Dyno Performance?

[sjx40250]

I recently dyno tested my 92.
I have a 4.0 and Auto. The test was done with 2wd
Peak HP was 129
Peak Torque was 200 lb-ft.
Does this sound low?
What shoudl be expected?
Does anyone know how to get the transmission to lock into 3rd? I want to do another run without the down shifting.

BTW I have 192K mi.

 

[BLSXJ]

you could unplug the tranny control module. this would lock it in any gear you select

in a 91 its under the kicker panel on the passenger side

 

[ZmOz]

Yes, that is very low, it should be more like 150 at the rear wheels.

 

[XJ Saga]

I recently dyno tested my 92.
I have a 4.0 and Auto. The test was done with 2wd
Peak HP was 129

All you have to say is Dowh! Homer Simpson style.

:repair:

 

[FUNKYTEE5]

I recently dyno tested my 92.
I have a 4.0 and Auto. The test was done with 2wd
Peak HP was 129
Peak Torque was 200 lb-ft.
Does this sound low?
What shoudl be expected?
Does anyone know how to get the transmission to lock into 3rd? I want to do another run without the down shifting.

BTW I have 192K mi.

Usually there is an accepted 12-25% drivetrain loss when running on a chassis dyno. But the exact losses for any given vehicle can be greatly affected by many variables in the drivetrain itself. In a 4wd setup there'll probably be more loss because you have to send the power through the the t-case and bigger, chunkier tires. Ideally you want to use the flattest and stiffest tires you could find to reduce roller friction. Tire pressure is another variable that needs to be adressed especially with larger tire sizes. We all know that running lower pressures will definitely hurt mileage. The gear that you are running during the test will also greatly affect the results. Most guys try to use 4th in a manual trans. or drive in older school automatics which is usually a 1-1 ratio. Doing a pull in OD will kill your hp results! If i am correct the AW4 is 1-1 in third gear? If so, if you could get it to stay in 3rd then your results might be considerably different. I see you're local! Where'd you get dyno'ed anyways? Horsepowerfreaks? Here's some links to absorb!

FUNKYTEE5

http://www.ultimategarage.com/dynapack.html
http://www.pumaracing.co.uk/power3.htm
http://toyotaperformance.com/dyno.htm

 

[sjx40250]

The tires are old Michlines that were on it when I bought it this summer. We pumped them up to 2 lbs below max.

They guys that did the work are very experienced. The owner is a a locally known mechanic for a locally known racer/dealer, Monte Shelton. He has been doing it for years. In fact, he just completed a motor for another nationally well known hot rodder, Lonnie Gilbertson, whom I have done some buisness with.

I am aware of the 15% - 20% Max and was disappointed in the results. On the way home today, another newer vintage Jeep raced me for half a mile or so. We were equal with neither of us pulling ahead of the other. Given that my rig is older and has 192K (today!) I thought that maybe it is in the ball park.

So if I understand correctly, by unpluging the TCU, the Transmission will stay in the gear selected by the transmission lever?

 

[Dr. Dyno]

Ideally you need to dyno the vehicle in the 1.00:1 ratio gear so that's usually 3rd in an automatic and 4th in a manual. The problem is that you'd need to go up to 120+mph to get a dyno run across the whole rpm range and the tires may not be rated to handle these speeds. The dyno operator may instead choose to dyno an automatic Jeep in 2nd and a manual in 3rd to avoid these problems.
Scan the dyno sheet and post it so I can take a look. Your torque number is very good but the HP number is low (150-155 would have been in the ballpark). At what rpm did you get the HP/TQ peaks?

 

[sjx40250]

DId for runs. Will post when I have the time to scan and post.

Max Torq was at 3480 for one run but most were around 185/7 at 3560.

Test machine was a DynoJet. So how do I keep it in 3rd?

 

[Ed A. Stevens]

Test machine was a DynoJet. So how do I keep it in 3rd?

Keep the gear selector (shift handle) in 3rd. Let the trans shift to 3rd and lock the converter, drop to a low rpm (~1800 rpm) and then foot the throttle. You may find it hard to keep the trans from downshifting from 3 to 2, so try a 2nd gear run (lock the TC and drop the gear selector to the 1-2 position). You can also override the trans controller to keep the TC locked and to keep it in 2nd or 3rd (to avoid the trans control downshifting).

Runs with 30 psi (hard tires) and correction for accurate tire height and total gear ratio (2nd or 3rd gear, and TC slip) usually net between 140 and 160 hp at the rear wheels for a stock 4.0L. The 2nd gear numbers usually perform better.

If you made no attempt at a tune up (old plugs, cap and wires, no injector, filter or intake cleaning) the 129 hp is not too bad (for 194K miles).

 

[sjx40250]

All,

Thanks for the replies. I will be trying out the "manual" controls.

Anyone interested in the results from the second run?

BTW. No new tune up stuff was done. New plugs about 6 months ago/10k miles.

 

[Dr. Dyno]

All,
Anyone interested in the results from the second run?

Yes, and please also tell us at what rpm the HP and TQ peak at.

 

[Dr. Dyno]

The 2nd and 3rd dyno runs are the most representative here. A maximum rear wheel torque of 187.4lbft @ 3550rpm on a stock XJ auto is equivalent to 234.2lbft at the flywheel (assuming a 20% drivetrain loss) so it's within normal spec.
What isn't normal is the 130hp at the rear wheels at only 3800rpm. Maximum HP typically comes in much higher than that at ~4600-4700rpm so something definitely isn't allowing the engine to rev higher. Could be bad plug wires or plugs gapped to wide causing a high rpm misfire. Change the cap & rotor as well if they're old.

 

[sjx40250]

Thanks for the info. I will do the minor changes before the next run. I will also let you know of the results.

 

[Dr. Dyno]

You could also have a plugged cat so gutting it might not be a bad idea. Alternatively you could just replace it with a piece of straight pipe. I don't think the smog cops in Oregon are too picky about this.

 

[ZmOz]

You could also have a plugged cat so gutting it might not be a bad idea. Alternatively you could just replace it with a piece of straight pipe. I don't think the smog cops in Oregon are too picky about this.

The main population of Oregon is Subaru driving hippies and tree huggers. They get their panties VERY bunched up about their cats....

 

[Dr. Dyno]

The main population of Oregon is Subaru driving hippies ...

Huh? I always thought hippies smoke grass and drive around in multicolor vans with a peace sign painted on each side. Times must have changed if they drive around now in WRX STI's.

 

[ZmOz]

Huh? I always thought hippies smoke grass and drive around in multicolor vans with a peace sign painted on each side. Times must have changed if they drive around now in WRX STI's.

Oh, there's plenty of those too. As they drive around in vehicles spewing clouds of oil smoke mixed with pot smoke, they want to arrest me for having a flowmaster. Pretty soon we're going to have to change the name of the state to "North California".

 

[Cjmartz2k]

Is there an O2 sesnor delete made for the 4.0 so you can take off the cat without it throwing a code? I thought any gains you would get from lack of cat would be erased by the computer thinking something was wrong with it.

 

[Dr. Dyno]

I thought any gains you would get from lack of cat would be erased by the computer thinking something was wrong with it.

As long as you have both O2 sensors still in place, I don't think the computer will be bothered if the cat is gone. The upstream sensor is the most important because that's the one the computer relies upon to set the A/F mixture. The downstream sensor merely monitors cat function.