I am going to be changing my rears gears in about 2 weeks but I am still undecided on what gears to go with and I am also curious on its effect on quarter mile times and mph.

To give you all some background my car now has a th400 with 4.11 gears and a 26.3" E.T. Street tire. Right now I have been working with Joe O. on tuning my car but no matter what he does to my tune the car runs about the same with differences only being about .5 tenth and .6 mph in quarter. These are with drastic changes like changing the timing curves totally around and taking out up to 20% fuel from 4000-7000rpm's. Me and Joe talked about it and seem to think it is running out of gear and that is why it does not respond to change. Right now my car has run the time in the sig and has been as fast as 119mph in the quarter on a cooler day. I have ran my car in really crappy weather recently and it will run 11.5's@117 even in the crappy weather so weather seems to not have any effect on performance as much as other cars. I am thinking that my car is way over geared. I do have a nitrous converter which stalls to about 4000-4200 on the t-brake. I have my shiftlight set at 6300rpms and my shift light is coming on right at the 1000ft mark and my car is screaming through the traps at ~6800rpms with the converter slip. Also, I am shifting into 3rd gear at about the 500ft mark and pulling 3rd the rest of the way through the 1/4 mile..if that helps

I am getting ready to put the nitrous kit on my car and I will be gradually working my way up to a 250rwhp+ hit so I need to change my gears reguardless. I will be running a 26.3" tall tire on the Na runs with the new gears and a 28.2" tire for the bottle runs. I plan to it ~135-140mph in quarter and do not want to change gears again so I want to pick the right gear now. I am thinking that a 3.70 gear would be the best gear to go with but I am not sure how high it will tach up on the nitrous. The people I got the converter from said to expect about 8% converter slippage so I have to account for that. I have done a lot with the gear calculators and I am pretty sure I want to go with a 3.70 gear. I do not want to go through the traps at more than 6500rpms on the bottle. The only other gear that is available is a 3.50 gear and I don't think I want to go that low.

Anyway any opinions would be great on this or if anyone has any experiences you would like to share. Secondly, what kind of gains losses should I expect to see N/A in mph and E.T.?

Thanks
Matt

 

3.73s?

Tire Diameter 1: 26.3 inches
Rear Gear Ratio 1: 3.73:1
8% converter slip

RPM 1st 2nd 3rd
1000 8 13 19
1500 12 20 29
2000 16 26 39
2500 19 33 48
3000 23 39 58
3500 27 46 68
4000 31 52 77
4500 35 59 87
5000 39 65 96
5500 43 72 106
6000 47 78 116
6500 51 85 125
7000 54 91 135

Tire Diameter 2: 28.2 inches
Rear Gear Ratio 2: 3.73:1
8% converter slip

RPM 1st 2nd 3rd
1000 8 14 21
1500 13 21 31
2000 17 28 41
2500 21 35 52
3000 25 42 62
3500 29 49 72
4000 33 56 83
4500 38 63 93
5000 42 70 103
5500 46 77 114
6000 50 84 124
6500 54 91 135
7000 58 98 145

http://www.smokemup.com/auto_math/mph_range2.php

I'm in a similar, but much different situation as you. I've got a 4L60E with a 3200stall Vigilante, 4.10 gears with a 26x10.5 15 ET Street behind the stock LT1. When trapping 98mph I'm at the very top of third going through the traps (5500) in my impala. But I want to put some nitrous on it, so I'll either have to go with a taller tire or less gear. For the track, either would work great. But it's a street car (daily driver), so I'll change the gears and get better gas mileage and give up a little wheel spin on the street

 

Thanks for the link and info...that helps out a lot.
Matt