This is what my tuner told me when I asked if I needed a retune for the gear/tires change:

"Because you have a 4l80 i think you would be okay because it doent look at speed for shifting. However you would probably benefit from it as it is a big change"

 

If youre honestly going purely for 1/8th racing you need to gear the **** out of it based on predicted trap speed. 4.10s in my old rig with 30" tires was rpm'd out at the traps with the converter unlocked. 4.88s or lower is not out of the question whatsoever in my opinion, the problem you'll run into is the weakness of the ring gear if 8.6"

 

RPM'd out in the 1/4 of mile right?

 

Update on this thread..
Went to the 1/8 of mile track this saturday..
Just by switching tires from 32" stock tires to 28" slicks my times in the 1/8th of mile droped from 7.70 to 7.43
Same boost level (2nd @ around 630rwhp)
Didnt have time to try my 3rd boost level @ 740ish rwhp plus the 75 shot of nos because a hose inside the fuel tank blew when I was heating the tires to race luckly...
Anyways, I did pay attention this time and my truck goes across the finish line exactly shifting to 3rd gear @ around 6500rpm..
Still dont know how to calculate if I should go with 4.88 or 5.13's
Any clue guys? And thanks for the help!

 

I will help as long as you stop calling it nos. NOS is a brand owned by Holley. Nitrous, N2O, or Nitrous Oxide is the stuff you spray into your engine. Thanks

What was your trap speed at the 1/8th? You are saying your finish right as you are shifting from 2nd to 3rd at 6500rpm?

 

My bad! Nitrous.. got it..
Unfortunately our track does not give us trap speed.. just times and reactions.. no more info..

 

A friend of mine went from a 4.10 NA down to a 3.55 when he put his turbo on just so he didn't have to shift one more time (granted, in the 1/4 mile). You're probably gonna want to dig a little deeper in the gear to cut some of the wheelspin.

 

I think going with a taller tire would have been more appropriate than a 28 unless you are trying to meet rules to run in a specific class.

 

Ah, well, you need to know what MPH you are going so you can calculate converter slip to accurately figure out what you need. If you are knocking on 3rd and can still add another 200hp your current gear might be pretty good honestly. Now if you get a tighter converter you will pick up some power automatically, and you may could afford a steeper gear also.

 

**** you Brah! He got enough NOS in there to blow himself up!