help! 500efi conversion

[Michael Garibay]

Hello all, I have 2 '93 502 efi mag motors in my '31 Scarab and have the opportunity to get two brand new 500 efi intake systems.This includes -upper/lower intakes,distributors,computers,wiring harneses,fuel coolers,fuel pumps,air filters-----the works.Question is-will this set up work on the standard 502s'.I know the fuel(vapor lock issues)have to be better.But the rest I don't know.I do know I need to upgrade the exhaust system.Any help in the matter is appreciated.Thanks,Mike

i'm not a mechanic or a motorhead. I have some basic knowledge, gleanned over many years of paying for them in my boats & cars. You need to take my reply with many grains of salt.

You will be buying only a portion of the equation with the 500EFI intakes & misc. The heads, valves, springs, roller rockers and cam are all different between the two motors. Then yopu start with different pistons, rings, fuel pump etc. The CMI full headers are $2,500. a set each. It would seem like a lot of time, money and aggravation and still not knowing if the results will be. Mercury Racing hand builds these motors and dynoes them to assure exact tolerances and their production of 470pshp.

[Vinny P]

I agree with Miami.

[rjcardinal]

Hate to drag up an old thread like this but I am attempting to do the same thing. I belive Check and Miami are wrong. The 500 EFI is very similar to the 502 Mag. The complete shortblock bottom end is the same. The 500's are the only engine that Merc Racing does not hand build. They start with GM 502 shortblocks. The heads are the same with the exception of the roller rockers and a valve spring to match the cam. Once you add the 500's EFI system, cam, and CMI headers you are real close. The only other major difference would be the 500 has an oil thermostat and slightly different cooling system plus some billet blue anodised pulleys. Looking at the wiring harnesses they are almost identical and you could probably even use the 502 Mag system and just have the ecu reprogrammed to the 500EFI spec.

I disagree that this is not a good conversion. If you can pick up the efi's for a reasonable price and dont mind spending the bucks on a beautiful set of headers then you are almost there. Roller rockers, cam, and a gasket set are not that much more.

Most engine modifications will hurt the resale value of the boat but people will pay more when they see the "Blue" engine. When I was looking at new boats the ones with the 500EFI were 20K more than the same boat with a 502 Mag. Same thing with slightly used boats, the 500EFI boats were 18-20K more.

Ron

FYI....the heads on the hp 500's are different. They utilize 2.250 intake valves vs 2.190 on the 502's. The valve train is also full hyd. roller as opposed to std. hyd used in the 502. The 500 also uses a different oil cooler in addition to the thermostatically controlled oil system. It wouldn't be the worst thing, but if you just try to bolt the system on, expect and be prepared for issues.

Being that the engines are 93's its probably time for them to be freshened and since you have to pull them to do the upgrade, I'd make some calls and see if you can find a pair of rebuilt HP 500's with warranty that you can trade them on. You'll probably have slightly more upfront money invested, but far less hassles and increase your resale for actually having legitmate HP engines.

Rod

[h2owarrior]

WOW rjcardinal that is a major suprise to me. I was under the impression that the 500 was based on the 502 but shared only the block. I was told the crank, rods, pistons, heads and entire valve train were upgraded from the 502 MAG EFI. And based on the reliability of the 500's, it was easy to believe. I was also told it was hand built at Mercury Racing.

Not that I have heard of problems with the 502's (beyond the early days and the siameese cylinder issues), but getting an additional 55 ponies out of the motor with the same reliability lead me to believe what I had been told.

You popped my bubble

[pachangalpina]

I have taken the 500efi system and installed it on a stroked 454 (496ci). My piece is very custom but still utilizes many of the stock EFI components and produces 625HP/625ft/lbs. The injection is basically stock except for the larger injectors, throttle body and reprogramed ECU. Arizona Speed and Marine helped me thru the project and everything performed flawlessly. First time on the dyno the injection preformed as expected without any issues on programming or injector sizing. I would say that the upgrade should go very well as long as you are getting the components at a fair price. To enjoy the benefits of the 500efi system you will need to upgrade the performance on the rest of the system also. I do not believe you will see any big gains by just switching the injecton system, it needs to be done as a package. If I were you, I would talk to someone at Arizona Speed and see what they think, they do extensive work with both systems.

[cobra marty]

I'll give you $1000 for that whole setup.

change the cam, you will have to get roller lifters as your 93 502 will be flat hydralic, valve springs, add roller rockers and you will be good to go imo, you should probably have the heads done, and a small thing sometimes over looked the thermostat for the 500 efi should be a 143,, the 502 mag is a 160