351w cam upgrade?

ultrarunner wrote: I have the GT-40 in my '99 Sport and while it doesn't have a ton of hours on it, they are working hours, so I suspect an overhaul will be in order in the next few years.... With that said, with it all apart, would your recommendation, for course and wakeboard use, be to go with P-heads, cam and rockers during the rebuild. It would seem the most bank for the buck and certainly a significant power increase over stock....

The 60hp increase comment was in reference to the base (240-255hp) 351w, not the HO (285-310hp). I would expect a 15-20hp upgrade over the 310hp GT40 with a better cam and P heads. The p heads are a *little* better than the regular GT40's that came on the GT40, but not a lot- so you wont see the same bang for your buck by upgrading.

That being said, it wont cost much more to go with new/refurb'd P's on the rebuild than it would be to have your GT40's rebuilt... and the P's dont seem to be as prone to external water jacket cracks as the regular GT40's are. So, while you wont see the big gain in hp by switching, you'll see something with the slightly better flow and smaller combustion chambers. Plus, if your GT40 heads are still in good shape, you can make some of your $$ back by reselling to a Mustang guy, as theyre more sought after for automotive applications.

I might add to that, the 351w properly maintained is designed to withstand a TON of working hours. I would not be surprised to see many of the boats on here with a thousand plus and still pumping strong.

Mark, Tim is right about the handling issues. If you have a 1.23:1 tranny, you're stuck with it unless you reverse the rotation of your engine when you change trannies. In other words, it would become expensive and involved and adding h.p. is a much cheaper route.

There's a reason Tim is a Grand Poobah here. He knows a ton about boats.

However...for a slalom and wake board boat, especially a larger heavier one like yours, I will say this at the expense of having my head handed to me. There is a reason that a less than 15 yr old Mastercraft boat company snatched top sales honors from Correct Craft and it was called the Powerslot(the 1.52:1 tranny). With the advent of wake boarding and so many boats going to v-drives, the direct drive had to become more versatile. A very small percentage of boats are direct drive now. Because the new engines made so much power, it made more sense to go to the 1.23 ratios. Like Tim says, they are better all around.

However, if you wanted a slalom/ wake board boat and could custom design the setup, the 1.52:1 is my choice 6 days a week and twice on Sunday. The difference in hole shot is overwhelming. That's just my personal experience without discounting anything Tim has said.

If you have a 1.23:1 setup, that's an expensive transition in order to keep the prop rotation right. However Tim, in these newer, longer, heavier, and wider platforms I would think that is less of an issue than it is in the older smaller boats. I could be wrong.

If you do have a 1.23:1 already, I would spend my money on H.P. For the difference in what the conversion costs, you could do some awesome power upgrades. The truth is, unless you do some aftermarket head work, I doubt you will get the 351 to do much better than 330 h.p. and still have normal functionality and that's about where the new rockers and 40P heads will take you. Porting the heads might get you a little more.

Question Tim. Was the 351w with the 1.23 still a RR engine because a LR engine opens some new doors honestly. I could swear my brother's Nautique with the 1.23 is LR. If it's LR, go roller, then think about the 40P vs. 40 heads. The roller cam allows the lifter to stay at the max. lift for longer and also allows for much higher lifts than the flat tappet cams.

What tranny do you have Mark? If you have a LH engine, you have more choices than the RR guys do.

Sorry Mark. I was so caught up in the RR talk that it didn't occur to me immediately you might have a LR engine.

So cool...I'd go roller cam then personally. Maybe the GT-40P heads and some porting. I wouldn't be surprised to see you climbing above the 1hp per cube mark that way but you need to make your head decisions before anyone can advise you on best cam.

What would you say Tim?

A little late to the party but if you are going to go with a set of P heads and spend money to have them ported it would be prudent to look into some aftermarket heads that will perform better out of the box than just about anything you can do to a set of P heads. If you're porting the P's yourself then go for it but I wouldn't spend money on them to have someone else do it, there are better options out there.

