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Does anyone know how Jeep squeezed the 9 extra ponies out of the 99+ 4.0L?


Head Lice

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Exactly, most dynos are too erratic to get an exact HP reading. There are so many variables going on and any of them can cause a significant difference.
Dyno is only an indicator . . . had my H-D FXRS on the rollers. Running 91 octane at sea level. We ran out of fuel, and refueled with same brand 89 octane. Picked up 4 hp . . . . . Since 89 is less expensive than 91, that would be cheap horsepower. :giggle:
 
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TJRick

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Around 2001 there were several 4.0L XJ owners on NAXJA that were testing the swap of the new style intake manifold. Some reported performance increases, but when their Jeep was tested on an actual dyno; there was about a 2 HP difference. In those years there were no tuners available for the 4.0L; only the performance modules with preprogrammed parameters. The only times the newer style intake manifold really showed an increase in performance was when it was used on a stroker engine.
I remember reading that same thing somewhere before.

The intake was changed for better emissions, and nothing more. It was never intended to perform better. Any performance gain on a stock 4.0 is negligible.
 

Rubicon John

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Have you tried modifying your timing tables? It really is a noticeable difference. The extra torque really helps with the 42rle. I don't remember the last time I turned of my OD, and there is no flat land where I live.
I have a Diablo handheld that I bought for my Silverado a few years ago. Are you aware of any compatible tunes with the Diablo for our TJs?
 

Skylinessuck

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Any tune of your Jeep pcm requires a few things. One is it needs the ability to interface with your specific computer. The only handheld ones that will do that which I know of are hptuners (very recently), syked, and SCT. Then you need either A) a canned tune which is made for a very specific set up like stock or certain standard mods like exhaust, intake, etc. or B) a custom tune specific to your vehicle which will require you having things like a wide band O2 sensor and some way to datalog or your tuner having the above for your running session. The canned tunes are still always going to be pretty conservative. Results, even on a bone stock setup are going to vary by how aggressive the stock tune was to begin with. Some OEMs leave a lot on the table, some don't. Also, it's a percentage gain, so there is probably a lot more power to be had tuning a stock 700hp Mustang than a 190hp Jeep.

Any forced infection will require appropriately sized injectors and a map sensor (on our Jeeps) that can read boost. If anybody tries to tell you otherwise, run the other way. Quickly.
 

astjp2

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The stroker I built 15 years ago is still pulling strong and there was a noticeable difference when I put on the 2000 intake and oversized throttle body.
 
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Brianj5600

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Fortunately my new TJ is a NSG370, which I am enjoying much more than the 42RLE. However, that's interesting about the timing tables. I assume you get to a certain point in modifying them where it makes it run worse though, no?
You can add too much timing and lose power without any irregular combustion, i.e. detonation, pre-Ignition and detonation of fuel before ignition. The top is the stock timing table with the altered table below it. Most of the table look like it should, but the lower right gets super conservative. I have been playing with it for a while and feel it is pretty close. I have a new tune ready to load with lower threshold for PTE, part throttle enrichment.

If you try to compare it to HPT the table is rotate 180 degrees from the syked table. I have only seen one HPT tune and the numbers seem to be the same, but the X and Y on the tables are different.

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I have a Diablo handheld that I bought for my Silverado a few years ago. Are you aware of any compatible tunes with the Diablo for our TJs?
 

whitrzac

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Superchips tuners adjust timing for sure, IDK what other perimeters, if any, they adjust.

When did they switch from a distributor to coilpacks? That might have made a difference too.

Header on the 00+ is different.
 

Jamison C

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Superchips tuners adjust timing for sure, IDK what other perimeters, if any, they adjust.

When did they switch from a distributor to coilpacks? That might have made a difference too.

Header on the 00+ is different.
2000 is when they made the switch.
 

Chris

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You can add too much timing and lose power without any irregular combustion, i.e. detonation, pre-Ignition and detonation of fuel before ignition. The top is the stock timing table with the altered table below it. Most of the table look like it should, but the lower right gets super conservative. I have been playing with it for a while and feel it is pretty close. I have a new tune ready to load with lower threshold for PTE, part throttle enrichment.

