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3.1's have the PCV running from the rear valve cover to the LIM, 3.1's have the PCV running to the plenum, so if it has a spot on the LIM for the PCV tube it's a 2.8....

oh and the crank isn't a 981 casting :lol: but pulling teh oil pan sux!
 

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Lets see....

1. the PCV line (Like Damon mentioned) 2.8's goes to the LIM and 3.1 goes to the bottom side of the plenum.

2. Plenum (the obvious)

3. EGR

4. Crank Casting

5. OPSU location, 3.1's should have it in the filter adapter, some 2.8's had a smaller threadded version into the block just to the left of the filter adapter.

6. It's possible that the head casting numbers could give it away, post them up.

Unfortunetly all of that stuff is interchangeable so you'll never know unless you drop the oil pan and check the crank casting number.. which is about 30 minutes work, a few quarts of oil and a $12 gasket. :)
 

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2.8 Gen 2 Phase one wheels have the cross hatch pattern on the center caps.

3.1 is smooth/clean center caps.
 

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VIN number. Unless motor has been swapped. all these things to tell if the motor is what it is. but the thing is. all these parts could have been changed. could have a 3.1 plenum on a 2.8 and vice versa. best way to see is by dropping the oil pan. there really is no difference between motors cept one drinks a little more gas and has a longer stroke. creating a little more low end torque. but that has already been mentioned lol
 
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