Engine conversion question

I appeciate your predicament but honestly, wouldn't you come out better to trade boats and find one with a smaller engine?

Brad,

Keep the hotrod motor, sell the kids and wife if you got to.

Maybe worth while to go up a few piches on the prop. That engine has plenty of power to turn one of you dont need lightning hole shots. I run a 12x15 RH on my mustang and I can ski at 35 mph and the boat only revs at 2300 rpm. It just cruises along like having a car in overdrive. It does not do well pulling more than one skiier out of the hole, but I dont care. I can go for hours compared to before. Also, I know for sure CLIMBHIGH has by far the most correct answer!!!!

The dealer is willing to do the conversion for free as he has the 351 (carb) sitting there from when he up-graded another customers boat to the GT-40 and he has a bigger boat with a 454 lump in (not a ski boat) with a cracked head.

If you put in a 351 and then load up the boat with ballast, how much will you save? I suspect not much.

Consider doing tests with a vacuum gauge hooked up to the manifold, and adjust your main jets, advance curve, PV vacuum, PVCR diameter, and try a different props to maximize vacuum when at boarding speed, then you can quantify your changes with the guage and thus reap good economy. If your power valve is indeed open when just bording, you'll be sucking gas bigtime, up to 30% too much. Get your PV to open when need more than boarding-cruise speed, perhaps 2-3" vac minimum delta.

There are two 454's.. one is 330 hp and has round ports. The other is 425 hp and has monster rectangle-ports and a larger cfm 4150 mechanical secondary carb. Its good for 55 mph and 5600 rpm with a 14x14 prop. I have an unconfirmed suspicion that the 425 454Hipo is std rotation while the rest are reverse.

If you have the Hipo engine, the boat is indeed a rare find, and best left as is, cuz your a lucky guy. You'd be a fool to trade an engine with a $7-8K value for some tired unknown bone 351. Also explains why someone wants your engine.

I suspect smart carb & ignition tuning specific to your usage can get you out of your pickle.

Beware, too much prop will drop cruise vacuum, enough to open the PV and destroy fuel economy.
A few degrees more advance at 20-2200 rpm while leaving the initial and final alone could boost savings significantly.

If you have the original mallory distributer, chances are the advance mechanism is boogered up, the plastic bushing tend to disintergrate.

here is a good introduction..read it about 5 times before undertaking, and I have found some errors in the document but for the most part its right on.
http://realbig.com/pipermail/detomaso/2003-June/028198.html

Brad, it takes fuel to produce power. When you think about it, trading to a smaller engine to save fuel is just a method of limiting power. There are some physics laws that apply. Ignoring changes in hull drag, engine efficiency, and internal engine and drive train friction, turning your prop at 50% of full speed RPM will result in approximatly 82% savings in fuel. (As compared to running wide-open-throttle). Turning your prop at 80% of full speed RPM will result in approximatly 50% savings in fuel.

I think you should try a boating trip where you seriously keep you hand off the throttle, so to speak. You may be surprised.

I brought this up in another thread a few months ago. (I also mentioned that in view of what I said how do I run my boat? WOT all day long!)

Good points jim,
Since its a quadrabog, perhaps disconnect the secondaries and board just off the primaries, and recheck fuel usage. Whoops, sorry mixed up originators..

emitchum,
I suspect he chances the advance curve of your automotive HEI distributer being optimal for your application are nil.
Best map the advance from idle to 4krpm every 3-400 rpm and compare to others.

I think i am going to stick with this engine and just it converted to gas, does anyone know how mush a set of manifolds would be?

grow up 79nautique

emitchum, I don't blame you for not liking the manner in which 79nautique delivers information, I have been his target also, but he is pretty much right on. I am the king of cheapskates but there is a reason marine ignition components cost more than auto type. No one would like to see your boat go up like a volcano on the lake which could happen if auto parts are substituted for marine duty components. Your auto engine operates in a well ventilated enviorment. Your boat engine operates in a relativly sealed enviornment. The theory is that marine electrical components are designed so when they burn up, like all electrical components eventually do, the flames are contained and will not find their way into the engine compartment - not necessarily so for standard auto components. This is not an area to try to save money. It's deadly serious stuff.

Ohh... Good. For me the marine part thing was a revelation and not too long ago either. You sound like you are not new to boating. I am brand new to boating. I have always thought of myself fairly comfortable around engines but I am alarmed by how much I am discovering that I don't know. Keep us posted on the progress. Do you have any pics posted?

brad k
did you surrender your 454 chevy for the ford 351? the suspense is killing me. dont leave us hanging