z.zuperboat

I dont know about you guys but I get nervous when I cant get 91 no less have to mix it myself. Some stations on the water dont even have 91. The pistons wil be like ballpark franks, THEY PLUMP WHEN YOU COOK THEM.

Unitek

I am already alittle ahead of you.. I have a 98 22' Scarab and Im already in the process of building it. I have the same motor 454 lx 315hp carb . Here is what I have done so far.

Im planning on keeping the stock short for this season because Im buying all my hard parts now.

Here is what I have already :

Edelbrock Performer Large Oval Marine Aluminum heads with the 100cc chambers
Lunati 1.7 roller rockers
TorkerII intake
Holley 750 CFM Marine Double pumper
HVH Super Sucker Carb Spacer
Full MSD Guages with 100mph GPS Speedo

Here is what I still have left to buy :

Crower Custom Grind Cam
Hardened Pushrods
MSD Ignition (coil, box, and distributor)
Gaskets

I also am trying to find a BlackHawk Drive and possibly a Stern Jack to go along with it..

Longrange4u

Ok so we are saying that the engines are acctully the same... but the difference is the demand that a marine application puts on a motor is much more high RPM for prolonged periods of time... so that has considerable implication on the accuracy of the rotating mass (Crank and Pistons).

I do know some shops localy that are great builders... but the build race motors for Drag racing. I am trying to educate myself in understanding the difference so that I can maxamize my money for the best results.

So besides the High RPM requirement... and Cam selection (Due to exhaust I belive) the motors themselfs are the same?

Thanks again guys!!!

Unitek

If you want to read up more about the 22' Scarab.. Go over to www.speedwake.com .. There are many threads about the 22 started over in the Scarab section by myself and others. Just figured I would pass it along . You may have to look back a few months in the Scarab section.

Mike

Longrange4u

Ok guys.. I have talked to a couple marine engine places on the phone. All of them are convinced that building a marine engine is so much harder than a normal performance engine.

What I dont understand is what is the difference besides that you need to build the engine to maintain 3000-4800 RPM consistantly and that you cant have a real agressive cam with exhaust if you have a through prop exhaust.

And something that nobody has been able to answer for me yet.... if I do heads, intake and cam on my existing '96 454 Carb 330 Merc will it hold up to the increase (Prob around 425???)

z.zuperboat

TO MAKE 425HP YOU NEED A SEMI LARGE CAMSHAFT, IN TURN REQUIRING SEMI DRY EXHAUST. BIG CAMS HAVE LOTS OF OVERLAP THAT GIVES IT THAT GREAT SOUND BUT WILL SUCK BACK WATER INTO THE MOTOR AT IDLE. THATS CALLED REVERSION. TO MAKE 425HP YOUR GOING TO HAVE TO SPIN THE MOTOR OVER 4500 RPM AND IT JUST A MATTER OF TIME UNTIL YOU BREAK THE CRANK IN 1/2. IVE SEEN IT TWICE.THE QUESTION IS NOT IF BUT HOW LONG. i ALSO HAD A FRIEND WHO SUCKED SOME WATER ON HIS 330 AND BENT A ROD TRYING TO START THE MOTOR.

PatriYacht

It's not hard to make 425 hp with a 454. The weakest link is the cast pistons. If you can, replace them with forged. The rods are ok, better rod bolts are good insurance. I'd limit the rpm's to 5000 with these rotating parts though. Edelbrock heads are a good deal and they come with good valves. They will flow well enough for good power and oval ports make good torque. For 5000 rpm the biggest cam you want is the old Merc 420 cam, Crane #132561. .530/551 lift, 228/236 duration at .050. Holley 800 on an Airgap intake. Msd ignition. You can use stock centerrise exhaust with this and it won't revert.

Unitek

Im gonna be using the stock merc exhaust manifolds for the time being till I can get a set of Lightnings .. I think before I buy those im gonna do the outdrive mods. I just want it to rip outta the hole with people on it and do atleast 65mph.

KAAMA

Longrange, The example of my cousin's engines in post #16 on page #1 within this thread is probably about as close as you're going to get for your answer. Like I have said, I and many of the guys on here are saying; ARP rod bolts, and forged pistons or at least hyperutectic pistons would be the wiser way to go, however, my cousin's engines does not have ARP rod bolts, and is only using cast pistons and his boat is still running (40 hours) with cast pistons @5000-5100rpm WOT, but he had good machine work done by a reputable, precision machine shop familiar with marine engines. For the most part, most machine shops will tell you or suggest that you use the parts that only they feel comfortable with because their name, and repuatition goes on it.

However, with some machine shops it still may not matter how accurately parts are machined or are assembled with either poor care or ignorance, then it still doesn't matter how good of parts you use. If it blows apart then what difference does it make?

My cousin does most of his cruising at about 4000rpm though. Who knows, it could be a ticking time bomb. Either way, I guess we'll find out....but at least for now he still has a smile on his face. You could build something like his and only run/prop them to 4800rpm and still make about 425hp or so. I cannot remember what his engines made at 4800rpm, but I would guess it would be close to 425hp.

I really don't know or haven't heard of enough situations with where cast pistons and stock rod bolts have survived in a Merc 330hp engine by just changing cams, heads, and intakes, etc and I don't know how exactly how much lift on the cam that you can use without kissing the tops of your cast pistons like we've experienced that back in the 80's (trial & error). However, that was with a cam that had over .550" of lift and more duration that what my cousin ended up using. A flat tappet hydraulic cam like his with .515".515" lift and 218*/226* duration might work---but you still have to check piston to valve clearences.

Who knows?----Your engine(s) just might survive while making 425hp @4800rpm. To me it seems like it would be fine, but that's one answer I cannot be confindently sure of. There's a lot to consider----it goes on and on.

Longrange4u

Grrreat reply's everyone!! I have learned so much in a short time. Here is the road I think I will go.

I have found a performance engine producer that is going to build me a Gen IV 496 and balance it to the Gen V flywheel. Forged Pistons with a Nodular Iron crank. The cast iron heads are worked over ported and polished with RR and fresh valves and springs. Edle Torqer II intake. We will go with a somewhat mild marine cam.

All this for about 4600 delivered... what do people think? Oh and I will add an Edle 850cfm DP carb.