Rookie17

I have two 420hp Gen IV engines in a 1991 29ft Fountain hooked to Bravo Ones.
Gil exhausts, rectangle port heads with new Holley 650's spinning 28P 4 blade props and she'll do 70mph any day, sometimes a few more. Speed is plenty for me, and she pops out of the hole pretty good with the twin wheels.
Fresh water use only, it'll never see salt water as long as I own it.

All is running good, did the externals last year when I bought the boat - new water pumps and all new water hoses, sea pumps, fuel pumps, fuel lines and filters, brand new Holley carbs, alternators etc. Tidied up a bunch of stuff (wiring / paint etc) and now it looks like somebody cares about the old girl.

Even though they're running fine, I guess I'm kind of fussy. I like to know what I have, and being in the motorsport business DNF's on the water on my days off will really pi$$ me off. I take a lot of personal pride in my stuff not having mechanical issues, because that's my job.

So I'm seriously contemplating pulling both engines and going through them so I know where I'm at. One of the starter motors find an iffy spot on the flywheel occaisionally too, so a good chance to fix that / replace starters, make sure all the freeze plugs in the block are in good shape, and tidy up under the hatch a bit more.

So... the 420hp Gen IV engines are rectangular port head / roller rocker / forged crank deals. Supposedly pretty good stuff... back in 1991 when it was new. This ain't 1991 anymore.

Thinking about going aluminum head with inconel valves, with an aluminum intake to get rid of the transom weight a bit. Four of those iron heads and two manifolds back there have to weigh a grip. Any thoughts on cylinder head direction without spending stupid money? Edelbrock?
Suggestions on port size would be appreciated too, I don't want to go too big and lose the low end torque for pulling out of the hole.
Does anyone know if the newer design aftermarket aluminum oval port heads are just as good as these ancient design cast iron rectangle port heads? At least for guys like me with my application?

Or do I go with a slightly bigger port and stroke it to 4.25" and build a 496? Seems like the longer stroke will bring the torque back with a bigger port and help it be happier on the top end.
Keep in mind we're pushing two Bravo Ones in a reasonably heavy boat, no need to just make the drives the (even) weak(er) link by getting silly.

Also seems like there are surely better camshaft / valvetrain solutions out now that are way better than 1991 era. No idea if these engines are currently just roller rocker or full roller cam, but I don't see the point in flat tappet cams any more.

I've built my fair share of engines over the years, but the requirements for marine use and my application are rather new to me.

As for budget, I'd be ok with dropping $10k for the two engine project, and realize thats probably on the light side and it could easily take more. Doing the labor myself of course, excepting machine work and maybe engine assembly if I get too busy.

Any advice or suggestions would be much appreciated

pantera232

If you have the big money can go with AFR aluminum heads.

Rookie17

Not really claiming to have the big money... just like my stuff to be as nice as I can afford it.

And don't like doing things twice, especially by being stupid and not asking for opinions first

I relatively new to the boat world, and don't claim to know much. Figured there's some people on here who know a lot more than me about these engines so time to ask for some suggestions...

MILD THUNDER

iTrader: (3)

You have very good parts in your motors. As for the heads, believe it or not the heads you have are good heads. Lots of guys running those heads with 600+hp. They are 325CC intake runners, which is a bit large for a 454CI, but they work.

Your engines should already have aluminum intakes on them. They actually are a good flowing intake.

I suppose it really depends on what you want to do, how much you want to spend.

My advice would be
basic Refresh on the bottom ends
Freshen heads with new springs, seals, guides, etc
Install a hydraulic Roller cam and lifters
Edelbrock RPM air Gap intake
Lose the 650CFM and go to a 800CFM.

with the right cam, you should be able to get 475-490HP. You may have to spin the motor to 5500 to get it. No problem with a hyd roller and your bottom end.

Of course you can go with new aluminum heads, but with that you are probably gonna be around 4k for both motors for a set of edelbrock marine heads. And probably around 5k or more for some AFR or Dart Pro 1's. That right there is gonna eat up a big portion of your budget.

Now, in my opinion, your best bang for the buck, and from a reliability standpoint also, would be to supercharge what you have. You can add a small blower like a weiand 177, or b&m 250, run 5psi of boost. A basic rebuild on what you have, and even using a hyd flat tappet cam (roller cam kits will cost around 900.00 per motor) you can make 550HP per side all day. You have forged cranks, pistons, and rods already that will support that all day. Also, you wont have to run a very aggressive cam and can make your power at 5000-5200rpm. usually you can find two small blower setups on here complete for 2500-3500 bucks. Leaves you around 7k dollars to spend on freshening what you have, etc.

naturally aspirated, around 500HP ish is about all your gonna get out of a 454 marine pleasure boat motor. Put a blower on it, and depending on the build combo and blower size, you can be anywhere from 525-750HP.

