-
Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.
4.0 HO vrs. 4.0 ?
- Thread starter manyjeeps
- Start date
langer1
NAXJA Forum User
- Location
- Mineral City,Ohio
I thought everything newer than 1990 was HO
deesiexj
NAXJA Forum User
- Location
- Portland, OR
it is, the 90 and pre have (i think) 177 hp, HO has 190 hplanger1 said:
jeepsrock
NAXJA Forum User
- Location
- LA California
Its funny bc i i drove the newer 4.0L engines they seem to feel weaker. I have a 94xj and it has a pretty hard pull to it. I drove my friends Renix engine and that a whole other beast whihc felt a bit stronger even.
I think the newer they get the more emission related crap they do and it all robs energy.
pete
I think the newer they get the more emission related crap they do and it all robs energy.
pete
bajacalal
NAXJA Forum User
- Location
- San Diego (North County), California
If you want to know what the technical differences are, the HO motors have a different head (supposedly flows better), manifold and completely different computer/electronics system compared to the earlier motors. Up until they started including things like pre-catalyzers on the later 4.0, I think this motor has few complicated smog devices even compared to the Renix (pre-HO) era 4.0. No EGR device, air preheater or smog pump. I think they dropped the "HO" moniker after 1997 even though the the motor is basically the same. "High Output" to me sound like a marketing gimmick anyway. The lower end of the motor, hasn't changed much.
martin
NAXJA Forum User
- Location
- Huntsville, AL
My understanding about the Renix engines and the HO engines beside the things previously mentioned the Cam is different.
Renix is 87-90
HO is 91 & later
So the marketing department got the engineers to change the cam so they could advertise more HP. Remember 91 was the first year Chrysler made their major "changes" to the AMC designed XJ and Ford was rolling out the "new" Explorer and dealers were selling everyone they had.
In order to get more top end HP you need to trade off torque at the low RPMs. That may explain Jeepsrock's observations.
I do not know about a HO engine but my 88 XJ will idle on a level road at 7 mph and will even pull itself up some hills. I just release the brake and it will accelerate to 7 mph, no goosing the gas to get it going. It is great for going down some trails, just let the XJ idle and it will clilmb over small trees across the road and pull you through holes in those old logging roads. I love low end torque!
Renix is 87-90
HO is 91 & later
So the marketing department got the engineers to change the cam so they could advertise more HP. Remember 91 was the first year Chrysler made their major "changes" to the AMC designed XJ and Ford was rolling out the "new" Explorer and dealers were selling everyone they had.
In order to get more top end HP you need to trade off torque at the low RPMs. That may explain Jeepsrock's observations.
I do not know about a HO engine but my 88 XJ will idle on a level road at 7 mph and will even pull itself up some hills. I just release the brake and it will accelerate to 7 mph, no goosing the gas to get it going. It is great for going down some trails, just let the XJ idle and it will clilmb over small trees across the road and pull you through holes in those old logging roads. I love low end torque!
Last edited:
sjx40250
NAXJA Forum User
- Location
- Alexandria VA
80% torque of idle!
The 96-98 is the same motor. Some emmision electronic changes in those years and to OBDII. The did some changes to the block in 96 and the head had some minor changes.. The Head changes in mid 99 with smaller exhaust ports.. I don't think there was a cam change between the Renix and original HO. The torque rating was only 1 ft-lb or so less.
Tom
Tom
bajacalal
NAXJA Forum User
- Location
- San Diego (North County), California
Of course the cam, I forgot about the cam...
My 96 also does this, you can let the clutch out slowly (its manual) in first gear on a level surface without the motor stalling even if you don't give it gas. It will even accelerate away without using the gas pedal. I could be wrong but I thought this had to do with both the fact that the AMC inline 6 has good low end torque and because both computer systems try to keep the idle speed at a certain RPM. When the computer detects a drop in RPM caused by engaging the engine with the drivetrain it increases the RPM by opening the idle air control vavle and adjusting the fuel mixture.
As far as what engine has better low end torque, thats a good question and I think you may be correct to say the HO has better peak horsepower at the expense of producing torque at low rpm. Does anyone have any dyno graphs comparing the motors?
My 96 also does this, you can let the clutch out slowly (its manual) in first gear on a level surface without the motor stalling even if you don't give it gas. It will even accelerate away without using the gas pedal. I could be wrong but I thought this had to do with both the fact that the AMC inline 6 has good low end torque and because both computer systems try to keep the idle speed at a certain RPM. When the computer detects a drop in RPM caused by engaging the engine with the drivetrain it increases the RPM by opening the idle air control vavle and adjusting the fuel mixture.
As far as what engine has better low end torque, thats a good question and I think you may be correct to say the HO has better peak horsepower at the expense of producing torque at low rpm. Does anyone have any dyno graphs comparing the motors?
