87 Merc 454 mag 330hp?

[71tahiti]

I am looking at a low hour 1987 Merc 454 Magnum . Its totally stock and the valve covers say 454 magnum 330hp? It has rect. heads and im assuming a steel crank and the bigger rods? I thought these Mag motors were 365hp? It also says WOT 4200-4600 Does anyone know anything about these Merc Magnum motors... Thanks for any info..

[DMOORE]

I had a Scarab the originally had twin 330's in it. Punched them out to 468's added some cams ,intakes, exhaust(all the hot rod stuff) and that boat flew. They are very solid motors to start with.
Darrell.

[cfm]

Most (99%) 454 Mags are 365hp, and these do have rect heads, steel crank, big rods, etc,etc.
However, there was a 330hp 454 Mag for a year or two in front of an Alpha. These have small oval heads, small cam, small rods, cast crank, etc. Pull a valve cover and see what heads you have. Or get serial # and call Merc.

[BDMar]

If it is a 1987 and you have an Alpha drive, it is the low perf 7.4. 1986 through 1988 the this engine was put in front of an Alpha drive and they called it a "454 Mag". It has the small oval port heads, cast crank, cast pistons, 3/8 rods, etc. The serial number range for this engine is OA631894 thru OB785148.
In 1988 they came out with the 365 HP 454 Mag in front of the first design Bravo.

[71tahiti]

Thanks for the info Ser # on valve covers says B606399? 1887079-2049044 ? Will Merc look it up or with they say Get F****d. I really would like to buy this engine, only has 340 hrs on it and is very clean. But I dont want to buy the low perf 454, I dont think. Can they be built for reliable 450-500 HP? Is there a # for merc to reserch serial #?

[71tahiti]

Thanks Brian..... Professional info makes things alot easier.....TY

[BDMar]

Thanks Brian..... Professional info makes things alot easier.....TY
Any time!:D

[Pismo]

The "454 Magnum" started as the old 330 with a new name, then first went to 350hp, then to 365hp years later, and 385 years after that.

[71tahiti]

I have heard that because an I/O engine operates under 5500 the oval port heads perform as well as rectangular. Is there any truth to that?

[BDMar]

I have heard that because an I/O engine operates under 5500 the oval port heads perform as well as rectangular. Is there any truth to that?
No :D

[obnoxious001]

No :D
Interesting no frills answer.
I am currently rebuilding a "magnum" engine for a customer, outdrive boat maybe 5500 rpm max. It came to me with a flat cam and some old oval port heads, one of which had the heat riser full of water, so I am going to put some 990 rectangular port heads on it to bring it back to "original"
On the other hand, I used to run mismatched ports on my flatbottom in the "old days", and made pretty decent power with it also.