Prowler 502 has low compression......need advice
 

Ran the boat last weekend. When I came into the pier after running pretty hard for about an hour the motor died. Was hard to start but finally did. Ran pretty bad. So I just got around to running a compression check on it and it was not good. I cleaned the plug surfaces before I did the test. I did the test twice and here are the numbers. Driver side front to back: 135, 90, 80 and 80. Passenger side front to back: 120, 120, 80 and 150. Looks like the valves and or valve guides are shot. Going to pull the heads. Would like recommendations from you guys on what to replace the heads with. OEM iron or aluminum heads. Motor had 377 hours on ot per the ECM. Going to use ARP studs vice normal head bolts when I install. Thanks in advance.

Was it the first time you ran it all season? Did you use old fuel? 1 hour running hard + old gas = detonation.

I would just re-work existing heads if you can or go with a 540 stroker kit from a respectable builder.

No it was the second time but the first time was just a short run to see if everyhting was working. I keep the boat full over the winter just to have a backup fuel supply in case of ice and or snow storm. I put 4 cans of Seafoam in the fuel as a fuel stabilizer and have never had a problem in the past.

When I bought the boat the motor had been apart before. From the literature I got with the boat the head gaskets looked like they were replaced. Probably will go with a good set of aluminum heads and exhaust manifolds. Might as well do it right while I'm in it.

Thanks for the info.

Ed

That sucks man. Was it a stock 502/415 mag efi? Tell us more about the motor that craped out. The stock setup is pretty good on the 502's. You can change the cam and valve springs and re-work the heads and get to 500hp. Much cheaper and will be more reliable IMO than aluminum heads. Might help resale too because it will still look like a stock engine and some will run away if they see aluminum heads with open cooling. If you do get aluminum heads don't buy pro comp heads and make sure it has a coating inside for marine use or they will not last very long assuming your running open cooling. I bought my boat with 3 season on a rebuild done with pro comp aluminum heads; the heads were junk after the 4th season and I ended up repowering and going back to stock 502 with cast iron heads. There is a weight difference with the aluminum heads as well, which could throw the balnce off. It did on my boat, was balanced much better after going back to cast iron heads. You will need a bigger oil cooler and could need bigger exhaust if you really bump up the hoursepower.