im trying to figure out if i have a 360 or a 390. the vin says 360 but it has a 4bl holly on stock manifold and everyone says 360 didn't have that. so can people identify with this picture maybe?

 

They look the same on the out side and some body may have just put the 4/bl intake on it. You can check the stroke but i will let some body else tell how that is done , i'v never done it .

 

1. disconnect the coil wire
2. remove one spark plug - for convenience, #1 or #5. As a Ford owner, of course you know which cylinders those are, right?
3. insert a wooden dowel (or other rigid object that fits)into the spark plug hole and manually turn the engine using a socket and ratchet on the crank bolt to bottom dead center for that cylinder. Try to keep the dowel is vertical as possible.
4. mark the dowel even with the valve cover rail (or other reference point).
5. turn the engine to top center for that cylinder and make another mark even at the same reference point
6. measure the distance btwn the marks.

A 360 will be 3.5 inches.... a 390 will measure a hair more than 3.75 inches (actually, 3.78 inches).

And there ya go...

 

'thought of an easier way...

Set the engine to TDC and then remove spark plugs #1 and #7. The latter will be 180° out of phase from #1.

Now insert into #1, mark, and then do the same in #7. Measure.

 

Great idea, with the stick. I think he means "put the stick in perpendicular to the piston head" - about 45 degrees, not vertically.
Between us we will get it right.

 

Sorta.. The spark plugs are at an angle so yer not gonna get it perpendicular - close but not 90°. Try the method in my second post and you'll see.

 

Engine at TDC.
Spark plugs at #1 and #7 removed.

Measure #1 and mark.


Measure #7 and mark.


Measure difference:


+/- 3.50 inches... = 360 cubes

 

Aw geez, I've been doing 1 & 5 for yrs same same....When at the junkyard and looking for a 390 block. I use a vehicle radio antenna ball tip first for a quick stroke check so, I don't need to carry a wooden stick about. a Felt pen always carry a tape Measure anyways tho.. my 2 cents orich

 

I am reopening a dated post here. I have been chewing on what Hio wrote for a week and have a couple of thoughts:
First, I think that this is the most informative, useful piece of information that has come across this site in a long time. For years I have seen guys post the same question: How do you tell the difference between a 360 and a 390. The answer always comes back: pull the pan, pull a head, measure, you can't tell externally. Hio has put up a simple method to tell the difference and proven it by photos.
I have a related question. Periodically the question of a slipped timing chain comes up. The short answer is pull the cover, have a look. But maybe Hio's method of measuring displacement can be used to feel out true TDC with a dowel and dial indicator and compare it with what the timing mark says?
Hio? Anybody?
Well done, Hio.

Semper Fi

 

Thanks...

The dowel measurement method has been discussed for a long time but I had yet to see pics so figured "why not" since my rig is disassembled and is less of a pain in the azz to do.... Btw, I purposely chose cylinders 1 and 7, instead of 1 and 5, because the cranks arms are 180° out of phase from each other.

I see what you mean by using the dowel method to feel out TDC. Yeah, it'll work but the dowel will be at an angle plus dowels swell and shrink with humidity. For an eyeball estimate, yeah it'll work.

 

Hmm well when I posted it was way pass my bedtime for an old fart of 70 yrs old and was not thinking clearly like always. #1cyl. & #4 are the ones easiest to check since #1 Will be set at TDC & # 4cyl. will be at the bottom.
So no moving to the other side of the vehicle. ..my 2cents..orich