aw4 shift points

[j99xj]

Oh. Sorry. I usually only shift into the 1-2 position when I'm climbing really steep Colorado mountains, and it sometimes kicks down to 1st with my foot on the gas going uphill around 25 too.

 

[BBeach]

Oh. Sorry. I usually only shift into the 1-2 position when I'm climbing really steep Colorado mountains, and it sometimes kicks down to 1st with my foot on the gas going uphill around 25 too.

I think it'll always kick down with you foot on the gas or not at 25-26mph, and at 31~mph under full throttle. I guess it depends on the vehicle, tps condition, tires, gearing, etc. But does anyone know why it'll go for 1st gear even at speeds around 40-50mph, it'll temporarily catch and you can feel the torque converter slip and go back to second or whichever...

 

[cal]

Sometimes the 1-2 sensor jumps between gears a little unexpectedly .. that's a lot of the reason compushift made a shift computer for the aw4 (no longer available, but you can find them, i got one last year for $75 on ebay). You can also control the 1-2 setup with toggle switches, search here.

 

[87manche]

www.awshifting.com
how much is that extra 400 rpm's worth?

 

[j99xj]

www.awshifting.com
how much is that extra 400 rpm's worth?

I'd say at least another 5 hp, maybe even more.

But its not just the top end I would gain, its the fact that I would be 400 rpms higher AFTER the shift to second gear.

Right now with a wot upshift at 4800 rpms, my tach falls to about 3200 rpms at the bottom of second gear.

If I could rev to 5200 or so, my tach would fall to 3600 rpms after the shift.

Since my engine makes more power and torque at 3600 rpms than at 3200 rpms, I should see a slight performance increase at the bottom of second gear, which should help me merge onto the highway.

 

[BBeach]

I'd say at least another 5 hp, maybe even more.

But its not just the top end I would gain, its the fact that I would be 400 rpms higher AFTER the shift to second gear.

Right now with a wot upshift at 4800 rpms, my tach falls to about 3200 rpms at the bottom of second gear.

If I could rev to 5200 or so, my tach would fall to 3600 rpms after the shift.

Since my engine makes more power and torque at 3600 rpms than at 3200 rpms, I should see a slight performance increase at the bottom of second gear, which should help me merge onto the highway.

According to my dyno sheets, power went down after 4600 rpms, im not sure exactly what you meant by another 5hp but when peak is say 4600rpm, then by definition of peak, its only go to be lower from then on to redline. It depends on the other modifications to the vehicle as well but in our case its only advantage would be starting off at a higher rpm in the next gear. But in all honesty, i wouldnt want to take the risk of going past 5000rpm for something so minimal as a couple hundreths of a second of your ET at a dragstrip.

 

[j99xj]

Yes, power falls and torque falls even faster at rpms like that.

But your forgetting about gearing.

I looked at your dyno sheet and I guestimated you have ~122 lb-ft at 4900 rpm, and ~187 lb-ft at 3600 rpm.

At first glance it would appear that you would achieve the best acceleration at 3600 rpm than at 4900 rpm, but thats ONLY for the current gear.

You make more torque at the wheels at 4900 rpm in 1st gear, than 3600 rpm in second.

122*2.8*3.55=~1213 lb-ft of torque
187*1.53*3.55=~1016 lb-ft of torque

Your torque would have to be less than about 102 lb-ft in order to make second gear a better choice ( and thus shift into it).


If you extend your torque curve down to the point where the torque output would be about 102 the rpms are about 5200, right at the rev limiter.

So that's why I'm convinced the rev limiter was set around 5250 or so because that is the optimum wot upshift point with the 4.0's powerband.

My problem is that mine shifts lower than that. :-(

 

[BBeach]

Yes, power falls and torque falls even faster at rpms like that.

But your forgetting about gearing.

I looked at your dyno sheet and I guestimated you have ~122 lb-ft at 4900 rpm, and ~187 lb-ft at 3600 rpm.

At first glance it would appear that you would achieve the best acceleration at 3600 rpm than at 4900 rpm, but thats ONLY for the current gear.

You make more torque at the wheels at 4900 rpm in 1st gear, than 3600 rpm in second.

