Allison 5sp: 3.42 vs 3.73

Bdsankey

Bdsankey

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I am wondering what everyone's opinions are on 3.42 vs 3.73 gears in a built 5spd truck. Main usage for the truck currently is sled pulling and occasional driving to work/to the store etc. Next year I am planning on heading to the strip more regularly than sled pulling and am wondering what results people have seen with 3.42s and 2nd gear TCM start tunes?

My track times to date aren't stellar (11.32 @ 126.8 with a 1.9 60ft, see attached image) but I'm not going to complain for my 2nd ever pass, being on 4yr old 315/75r17 BFG MTs at full hard, AND being in Denver with a big single. Going to 3.42 gears will greatly help the truck sled pulling in regards to the RPM I will run down the track in 3rd but I am concerned they will hurt the truck at the strip.
 

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Tothemax

Tothemax

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Oct 16, 2014
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I did 3.42 gears in my lbz this spring. My track times basically stayed the same as the 3.73. 2nd gear start usually gets me a mid 1.6 60ft. Nice driving 3.42 on the street pick up 1mpg
 
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buick455

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Sep 26, 2010
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I don't know if you've made the gear change yet but what are you figuring for power? 3.42's for the 1/4 mile are great as well as street driving. I think 3rd with 3.42's for sled pulling is only good in a certain power range, turbo setup is an important factor in this. I have ran 3.42's pulling in the 830hp range and it was not what we needed. 4.56's worked better. Now I think from say 600hp-800hp they would work better than 3.73's obviously but any more power they are not ideal for pulling. I've tried quite a few different combo's as far as pulling gears go. It is worth it to swap gears and/or have spare front and rear axles to swap in if you are serious about pulling and want the best times in the 1/4 mile.. just my thoughts from what I have tried and noticed.
 
Bdsankey

Bdsankey

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3.42 and 3rd work very well sled pulling with 4 digit power. With that said, I haven't swapped gears yet. I will never put 4.56 in my truck simply because I want to enjoy driving it.


I am stepping up from a single 480/96 to triples with 2x s369 over a s472 and aiming for 1500hp+ (previous best was 1340hp/2200tq). At this power level 3.73 aren't enough gear for sled pulling as it RPMs out too fast even on 35s.
 
Bdsankey

Bdsankey

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DuramxMan said:
Can you still get 3.42? Last I looked they were not available!
Click to expand...

Yes, they most certainly are available. If I recall Nitro used to have a 3.42 option for the 9.25" front diff but I can't find it anymore.

Front:
G2 = 1-2096-342
Yukon High Performance = YG GM9.25-342R
USA Standard Gear = ZG GM9.25-342R


Rear:
G2 = 1-2024-342
Yukon High Performance = YG GM11.5-342
USA Standard Gear = ZG GM11.5-342
AAM = GM11.5-342
Nitro Gear = AAM11.5-342-NG
 
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buick455

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Sep 26, 2010
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That is a lot of power on a well built factory drive line that is setup to pull. You will scream rpm's, probably 5000+ pulling with that setup which isn't ideal but on the other hand I do 100% understand where you are coming from with wanting to enjoy it on the street as 4.56s are not ideal in that realm. It'll be sweet to see how it performs when it's completed!
 
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