If you try to compare it to HPT the table is rotate 180 degrees from the syked table. I have only seen one HPT tune and the numbers seem to be the same, but the X and Y on the tables are different.

View attachment 173275

View attachment 173325
So you’ve definitely noticed some increase in power though? At what point do you need to start using premium fuel? I suspect at some point after messing with the timing you’d need to make a switch to a higher octane?

What are the blue numbers?

I need to get out my HPTuners software and play around once I find the time.
 

Brianj5600

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So you’ve definitely noticed some increase in power though? At what point do you need to start using premium fuel? I suspect at some point after messing with the timing you’d need to make a switch to a higher octane?

What are the blue numbers?

I need to get out my HPTuners software and play around once I find the time.
Yes there is definitely a noticeable increase in power.

The table above is a little bit too much for my Jeep on 87 octane. I occasionally get a little rattle on 87. Both ACT, air charge temp, and ECT, engine coolant temp have their own tables that add or subtract timing too. I am going to try adding a little fuel in the area that it is unhappy and see if it helps before pulling timing.

There is a point where adding timing will require more octane, but in a low compression engine you can put too much timing in and reduce power without irregular combustion. I would be surprised if there was much, if any, to gain by higher octane.

The blue numbers usually are lower than stock values. The second one though that is slightly lighter, is where the cursor was.
 
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Chris

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Yes there is definitely a noticeable increase in power.

The table above is a little bit too much for my Jeep on 87 octane. I occasionally get a little rattle on 87. Both ACT, air charge temp, and ECT, engine coolant temp have their own tables that add or subtract timing too. I am going to try adding a little fuel in the area that it is unhappy and see if it helps before pulling timing.

There is a point where adding timing will require more octane, but in a low compression engine you can put too much timing in and reduce power without irregular combustion. I would be surprised if there was much, if any, to gain by higher octane.

The blue numbers usually are lower than stock values. The second one though that is slightly lighter, is where the cursor was.
I was going to pay to have mine professionally tuned on a dyno, but seeing what you’ve posted it looks like I may be able to do a lot of the tuning myself.

I wonder how many extra ponies one might be able to squeeze out by doing these adjustments and adding a higher octane.
 

astjp2

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Too bad there is not a tuner for the 94, my stroker could use some loving when it comes to adjusting the PCM
 

Ephry73

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Wonder if adding higher ratio rockers to the stroker motor will add more power without changing the timing at all. In theory it should.
 
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Nimbley

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Just to clear this up...Timing will not ever require a change in fuel octane. Only engine compression ratio and elevation change will require different octane requirements. Pre-ignition and detonation are two different things caused by different things. Ever notice that in low elevations at the pump your low octane fuel will be higher than even the premium octane sometimes in high elevations? 86 octane is common at high elevation and 89 is about as low as you'll find at low elevations.
 

astjp2

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Just to clear this up...Timing will not ever require a change in fuel octane. Only engine compression ratio and elevation change will require different octane requirements. Pre-ignition and detonation are two different things caused by different things. Ever notice that in low elevations at the pump your low octane fuel will be higher than even the premium octane sometimes in high elevations? 86 octane is common at high elevation and 89 is about as low as you'll find at low elevations.
Well I guess that 100 years of automotive engineering must be wrong. Ask a gen 2 hemi owner what happens when when they go to 36 degrees total timing.... at 32 it will run on 91 at 36 it is blowing holes in pistons
 

Nimbley

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Well I guess that 100 years of automotive engineering must be wrong. Ask a gen 2 hemi owner what happens when when they go to 36 degrees total timing.... at 32 it will run on 91 at 36 it is blowing holes in pistons
Octane has nothing to do with it. The heat and late explosion is what burns the hole in the piston. The definition of octane rating is as follows...
An octane rating, or octane number, is a standard measure of the performance of an engine or aviation gasoline. The higher the octane number, the more compression the fuel can withstand before detonating (igniting).

So, unless you've done something to change compression ratio (pistons, head, or forced induction)a higher octane rating will gain you nothing.
 
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