502 merc
 

I bought a 91 fountain 32 fever. It seems to have 1 replacement engine and 1 original engine. The original engine consumes some oil but runs good. I would like to know if anybody has any info on these engines? Is the original a gen IV or V? (they are 502 mags)
Does this engine have a flat tappet or roller cam? Are the heads
square port or oval? Are the pistons forged or cast. The engine that was replaced has to fuel pump on the seawater pump. Does this mean it is a gen v engine? It has the squared off valve covers as opposed to the more rounded ones of the other engine.
Are these replacement engines usually 415 hp instead of 390 hp?
If so, what is the difference in the 2 engines internally? lastly I am
looking to juice them up a little. The boat runs 75 mph & would like about 80 mph. I dont want to sacrafice reliability. I am an auto
tech by trade & dont want to my entire weekends under the hatch, thats for our long upstate N.Y. winters. THANKS!!!!!

The early 502 carb motors were 390 hp.

Formulafastech, gen V , genIV, gen VI, markIV.....I'm all confused

Thanks formulafastech,that solves the gen 4,5 &6 question. Does
anybody know the differance between the 390 hp & the 415 hp
engines? Can you get 475-500 hp out of these engines with
just a cam,carb & intake?

You mention the fuel pump on the replacement motor is on the water pump bracket. This makes it a Gen5 or Gen6. I assume since you pointed out the difference, that the original motor has the pump on the side of the block in a "normal" fashion. If so, then the original motor is a Mk4 (leftover from the 1990 batch).

Yes, the original engine is mark IV. The replaced engine is
probably a gen V. The reason I wanted to know is that I
have to address the oil consumption of the original engine
so rather than rebuild it,I will replace it. The problem is I don't
know the HP of the replacement engine. Is the only difference
from the 390 hp engine & the 415 hp engine the cam? I see the
gm crate motors advertised at 415,425 & 435 hp. Whats up with that???????????

gen 4 has mech. fuel pump gen. 5 has electric

STOP CONFUSING ME! :-)

The "replacement" 502 Gen VI is rated at 425-430 h.p. The efi version is 415 h.p. The Gen V (carbed) version was rated at 390 h.p.

The main differences are the roller cam and efi, depending on the year and version.

Did I make it worse?

Most of the info above is correct, but only applies to the 502 Mag motors, not the GenV HP motors: HP425, HP450, HP465, HP500. That's where some of the info does not apply. Such as adjustable roller rockers and V/C gasket type. Gen V motors have a mechanical fuel pump mounted on the sea water pump.

So take note of the type of motor you are dealing with. ;) Different animals.