Go Back  Offshoreonly.com > Technical > General Q & A
GMPP Ram Jet 502 vs Merc HP500/525 EFI >

GMPP Ram Jet 502 vs Merc HP500/525 EFI

Notices

GMPP Ram Jet 502 vs Merc HP500/525 EFI

Old 08-21-2007, 01:43 PM
  #1  
Registered
Thread Starter
 
Join Date: Aug 2006
Location: IAD/FLL
Posts: 2,090
Likes: 0
Received 0 Likes on 0 Posts
Default GMPP Ram Jet 502 vs Merc HP500/525 EFI

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 is offline  
Old 08-22-2007, 05:23 PM
  #2  
Registered
Thread Starter
 
Join Date: Aug 2006
Location: IAD/FLL
Posts: 2,090
Likes: 0
Received 0 Likes on 0 Posts
Default

anyone?
handfulz28 is offline  
Old 08-23-2007, 06:31 AM
  #3  
Registered
 
Join Date: Feb 2001
Location: LANCASTER, NEW YORK 14086
Posts: 422
Likes: 0
Received 4 Likes on 2 Posts
Default

The spec sheets indicate it requires 92 octane!
David Stotz is offline  
Old 08-23-2007, 08:52 AM
  #4  
Registered
Thread Starter
 
Join Date: Aug 2006
Location: IAD/FLL
Posts: 2,090
Likes: 0
Received 0 Likes on 0 Posts
Default

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?
handfulz28 is offline  
Old 08-23-2007, 10:59 AM
  #5  
Registered
 
Join Date: Feb 2004
Location: MT. JULIET, TN.
Posts: 3,710
Received 2 Likes on 1 Post
Default

Hell Dude, you can get a 572 cheaper than a freakin' blue motor!
kennyo is offline  
Old 08-23-2007, 11:21 AM
  #6  
Registered
Thread Starter
 
Join Date: Aug 2006
Location: IAD/FLL
Posts: 2,090
Likes: 0
Received 0 Likes on 0 Posts
Default


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.
handfulz28 is offline  
Old 08-23-2007, 12:05 PM
  #7  
VIP Member
VIP Member
 
Pat McPherson's Avatar
 
Join Date: Oct 2002
Location: Ivoryton, CT
Posts: 5,246
Likes: 0
Received 3 Likes on 3 Posts
Default

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.
__________________
Patrick
Pat McPherson is offline  
Old 08-23-2007, 12:40 PM
  #8  
Registered
Thread Starter
 
Join Date: Aug 2006
Location: IAD/FLL
Posts: 2,090
Likes: 0
Received 0 Likes on 0 Posts
Default

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.
handfulz28 is offline  
Old 08-24-2007, 01:39 PM
  #9  
Registered
 
Join Date: Jun 2007
Location: Texas
Posts: 271
Likes: 0
Received 0 Likes on 0 Posts
Default

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.
22 DAYTONA is offline  
Old 08-24-2007, 01:57 PM
  #10  
VIP Member
VIP Member
 
Pat McPherson's Avatar
 
Join Date: Oct 2002
Location: Ivoryton, CT
Posts: 5,246
Likes: 0
Received 3 Likes on 3 Posts
Default

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.
__________________
Patrick
Pat McPherson is offline  

Quick Reply: GMPP Ram Jet 502 vs Merc HP500/525 EFI


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.