Big Block engine build?

[SUPRA_ALLEGRO_LANE]

Maybe I missed it in the search. Has any down a big engine build or swap with there Big Block?

[Wulphie]

I dropped a mercruiser 7.4 in my Pirata. In my area there is no shortage of used strong running motors. Some guys repower with diesels and some guys are starting fresh with blower motors, either way you can get good low hour motors.

One drawback with Mercruiser is that with 4" manifold/risers and exhaust they might not fit under your doghouse. The easy access oil filter and fuel filter also make the over all package wider.

I was tempted by some of the 496 out there but really whats the point, its a ski boat haha.

[CJD]

The last big block rebuild I did ran $6k, just for the basics...machine work, pistons, rings, bearings etc. the sky is the limit if you plan to "jazz it up" a bit. If reliability is important, do the rebuild yourself or use a reputable builder. Plenty of used or "rebuilt" motors are available, but they are really a roll of the dice as to what you are getting. A $.05 pushrod guide can shell a complete motor if it lets go.

[SUPRA_ALLEGRO_LANE]

Yea, I'm wanting reliablity but also like to get around 400 /450hp. May go fuel injection also. Just curious what anyone else has done in theirs.

[haugy]

If your motor is good just old and tired, I'd have the block inspected by a professional shop. If it checks out 100%, do a stroker motor build on that block. I looked at doing some stroker mods to my 454, and for the money it would be overall less than a full custom block build. Same engine bolts up to everything, just a lot more oomph. And it would be easy to get 400-450hp from a stroked 454 and still maintain good reliability. But as someone else said, going cheap on certain parts can kill ya. If you do it, do it all strong with quality parts.

I might be pulling my 351w this weekend and it may be a candidate for a 409 stroker as well. That should get me low 400's high 300's hp if I do it right.

[Wulphie]

Sounds like you want a 496 HO. Good motor, forged internals, balanced etc. They can take a beating. If you want super reliable power look for a 525, but keep in mind they have real tube headers and will definitely take some modification to fit in a ski boat.

[SUPRA_ALLEGRO_LANE]

Yea still up in the air with what I'm gonna go. Haugy makes a good point and motor swap not bad idea either.

[Wulphie]

Keep in mind if you really want to make and use 450hp you will probably need a bigger gas tank. I would guess 80 gph at wide open throttle. I learned real quick my pockets are not deep enough to go fast on the water haha. I learned my lesson with a 28' warlock world class, twin 350 magnums 320hp each. They burned 60gph each so you could suck the 125 gallon tank dry in just over an hour. And that boat wasn't even fast haha

[cadunkle]

60 GPH each for a small block means something was very very wrong, or you had done a lot of work to those small blocks and they were making big boy power ready to split the blocks in half. I'm guessing it was closer to 60 GPH for the pair as 30 GPH for a moderate power small block is high but not totally unreasonable.

Fuel consumption is tied fairly close to horsepower, rather than displacement. Engine design, primarily head design, is where a lot of efficiency (or inefficiency) can come from. Of course if you have a small block and want to get much above 1 HP per cubic inch you're going to lose efficiency from the cam you'll run to get those power numbers and also from the high RPM required. Anyhow, for a 496 of modest HP (< 1 HP per cube) you're looking at 30-35 GPH wide open according to (http://www.boat-fuel-economy.com/mercury-mercruiser-3.0-181-fuel-consumption-us-gallons).

Those numbers look similar to every number I've ever seen. Small blocks generally around 20 GPH, big blocks 25 GPH, for stock low HP engines. I've read 25 GPH wide open for the 330 HP PCM 454, but that's not a very relevant figure unless perhaps you're a barefooter and are at or near wide open all the time. A more relevant number is the 6-7 GPH it burns over a typical day on the water mostly pulling a rider at 22 MPH.

[SUPRA_ALLEGRO_LANE]

WOT fuel usage doesnt seem to very important to our kind of boats. We rarely run WOT for any amount of time. From the previous owner my Allegro gets 8-10 GPH for a typical day of pulling skiers/wakeboard/tubers. I have a 41 gallon fuel tank. Not sure what everyone else has in there boats.

I'm really looking on the engine build for more HP and Torgue, I'd like to get my cruising speed and Top end speed Higher. Not sure how high im gonna get. I know these are not speed boats, but I know I can hit 55 mph maybe even 60 mph.

[Jetlink]

Hull design might be your stumbling area. Not sure how the hull looks on yours but as you get going faster, the stern wants to lift and shove the bow down on my boat.

[cadunkle]

Yes, be careful as you approach 60 MPH. It can get hairy on inboards with a steep shaft angle like ours. Pushing the bow further down at higher speeds can have a tendency to catch the bow and pull hard one way or the other.