SB

Is this MAG a 385hp MPI or 365/370hp carb ?

MTScott

365 carb version

dereknkathy

i believe promaxx is patriot heads. and i believe they are chinese castings. i also believe if you stay with the stock cam, you are staying with 365 hp...less weight in the stern and shiny aluminum, but...

MTScott

Anyone know if this is a roller or flat tappet cam?

MTScott

Thanks for talking me down on this gents .

After doing some research, this engine is a flat tappet cam motor. The roller cam didn't start in the Gen 5 until the 1996 version.

Me thinks, that if I do a head upgrade, a roller cam swap might be in order, and then I can match it with the heads based on whatever the experts tell me to run. A roller cam swap isn't cheap, but I do feel roller cams are superior to flat tappet cams.

So, it snowballs, like it always does. Power isn't cheap! I don't think I'll mess with any of this until I have to. With the way I run this engine, I doubt I'll have trouble for awhile. I have 430 hours now, and at least 50% of those hours are putting speeds, and 40% is easy cruising at 3200-4000 rpms. Very rarely am I running WOT. I'm not sure how long these last, but I'd like to think with my use I'd get 1000 hours out of it before work is needed. I seem to put about 100 hrs on a year.

In the mean time, I do think I'll be looking into some exhaust manifolds, possibly these guys here here:
Big Block GM Hi-Torque Standard Kit - CP Performance

or something like it. I may also look into the Rev 4 prop. I've been told by a few now, that no matter what turning point says, there is no way they can make an aluminum prop perform a like a stainless, so the rev 4 may give me just enough additional performance to make me happy.

1BIGJIM

Any engine build needs good exhaust first with out it your wasting time and money. I have used Eddie Marine heads they come with Inconel exhaust valves. No springs because you want the springs to match what is required for the cam. This is really important exspecially for Roller Cams. Withs springs and retainers set up correctly your close to 3k. I had my port matched to intake also which is more $$$. Was it worth it, probably not. If you pick up 30jp that's $115 per 1hp. Welcome to power boating😄

MTScott

Makes sense to me... I think that's why maybe i'll invest fun money in exhaust manifolds first.

On the head topic, AFR has been mentioned several times, and I see fawning over them from all sorts of hotrod sources. At this point, many of you can tell my knowledge is lacking and dangerous at best, but I'm here to learn, annoying as it is.

It seems a good match for improvement on this engine, could be the oval port AFR 265s:
265cc BBC Oval Port Cylinder Head - Air Flow Research

At 2200 a pair, that isn't bad. They'll flow more than the rectangular port heads despite having less volume, so more velocity as well, meaning more low end torque. Straight out of a hotrod.com article (for what that's worth) at .0.500 lift the AFR 265s flowed quite a bit better. Above 0.600 they start to get closer but even if it were "equal" flow, the AFR still yields better velocity. From what I understand the stock cam in this motor is .510 lift:

Flow at 0.500: int/exh
AFR 265: 332/260
RECT PORT: 287/188

I'm sure other factors are involved and I'm not sure how LSA and dur will affect this, but it seems a good match even for the stock cam. Given more flow and greater velocity, I think it would gain the power where I want it, and out perform on the high end as well. If this motor were to run at 7K RPM, maybe the rect ports would prove themselves, but.... given the "recommended" WOT run is 5K.... would this AFR head be a better solution? The "large" oval ports on the street seem to be favored over the rect ports because of it's strength in the lower rpm range. These heads also come in either 109, or 112cc chambers, which would yield a comp increase.