390 or 360?
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Mountain Pass
Joined: Jul 2002
Posts: 177
Likes: 3
From: Tornado USA
390 or 360?
I've read in two other posts that one would have to check the stroke to see if they have a 390 or a 360. Can someone please explain this? I am pretty mechanically inclined, but I'm just not sure what is meant by this. Thanks.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
390 or 360?
David, The 360 & 390 use the same bore (dia. of hole). The 360 uses a 352 crank, the absolute travel top to bottom (stroke) is shorter than the 390. The 390 can draw more unburned fuel into the combustion chamber due to the longer stroke and that makes more power. There were just a few 390s put in trucks. Most were either 352s or 360s. The thing is you can't look at them and tell the difference. You have to look for the numbers and measure the stroke. 
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John
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John
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Postmaster
Joined: Apr 2002
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From: Coal country
390 or 360?
Here's the easy way to check the stroke without removing the head. Get a straight 12 inch piece of coat hanger wire or stiff electrical wire. Whie color is very good, but not necessary. Get a magic marker. Remove the number 1 and number 8 spark plugs. Turn the engine over until the timing mark is at TDC. Put the wire in the number 1 spark plug hole with wire resting on the top of the piston. Make a mark on the wire even with the lip on the valve cover. Now move the wire over to the number 8 cylinder and mark the wire again, using the valve cover lip as your reference point. Measure the distance between the two marks.
For those that don't know: 3.98 is the stroke for the 410 and 428 engines; 3.78 is the stroke for the 390, 406 and 427 engines and 3.5 is the stroke for the 352 and 360 engines.
Don't worry about being TOO exact. If your stroke is about 3 and 3/4 " you're a 390, but 3.5" you have a 360 or 352. Most likely a 360.
For those that don't know: 3.98 is the stroke for the 410 and 428 engines; 3.78 is the stroke for the 390, 406 and 427 engines and 3.5 is the stroke for the 352 and 360 engines.
Don't worry about being TOO exact. If your stroke is about 3 and 3/4 " you're a 390, but 3.5" you have a 360 or 352. Most likely a 360.
