weighing around 4200 lbs. Runs 45 at 4300rpm with stainless 19 pitch. The cam really wakes up midrange but the boat runs out of ass on top. Is it choked by the exhaust? Stock manifolds now about three years old and in the salt around here I am starting to think about replacing them. Would a good set of manifolds and thru hulls make a decent difference in this boat? With two daughters in college I can't do much right now. Any and all input welcome, thanks.

Dave M

I am not an expert but I thought that exhaust mods won't do much until you get to the 500+ hp range. That's a big boat for a SBC. My .02

dyno

at least go to through hull.....you can get a set of tips on the board here fairly cheap....then its just time and clamps!if nothing else it will sound better...

excaleagle42

hey bucky,
i took two pairs of 3" stainless exhaust tips off last season and replaced them with 4" for my big blocks. i bet they would work well for you for your small block through hull. if you want them you can have them for free.

KAAMA

Let it breath. If you switch your exhaust from running through the prop hub to an above the waterline through hull set-up you will definately see an increase in RPM----especially if you install an aftermarket exhaust.

Back in the mid 80's a friend of mine bought a 1979 30' Scarab. The boat came stock with a pair of 330's and the exhaust exited out the through prop hub form. With that set-up the engines ran at a tops of about 4200-4300rpm. MY friend bought some Hardin P-1000 (through hull) exhaust manifolds (it's an aftermarket exhaust system very simular in performance to a GIL system) and we in stalled them ourselves. Just from that modification the engines then ran at about 4700-4800rpm @WOT. Back then we didn't even have a speed-o on the boat and there was no such thing as a GPS at the time so we really didn't know how much speed we actually picked up.

New aftermarket exhaust manifolds are available, but if you can find a USED aftermarket marine exhaust system for the SBC (they're NOT the easiest thing to find), the boat and engine would definately bennefit from the mods. I think Stainless Marine makes them new for the SBC.

Dennis Moore

Check out the thread;
Future Magazine Article II

bucky

Thanks for the input guys, I appreciate it. Escaleagle42 that is very generous, you've got mail.