what engine do I have?

F

Fordestes

Well-known member
I rebuilt my supposed to be 390 F.E the stock bore was 4.050, the rods were c7ra?? full floating pins the piston lacked about 1/4 inch or so going to the deck surface.
Did some geniouse put the wrong crank in, someone told me years ago that the rebuilders sometimes use 360 crankshafts in place of the 390 shaft.
does this sound like what has happened here? or do I have the wrong pistons,the engine was rebuilt before I got it and someone sugared the fuel tank thus warranting a rebuild.
Fordestes,
 
Sounds as though you have a 360 crank. Both the 390 and the 360 used the same bore, but the 360 used a 3.5 stroke and the 390 used a 3.78 stroke. measure the stroke and you just might find the problem. Back before I retired, we used to put 390 cranks and rods in 360s for customers that complained of the 360 lack of pulling power. The 360s lasted for ever, were dependable as Lassie, but slugs thus the 390 conversion.
 
what pistons were used 390 or 360 ?I am thinking of trying to correct the problem, as this engine is a little too light in the loafers for me. I may have a line on a 361 truck engine with steel crank , I have considered machining the crank to fit the 390/360 block ,what is your input on this arrangement, I want power and dependability, I dont think I am getting the power output for the fuel consumed,Less compression?
 
originally a 360 piston was the same p/n as a 4v 390 piston. I haven't seen a combo that would be short on coming up the cylinder. I have seen 390 cranks used, with 360/352 rods, and the piston comes out the cylinder. Measure the stroke
 
The 390 truck engine has a low compression ratio and does so by using a higher piston pin height. Going from memory, it seems that it should be about 1/8" from the deck. The 390 has a bore of 4.050" and stroke of 3.785". Check to see if that is what you have.
 
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