im picking my gears. gas is getting everyone in the *** but my goal for the truck is 13.5 n/a in the 1/4.

mods are in the sig. i'm going to get a 3k stall when i do the trans. and a tru track when i do the gears.

so whats your rmp at 70. and avg. mpg on a tank thats mix city and highway.

3.73

3.90

4.10

do you think 13.5 is realistic?

 

There is an Excel file on the forum that you can enter your tire size, trans gearing and final drive ratios into and get rpm at any given speed....somebody should post it up here!

 

2400 rpm @ 70. 3.73, 255/35 20 tire (27").

 

With a 30" tire:
4.10 gears-2250(roughly)
3.90- 2150
3.73-2050
3.42-1975
3.23- 1750

EDIT-
That is a little high. You should be turning around 2250 rpms with that setup according the the 4l60e gear ratios and such.

 

It was pretty windy today, maybe thats why its reading high. When I had a 28" tire, it was closer to 2250 rpms.

 

um I beleive with my 3.73s at 70 Im about 2100. I take the freeway every day to work, my speedo is maybe ~1 MPH off still.

 

I'm using the excel spread sheet Trever1t is talking about. I forgot who created it, but it wasn't me.

 

i think i am at ~2300 @ 70 with 4.11's....

i used to be over 80mph and not even 2100 rpm with the 3.23's. oh well, it goes faster.

 

Mine does 2350 @ 70mph with 410 gears on 275/50/17's (28" tire).

 

Here's one:

http://www.ringpinion.com/Calc_RPM.aspx

According to calculator I should be turning 2274. I'm going to go check...