Quote:
Originally Posted by ZRXMAX
If you look at the speed in each gear you will see that tallers gears add mph at the shift points as compared to shorter gears.
Here are the numbers for 3.07 compared to 4.10s
7000 rpm and 25.5 inch tall tire with ZF-6 ratios from Procrastination Racing's website.
http://www.angelfire.com/fl/procrastination/rear.html
3.07 1st 65.5 mph
4.10 1st 49.07 16.43 mph difference
3.07 2nd 97.17mph
4.10 2nd 72.76 24.91 mph difference
3.07 3rd 133.05
4.10 3rd 99.63 33.42 mph difference
3.07 4th 172.97
4.10 4th 129.05 43.92 mph difference
You are correct... the difference is "time" spent in each gear to gain those additional mph between shifts. The starting rpm at each shift is right around 4720 rpm.
However... It sure does seem like the rpm drop is increased with 3.07s 
My speedometer calibration was off almost exactly 25% when switching from 4.10s to 3.07s. I made up a paper speedometer reference sheet for ORRing so I could look at the speedo and then look at my reference sheet.
I bought a Dakota Digital box years ago that was designed to allow me to calibrate my speedometer regardless of what gears I as using. I never could get it to alter the signal to the ECM to give me the correct speed. Has anybody here ever tried one of those boxes ? |
I use that same rpm calculator as well, small world.
In this example, you are comparing how much MPH youwwill get out of each trans gear using a 4.10 or 3.07 gear. Not the amount of engine rpm drop that will occur when you shift from 1st gear to 2nd gear.
Using the exact same parameters you have used.
3.07 rear gear ratio
shiftpoint=7000rpm
tire height 25.5"
rear gearing 3.07
trans 1st rear ratio=2.64:1
=65.5mph @ 7000rpm in 1st gear
Now you shift to 2nd gear from a hypothetical shift rpm of 7000rpm, same variables except the 2nd gear trans ratio of 1.78:1.
Now you will be travelling at 65.5mph in 2nd gear, with your tach now registering 4725 rpm.
Shiftpoint rpm minus resultant rpm in 2nd gear, for 3.07 gears
=7000rpm - 4725rpm
=2275rpm
= For 3.07 rear gears the RPM drop of 2275rpm when shifting from 1st gear to 2nd gear
4.10 rear gear ratio
Now lets repeat for a 4.10 gearing scenario
Shiftpoint =7000rpm
tire height 25.5"
rear gearing=4.10
trans 1st rear ratio=2.64:1
=49.0mph @ 7000rpm in 1st gear
Now we shift to 2nd gear at our hypothetical 7000rpm shiftpoint, same variables except 2nd gear ratio of 1.78:1. Now we will be travelling at 49mph in 2nd gear, with the tach reading 4725rpm.
Shiftpoint rpm minus resultant rpm in 2nd gear, for 4.10 gears
7000rpm - 4725rpm
=2275RPM
=For 4.10 rear gears, the RPM drop of 2275rpm when shifting from 1st gear to 2nd gear.
As you can see, the rpm drop in both cases is exactly the same, therefore rear gear ratios have no effect on amount of engine RPM drop when upshifting. The only way to change the amount of rpm drop during an upshift is to change the gearing inside the transmission.