122*2.8*3.55=~1213 lb-ft of torque
187*1.53*3.55=~1016 lb-ft of torque

Your torque would have to be less than about 102 lb-ft in order to make second gear a better choice ( and thus shift into it).


If you extend your torque curve down to the point where the torque output would be about 102 the rpms are about 5200, right at the rev limiter.

So that's why I'm convinced the rev limiter was set around 5250 or so because that is the optimum wot upshift point with the 4.0's powerband.

My problem is that mine shifts lower than that. :-(

Somebody correct me if im wrong, but when you do the math out with the transmission ratio (2.8 for 1st and 1.53 for second), thats when the torque converter is locked and when at WOT, when left in the D position, its not going to be locked. Also, it just seems that when you leave it in second to the redline, that it just doesnt "feel" as fast as when you're already in the next gear. This is the point where im starting to not have so much knowledge as far as if you're going to cover more distance (the point of a race) in a certain amount of time between those last few rpms vs. just starting off in the next gear. Im not sure if im getting my theory across and id rather let someone like dyno chime in. I would say an easy way would be for you to take it to a track (like i did with same experiement a while back), and hold it in 2nd till redline, and the next time just go all out in D.....from when i did it i got quicker times with the just leaving it in drive so idk. Sure there are variables such as different temperatures (very slight change,it was maybe 20 minutes after the first run i got another in) and such but I still feel that its better to just leave it in Drive. Im not sure if you get my reasoning, but maybe if you think of it this way, the time it covers to go from 5000rpm-5300rpm and then starting higher in the next gear vs time it takes to do the next gear, even if at a lower rpm.

 

[j99xj]

I think its different for everybody. I say do whatever gets you the best times. I just think mine has a little extra juice in the last available 500 rpms or so.

I think it all has to do with how well your engine can inhale and exhale. Everything from air filters to mufflers has an effect.

 

[lawsoncl]

Cripes, are we still beating this dead horse?

If you have a Renix or ODBI era Jeep (ie pre 1996/1997 changeover), then the TCU has no idea what the actual engine rpm is since it only has an output shaft speed sensor. So if you're getting slightly different WOT shift pints, the difference is probably caused by the unlocked torque converter slipping more or less.

Why flog your poor engine by redlining it anyway?

 

[PETEY]

If you wanted a "race" car, why did you buy a jeep? Jeeez, it's still just a low tech "tractor" motor. (sort of)

 

[BBeach]

Both of us have jeeps with OBDII for one, and lawsoncl, i said it wasnt good to redline it and rather shift at where it was designed to, so im not sure if that was aimed at me or what. And to PETEY, i didnt buy it, this was passed down to me as a graduation gift/birthday present two years ago. Sure, if i had the money and at the time was allowed to buy a "race car" i surely would have bought something other than a jeep. But some of us have to make due with what we have, for me to go and buy a $5000 car is out of the option, but for me to put a couple hundred into my jeep to make it a tiny bit faster (obviously not a race car) for whatever reason is an option. For every man his own right?

 

[j99xj]

People race lawn mowers with "low tech" engines too....

Like BBeach said some people have to make do with what they have, myself included.

I don't modify my Jeep to try and make it competitive against real sports cars, thats just foolish. Anyway I need a little extra performance because I have bigger tires with stock gears.

I modify my Jeep for the hobby of it, not the sport.

A few years ago I was bored off my ASS so I thought to myself, I wonder what a cat back exhaust system would sound like?? So I installed one and liked what it did for my Jeep.

And I've been hooked ever sinceu buying small and simple mods here and there, and the Jeep runs great.

Anyway if there weren't people concerned about performance I'm sure there wouldn't be the "street/performance" section of naxja. (even though I put this post in the oem one.)

 

[lawsoncl]

Both of us have jeeps with OBDII for one, and lawsoncl, i said it wasnt good to redline it and rather shift at where it was designed to, so im not sure if that was aimed at me or what.

Nope, not aimed at you. I was just pointing out that the TCU on pre OBDII doesn't know the actual engine rpm since a few of the postings were for the older Jeeps. The ODBII AW4 has a front shaft input speed sensor, but I'm not sure if thats even used for determining shift points. It was added for diagnostic purposes so the TCU could determine if the tranny is responding properly (ie in the right gear and if the t/c converter is actually locked).

Merry Holidays!