[Mike S]

Broke my ring gear last night and have to change it. I am running a 4.10 now. Thinking of going to 3.90 to get some mph up top.
Converter flashes to 5000 now. Launch with a trans brake at 3800. Shift at 6400 and go threw the traps at 6800. Last night had a 1.35 60' and 9.98/133.
I have the car set up to run 10.00 index. So I have a restrictor plate under the carb and 200lbs in the trunk. Out of all the 10.0 cars I run I have the lowest 60' and lowest mph. Most are 1.4 something and run 135 to 136mph.

Just wondering what happens to stall speed and converter efficiency from the gear change 4.10 - 3.90.

[Mike Davis]

Mike,
I am running similar times to you.
I went from a 4.10 to a 3.90 2 years ago. Converter flash went up about 150rpm. MPH went up about 1.5. I leave at a idle off foot brake. My car actually runs about .07 quicker with the 3.90 vs the 4.10. OF course tire size, weight and torque play big part.

[aaronman]

Here's an article that addresses this question.
https://www.jbspowercentre.com/wps/w...20car%20moving.

[grnmnstr]

I would stay with the 4.10.
Better for reaction time, especially with a Pro tree.
I assume you are running a Pro gear, might be harder to get a 3.90.

[Scott65]

Originally Posted by grnmnstr

I would stay with the 4.10.
Better for reaction time, especially with a Pro tree.
I assume you are running a Pro gear, might be harder to get a 3.90.

This is true. However, he can manipulate the launch rpm to regain that since he's on a rev limiter below converter lock up. If the traction is there anyway.
But if there's no pro gears in a 3.90 its moot...

[Mike S]

Actually I have been running street gears. This has been the second time they broke. This gear made it 3 years. I will be spending the extra money and up grading to pro gears this time. I will be staying with the 4.10's. Don't think they make 3.90's in pro gears anyway. It has been working great with the 4.10's so I will leave it alone.
I took the cover off tonight. The pinion gear lost 1/8" off the outer edge of a tooth. Looks like that piece got mangled in a few teeth of the pinion gear. I will know better when I pull it apart.
Think the trans brake is hard on the street gears.

Thanks for the input.

[Richie Hoffman]

pro gears will handle the transbrake better than street gears

[Half-Inch Stud]

if you use a stock 1st gear, then the Converter probably wont even notice 3.90. How about 3.73 FTW?

[adam woodmancy]

I'm interested in this too.. I went from a 4.30 to a 3.70 in my car, but i haven't personally raced it with the 3.70 yet. I changed it so a buddy of mine could borrow it to run 1/4 at the d3 bracket finals race of champions race and it broke the balancer, crank, and block the following weekend. I'm curious to see how the higher gear changes my reaction times and the track times.