well got to work on em a bit today, got everything taken apart ready to be cleaned, i was also able to get the 2008 4.0 dodge nitro engine specs from the school resources, it would seem that the 4.0 has a few differences but seems Chrysler followed suit of what they did from 1st to 2nd gen....
even lighter pistons then the 2nd gen trep, (which is even lighter then 1st gen), for a difference of 515g in 1st gen trep to 375g in the nitro, thats around 140g per piston, heavier connecting rods from 626g in first gen to 693g (total weight), resulting in + 73g, so becides the deeper cranks the rotating assembly is a full 767g thats almost two pounds off your crank!
while from 1st to 2nd gen trep they increased the intake valve head diameter by about 1.5mm, and softer springs (some say the main cause of the gains from the 1st to 2nd gen is from these two things) and while in the 4.0 the valves stay the same size they actually have .85mm more lift for intake, and around .5 for exhaust valve over 1st gen, and about .5 more both intake and exhaust compaired to 2nd gen, as well for the 2gen it uses softer intake and exhaust springs then the 1st, while the 4.0 keeps the softer intake, the exhaust are more similar to 1st gen rather then 2nd in terms of tension.
so more research on interchangeable springs, valves, etc... i cant figure about where the extra lift in the valves comes from, i think it may be both the cam and exhaust valve together.... the 4.0 exhaust valve overall length is .5mm longer then in 3.5s that explains the lift their, but the intake is the same, as well all cam specs are the same but it does not give me the size of the lopes on the cam (i think thats what they are called)
im going to make a thread with all the 4.0 specs later tonight, the info i have is just printed out so just engine build specs no full section on engine from FSM... yet
The only restriction to tuning would be in the computer.
yea i was meaning on the computer side of things i would think a OBD1 ECM would have less strict programming then a OBDII, and more comparing with the 2nd gen guys rather then the two engines i was looking at but like i said its just a wild guess guess with no merit behind it