360 vs 390 rpm

[390owner]

I just installed a tach in my 74 one ton that I was told had a 390 in it years ago when I got it. My 79 bronco has a balanced 390 with comp cam. I have often wondered if the ton had a 360  Anyway My bronco will wind up to 5 grand no problem and is pulling hard. My ton truck once it gets to 3 grand sounds like it is about to sling a rod. Anyway  what to you guys think ?

[390owner]

I guess what I am asking is will a 390 wind up easier than a 360?

[Urgefor]

In general, the main difference between those two engines is the stroke.  360 is 3.5" and 390 is 3.78".  Bore is the same on both at 4.05". There are of course differences between heads, camshafts, etc. used on different model years.  Difficult to answer without knowing more about each engine.

[390owner]

I was just wondering in general if a 390 would wind up faster and easier than the 360 both being stock engines.

[GerryP]

The one with more horsepower will wind up (accelerate) faster since horsepower is work over time.  The rotational and reciprocating mass are roughly equal.  But your meaning of "wind up" could be different from mine...the problem of using ambiguous language.

[MeanGene]

Is it possible that your tach is variable amount of cylinders? I used to have a 4-6-8 tach in my Mach1, with a little switch on the back. Was lots of fun showing the Chebbrainwashed that my 351W would spin 7500

[frnkeore]

Yes, a 390 (if in good shape) should wind up faster (take less time to get to a particular rpm) than a 360, especially under any load but, the cam timing and carburetion will also limit the rpm and time it takes to get to that rpm.

i.e. The 63, 352 2v was rated at 4300 rpm, while the 390 4v was rated at 4600 rpm. Different cams and carbs.

[390owner]

Thanks for the replies

[JacksFordParts]

For easy confirmation. Put #1 at TDC, when #1 is at TDC, #4 is at BDC. Stick a dowel down both spark plug holes and mark the dowel at the valve cover. Measure the distance between the marks...