the reputation these motors have for durability and the amount of abuse they'll endure borders on myth, but can they make a respectable amount of power and hold together as well? asking for a friend....
The AMC 4.0 is a good engine but the JEEP cooling systems suck rotten eggs. It suffers from pisspoor compression ratios too. There is a HUGE spread between the Static and Dynamic compression ratios. The stock cams have HUGE overlap.
But the 4.0 has a big bore and shorter stroke so take the crank and rods from a 4.2 (258) with its longer stroke and the 4.0 is now a 4.5L. Over bore it 0.030" and its a 4.6L. At 0.060" over and its a 4.7L.
A 4.7 with a ported head, bit hotter cam in a 1991 Cherokee with full time AWD will smoke many Rustangs.
And like the \6 and the 2.2/2.5 4's, it is not a cross flow head so a bit of loss in "HOP UP" power.
But I think this engine is too tall for most early Abody's. At least for the sloped nose of the 1962-64