4.0 vs 4.0 ho?

[STERLING STINGER]

you dudes prob think this is a stupid question but here goes

 

whats the diffrence between a reg 4.0 and a 4.0 high output?

is that just what it says??? :huh???:

high output= upgraded exaust system???

thats my guess lets see if I'm right :dunno:

[Geonovast]

The HO's did have a better exhaust system, yes, but it's more than that.

 

The HO was introduced when Chrysler switched over to their control system. All new wiring, ECU, vacuum, etc.

 

Physical differences are different port locations on the head, The timing is slightly different, and the pilot hole on the crank was changed (no idea why, but it was)

[64 Cheyenne]

4.0 Renix was a collaboration of Renault and Bendix Corp. to produce engine controls. 87 t0 90 model years.

4.0 HO engine controls produced by Chrysler 91 and up model years.

Renix and HO engine parts and controls are not interchangeable.

[HOrnbrod]

And HOs are better. :popcorn:

[Pete M]

Renix is better. :D

[HOrnbrod]

Ah Pete-man. We always agree to disagree. :cheers:

[cracker]

And HOs are better. :popcorn:

 

x3000000

 

My Renix on 37s can't keep up with the HO on 42s :wavey:

[mvusse]

Renix all the way.

 

My HO, even with a stick shift can't touch the mileage of my Renix/auto.

[HOrnbrod]

It's all in what you want to do with your rig. In stock form w. no mods just for use as a d/d, I'd consider a Renix if someone gave me one. But I'd never buy one because of the hodgepodge of antiquated sensors on the Renix, all of which interact with each other and can affect starting, ignition, idling, mileage, and performance in different and non-consistent ways. When the Renix is right, it's okay, but there's no usually no rhyme or reason to troubleshoot it logically especially when there are multiple sensors involved, and it usually ends up easter-egging sensors one after the other to fix it. I've had plenty of both, and for me troubleshooting the OBDI 91+ HO is cake compared to the Renix. 1996 and above OBDII I don't like either.

 

If you want to build or stroke a 4.0, forget the Renix. Too many problems with the intakes, heads, exhaust headers, etc. Just doesn't make good sense. :D

[STERLING STINGER]

wow lots of info......so high output beats 4.0 as a dd

and renix ( which i assume is the regular 4.0) is better for off roading?

 

i just really wanted to know the stregnth and speed diffrence

oh yeah and since it IS an upgradeed exhaust system, shouldnt the intake be upgraded as well to get the proper air flow .......to match the output?

the one i have now is the same as my 88...not upgraded

[DJM/78]

wow lots of info......so high output beats 4.0 as a dd

and renix ( which i assume is the regular 4.0) is better for off roading?

 

i just really wanted to know the stregnth and speed diffrence

oh yeah and since it IS an upgradeed exhaust system, shouldnt the intake be upgraded as well to get the proper air flow .......to match the output?

the one i have now is the same as my 88...not upgraded

 

I think its the other way around , the renix has about 10-20 hp , less than the HO .

 

The renix gets a little better fuel consumption .

Thats also why I'm putting the cold air intake on my HO .

 

The larger exhaust is matched with more vacuum lines .

[WahooSteeler]

HO has more HP and is higher/faster revving. Renix is less HP than HO and slower revving as I have come to understand on here.

 

Funny this topic has come up again, as I recently drove, for the first time in a long time, my sister's '96 XJ 2dr 4x4 Sport, 4.0HO w/5spd manual. I forgot how fast that thing was. Total night and day on how it revs compared to a Renix.

[JeepcoMJ]

one of them works better when it's standing on a corner. the other one typically never gets off it's back.

[Pete M]

it's like autos-vs-manuals or buckets-vs-bench. there's no cut and dry winner and it becomes a matter of personal preference (or MJ availability in your area). HOs have better aftermarket support since they built more of them.

[STERLING STINGER]

HO has more HP and is higher/faster revving. Renix is less HP than HO and slower revving as I have come to understand on here.

 

Funny this topic has come up again, as I recently drove, for the first time in a long time, my sister's '96 XJ 2dr 4x4 Sport, 4.0HO w/5spd manual. I forgot how fast that thing was. Total night and day on how it revs compared to a Renix.

ya ive noticed that every corner i take at like 25mph or so on gravelor snow and give it just a little gas, it seems to be in a lower gearing or something cuz when it downshifts the @$$ end kicks out on me. not thatmy supreme driving skillz can't straighten it out. and its crazy fast on the highways...i had a 1997 eagle talon turbo awd and i think it would of given it a run for its money!!!

but my 88 has like a "sluggish" response......unless i flick the transmission switch on the dash...then its a little better, but dosent compare to my 92 though. just some input

 

i also need tires and rims to buy or trade....and a 3" lift if anyone got one laying around....i know....another thread :doh:

[Pete M]

all Jeeps will be sluggish with the trans switch in "comfort" mode. that's the point of it. :thumbsup: When they got rid of the stupid thing, the trans was permanently put in "power" mode.

