4.0 and HO 4.0

[gtmud]

CAn anyone tell me the base engine differance between the 2 engine designs?

[AlohaBra]

I will indicate the specs (from the sticky on top of this forum:

4.0L I6 "Power Tech" - 177 hp @ 4750 rpm, 220 ft lb @ 4000 rpm - used 87-90 called "non-HO"
4.0L I6 MPI "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in 91-95 and updated in 96-01 to 225 ft lb torque @ 3000 rpm (00-01 models use a distributorless ignition system)

**********************************
In 91--The HO version made changes to the head design, cam profile, and the block casting. The YJ version rated 180HP while the XJ version rated 190HP (due to exhaust and air cleaner variation).

In 96--upgrades were lighter pistons, a new head casting with better exhaust flow, new two piece thin-wall cast exhaust manifold and steel valve covers.

In 97--the block was tweaked to relocated the oil filter mounting, primarily for Grand Cherokee installation fitment.

In 99--The last improvements were made. New direct-mount accessory drive bosses, a thrust washer added to the camshaft, a new chain oiling system, and a larger diameter casting on the camshaft for increased stiffness are included changes. On the head, ribs were added to the rocker pedestals for the screws holding the new distributor-less coil rails.

In 2001--XJ (Cherokee) production was ended, but the 4.0 continued in Grand Cherokee and Wrangler until 2006.

In 2006--4.0 Liter six production was ended.

[gtmud]

ok, so with the different casting and head design, was there any changes that would prevent putting an HO head on an 89' 4.0? Sorry I started another thread related to this matter. I have piston slap on # 1 cylinder, but the engine runs good and pressures are at 45 hot, in gear.

[AlohaBra]

I had not done this, but my research shows that it will bolt on. I know the fuel injection stuff is different and exhaust and stuff.

http://www.jeepforum.com/wiki/index.php/4.0L_I-6

[Gnatow]

Thank You! It's interesting!
[email protected]