I have searched to no end, and still cannot find a definitive answer on this subject. My 509 EFI is knocking, so its gotta be torn apart after 90 hours +/-, so i figure why not dress it up a bit?

first and foremost i need to figure out what is wrong with it obviously, then id like to rebuild it with some quality parts, or salvage the good parts already in it (eagle crank, carillo rods, etc) hitting any particular HP # is not critical, though the motor right now is in the low 500's.

question is, can I use a standard 500 EFI mainfold & plenum (with fuel rail/filter/injectors/pressure regulator/coolfuel), TB, map sensor, thermostat housing, temp sensor, and distributor and plug them into my 502? I'd like to use my 502 ecu and send it out for whatever adjustments are necessary for possibly more airflow. Again im not using the manifold for power, looking to address my otherwise blah looking engine compartment, the black MPI manifold doesnt do it for me.

thanks!

Chain- you will need to use a mercury crank position sensor and I would think it would work. I don't know if the Merc heads on the 502 are different is my question. You will need to remap for your cam. Or use the cam from a merc 502.

Wannabe

Would the black 502 wiring harness work with the sensors (reach them)or would he need to upgrade it to the blue harness?

your thinking of the 525,,500 efi used a dist...he may be able to use the 502 harness and dist and such,,i think he may have to change the plugs on the iac and tps..

I did this same swap on my Fastech 271. The 500 efi manifold bolts right up. I used the 502 mag wiring harness and just needed to extend a couple wires. I reused all the 502 mag sensors and just needed to use the 500 efi IAC sensor. I also reused the 502 mag. ecm and had it retuned by Precision marine. If you have any other questions let me know. Jeff Wurl

Thanks for all who responded! im glad i got the answer i was looking for, looks like i can freshen up the engine bay a bit now, actually looking forward to this winter project