Hey all, I'm finally pullin the trigger on the engine build on my 1989 Formula 242ls. I have found this site the most imformative and technical related, so maybe someone can answer a few questions? I will give you the tech sheet first. It will be a stock displacement gen6 454, stock oval port open chamber 100cc heads (casting #10141279) with some good port work, and possibly some bigger valves if budget permits. It has flat-top pistons, and should be right at 9.62:1 compression ratio. I have decided on the Comp Xtreme Marine hydraulic roller cam (XM284hr) with 112 lobe separation, 110 intake centerline, 0.547 lift, and 230/236 duration @ 0.050. I will be re-using stock roller lifters, getting roller rockers, using a Edlebrock performer RPM air gap intake, 850 carb, and CMI long tube headers w/ dry tailpipes. The question I have it on the cam, is that they say it requires machining of the cylinder heads, but doesn't specify what I'm machining? And the other question I have is about the headers... One of them is leaking, if I pinpoint which tube, can it be separated at the bad spot, fixed, and then the outer sleeve re-welded back on? They are soo damn high $$$ so I really wanna fix em instead of goin with manifolds!!! Any and all help is greatly appreciated guys, this has been a wonderful site and look forward to some responces. I figure if all this should put me around 450-475 horse, 500-525 ft/lb torque, so if I can hit 65ish I'll be happy, I know they are heavy boats... (btw, I'm thinking a 4-blade 23 or 24p to start? I used to have a 22p 4 blade and it ran at 4500 at WOT and got up nice and cruised at a nice speed too. Not doin a 3 blade, makes the boat drive like ****. lol)

Anybody? C'mon now, I know I'm not the first person out there to build a gen6, and who also has a slight hesitation to throwing away a $5,000 set of headers!? lol

The header fix will depend on how bad the corrosion is. If they stainless inner and outer your probably in good shape. Some are stainless inner and mild steel outer. Lots of factors involved, but 99% of the time not a problem to fix them.

A friend of mine has a 88 formula 357 with 454's that are close to what you are planning except for the heads. He is running ported GM 990 rectangle port heads the same comp. XM284hr and weiand 8018 intakes. His motors dynoed at 475 and 495. I have never messed with the GM vortec heads but with the right port work I would expect similar results. If you have the work done professionally you will be real close to the cost of new aluminum castings and if they need guides too than you might exceed the cost of new castings. Also 9.62 comp. ratio is pushing it with iron heads, most guys stay around 9.2

Well the engine has VERY low hours on it, and was babied, so everything is in really good shape... I will be doing the port work myself (have ported many many heads with great results, so that will save $$ there), and from what I am reading, these are actually really good design heads, so hopefully they preform well. As far as the compression ratio goes, that was what it came up with using a pretty thin gasket, so maybe I can throw a thick head gasket on there and drop it a few 1/10ths?? I was planning on running premium anyway as I trailor my boat everywhere anyway, so I gas up on land. Think I'm in the right ballpark with starting with a 23 or 24p 4-blade?

Ditch the air gap intake. Run a big single pane. The intake air temps in a boat are higher in a boat and you need more plenum volume. Cam looks good for your goal, heads are decent but can easily exceed the cost of a new set going through them. Save yourself the aggravation and don't plan on using the headers. Sell them for what they are and buy a new set of stainless marine manifolds. Unless your willing to take a gamble on ruining your fresh heads when they pop another leak.

If you can port the heads yourself than go for it. I am contemplating the same thing right now but I am leaning towards new aluminum castings. The last set of heads I did took about 20hrs so the 40hrs of grinder time to do two sets is not exciting me very much.

I'm a single plane intake fan too. You will have plenty of torque in the 2500-4500rpm range with the oval port heads either way so why not take advantage of the top end the single plane will produce. That cam will make power up to 5500+ rpm. I have had excellent results with the Dart single plane oval port intake #41214000 at higher rpm but a victor jr. or team g might be a better choice.

I would not worry about the prop until later. If you can spin your 22p at 5500rpm you will meet your speed goal.

Adding thicker head gaskets is fine to increase combustion volume but quench clearance is just as important. If the thicker gasket gets you much above .050 quench clearance there are better ways of increasing combustion volume.

I'm glad to hear positive feedback about the various single plane intakes... I was wanting to run one anyway, but was just worried about makin as much torque as possible because of how heavy and underpowered this boat feels as is, not a big fan of takin all day to get on plane, lol. I think I'll be able to get these heads prepped and worked over pretty cheap, so I'm definitely gonna give it a shot using them. I work in a shop myself, and have basically unlimited access to machine shops and any tooling I need, so I should be good to go. I'm glad to hear that your buddy did the same build and made right around 475-500hp, gives me some hope! lol

I'm building a similar gen 6 454 right now as a backup to my 548. I am retaining the vortec heads, doing some cleanup work in the runners, .620 lift cam, Edelbrock Pro Flo XT intake with 102mm throttle body, and will use the Holley HP ECU that I can use on my 548 when it gets back together. I am hoping to get close to 475-500 hp. We will see what a bunch of assembled spare parts can accomplish here. This project started life as a running take out truck engine for $450.

I will also need to machine the valve guides down, install spring rotator eliminators, and machine for 7/16 rocker studs. I will be using stock sized valves. I have read that installing larger valves only worsens the valve shrouding in the chamber due to the fast burn protrusion.