supercobrajet

Bear with me, I am at the beginning of the learning curve here. I have 1992 twins that are supposed to be Gen IV 465hp 502's with Gil exhaust. One motor was rebuilt and "brought up to HP500 specs". It has a team G dual plane and I have a cam card for 168771, which I think is for Gen VI. Also handwritten on the back of the card are a # for a marine cam 139651, springs 99896, lifters 16535.

Is this an appropriate cam for HP500?
Will it work in Gen IV, or can I assume the Gen IV block was replaced in the rebuild?
What is the difference in the cams between block generations?
Should I be concerned with reversion?

Both motors have block mounted fuel pumps - does that indicate that they are Gen IV?

The other motor has never been rebuilt and gave out on me last week, so I want to bring it to similar specs - or change both of them.

I will hang in the bilge in the morning and see what markings I can find if that helps.

Thanks for informing the un-knowledgeable.

Joe

PatriYacht

That cam is actually larger than the cam used in the HP500 or HP525. It is a very good hp producing cam if you don't mind the idle. Because of the steep opening and closing rates, keep an eye on valvetrain components. I would replace springs and lifters every 200 hrs. and conduct periodic visual inspection. A good set of 3/8 dia. .080 wall thickness 1 pc. pushrods would be a good idea also. Make sure the rev limiter( if you have one) is set up to 5800 or so and prop the boat to turn 55-5600 rpm's. That's where those cams will make power.

PatriYacht

HP500's came with Holley 800 double pumpers and Dart single plane manifolds. They would make more power up top but probably worsen the idle and low rpm manners. Yes those are mark 4 blocks. The first 502's were bowtie blocks, very strong. Check to see if you see a bowtie cast into the side of the block anywhere.

PatriYacht

I have to correct myself. I thought, after reading your post quickly, that the 651 was in the engine. So all of my comments refer to the 651. Sorry.