cloudmaster_321

what about the higher idle rpm and beating on the drive issue?

Gary Anderson

Not true unless you go really big on the cam. Merc made the 454 in 330 (yours), 365, 400, and 420hp versions. None have high idle.

Gary Anderson

BTW, a big part of those other motors making more power, in addition to bigger ports and cams, is that they can spin to 5000-5200. Your cast crank will survive to 5000rpm if you dont abuse it. The valve springs wont like those rpm, so add that to your cam, lifter, springs, headwork upgrade too.
Gary

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iTrader: (4)

Not to jump off topic, but it somewhat pertains to this thread. It was mentioned earlier that he could go with 1.8 rockers. I have 420's or 425's with the lager rectangle I think 049 heads, or the HI Performnce chevy head. They have been pocket ported, and I was thinking of replacing the roller rockers, 1.7 Scorpions, to 1.8's. would I have to do much to use 1.8's and would it be beneficial. Or would it be pushing the HP up in the 55-5800 range where I wouldn't want to spin the engine at. By the way where is the peak power made in the 420's or 425's.

SeaRay Jim

From that, I think if you share what your goals are that might help. If you end up making changes that add power, you could easily end up sacrificing low end torque for higher RPM and power and defeat the purpose you have your boat for. I'm going my the skier comment and making assumptions but knowing exaclty what you want to accomplish is the first step in making any modifications.

At least that's my opinion.

deboatmon

If you do much of a cam upgrade at all, the rocker arms may be suspect. Depending on your particular parts, you may have the lower grade rockers. They are prone to excessive wear at the pushrod with higher spring tension and extended lift.

The gains you will get from what you describe here will be minimal in my opinion. You will change the sound a little and make the ultimately reliable 454/330 less reliable. Maybe gain a couple of mph if you are very lucky. Maybe ! Cam changes for this motor make more power at higher RPM.

Personally, I would add a safer for the engine, better and lighter exhaust system, maybe a better flowing flame arrestor, upgrade the oil in the motor and drive and call it a day. You'll get similar performance results but INCREASE your overall reliability instead of decreasing it.

Just a thought.

tomcat

WARNING: You are about to take the first step onto a slippery slope; the need for speed is a disease! I had a 1990 boat with a 7.4L so I can tell you exactly what I did and how it performed. It's also how I got hooked.

It's no use changing just the cam. You need a better intake, at least port your heads and change the cam and lifters. I basically copied the 454 Magnum. I used the stock Qjet with richer secondary rods, and Edelbrock Performer - O intake and a Speed Pro cam that had the same specs as the 454 Magnum cam (224 @ 0.050", 0.510 lift with stock rockers). Staying with this lift meant I didn't have to change the springs, but I checked them for tension and coil bind first. I don't know if 1.8 rockers would help. If I was going to use them anywhere on the engine it would be the exhaust side due to the single pattern cam and stock exhaust manifolds. But now exhaust lift is 0.540" so check the springs again.

I had the heads pocket ported and valve job done by a professional and matched the intake ports to the intake manifold myself. (That's a lot of cast iron to remove and you will only do it once!)

In stock form the boat went 60 mph spinning a 21 Mirage prop at 5000 RPM. Modified I could spin a 23 Mirage at 5000 RPM for a 5 mph gain. This confirms that the changes turned the 300 HP 7.4L into a 365. This is the easiest HP you will ever get in a boat, after that you really need to start thinking about better parts.

Do a search on "330 on steriods" and you will find a bunch of stuff about turning your engine into 400 HP. Better heads are the key to that.

P.S. There was no discernible effect on idle quality or speed or bottom end power. Your mechanic is thinking about the effect of much bigger cams.

Tom

cloudmaster_321

i didn't know my boat was 330hp, thought the pshp was only 300, mine is on a baja 210 ess btw

tomcat

Your engine is only 300 HP. But the previous model had better heads and was called 330. That thread has good info if you switch to regular oval port heads instead of the panut port heads that you have now.

Gary Anderson

Hmmm, I thought they just rebadged the peanut port engines from 330 flywheel hp (330 TRS) to 300 shaft hp (7.4L) in the mid/late 80s.
Gary