[STERLING STINGER]

so it won't hurt me to leave that switch on?

i don't do that much highway driving

[Pete M]

won't hurt a thing. :thumbsup: fuel economy might actually improve.

[jpnjim]

Both set ups are very good.

If HO MJ's were falling out of tree's, I'd say don't bother with Renix MJ's, just because they're older, less understood, and somewhat more complicated.

 

But Renix MJ's are by far more common than HO's, so by avoiding them, you would be eliminating the largest pool of MJ's from your consideration.

 

 

Positives of Renix MJ's (in no particular order):

 

1) Greater low RPM, off idle torque.

A cam change in 1996 finally brought the HO's low RPM torque up to where it was in the 87-90 4.0L's.

2) Cheap, simple GM alternator, without the complication of the voltage regulator being inside the ECU

3)Knock sensor:

Renix 4.0L's ignition timing is more advanced than HO's, with a knock sensor used to retard it when a knock occurs,

advancing timing is a very good way to increase power & efficiency at low loads, with the HO this feature was eliminated (cost cutting), and timing was retarded from the Renix's default setting.

4)EGR (Exhaust Gas Recirculation):

still considered 'emissions junk' to many people.

At low load/cruise conditions, exhaust gas is substituted for a portion of the intake charge (spent exhaust is put back into the engine).

This dead, spent gas is inert to the combustion function, but it does displace a portion of the air/fuel mixture that would normally be present.

With a smaller air/fuel mixture charge needed to 'fill' the engine, it 'acts' like a smaller displacement engine while EGR is activated, increasing MPG.

On Renix's EGR is only activated under cruise conditions, so it does not effect passing power.

This was deleted as a cost cutting measure with the introduction of the HO.

Although some sources say a cam revision made EGR unecessary on the HO, this is untrue, since cam timing was unchanged from 87-95.

 

Negatives of the Renix 4.0L:

 

1) Less efficient lower port cylinder head.

still a vast improvement over the 258, the HO head is again a great improvement over the Renix.

2)Less efficient exhaust header. Exactly as above, Renix is leaps and bounds better than the 258, and the HO is an improvement over the Renix.

3) Smaller throttle body

the above three also contributed to the Renix's strong off idle torque, so it's not all bad, but the HO is more efficient & more powerful because of these improvements.

4) Renix doesn't record trouble codes, and there is no check engine light (only a "maintenance req'd" light, on a timer).

you'll never fail inspection for a check engine light (unless they're stupid, and fail you for not having one :doh: ),

but it's more work to diagnose issues.

HO's are OBD I compliant, and easier to work with.

5) Most Renix's also have the C101 connector on the firewall that's a source of problems on early 4.0L's.

More like a bad design that was in place during the Renix years than truely the fault of the renix, but it's a negative just the same.

I guess you could also 'blame' the renix for using a speedo cable vs the electronic VSS, smaller 21sp 4x4 tranny output vs 22spline, and the poorly designed closed cooling system.

 

 

Renix also used a heat riser from the exhaust, into the intake, to aid in cold weather engine warmup.

It was eliminated to cut costs, and to streamline the design.

It probably was worth a couple MPG in the first few minutes of startup, on a cold day, but deleting it really doesn't seem to have changed much, so I'll call this one a wash.

 

I'm sure there's a few I missed, but those are the things I think of when comparing a Renix to an HO.

[LEAD_NOT_FOLLOW]

Just cause the information is available I'll post it;

 

4.0L I6 EFI "Power Tech" - 177 hp @ 4750 rpm, 220 ft lb @ 4000 rpm - used 87-90

4.0L I6 MPI "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in 91-92

 

 

The TQ numbers are the same but I feel like the Renix puts the TQ down in a better curve than the HO does....

[jpnjim]

Just cause the information is available I'll post it;

 

4.0L I6 EFI "Power Tech" - 177 hp @ 4750 rpm, 220 ft lb @ 4000 rpm - used 87-90

4.0L I6 MPI "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in 91-92

 

 

The TQ numbers are the same but I feel like the Renix puts the TQ down in a better curve than the HO does....

 

 

I have the 89' Factory Data book here next to my computer (I was looking up stuff for the new 'Grandpa Jeep :D )

 

It lists 89' 4.0L (Renix) specs as:

177hp @ 4500rpm

224 ftlbs @ 2500rpm.

 

I'll look the other years up in the factory books (I know 87' was slightly lower).

[Oizarod115]

the renix is very good for now on availability and price of parts, but that won't last forever.

[Pete M]

that's why I stock up at the junkyard. :D

[comanche13]

the someone told me the renix is better to stroke because it has a bigger block is that true?

[jpnjim]

Some say the Renix era blocks have a higher nickel content (= stronger).

 

AMC did spec out a higher than typical nickel content for the iron used in their V8 blocks,

so it's reasonable to think they extended this to the 4.0L engines.

 

I guess it's also reasonable to think Chrysler 'could have' spec'd out a more typical cast iron after they took over,

but :dunno:

 

The block itself isn't any bigger, or smaller tho.