GMPP Ram Jet 502 vs Merc HP500/525 EFI

handfulz28 · 08-21-2007, 02:43 PM

http://www.gmperformanceparts.com/En...9121&engCat=bb

Other than some obvious issues with marinizing the crate Ram Jet, just how far apart is this motor from a Merc blue motor? Is a "GM" MEFI 4 easier to get access to than a "Merc" MEFI 4, for custom programming? Is the Merc HP EFI intake a GM part?

handfulz28 · 08-22-2007, 06:23 PM

anyone?

David Stotz · 08-23-2007, 07:31 AM

The spec sheets indicate it requires 92 octane!

handfulz28 · 08-23-2007, 09:52 AM

It's got a high compression ratio...perhaps a head gasket change would help. A good marine cam would replace any HP lost by lowering CR. Still cheaper than Merc blue?

kennyo · 08-23-2007, 11:59 AM

Hell Dude, you can get a 572 cheaper than a freakin' blue motor!

handfulz28 · 08-23-2007, 12:21 PM

I know, just trying to use something "widely available" and familiar as a comparison point. Also something that's not very exotic. And has to be EFI.

Pat McPherson · 08-23-2007, 01:05 PM

Quote:

Originally Posted by handfulz28

http://www.gmperformanceparts.com/En...9121&engCat=bb

Other than some obvious issues with marinizing the crate Ram Jet, just how far apart is this motor from a Merc blue motor? Is a "GM" MEFI 4 easier to get access to than a "Merc" MEFI 4, for custom programming? Is the Merc HP EFI intake a GM part?

I'm not sure what cam is in the crate engine, but regardless, a more marine friendly cam should be installed. I don't think the bottom end is different.
The electronics and computer are not that different, in fact Volvo and others used the GM stuff on marine engines. The computer would need to be reprogrammed from scratch.
The intake on Merc Racing is from AZ Speed and Marine.

handfulz28 · 08-23-2007, 01:40 PM

Quote:

Originally Posted by Pat McPherson

The intake on Merc Racing is from AZ Speed and Marine.

Thanks Pat for chiming in. I wonder if the lower intake is a GM piece, and just the upper is different between the AS&M versus the GM Ram Jet? Now that I've found these Marine Power brand engines, I see they're also using the AS&M intake/upper.

22 DAYTONA · 08-24-2007, 02:39 PM

I have a buddy running a completely stock 502/502 with a Demon 850 and MSD ignition. He has run the hell out of it for 4 seasons with no problems at all. It turns 5800 rpm all day in a 23 foot Wellcraft Nova. The boat runs an honest 70mph. The old motor ran about 55 or so. I think the cam in the EFI motor is the same. I would not be afraid to run the ram jet out of the crate.

Pat McPherson · 08-24-2007, 02:57 PM

Quote:

Originally Posted by 22 DAYTONA

I have a buddy running a completely stock 502/502 with a Demon 850 and MSD ignition. He has run the hell out of it for 4 seasons with no problems at all. It turns 5800 rpm all day in a 23 foot Wellcraft Nova. The boat runs an honest 70mph. The old motor ran about 55 or so. I think the cam in the EFI motor is the same. I would not be afraid to run the ram jet out of the crate.

I have heard both good and bad stories of guys bolting the ZZ502 in boats. One thing I do know that needs to be changed is the 11psi oil bypass. Without changing that, oil does not get filtered and cooled in a marine setup.
The cam in the EFI and Carb engine is most likely different. The EFI engine would not idle worth a crap with a ZZ502 cam.