I think the AMC 4.0's are the best of them. Good torq, good hp, very dependable and durable, fuel injected. The slant's were reliable and fit under the hood of a car but only made 1/2 the hp.

As far as why dodge made the 3.9 instead of updating the slant, the dakota is the only reason I can come up with. Either the dakota was originally designed around the 2.2L and later they decided they needed a 6 cyl and the slant was too long or from the get-go they decided they wanted a shorter hood on the dakota. The decision making process at the time really boggles my mind. Here for the 1987 model year they debuted the 3.9 V6, carbed at 125hp which was less HP than either the fuel injected 2.2 turbo engines or the fuel injected mitsu 3.0 that were both available that year making 140hp. Then in 1990 the 3.3 V6 comes out at 150hp and the next year the 3.8 V6 comes out. They spent millions on developing the 3.9 really for no good reason and it wasn't any good of an engine anyway. I don't know if the fwd and rwd departments just didn't communicate and share or what because it seems like one big waste.