502 Mag to HP500??
10-08-2013, 01:49 PM
#11
Charter Member # 55
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I have always used what the cam manufature recommends and used the same brand of parts. That way if something fails, they can't blame it on another manufacturer's product.
You best bet would be to call or PM rmbuilder. He can get you all the parts you need and give you excellent advice.
You best bet would be to call or PM rmbuilder. He can get you all the parts you need and give you excellent advice.
10-09-2013, 08:55 AM
#12
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Well I did a comprssion test last night to try and confirm how the motor was running. All cylinders seemed low(bewteen 90 and 120) Cylinder 2 had a little less than 90, cylinder 4 had 100 or so, and cylinder 6 had ZERO. I figured it had a bent valve so I pulled the valve cover and everything seemed to function. How can one cylinder have no compression??
10-09-2013, 06:36 PM
#14
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HP500 heads are the same heads as a 502Mag.
HP500 heads DO have inconel valves, different springs, Crane Gold rockers (with three of them having hand-done grinding on them to clear the valve covers).
The cam is different (a 731 or similar will be close enough). And you haven't said what year it is, but if it is a MkIV block, you will need a cast aluminum timing cover, a needle bearing cam button and a thrust plate as well as a bronze distributor gear).
The HP500 uses Crane retro roller lifters. If you have a late Gen 5 or Gen 6 you can probably get away with the less expensive "long travel" dogbone lifters.
The HP500 uses the Dart single plane marine intake (if you are in fresh water, you don't have to get the marine version). You can also choose an Edelbrock Performer RPM Air Gap rectangle port intake and only lose 3 or 4 hp on top while gaining almost 60 ft-lbs of midrange torque (acceleration....).
You'll also need to make sure you have a fuel pump that will feed the beast, as you will go from 36gph WOT to 44gph at WOT at 7psi thru a restrictive marine fuel system. The restriction is on the "suction" side but if you seek out a pump that will deliver 75gph or 280lph at 15psi, you'll be in the ballpark. I recommend block mounted mechanical fuel pump (which you can certainly get in the needed size), although a lot of guys like electrics for not having to crank the motor to get fuel in the bowls after sitting a week. Holley does have a mechanical marine rated pump that has a 130gph free flow capacity (about what you'd need for 470hp or so in a boat).
HP500 heads DO have inconel valves, different springs, Crane Gold rockers (with three of them having hand-done grinding on them to clear the valve covers).
The cam is different (a 731 or similar will be close enough). And you haven't said what year it is, but if it is a MkIV block, you will need a cast aluminum timing cover, a needle bearing cam button and a thrust plate as well as a bronze distributor gear).
The HP500 uses Crane retro roller lifters. If you have a late Gen 5 or Gen 6 you can probably get away with the less expensive "long travel" dogbone lifters.
The HP500 uses the Dart single plane marine intake (if you are in fresh water, you don't have to get the marine version). You can also choose an Edelbrock Performer RPM Air Gap rectangle port intake and only lose 3 or 4 hp on top while gaining almost 60 ft-lbs of midrange torque (acceleration....).
You'll also need to make sure you have a fuel pump that will feed the beast, as you will go from 36gph WOT to 44gph at WOT at 7psi thru a restrictive marine fuel system. The restriction is on the "suction" side but if you seek out a pump that will deliver 75gph or 280lph at 15psi, you'll be in the ballpark. I recommend block mounted mechanical fuel pump (which you can certainly get in the needed size), although a lot of guys like electrics for not having to crank the motor to get fuel in the bowls after sitting a week. Holley does have a mechanical marine rated pump that has a 130gph free flow capacity (about what you'd need for 470hp or so in a boat).
