I just installed a cam and made my own 4" CAI for my truck and am going to add headers when they show up. The first time I dynoed my truck I had to do it in second because I didn't know there was a MPH limiter. Only got 260rw or so in second with Intake and Cat back. Now I have completely custom tuned it and want to get after cam results and then after exhaust results. I have always dynoed in the 1:1 gear. I was reading that with 3.42's and 31.7" tire it is a bad idea to use 1:1 due to tire speed. What do you all do? This is my first truck and don't want to jack it up. I really do want to use 3rd though.

 

You'll have some serious mph if you Dyno in third with that tire size and gear ratio

 

third gear will go till about 150mph at 6000 rpm. That's kinda high for the tires and the driveshaft. If you do it just be careful

 

+1
Since your previous pull was in 2nd, Id run the same gear. Better comparison of hp gain.

 

I have a 3.42 and 31.7" tall tires.

I didn't think about the drive shaft. I am used to Vette's and what not where all you are hitting is in the 130-140's and the car is designed for it.

I was going to do a second gear pull to get an apples to apples but wanted a 1:1 run to get the real numbers. The gear reduction seems to scew the numbers to the lower side.

 

Vettes also only have 26" or less tires. I wouldn't do a 3rd gear pull if I were you

 

Seems like the consensus is to just do the pulls in Second. As long as that is the standard around here I will roll with it.

 

Id do 2 gear, that would give you a better idea of what you gained, iv never really cared that much about peak dyno numbers I just like to see how the power curve looks to help you along with your build. Im always afraid of my driveshaft coming apart.

 

I've done 2nd, and 3rd. The numbers weren't very far off from each other, but the 3rd gear pull was a bit scary.

 

There's several videos online about stock 2wd truck drive shafts coming apart around 120mph. If you're on the stock drive shaft, I'd definitely do a 2nd gear pull.