I have a 93Z with a 94+ 6spd. The gearing is as follow:

M29 94+
2.97 2.66 1st gear
2.07 1.78 2nd gear
1.43 1.30 3rd gear
1.00 1.00 4th gear
0.80 0.74 5th gear
0.62 0.50 6th gear

I still have my stock 3.23 rearend instead of the stock 3.42's with this rear. Right now I cross the 1/4 mile at the end of 3rd gear without shifting to 4th.

Isn't this optimal to be crossing at the end of the gear instead of having 3.42's and having to shift into 4th? How is the 3.23's hurting me. Mods and times below-

 

I'm missing something here. Why are there 2 different gear ratio columns?

Either way, I'd say start off in second gear. The first gear in both those lists is too deep unless you have highway gears. You also might be better off using 3.73 gears so that you can shift into fourth gear.

If the ratio, gears, shift point and tire height are matched properly, you should cross the finish line at the top of fourth gear.

 

The first column is for what the original transmission had. I now have the 94+ transmission with the gearing listed in the second column. I guess my question is why would i want to shift into 4th? Isnt it better to not have to shift that last time (thus saving time)? My rear gears are 3.23's.

 

yes and no. Shifting does waste time but fourth gear is 1:1. When the power is going directly through the transmission and not through a gear set, there is less power loss through the transmission. You should be in fourth at around the 1/8 mile mark and the last 1/8 mile is a high gear, brute hp, pull to the finish line.

 

I agree, you should be in the 1:1 ratio at the 1/8 mile and let the HP pull you through, I have a video of my car shifting into 3rd (Auto) before the 1/8 mile.

Also it depends how high RPM you can turn. With me my RPM at the trap is 6200rpm, my shift points are setup to 6400rpm. Just need to find the optimnum (sp?) shift point and relation to peak HP.

 

I was thinking about my last reply all day and need to add something.

Gearing is for torque multiplication. You need it get get the mass of the vehicle moving and up to speed. At hi rpm, torque has very little effect and HP is what moves the vehicle. A torque curve starts high at low rpm then falls after a certain point. HP is the opposite and depending on the engine, can keep climbing well after the torque has dropped.

Vehicles like top fuel and funny car don't use transmissions but are high gear only with multi stage clutches. Except for cars like Prostock that still have to use a manual transmission, most "fast" cars use a 2 speed powerglide. Once the car gets moving, they get into high gear as soon as possible.

A heavy, low hp car needs the extra gearing in the tranny and diff to get moving but once you get into the hp curve and out of the torque curve, the extra gearing for torque mutiplication isn't needed.

 

The time honored optimum for a manual tranny car with a power to weight ratio in the range we are talking abut is to go through the traps just past peak power in 4th gear. If you had a race tranny that could be rapidly power shifted (like a Lenco) you might go faster with 5 speeds, going through the traps at the top of 5th. But with a street tranny and the broad power band of an LT1 (or LS1) the time lost shifting would outweight the torque multiplication advantage of another gear.

So, you pick your rear end to put you just past peak power through the traps in a 1:1 gear and ideally chose a first gear/clutch/tire/suspension combo that let's you launch hard without blowing off the tires. Since we can't change (generally) 1st gears in a street tranny, you can only adjust the other variables. Tire diameter and rear end ratio are directly related, of course. In your case, the closer ratios of the newer tranny are an advantage because you don't need the steeper first gear in a car that is as traction limited as a 4th gen. But you need a steeper rear end ratio, probably 3.73's.

Rich Krause

 

In my bolt on car and on motor, the 4.11's seemed to be perfect. At an 1/8th mile track, I'd wind out 3rd and come through at about 6300. At a 1/4, I'll shift it at 6100 or so and come through in 4th gear at about 5900. Car made peak power at 5600. By the way, I 60 ft better on street tires with my 4.11's than with the stock 3.42's.

 

The thing is that I am crossing the traps at the end of 3rd gear. Everyone seems to be saying that that is best. I cross the line at about 5900 RPM.

I am hurting in the 60 foot range though. My best 60' is about a 2.35 or so. This is on street tires also.

thanks for the input.

 

You aren't getting it. You should be going through the traps in 4th gear. With a higher rear gear, using four gears instead of three, the area under the torque curve (torque over time) will be greater and you will accelerate faster. Of course, your 60' is a function of not enough torque. Even with street tires and a stock suspension you should run 2.0-2.2sec in the 60'.

Rich Krause