took 392 to track

[forcefedjunkie]

Took the 392 to the local 1/4 mile test and tune. Best time attached below, 12.80 @ 103.9. I used my Aeroforce gauge to set the tire size smaller so I wouldn't hit the 100 mph limit. Could have been better but was surprisingly getting tire spin in first gear that hurt the 60' time, and 4 deg of knock retard during the run. I'm running 93 octane so was surprised at that. Without the knock and tire spin I think 12.50's could have been possible. Has anyone seen that much knock on the stock tune? Just wondering if that's normal or maybe I had a bad tank of gas.

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[Ten4Jeep]

Took the 392 to the local 1/4 mile test and tune. Best time attached below, 12.80 @ 103.9. I used my Aeroforce gauge to set the tire size smaller so I wouldn't hit the 100 mph limit. Could have been better but was surprisingly getting tire spin in first gear that hurt the 60' time, and 4 deg of knock retard during the run. I'm running 93 octane so was surprised at that. Without the knock and tire spin I think 12.50's could have been possible. Has anyone seen that much knock on the stock tune? Just wondering if that's normal or maybe I had a bad tank of gas.

nice run!!! This is hands down the most powerful and funnest wrangler Jeep has ever built!!! Very clever to trick the limiter with tire size as I believe many have been waiting for someone to do just that ??

I’ll be subscribed to see your findings on the timing. Well done!!!

 

[steve97ag]

Curious what you ran against! Can't wait to get mine!

 

[DaltonGang]

Curious what you ran against! Can't wait to get mine!

Whatever he was racing beat him off the line, but was very very slow throughout. My guess, a Toyota Corrolla.

 

[OldBlue]

Dragway 42! Love it! I live about 15 miles from there!

 

[Dyolfknip74]

That's a great idea to get around the limiter. Lol

 

[Rosco P]

Tell us about your jeep. XR? 33s? etc.

 

[Hpc3]

Took the 392 to the local 1/4 mile test and tune. Best time attached below, 12.80 @ 103.9. I used my Aeroforce gauge to set the tire size smaller so I wouldn't hit the 100 mph limit. Could have been better but was surprisingly getting tire spin in first gear that hurt the 60' time, and 4 deg of knock retard during the run. I'm running 93 octane so was surprised at that. Without the knock and tire spin I think 12.50's could have been possible. Has anyone seen that much knock on the stock tune? Just wondering if that's normal or maybe I had a bad tank of gas.

Good pull, like the idea of changing the tire size. Would like to know:
- what tire size? brand? wheel? Psi?
- 3.72 or 4.56?
- did you hit the limiter even with the 103mph?
- how much gas in the tank?
- stock weight or did you remove the spare? Hard top/soft top?

Can't speak to the knock, what rpms? What was the timing advance if you logged that?

Thanks for the post. I think without the limiter and some drag tweaks (lighter wheels, TC launch, low elevation) these are 12:50s easily, stock.

 

[forcefedjunkie]

Thanks, it was against an F-150. I had much closer runs, that was a blow out.

It's a 'standard" Rubicon 392, stock 33" BFG tires and wheels. No mods except for the gauge.

I didn't air down the tires so they were around 37psi.

I have the Sky top. 3.73 gears, no weight reduction including stock spare tire. 1/2 tank of gas. I used the factory launch control (stomped on brake and gave it throttle.). Not exactly sure what RPM is was launching at.

I did not hit a limiter, my speed was reading about 10 mph low with the tire size I entered (29"). I was just watching the parameters shown on the Aeroforce gauge and viewing peak values at the end of run. I was mainly watching IAT and knock and oil/coolant temps so didn't note ignition advance. I can log knock vs rpm so will do that next time.

Todd

 

[TaiMc]

Whatever he was racing beat him off the line, but was very very slow throughout. My guess, a Toyota Corrolla.

I just can't... LOL!

 

[jaymz]

I wonder if changing the tire size “tricked” the ECM into doing stuff that hurt your time? I’ve not researched programmers thoroughly enough to know if any of them can change/disable the limiter, but I’d try that and do some more passes if possible.

 

[2nd 392]

Video of early 392 times was ~ .2 sec quicker removing ~85lbs of spare. 37 psi will make tires harder and increase crowning decreasing traction. BTW, I run 32 lbs. Edit— setting to 31” tire would still give you ~ 104 mph limit. Try it and test jaymz theory.

 

[stumblinhorse]

I wonder if changing the tire size “tricked” the ECM into doing stuff that hurt your time? I’ve not researched programmers thoroughly enough to know if any of them can change/disable the limiter, but I’d try that and do some more passes if possible.

No, changing tire size will not do anything else in a 392. The ZF8 will adjust over time. But if you just change at the track nothing else will be effected for a couple runs. then change back to go home.

@forcefedjunkie did you brake torque launch, that will shave a tenth or so off…

 

[TheBirdie72]

I just took my Jeep to the track too!

(Plainridge Park Horse Track)

 

[utjmac]

I was just thinking about the tire size compensation this weekend, if you could modify it to get a higher max speed, so you just answered my question. I'm curious how "small" you can set the tires to increase the top speed? A shop next door has an interface that can do this without going to the dealership...any insight to settings?

John

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