You can find aftermarkets starting around $1000/set fully assembled and they will blow the P's away. Check out RHS and of course AFR are very popular but do some homework on whats out there. P's are a great drop in for a stock 240 hp base motor but the gains per dollar might be greater with something else.

Ancient history for me now but my 81 was up around 380 hp with a set of cast iron RHS heads ported and gasket matched to the intake and exhaust and that was running a fairly mild .460 cam.

I also don't like the geometry of the 1.7 rockers so I would try to spec the cam properly from the start and stay with 1.6 ratio rockers. Assuming you go with aftermarket heads you will need stud rockers and my 1.7 rockers bound on the studs and needed some machining to get them working properly. I just think there's some more planning needed before you jump the gun and start buying parts. Any head swap costs a lot more than you think once you get into gaskets, etc so do it once and do it right.

phatsat67 wrote: RHS kicks but at all 3 of the big 3 heads and they are cheap!

Plus, you will never get the ports on the top set of heads from the heads in the bottom of the photo.


And don't forget about the larger valves aftermarkets will have


I just think it's time to stop and do some more homework before spending any money.

Again, the 1.52 is not worth considering... LOTS of expense with all new running gear, and you'll end up with a LH prop unless you revert back to a reverse rotation engine (a whole different can of worms and $$$). For what might amount to a VERY slight holeshot advantage and a reduction in top speed. Ive held my own against 330+hp 'slot boats with my 1.23 out of the hole, and then walked away. The PCM trans is a great all around box with the reduction, and also allows a LH engine to turn a RH prop. Win/win/win, dont try and reinvent the wheel here.

I agree with Alan... if wanting to freshen things up and get a little more hp (~325ish) then bolt on some P's and throw in a flat tappet Cam Research stick. Paul's '95 siggy runs real strong, as he said. If wanting to push it beyond that point, aftermarket cylinder heads and a roller cam are worth considering... in the end those 2 upgrades will probably set you back an additional $1000-1500 over the p-head combo, and allow you to push the 375-400hp mark, if done right. Whether the stock GT40 fuel and ignition system will allow you to take advantage of the better parts or not remains to be seen... if youre going to be upgrading injectors and remapping A/F curves, the project becomes a bit more involved (and expensive). It all depends how fast you want to go and how much you want to spend. Like Joe said, "Whats money, but paper waiting to be turned into horsepower?"

You can go as fast as your wallet.

gun-driver wrote: As Tim said about the GT-40 I don't think you can do too much untill someone comes up with a tuner for the computer.

Youre probably right, but its still TBD how far you can push it based on the stock GT40 ignition, fuel system and ECM. Theres at least one stroker GT40 in existence, no idea how extreme it is or what modifications (if any) were made to make it run reliably (or not).

Personally, Im waiting on Joe to be the pioneer... he's got that '95 GT40 dissected and all the parts identified- just waiting for some love. I plan to follow suit with an EFI Ford stroker, right after he figures out all the hard stuff.

I dont think its possible to reprogram the existing ECM- PCM has it locked down. It could, of course, be replaced with something tunable... but you'll be starting from scratch on the A/F curves. I would guess it to be a slightly more complicated than a "fairly easy" task, as surely there are significant differences between automotive and marine applications (otherwise PCM would be slapping a generic tune on their motors rather than putting the R&D into their own). But then again, Im no software guy!

A healthy 351w (north of 1hp/ci), or better yet, a stroker 351 (393/408/etc) thats built properly should outperform the Python powered boats without much of a problem... and not have the 300 lb weight penalty associated with the big block. Those Python boats only ran 50-51mph.

Just to clarify Tim. I thought we were initially talking about a RR engine with some limitations because of the cam sizing available. That is why the suggestion of the 1.52:1 for hole shot. However, with a LH engine, that's another story. Lots of better options to choose from.

I was unaware AFM heads could be had that cheap. The ones I've seen have been twice that much.

As far as the ECM's go, there are definitely tunable marine ECM's out there. They start around a thousand bucks or so.



Programmable ECM's