Vortec heads on a Mercruiser....

Obviously, non-GT40 related....

I have a 1988 Malibu Skier ski boat which is just a little gem. It has a Mercruiser "MIE 260" in it which is basically a marine version of a Chevy 350. The marine version has a few changes from the road version including different cams, hard fuel lines, bronze impeller on the WP, etc....but basically it's the same aside from these things. It also has "risers" which are essentially water jackets cooling around the exhaust manifold so as to keep things cool and not light the sides of the enclosure on fire (the "dog house" in which the engine sits in the middle of the boat).

I really like this boat because it's super simple, has a lot of balls, and looks great. Normally I just put put along with my kids at around 25-30mph. Max speed is right at 50mph (GPS). I'd like to get some more hp/tq out of this engine and have heard on another site that the chevy Vortec aluminum heads are a good upgraded head for this engine, both saving weight and adding a good 50-75 hp/tq over the stock iron heads. I'd also like to add an aluminum (low rise) inlet manifold to replace the steel manifold, the goat being to save weight.

Does anyone have any experience with these type of mods? Is this a bolt-on upgrade or am I going to need to do some machine work? I've heard the port shape is slightly different with the Vortec heads so there may be some porting work to be done. Any help is appreciated.

Ultimately, I'd like to be able to get 55+ mph out of her. I'm no speed demon on the lake but sometimes it's fun to put the hammer down (in a safe manner).

I have no idea about the head swap compatibility, but, an easier method might be to have your current heads ported and maybe larger valves installed.

A simple cam swap would do it. Have to re-prop too.
Those risers for raw water cooling + aluminum heads would be problematic down the road. Put a slightly more agressive cam in it and you'll get the extra oomph you're looking for. I'd suggest same diameter prop with a little more pitch.

The RPM band will be extended enough to use it well.

Cliff:
I don't know much about the heads but I do know if you have an alum prop and change out to stainless you could gain that 5 mph.
I would think you probably have a Bravo drive...or possibly an Alpha, you are right at the changeover year there.
I am going to guess maybe 14" prop at 23 pitch might do.
If you already went the prop route then I gotta think that boat should hit at least 60 in the right trim, just my 2 cents.
One pitch number up will drop your rpm 300 but without the torque you will lose speed. I think that full throttle on trim should show about 4600 to 4800 rpm, and past that number the cam you have is not making any more power. You can also go to an even number pitch by having the prop "Cupped"...I used to run a 14 1/4" 23 pitch cup on a 25 footer and with more than two persons it was tough to hit 4600 rpm (454 chevy) but in the right conditions I could hit close to 70.
Cheers
Phil

Max recco RPM x .75 will equal a comfortable cruise. Target should be around
3700 - 3800 max for cruise speed. A lot depends on the prop used. As Phil mentioned, a one-inch increase in pitch will drop 300 RPM and conversely a one inch decrease in pitch will raise 300 RPM. Your same prop spec with a slight cup may just give you the extra 5 MPH. It all has to work together. I'd concentrate on the prop first before spending $$ on engine work anyway.

The go-fast folks don't hesitate to spend 50K to blueprint a hull bottom for 2MPH!
The Malibu Skier is a great classic little boat. Hang on to it!

Malibu has been one of my favorite clients since 1997.

One thing to be careful of is the corrosion factor. I couldn't swear to it but I believe the marine engines had the water passages coated with an a corrosive resistant process, at least they used to do it. Even in a fresh water boat or salt water where it is flushed after use, you would still need to use something to lessen the effect during storage. If it's got a heat exchanger (can't tell from the photo), no problem.