Brain tickler: updated in 96-01 to 225 ft lb torque @ 3000 rpm

[honesT]

Could a mechanically incline person please explain to me what was done to the 242 in 1996 to give it the same torque at 3000 rpm instead of 4000 rpm ? updated in 96-01 to 225 ft lb torque @ 3000 rpm

Need to know it`s just stuck in my brain and I think it has something to do with the small diameter exhuast pipes but I`m not educated enough to pull out the right answer without days or torment infront of this dam computer

Thanks in advance for your time :confused:

[brandonlp]

96+ is Obd 2 the computer has a bit more control on the functions on the motor, also they changed the fuel pressure in 96 to 49 psi instead of 39 in the pre 96 models and run larger injectors.

most of the change come from tuning in the computer and changing the perimeters of the timing and fuel latency values.

i wish someone would create an open source tuning software like they do for subarus, it would give us full control to change the settings on the computer, i came from the subaru world and did alot of tuning myself and i must say if jeeps had that access we would gain so much more.

[honesT]

Thanks for the detailed response that makes alot of sense. Here is what others have stated Quote :

Sometime between 1996 and 01 they went to a new intake manifold. That would account for most of the power increase.

the change in 96 was due to the required changes to move to ODB2 - the sensors, more complicated/calculating computer causing an overall increase in output. Methinks there was a new head design or intake design then too..

Also worth noting, the displacement is difference between the 1990-1995 and 1996-2006 engines by 2 cubic inches. Both had a bore of 3.88 in, while the stroke decreased slightly from 3.44 inches on the earlier engine to 3.41 inches on 1996 and later engines. The displacement of both engines still rounds to 4.0 litres (3999.83 cc vs. 3964.95 cc). May be why the power curve is in a different spot.

i think it has something to do with a different head...I think the intake/exhaust ports are different

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From Wikipedia - http://en.wikipedia.org/wiki/AMC_Straight-6_engine

Quote:
The 1987 RENIX 4.0 made 173 hp (129 kW) and 220 lb·ft (300 N·m) of torque. In 1988, the 4.0 received higher flowing fuel injectors, raising output to 177 hp (132 kW) and 224 lb·ft (304 N·m). In comparison, "this engine made more power than the Ford 302 V8, Chevy 305 V8, Chrysler 318 V8, as well as any of the 6 cylinder engines the Japanese were putting in their trucks... and it had comparable or better fuel economy."[12]

In 1991, Chrysler redesigned the RENIX engine control computer and raised the intake ports approximately .125 in (3.2 mm) for a better entry radius.
Chrysler also enlarged the throttle body and redesigned the intake and exhaust manifolds for more efficiency, and the fuel injectors were once again replaced with higher flowing units.
The camshaft profile was also changed. The net result was an engine that made 190 hp (140 kW) and 225 lb·ft (305 N·m) of torque. Badging on most Jeeps equipped with this engine read "4.0 Litre HIGH OUTPUT."
The new cam profile combined with altered computer programming eliminated the need for an EGR valve and knock sensor, but made the engine more sensitive to alterations, especially where emissions are concerned.

Small changes were made to the cylinder head for the 1995 model year. In 1996, the engine block was redesigned, and a new strengthened unit was then used.
The new block made use of more webbing cast into the block, and a stud girdle for added rigidity of the crankshaft main bearings.

The cylinder head was again changed around 1998 to a lower flowing, more emissions-friendly design.

Thanks to all who replied on this forum and others :thumbsup:

[brandonlp]

you will gain zero performance from the newer manifold, 1 to 2 hp but nothing you would even feel, there were some changes to the motors but to be honest the block is the same, theres no big change i see more changes in the computer than anything, im going to look in the overhaul manual and compare but i dont think they changed things enough to drop the torque range 1000 rpm

[honesT]

More insite I found online: A shorter pipe improves torque after the peak (reduces it at lower RPM), preventing the
torque curve from falling off so quickly as speed increases. A longer pipe extends the torque curve
backwards to improve the engine's flexibility, at the expense of after-peak torque.

For more detailed information go here and scroll down to Exhuast manifold : http://www.scribd.com/doc/15418414/jeep-Engine-and-Cam-specs

[honesT]

1st 30 seconds of video most informative :
http://www.youtube.com/watch?v=ICAWQPLNFAc

[honesT]

Another :
http://www.youtube.com/watch?v=9A6S1NUjg_A