Supercharging 260 mercruiser, good idea or no?
 

Thats basiclly my question, I have an 84 Scarab 1 with the 260 hp 5.7. My question is will this motor handle low boost from a centrifugal supercharger? The engine is completely stock with about 100 hrs on a rebuild. I dont know what kind of quality the bottom ends are or if its a 2 or 4 bolt main.

Part 2....I have a chance to buy a new Procharger kit brand new for a really good price. Problem is its for 87 and later 350 or 305, will I be able to use it on my older model with minor modifications or should I abandon this idea entirely?

Any help is appreciated thanks.

You will probably break it.

If your thinking to just bolt it on and run it. then Im going to say no not a good idea at all. I would think its going to turn into an expensive project. But if done correctly its fun having boost :evilb:. Bottom line I say enjoy your boat the way it is and then sell it and move up to a different boat with more power already.

I was thinking it might not be a good idea lmao at GPM response. I have a supercharged Mustang and I love it so the idea of a "easy" 10 mph with boost was appealing. I guess I would also need a different carb right? Has anybody actually done this succesfully?

Don't know about 350's, but you will find plenty of sad tales of woe from those who tried to supercharge stock 454's with cast internals. It might live for a while, but when you least expect it and can least afford it, KABOOM! Remember, even that little 350 is under a whole lot more constant load than your 'Stang, even if you drive it like you stole it. Picture hooking your 'Stang up to a 12000 lb sled, then pulling it uphill for about 5 miles with your foot to the floor. That's what your boat engine is seeing under full throttle. Water is not nearly as forgiving as air and asphalt. :)

Your Alpha drive is the weak link and will not like it.

Been there.
I've done it on a similar small block merc,
I would not reccomend it as a bolt on only without making a bunch of other changes.

stock exhaust has too much back pressure an the factory heads and is hard on the valves - need to upgrade exhaust and if you can put hardened valve seats in- better yet throw on a set of aluminum heads.

Just 1 bad tank of gas and you can hammer the bottom end to pieces regardless of how conservatively to drive. Better to use forged internals. cast (hypereutectic) pistons are brittle.

The stock ringpacks wont hold their seals for long under the extra pressure and will start to blow compression by quickly leading to excessive crankcase pressure and oil being pushed out the dipstick.

The stock rods are fine to about 600HP but the bearings and clearances need to be spot on or youll hammer everything egg shaped quickly.

The extra HP heats up the oil big time and without an external cooler your get waay hot under any kind of extended load.

Better get your jetting and timing looked at by someone who knows what they are doing - you can lean burn a blown small block pretty quick with the wrong tune.

Stock merc ignition is surprisingly good.

In short- Ive blown up so much stuff the rule I follow is when it comes to supercharging either redo it almost all of it, or build a second engine and keep the stocker there to put in and out and to sell it with.


Uncle Dave

Only if you want one big headache, run her how she is and have fun.

The only way to do a blown sbc in a boat is to build it for boost and keep a spare stock block. Uncle Dave kind of said this. If you don't want to build an engine for boost, buy the supercharger, and drop it over board, it'll save you double what you spent on it :lolhit:

Seriously, you can build a boosted sbc with even a stock bottom end but you need to consider 2 hugely import things. EXHAUST and FUEL. It cannot run lean or with excessive egt's. Those 2 things will kill a marine motor in less than an 5min. A cheap build would be better rings, an oil cooler, and a better set of heads. Get a good 4bolt block off craigslist and assemble it for a grand with brass freeze plugs, and a marine cam. Good luck finding exhaust for the boat. The blower isn't going to like log style manifolds. Even center risers aren't going to do much good. When all is said and done, she might last for a whole season!

Aren't we an encouraging bunch??? :angry-smiley-038:

I gained 11 MPH in my 24 Chris craft going from a stock 350/260 to a stock roller 350 from my buddy's camaro... zz4 cam....edelbrock aluminum heads wieand stealth and a Holley 650 on alpha drive..3 seasons no issues at all... I added oil cooler also... that was a great boat andgreat MPH gain for the money....