Question about GMPP 502ho crate engine.
07-08-2014, 07:50 PM
#52
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Cant get this thing jetted.
The stock jetting 85/93 seems way too rich....plugs are black and it runs worse with the arrestor on than without.
Dropped to 80/90 and still dont want to get on plane good, and wont pull more than 4100 RPM or so...which is better than the 3900 it was pulling before.
Is the 850 Demon too big for this engine with the mid sized cam?
The stock jetting 85/93 seems way too rich....plugs are black and it runs worse with the arrestor on than without.
Dropped to 80/90 and still dont want to get on plane good, and wont pull more than 4100 RPM or so...which is better than the 3900 it was pulling before.
Is the 850 Demon too big for this engine with the mid sized cam?
07-08-2014, 08:41 PM
#54
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Oh I agree I need to try that...I just thought I would try what came in the carb first. Holleys and BG Demons do pull air and fuel different and will not use the same jetting.
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07-09-2014, 09:16 AM
#56
Don't take this as gospel, because it is not first hand experience, but I have read that the Demon carbs are wet-flow rated instead of dry-flow rated like the Holleys. That means that your 850 Demon will flow considerably more air than an 850 Holley. I think the 800 Holley would be more suited to your application, but you should be able to get the Demon to run decently with the proper setup. Time to buy a Holley jet kit if you do not already have one.
11-17-2014, 07:11 AM
#58
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I was always told you cannot use a automotive crate engine in a boat application.
1- cam profile
2- head gaskets
3- freeze out plugs
4- clearances (bearings) rings
What weight oil do you use.? The clearances on a automotive engine are tighter than a boat engine. A marine engine is always under extreme load so the clearances are different.
1- cam profile
2- head gaskets
3- freeze out plugs
4- clearances (bearings) rings
What weight oil do you use.? The clearances on a automotive engine are tighter than a boat engine. A marine engine is always under extreme load so the clearances are different.
11-17-2014, 09:32 PM
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There are a few cam frofiles in the crate motor line up that are shared with the mercruiser mag andstd and eve nl the l29 Vortec motor .specs are different from merc book to gmpp cataog but same cam .(s) and freeze plugs .and head gaskets . The gotcha is in the vac advance hei dist and oil bypass plug pressure specs .seems the ones slated for marine use have a little better q.c.