Cold Sweat

First question is, did you put the 420's in the boat, or did it come with them? I had a 1990 29 Fever and it came with 365hp. mags. I'm not certain,but I thought the 420's were late 80's engines and not an option in a 91 Fountain. Like I said, I could be wrong, someone else here would know for sure.
I have an '88 Formula 357 with 420's. I did redo both 2 years ago. I had them bored and stroked to 496's. Kept the cast heads, new inconel ext. valves etc. Roller cams, used the original single plane intake with 1 inch spacer and 950 Quick Fuel carbs. Upgraded and changed everything on the fuel and oil systems. I have TRS drives behind them, so I kept them conservative. They run great and have lots of torque. They push my tank to 65 on the gps.
Two sets of good aluminum heads and intakes would make a difference, but how much? I would change over if it made sense. I have read that the big oval port aluminum heads are a good choice. There are alot of repower options out there, you never get your money back on engine upgrades. It's just part of the sport.

MILD THUNDER

iTrader: (3)

More than likely his boat had came with 365HP magnums. Ill bet someone converted them to 420HP versions with a cam change and roller rockers. Bottom ends were the same. 420's came with GIL exhaust manifolds, 365's did not.

Which brings up a good point. if you have the stock cast iron exhaust manifolds (with cast iron elbow) you need to make new manifolds first thing on the list to buy. Otherwise, all the other upgrades are not worth it.

Cold Sweat

Forgot to mention, i changed from stock manifolds to SM with long risers dry to the tips. Also lost the water circ. pumps and used cross overs w/bypass and t stats. It goes on and on $$$$$
10 grand is easy to spend on just new accessories.

Rookie17

Great points, and thank you all for the advice.

The 420's were in the boat when I got it, and I'm pretty sure they were in it from new. This boat was purchased by a prominent NASCAR driver when new and it'd make sense such a gearhead would have the biggest engine options available at the time.
I think the 420's had been replaced in the merc line-up with 425's by 1991, but perhaps they were leftover unsold new engines?

No doubt they are in fact 420's, with the Gil exhaust manifolds and stainless risers all the way back through the transom. You can see the Crane gold roller rockers through the oil fill in the valve covers, which also have Mercruiser 420 stickers still on them.

My price on Edelbrock oval port marine heads is around $840 each (with valves but no springs / retainers) if I do the smaller 110cc chamber / 290cc ports.

But as Mild Thunder kindly pointed out, the rectangle port heads I have now are 325cc ports and maybe a tad big - so it seems I should be looking at the larger 118cc chamber / 315cc port aftermarket rectangle port heads. (Edelbrock #61559)

Because I'll be replacing springs / retainers / pushrods / new roller cam and rockers no matter what head I go with, do you think the weight saving and 'niceness' of 4 brand new aluminum heads with brand new valves is worth $3400 my cost? Just not sure on the effect of the weight reduction and if it'll make much difference with the Fountain 'ass heavy' syndrome when anchored in the lake. Waste of money maybe?

Typo on the carbs, they're Holley 80537's and 750cfm, not 650cfm. My bad.

Don't really want to go the blower route, I don't need the power for the way I boat (lol... famous last words perhaps...)
475hp to 490hp is plenty enough for me since there are two of them back there, that makes 950 - 980hp in a 29 Fountain with a semi-newbie at the helm. I'm too old to be stupider than that

I like the Edelbrock RPM air gap manifold idea, any opinions on cam selection as far as lift / duration / lobe center?

Man I love this site. You guys are awesome!

Rookie17

How does this cam look? Its a hydraulic roller.

I know nothing about reversion issues in boats, so any advice would be very much appreciated.
Exhausts are Gil manifolds with stainless risers all the way through.

Duration Advertised 335° Intake/329° Exhaust
Duration @ .050'' 236° Intake/245° Exhaust
Lift @ Valve .625'' Intake/.639'' Exhaust
Lift @ Cam .368'' Intake/.376'' Exhaust
Lobe Separation Angle 112°
Intake Centerline 109°
Intake Timing @ .050" Open 6° BTDC
Close 51° ABDC
Exhaust Timing @ .050" Open 54° BBDC
Close 11° ATDC

Stock 420 cam is as follows for comparison:
Duration at .050”: 228, 236
Lift: Intake @Cam 312 @Valve 530
Exhaust @ Cam 324 @Valve 551
(with Rocker Arm Ratio 1.7)
LSA is 114

Am I correct in assuming the LSA change is the bigger thing to worry about with reversion, and is 114 to 112 with these specs an issue?

Any opinions would be much appreciated Yeah, I know just enough to get myself in the chit probably

picklenjim

If that advertised duration is correct it is waaaaay to much. That's a lot of lift also. I would look at something more in the range of 288/296 duration and 575/600 lift.