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H.O. questions

XJHICK

NAXJA Forum User
Location
TOOELE UTAH
I'm looking to buy a 92 xj for dirt cheap, it is in moderate shape. The Q. that I have is, did the H.O. come in all xjs after 91 or was it just limited to the high end modles? The reason I'm asking is because I have a 90 lorado, and this 92 is just a cherokee, but I'm not seeing any differance in either one. The ther prob. is that it has over 2k on it.
 
will it be a daily driver, or highway driver, cause 200k which is what i assume you mean, is not overly high for a 4.0, but it is pretty high... as for is it HO, look at the rear hatch there should be a thing that says 4.0 high output, im not sure if its the renault motor, or 4.0 standard, i just wanted to let you know that if it runs decent, and its dirt cheap it should last you your moneys worth
 
All 4.0- engines are AMC-designed. 1987-1990 4.0 used the RENIX (RENault/bendIX) control system - spec'd by Renault, built by Bendix/King.

From 1991, the 4.0 got ChryCo electronics. The power output figures were bumped up slightly, giving rise to the "High Output" designation. Technically, all 1991-up XJ w/4.0L are HO (still an AMC engine, but with ChryCo control electronics.)

The increase in power output was not, in my mind, significant - say 3-5%.

5-90
 
5-90 said:
The increase in power output was not, in my mind, significant - say 3-5%.

5-90

177hp @ 4500rpm and 224lbft @ 2400rpm for the Renix-controlled 4.0
190hp @ 4750rpm and 225lbft @ 3950rpm for the '91-'95 HO 4.0
 
5-90 said:
The increase in power output was not, in my mind, significant - say 3-5%.

Yep. I swapped a '91 HO into my '87 RENIX, and it feels exactly the same.

I thought the couple extra hp came from a different cam and head porting on the HO, but it might be just the electronics. I'm running my HO block and manifolds with all the Renix sensors and electronics.
 
anony91xj said:
Yep. I swapped a '91 HO into my '87 RENIX, and it feels exactly the same.

I thought the couple extra hp came from a different cam and head porting on the HO, but it might be just the electronics. I'm running my HO block and manifolds with all the Renix sensors and electronics.

Actually, they used the same cam for RENIX as OBD-I - it might have been installed a bit differently. I'm fairly sure of that, because the mechanism to delete the EGR valve (circa 1991) was "exhaust valve reversion," which can be handled by exhaust valve closing event timing (at least you don't have parts to fail, and exhaut gas crapping up your intake manifold.)

The main reason the early HO makes power over the RENIX is simple - the #7120 head breathes better than the #2686 head. Moving more air means the ability to burn more fuel, and therefore make more power. The electronics don't really play that big a role, IMO.

5-90
 
5-90 said:
Actually, they used the same cam for RENIX as OBD-I - it might have been installed a bit differently. I'm fairly sure of that, because the mechanism to delete the EGR valve (circa 1991) was "exhaust valve reversion," which can be handled by exhaust valve closing event timing (at least you don't have parts to fail, and exhaut gas crapping up your intake manifold.)

The main reason the early HO makes power over the RENIX is simple - the #7120 head breathes better than the #2686 head. Moving more air means the ability to burn more fuel, and therefore make more power. The electronics don't really play that big a role, IMO.

5-90
Makes sense, but my new HO engine still doesn't feel even an iota stronger (or weaker) than the old Renix engine :D
 
anony91xj said:
Yep. I swapped a '91 HO into my '87 RENIX, and it feels exactly the same.

I thought the couple extra hp came from a different cam and head porting on the HO, but it might be just the electronics. I'm running my HO block and manifolds with all the Renix sensors and electronics.

The extra 13hp from the HO came from the better flowing 7120 head and a larger TB. Both the Renix 4.0 and the '91-'95 HO use the same cam but it's possible that the cam timing was retarded in the HO, as Jon said, to reduce the risk of detonation since the knock sensor and EGR were deleted.
The computer programming wouldn't have made any difference and in any event, all '87-'95 4.0's are programmed to run rich at over 70% throttle.
Since most of the extra performance of the HO came above 3000rpm, you'd be hard pressed to notice any difference from the Renix 4.0. If anything, the Renix engine's probably slightly stronger at low revs.
I still don't know why DC even bothered to call it a High Output engine. The 4.0 only put out a specific HP of 48hp/liter and a specific TQ of 57lbft/liter. Those outputs weren't exactly impressive back in '91 when the HO 4.0 was introduced and by today's standards, they're downright pathetic.
 
Dr. Dyno said:
I still don't know why DC even bothered to call it a High Output engine. The 4.0 only put out a specific HP of 48hp/liter and a specific TQ of 57lbft/liter. Those outputs weren't exactly impressive back in '91 when the HO 4.0 was introduced and by today's standards, they're downright pathetic.
Marketing. Just like their "Hemi" engines. :rolleyes:
 
Well the reason I wanted to know is that I want to build a 4.6. Mainly just to say that I did. AS far as I know is that it had bigger valves in the head a different intake and bigger injectors. But right now it has a broken valve spring so if it is what I'm looking for i'll just start there. The other reason I want it the engine compartment is cleaner, it actualy has a radiator cap instead of just the over flow bottle, there are no high presure brake lines, there is just not as much junk going all over the place...
 
rocklandxjer said:
will it be a daily driver, or highway driver, cause 200k which is what i assume you mean, is not overly high for a 4.0, but it is pretty high... as for is it HO, look at the rear hatch there should be a thing that says 4.0 high output, im not sure if its the renault motor, or 4.0 standard, i just wanted to let you know that if it runs decent, and its dirt cheap it should last you your moneys worth
High way driver mostly, about 80-90 miles a day, at 75-80 mph. asfor the rear hatch it just says Cherokee nothing more
 
XJHICK said:
Well the reason I wanted to know is that I want to build a 4.6.

The HO engine is an excellent base on which to build a 4.6 stroker (BTW, it has the same valves as the Renix 4.0). I finished building mine 26 months ago and have done 30k miles on it since. To call the performance difference between the stroker and a stock 4.0 merely "night and day" would be an understatement. My stroker has a bunch of ancillary performance mods attached to it so it absolutely obliterates a stock 4.0, and indeed it would obliterate most other SUV's on the planet. If you follow my example, you'll adore it.

http://www.angelfire.com/my/fan/stroker.html
 
Okay so if a motor has a 2686 head, can you pull it off and put on a 7120 head?

Are there any complications with this? Or is it straight forward....just swap em out?

Any electronics need to be swapped?
 
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