was trying to find a couple used,, can't find anywhere needs to be a MEFI- 4b, not sure what the b is for? Anyone..

MEFI-4B is a very desirable ECM. It is user friendly with the MSD programs and is easy to install O2 sensors. 4B offers nice boost fuel corrections, timing adjusements and other variables to allow the ease of EFI on a blower motor. I have one each on my 1000 SCI's and they work like a charm.

Does the 4B offer sequential injection or just bank fired?
Also can a GM for a 502 ramjet Mefi be tuned for a 600CI motor?

bank fired and it doesn't matter how big the motor is.

Crate Engine depot has the best deal around. I bought one last year complete with harness for just over $600.

Thanks, Thats what I was wondering,, The engine builder wants to use these when adding prochargers...

Are the motors EFI now? What system?

I believe that innovation marine uses these and have it working with sequential injection. It was used on the 800's for the 50' Hustler in last years boat show.

4 4a and 4b
differences are mainly memory cpacity and OS version change. All support narrow band O2. All support Coil on Plug, and Wasted Spark ignition, as well as, Various Distributor types. The 4 variants have greater granularity with in the tune parameters...

Only the MEFI 5 will support sequential

Have source for 4b if needed. Crate engine depot excellent source and great value.