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 added torque ? 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 :stars:

Thanks in advance for your time

[bigjim350]

I would think it had to do with switching to the OBDII computer system in 1996. Therefore the motor could be tuned better to produce more torque.

[4.3LXJ]

Yup, OBDII. It allows the ECM more control of emissions and other parameters. That is why almost all of the super tuning gizmos go on an OBDII system.

[honesT]

I had someone say the head was different and maybe the exhaust ports...

[bigjim350]

I don't think the 96-01 head is different to a 92-95. However the 00-01 head is a bad casting and is prone to cracking. I have read about small power gains by swapping on 99+ intakes onto the older motors though, so they must be different.

[ice_cold]

This may help. Pulled it off another site when I was looking for a new head for the Jeep.

Cylinder head

The stock cylinder head is cast iron and weighs 60lb. The valve head diameter is 1.91" intake/1.50" exhaust. Casting numbers are as follows:

Year............Casting No
1987-90......2686
1991-95......7120
1996-98......0630
1999-04......0331

Cylinder head flow figures (cfm) at 25inH2O pressure drop are:

Non-HO head #2686

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 122.0 168.0 186.0 189.0 192.0
Exhaust flow....88.0 114.0 130.0 134.0 138.0

Ported non-HO head #2686

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 124.0 183.0 197.0 207.0 216.0
Exhaust flow....87.0 113.0 138.0 153.0 159.0

HO head #7120 & #0630

Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 66.0 128.0 179.0 206.0 209.0 209.0
Exhaust flow. 55.0 100.0 120.0 136.0 141.0 141.2

HO head #0331

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 114.0 165.0 194.0 199.0 205.0
Exhaust flow....94.0 117.0 126.0 130.0 133.0

[4.3LXJ]

I had someone say the head was different and maybe the exhaust ports...

The head was changed for the HO engines to breathe better, then again in 99 to breathe a little worse but with a corresponding change in the intake manifold to allow the HP to remain the same.

[ice_cold]

Exhaust ports were changed to get the heat up faster for emissions . It gets the cat up to temp faster.

[honesT]

Found the answer: it appears to be the camshaft timing :driving:


'96-'99: 190hp at 4600rpm, 225lbft at 3000rpm, redline 5300rpm
In 1996 engines received noise, vibration, and harshness fixes. The blocks were stiffened with extra ribbing, a main bearing brace was added, and lighter cast aluminium pistons were introduced to improve efficiency and reduce cold start piston slap. Engines also received revised camshaft timing for more low rev torque. Heads are similar except that they have no water temp port. (The OBD II system drives the guages and, only requires one port, these can be drilled and tapped for the sender used in earlier models if you're doing a head swap.)


Here is the site I found this info at http://hjeepxj0.tripod.com/id15.html

[brandonlp]

well...i believe that info to be a bit inaccurate about the water temp gauge, because i have 2 temp sensors one for the computer to control open loop and closed loop fueling along with start up fueling, and the other that sits on the rear of the head that lets my gauge work, and yes mine is a 96, the computer does not control the gauge.

it more than likely does have a different lift cam in it but it has some perimeter changes in the computer for timing and fuel latency values and dont forget the 96 is the only year they use 23lb injectors. 97+ uses 22.5

[ice_cold]

well...i believe that info to be a bit inaccurate about the water temp gauge, because i have 2 temp sensors one for the computer to control open loop and closed loop fueling along with start up fueling, and the other that sits on the rear of the head that lets my gauge work, and yes mine is a 96, the computer does not control the gauge.

it more than likely does have a different lift cam in it but it has some perimeter changes in the computer for timing and fuel latency values and dont forget the 96 is the only year they use 23lb injectors. 97+ uses 22.5

I have a 98, and it has just the one at the thermostat. The head that I installed was from a earlier model..when filling with coolant I discovered the rear port for the rear temp sender.

96 has a sender and a sensor, in 97 they went to just the sensor.

[honesT]

What I`ve found on the net Quote:

'96-'99: 190hp at 4600rpm, 225lbft at 3000rpm, redline 5300rpm
In 1996 engines received noise, vibration, and harshness fixes. The blocks were stiffened with extra ribbing, a main bearing brace was added, and lighter cast aluminum pistons were introduced to improve efficiency and reduce cold start piston slap. Engines also received revised camshaft timing for more low rev torque. Heads are similar except that they have no water temp port. (The OBD II system drives the gauges and, only requires one port; these can be drilled and tapped for the sender used in earlier models if you're doing a head swap.)


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 liters (3999.83 cc vs. 3964.95 cc). May be why the power curve is in a different spot.


Injectors *********

The following is a list of the injectors used on the 4.0L since 1987 along with their rated static flow:

Model Year, ...Part #, ......Color, .....Fuel Pressure, ...Static Flow,
'87-'90, ........53003956, ...Dark Tan, ...39psi, .................18.6lb/hr
'91-'93, ........33007127, ...Brown, .......39psi, .................21.0lb/hr
'94-'95, ........53030343, ...Tan, ...........39psi, .................21.0lb/hr
'96-'99, ........53030778, ...Grey, .........49psi, .................23.2lb/hr
'99-'01, ........04854181, ...Blue tip, .....49psi, .................22.5lb/hr

[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

[brandonlp]

umm jeeps dont use vvt so...what are you trying to get at

[honesT]

Just another visual. Too many beers last night. I thought I was going somewhere with that, maybe just to push the point accross how important it is to have %100 of the spent combustion chamber gases removed before the next explosion...:out: :smiley-talk024: