Question about inframe on 3406b 7fb 350hp cat engine

If your fix'n to go to all that expense .. why not just pull the B model and swap in a C model ?

 

I don’t know the answer but I can provide disposal services of the b model lol

 

I think any time you change a crank, the block needs to be line bored first. That’s what I was told recently by Detroit, anyways. In other words an out of frame overhaul. They claimed you can’t just swap a new crank in, I’ve also been told it needs to be done on a second or third overhaul. Maybe it depends on the engine and amount of torque it has? I don’t know. My Detroits on its second inframe. No need to line bore. Not enough torque to stress and twist the block. I’d guess the heads are the same. I don’t know enough about them even though I had a C model for 4 years. @wore out is who would know for sure.

 

A C model head won’t flow as well as a B. That said you can’t get the B square port head from CAT any longer. All that’s offered is round port. The B square port manifold will seal on a round port head, and actually is Bigger has better flow that a stock round port manifold as well as the aftermarket round port manifold I run. That said I think a round port head does better with a round port manifold.

Don’t let the uninformed convince the bottom of a 7FB is weak. Is a C stronger looks to be yes so we’ll go with that. However I have seen too many narrow journal engines turn 2350 all #### night, night after night dragging a cow bus across 80. I have seen as many crank failures on C as B. C has way more rotating mass something to think about.

 

You can build a 7FB to 5YG 460hp specs. The 5YG uses the wide rods but small pin like the 7FB. Use the 7W-7031 nozzle leave the 7FB pump timing stock do not advance it. Put 8M-9141 govnor spring in the pump, if it’s in good shape. If not go through it.Put a 78mm in a 1.45 Borg Warner turbo on it and make sure you have no boost leaks. I personally would check timing on a meter so you know. I assure you that is all you’ll really need. Both those pistons are 14.5 to 1 compression but have very different bowls you want to go to the 5YG piston to use that nozzle. That piston and nozzle were also used in a 3ER genset engine that was rated 580. However you get greedy with the screws and especially the timing you will burn it up in very short order.

For what we’re doing and who we’re doing it with square port head or round doesn’t make enough difference to matter in my opinion. I run a round port with an after market manifold cause it’s the head I got from CAT. I think if you’re pulling a sled or racing it would absolutely matter. But for street use I’d use what is good and available