I am looking at a used boat with 502 with 415 hp. The boat has 270 hours and appears to be in good shape.On a score from 1 to 10 its peobably a 9.5. My present boat has 454 with 330 hp and has 600 hours and have never had engines issues. I have heard that the 502's have valve issues and some boaters even say that all 502 will eventually have them. Is this true? Am I better off to look at a boat with 454's or the newer 496 motor?

The ones you've heard about are the blue 502/500HP motors. Those 502 mag/415HP motors will run forever.......burn a little oil there entire lives but they do that when brand new. It's a great motor, go for it.

I have personally seem them go over 1100 hours untouched in a performance boat.

The 502 is a great motor except for the factory exhaust system. It sux big time. They really come alive with aftermarket exhaust.

Your bigger issue is why it will only run 66. I've been looking or an update on that in the PQ forum. You need to get that figured out as it may be a result of engine issues.

Have you run it with different props yet?

The stock 502-415HP is a much better engine than the 454-330hp. Are the 502's cool fuel or EFI or carb'd?

Maklin is right about the exhaust. Get some good after market exhaust. Much better all around performance and worth the $$ you spend.

The 502's are the EFI 2000 year motors. They are on a Powerquest 340 Viper. They seem to run ok but the boat will only do 66 all trimmed out. They have 30 pitch props . I feel the boat should do in the low to mid 70's. I am going to talk to the dealer and see if they can swap and put some 28 pitch props to see what she does. I like the boat was wondering about te 502's. I had them checked the compression and they told me that all their used boats have all been checked and the compression is ok. They did not give me any numbers.

Thats a pretty heavy boat depending where the RPMs are you might be able to push 70 w 28s

Those are great engines that is what I have in mine with about 410 hours.
Mine are all stock and have never been apart. I regularly hit 67-68 m.p.h. on the G.P.S. and 69.5-70.0 in perfect conditions, light load, cool air, good water. My boat is a non stepped hull and has an advertised dry weight of 9200 lbs. I am running non labed 25 p 3 blade Mirage plus props spinning in. W.O.T. R.P.M. is about 4800 r.p.m. That Viper your looking at has a stepped hull and is about 1500 lbs lighter than my avenger. I would think it should definitely be 3-5 mph faster than mine.