Edward R. Cozzi

I think GM uses those 502s in bigger trucks and motorhomes.

I would be leery about using a crate motor in a raw-water cooled application without changing the head gaskets.

Bawana

If you can, get the book "Big-Block Chevy Marine Performance" , Author Dennis Moore. Its from HP Books. Its a great book, every boater should have. It will tell you first hand about this situation, and many other important things.
Dennis Moore is very respected and knowlegable in the marine industry. My .02, but why not get it from the horses mouth, get the book you wont regret it.

hunster

I bought some so called gm marine long blocks for my 29 scarab last year. I was replacing my tired 350 carb. mags . I saw a nice ad showing some 270 hp roller cam long blocks at a attractive price. Merc only sells reman now to replace these. I opted for new blocks rather than some old used rebuilt ones. Sounds good but what a nightmare! They are definatly cammed wrong. There is no way the hp rating could be even close, I had to drop the pitch of the props 5 degrees to get the thing to run at 4800. I'm not that good that I could screw up both engines to run exactly 1000 rpm low. I tried to get a build sheet to see what was in these engines. No luck there , please what engine builder doesn't tell you what is in there. Anyway I'm out in the garage swapping all my bolt ons to a set of quicksilver merc remans right now ! Losing 10 mph was no fun and a lot of work. They ran great, just didn't make the hp. Beware! If a deal sounds togood to be true , it is. P.S. 2 small blocks and 19p mirage pluses 4 sale cheep!

BillK

Other than the cams, I cannot see any difference. They use the same head gaskets, and come with brass freeze plugs. One of my customers is finishing installing 2 of them in his boat. We did change the cams and valve springs etc to match. Should be interesting to see how they perform. I know of several guys that have installed them just the way they came from GM, one in a jet boat and the other in a Fountain. Have not heard any negative comments from either.

stevesxm

if i had a good combo v-8 in my boat that i was happy with and it was just houred out i would use one of the crate motors in a heartbeat instead of some one elses rebuild. i looked at the crate specs out of curiosity and dollar/power are a terrific deal in my opinion.

let me say that when/if i hour out my 502 mag mpi i will buy a couple crates and switch over the ancilaries and go... altho i suppose i would replace the cams w/ what merc put in or very similar as well.

my lap top is elsewhere so i don't have the web site ( but i published it here some time ago) that had all the crate specs and prices... pretty mazing stuff for brand new factory stuff and am certain that that the new 502's on that 1 800 web site above are crate motor coversions to marine.

MOP

True they are pretty much the same, pistons and bearings can be an issue. Standard automotive stuff will not hold up to the constant load of marine use. Important to find out what grade of bearings and if it has hypernetic or forged pistons.

I am curious why "hunster" did not opt for a decent set of "Hi Perf marine cams" in the SB's he had which would have gotten him into the 300HP range, that would have saved a ton of $$ to be spent on the $3 per gal we will be paying come summer.

Phil

pullmytrigger

you should be sure the valves you get in the crate motor are up to the marine task also......the crate motors say "stainless steel" valves.......my engine builder showed me the catalouge of one valve manufacture (I think it was Manley) .......they had about 5 different levels/grades of "Stainless steel" valves......only the top level of stainless(severe duty) and inconnel is suitable for a hi perf marine engine......if your only going to run in the 350/400 hp range.......you could probably get away with a stock crate motor.......did you check the ZZ502 DUD thread????.....a real eye opener

ROTAX454

Correct me if I am wrong, isn't brass freeze plugs the preferred material for marine application?

offthefront

yup .... brass would need to be installed ...

stevesxm

read the two threads refered to in above posts and have to say that virtually all problems encountered , in my opinion were self inflicted and had nothing to do at all with the suitability of the hardware.

bottom line is that if you don't lnow the fundemental and elemental techniques for the task you are attempting , you can't blame the hardware when you screw up. the crate motors are professionally built to a specific spec out of good parts by people and enginmeers that know what they are doing. if you are dumb enough to mis plumb or intstall in an application without suitable cooling or not smart enough to realize you need the right oil pan, relief valve or oil cooler then thats your fault... not the hardware. suitabilty to application is the fundemental precept for any design.

bottom line. for 5 grand or so you can buy a 500 hp fuel injected crate 502. thats cheap. if you have to spend another grand on a marine cam , brass freeze plugs and a handful of other stuff thats STILL cheap. call me a cynic but the marine industry seems to be the same as the aircraft and racing industry in so much as they would have you believe that everything is magic or special to such a degree as to warrent crazy pricing and the " you wouldn't understand because its special" philosphy.... hardware is hardware and the laws of physics and materials aren't any different here than anywhere else. GM produces the crate motors cheap because of economy of scale. if you have basic mechanical skills and specific marine knowledge the conversion to top flight marine hardware is a piece of cake... and it really is that simple. if you LACK those skills...well then maybe a crate motor isn't for you... but that isn't the motors fault.