3406B, 4MG vs. 7FB

7FB could be JWAC or ATAAC. The JWAC were 24 degree timing with 14.5 to 1. The ATAAC were 21 degree. The 7FB has a sharp steep cam lobe that was hard on lifters. The timing advance is also hydraulic advance spring return. Uses 3421 nozzles


The 4MG is ATAAC (@425hp) has an 18 degree pump cam with a full hydraulic advance. (Both advance and return) the timing on a 4MG will respond a little faster, that and 15.2:1 compression will make it seem to be a little quicker or pull harder down low. They use 3423 nozzles.

Both use the narrow rod crank which is nothing to be concerned about just keep up on bearing rolls at 250k. I think the 4MG is the best of them personally.

The thing to remember is the nozzles have to match the pistons and the pump needs to match the nozzles for them to run like a few have the reputation of having

 

Are you sure that you are reading the engine stopped side of the stick and not the idling side?

 

I am not sure if oil capacity is a serial number break or not. I think it’s more of an arrangement number deal. That’s the number that gets you the internals of different hp, front or rear sump, oil fil location etc. another words how the naked block is assembled so to speak. The OT-spec will get you timing and fuel settings etc.

 

Ok. Mine have a side for idling and a side for shut off. I was just wondering if you were reading the right side. Come to think of it I am bassackwards anyway as it will read higher when shut down.

 

Were you looking at a Brakesaver engine? They were 2gal bigger than Jake engines. Other than those 2 the only oddballs for B’s I remember were the Leaning Tower of Peoria pans for the Louisvilles.