Low Hp Air or Exhaust
08-01-2011, 06:44 PM
#1
Low Hp Air or Exhaust
I have a rebuilt 502 engine, it does not seem to have all its power. The engine is a gen6 502, small dome pistons 9.6 compression ratio, brodix RR oval port heads 270 runners, edelbrock RPM Airgap, 830 carb, MSD ignition, stock bore eagle standard rods, lighter rotating assm, stock 502 roller cam, imco power flow exhaust. The engine runs great good compression but can't pull over 5K with a old mach stern 25P 4blade propthat I'm running if I change the prop I will get more RPM but less speed. The boat is a 22 donzi classic the most I can get out of it is 72 on GPS stock 502 donzi's are running 74 to 76. What Hp would this set-up make, could the exhaust or not enough air flow hru the hatch to carb make low Hp. Any suggestions
08-01-2011, 10:10 PM
#2
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I would have to say that the heads are holding you back. What is the valve sizes? I am going through some of the same things right now and have changed everything but heads.
08-01-2011, 10:25 PM
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Carb sounds to big what's the jetting? Who's carb is it built for that motor? Was the motor built for a car motor ect.. Need more info
Prop types brands, blades give us more we can help
Prop types brands, blades give us more we can help
08-02-2011, 06:25 AM
#4
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502 cam as in 502carb Magnum or 502-415hp EFI? If it won't rev, it's because of the stock cam and valvesprings. You need some more lift and duration. Carb is the correct size, intake is good, heads are a little small but not bad. A cam like the HP500 EFI hydraulic roller would really wake the engine up.
08-02-2011, 07:57 AM
#7
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I agree that the cam is too small, but I also think you have something else going on. That is awfully slow for a 22 and a 502.
08-02-2011, 08:08 AM
#8
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Are the hulls all the same? On newer models, many maufactures are tweaking the bottoms and reducing weight with improved laminates and resins. 100-200 lbs will make a difference.
08-02-2011, 09:35 AM
#10
The cam is out of a 502 mag Mpi, I talked with a cam manufacture yesterday he claims the exhaust of fuel system would hold me back. He said he could may a bigger cam but you would only gain 15 hp.The valves are 2.30 and 1.88.
