pullmytrigger

If you take it to Mike at Active be prepared for the "OOOHHHHHHHHHH you thought youd save some money and buy a crate engine.....and now you want me to fix it up" tongue lashing "you know a crate engine IS NOT a marine engine........"

Im not saying dont bring it there because hes one of the best around here.......but just so you know

pullmytrigger

hope everything works out ok........

Firewalker

Ya, I already got that. I have know Mike and Wayne for years with the STV boats. And he build me some blower motors.

RT

PatriYacht

Cold water on the thermostat??? That sounds weird. Got any pics of the plumbing? Std. cooling goes in the front of the block, up to the back of the heads then forward to the thermostat. Then it's dumped overboard through the tailpipes. With your ignition timing and decent gas, I wouldn't think detonation was the problem either.

razor1115

Cooling sounds correct. Water comes from outdrive to sea water pump to oil/ps cooler to top of thermostat housing which has one inlet, three outlet and sits on top of the thermostat. At that point the engine water pump is one of the outlet and pumps water through the block into the heads up to the intake manifold at the thermo housing under the thermostat. This allows the water to come up to thermostat opening temp (usually 143 deg) then pass back into the housing. The other two outlets from the housing route to the exhaust manifold then to the riser and out the exhaust.

I have to agree, 500hp is way too much for that stock 330hp cooler. Your oil temp is probably way too high. I had same problem when I upgraded from a 502 to a 600hp 540 cu in. I have a 3 X 18 cooler in my hands ready to install. I also run straight 50wt now. Multi 20w50 did not act as a 50wt once warmed. Gained 10lbs oil pressure just from oil swap. Need another 5 from cooler to be comfortable. Also note, crank windage will foam your oil...

As fro falling on its face, sounds like lean on the top end (like other suggested). Need to check with a NEW set of plugs, run max throttle, SHUT DOWN QUICK AS POSSIBLE( no idling), do a plug read. Everyone else here has some great info as well.

As for crankcase press, sounds like the breather assembly is too restrictive or there is a blow-by issue with the rings.

Firewalker

some interesting ideas here

Do any of you think an 800 Holley is too small a carb for this motor?

RT

razor1115

How many rpm are you wanting to turn? Rule of thumb is

cu in X rpm X vol eff. / 3456 = carb cfm

Your case
502 X 5200 X .90 /3456 = 680 cfm should be ok and have a good carb if heads are done or flow better than expected.

I actually have a 950hp. I turn 5400 with ported heads, manifolds. Went to a 1100 race modified carb on the dyno and lost some horsepower and torque.

Firewalker

you guys rock

Firewalker

here is the motor showing the plumbing, the oil system and pullies are not on it yet. But you get the idea.

Pat McPherson

The 6 quart pan that comes on a ZZ502 is too small. You need the 8 quart pan. GM performance parts makes one; same as the marine pan.
I would do a compression test and leak down test to see if the engine is OK before making a lot of changes.
Good Luck...