M5Power
Considering its age, it's quick as hell - the current Grand Cherokee 4.0 does 0-60 in about 8.6 with that engine and Wranglers do it about a second slower. But that engine was lapped for refinement some time ago. Until the Liberty, it had been used in every Jeep model since its creation, but it's destined to be phased out with a new Grand Cherokee sure to use the same 3.7-4.7-5.7 combination as the Durango. Wrangler will still use it, but not many people buy new Wranglers anymore.
Still - that engine's in millions of vehicles and though it wasn't particularly reliable until the mid-90s, it gets the job done. But not in the Comanche.
The Comanche was the fastest compact pickup truck at the time. Not surprising really, when in '87 the Ranger's top engine was a 2.9L V6 with 140hp, the Dakota's was a 3.9L V6 with 125hp and the S-10/S-15's was a 125hp 2.8L V6. All the while the Comanche had the 4.0L I6 (in non-HO format; I'll explain it later for milefile), good for 177hp. In fact, the competition needed until 1992 to beat the non-HO's 177 ponies. By that time the High Output version debuted, with 190hp.
As for the 4.0L on the whole, it isn't meant for speed. Never was, really. With poorly designed heads, and saddled with pushrods, it'll never see high rpm action. It's optimized for low-end power.
As for the differences between the original non-HO, HO, and later non-HO (aka Power Tech) versions of the engine, the biggest ones, between the '87-'90 and '91-'95, were the heads and the electronics. The '91-'01 received new higher-flowing heads by means of raised ports. The '87-'90's also had a 'Renix' fuel injection system, a mish-mash of Renault and Bendix electronics. It's very...different..compared to most electronic fuel injection systems on a very basic level. Sensors and the like used very different signal voltages than most EFI systems. Not that this is bad, it's just... different. None of this really matters though, because the Renix injection proved to be relatively rickety compared to the '91-'01's Mopar EFI. This was complemented by a new Mopar computer which could store and allow access to error codes.
With the new heads and fuel injection, adding 13hp to the bottomline, Chrysler named the new version "High Output" simply because it made more power than its previous iteration. The next big changes happened in '96, with new piston skirts to reduce noise (which is one of the 4.0L's biggest 'problems'; I think it gives it character) and changes to the main bearings. No changes in power though.
In '97 peak power and torque were numerically the same, but came at lower rpm due to new timing. It didn't really change the overall response of the engine. In the late '90s-early '00s the block was reinforced with some new ribbing, and the old distributor was dumped in favour of a DIS.
So milefile, there aren't really many appreciable differences between my '93 Cherokee's HO 4.0L and yours' non-HO. Just the name.
