Competition High Range with an Automatic, sled pulling

[Bobcat698]

Just curious guys, I've heard of some Duramax's that have run 4HI while pulling. .



Now that I have a 271 TCase, is there ever a situation that I should consider using 4HI while pulling or should I just stick with the low side?

 

[MMiller]

High side of the t-case usually causes more breakage and stress to the output of the transmission. By using the gear reduction in the t-case you are moving your high torque-low shaft speed further down the drivetrain. If you use 1:1 in the tcase, then the trans has to do the gear reduction, and your high torque-low shaft speed is moved to the back of the transmission/front of the tcase.



Are you running out of gear right now? I *suppose* if you were hitting the governor, and your auto was pulling out the end gate in OD, high side of the t-case would be an option.



In my experiance with truck pulling, when using high side of the tcase, the transmission output, coupler or t-case inputs break at the big end of the track. If you look at the big boys, there forward/reverse box's are 1:1, and they use big reductions in the drop box.



Michael

 

[Bobcat698]

I've got 2 hooks running 2nd gear, at ~3500RPM down the track. .

Seems to be working fairly well.



I appreciate your input on this. I was also looking for the logic in running high-range. . I've had several people say "RUN HIGH RANGE!" but I wasn't going to with the DLD 241.

 

[MMiller]

With a manual transmission, a guy can get a little bit different ground speeds with using differnt gears, and high/low of the tcase. You run more risk of drive train breakage running high side though. I can't see any point of you running high range, except maybe to try and boil all the ATF out of you auto. Maybe someone else can shed light on this.



Have you ever let it shift into drive? You know your truck, would it run out of power in drive?



Michael

 

[dlange]

I've ran high range alot, but its hard on parts. Like it b/c I can get more speed, faster. I also run 4. 10s though, so that makes a diff over your 355's. I caught 2nd high 1 time this year. That was some good tire speed.

 

[Bobcat698]

I've ran high range alot, but its hard on parts. Like it b/c I can get more speed, faster. I also run 4. 10s though, so that makes a diff over your 355's. I caught 2nd high 1 time this year. That was some good tire speed.

I have 4. 10s with 35" tires. .

 

[smokinrod]

I have 4:10's with 33's and never run out of ground speed . I average 4000rpm down track in drive (low range) and then sometime will down shift at the end and hit 4500+rpm ( allthough my trans shifts at 4000rpm to witch helps me get my ground speed up sooner).

it has been doing very well for me? Friday I took 1st in the Hot diesel and 1st in the open unlimiteed classes at Reading MI. I have found it is all in the tires and set up.

 

[dlange]

how soon are you guys locking the convertor?

 

[smokinrod]

I have my lock-up hooked up to a hobbs switch so it comes on as soon as I hit 20psi , witch is still in first gear and then I leave it locked the rest of the way.

 

[Nate]

Hmm. Not sure what kinda sled you are pulling and what power #s.



I know the sled I pulled, I don't think I could have moved it in hi range. Low range, 2nd gear WOT and it shifted down to 1st/back to 2nd a few times even.

 

[zstroken]

Think you could start the sled in 4L if your transmission was in drive??? If so then you could probably do it in 4H. I thinkt he 271 has the same Low ratio as the 241. 2. 7? Well your first gear is 2. 45 so if you use 4H it will be slightly lower than taking off in drive on the L side. transmission temps would be scorching hot. So it better be a super light sled. I don't think Dave wants to see you again so soon. The Dmax has a pretty low first gear(3. 1)??, but I still would doubt that they could do it. The people that use the high side are probably the manual transmission guys.