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looking for a way to determine weather i have a 428 or possible 390 engine in my 70 r code, ive read the specs for telling if it is a 428 but havent seen anything to tell me if it is or is not, is there a way of telling if its a 390 with out pulling the engine apart
 

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Try www.428cobrajet.com ] www.428cobrajet.com [/url]. Scott there has some very good info and some info on 390 id. Unfortunately the best way is with the motor out of the car. You can also pull a head and the bore will be smaller 4.08 for 390 and 4.13 for 428. I have been through this recently with my cj, it came with a 390, and I just purchased a 428 short block. Let me know if I can help any other way. By the way if it is a 390, I can point you to several good sources for a motor.
 

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I recently had the same problem. Found a new rebuilt FE in a junk yard and had no idea as to what size it was. The casting # gave me a choice of 390 PI, 390 GT, or 428. I pulled the pan and id'd the crank. It's a GT. 390's have 1U and 428's have 2U stamped on the crank. It was easier to pull the pan than to disturb a new set of head gaskets.
 

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if it were me, I would pop the cross member under the oil pan and drop the pan and look for the correct 1UB crank AND the extra webbing that is apparent on the main bearing saddles on cobrajet blocks. if you need a pic of what I am talking about, PM me and I will take a digi-pic of the area I am talking about....

randy
 

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Take it to the drag strip and make a couple of runs. The 428 CJ will run 14 flat stock and the 390 will run slower than my 289 Hipo Shelby
 
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It may be possible to measure the stroke through the spark plug hole. Insert a piece of stiff wire (coathanger, etc.) into the bore & have a friend turn the engine until you feel BDC, mark the wire at the edge of the plug hole. Hold the wire in place & turn engine to TDC, mark again. Measuring between the marks will give you an approximate stroke. It is important the wire is lined up with the bore as close as possible & is held on the same spot on the piston during measurement. The 390 stroke is 3.78" the 428 is 3.98". There should be enough difference to get an idea what you have. I havn't done this myself but a few people I know claim it works.
 
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