Hei Guys.
My combo looks like this:
SB 406 348hp/459lb-ft
TH 700r4
Corvette converter with lock up
3,08 final
26,1" tyres
Want a little better launch at start.Thinking about install 3,73 gear.My axel is 10bolt 8,5" .Is there only one of that kind or should i know anything more befor i order the parts.

All of the 8.5 rear ends use the same gears. Some of the '90s rear ends used a sensor on the pinion gear, but otherwise they are the same.

I figure my prior 406 puts out not quite as much as yours does, but I screwed up and went with a 292/230, .480 RV type cam so it is a dog until it hits about 2500 or a little higher.

My car at that time was an M-20, 3.31 and 26.5" tall/WIDE, L-60/14 tire car and I honestly think your, (I think, 3.06 first geared 700), should accel. better then mine b/c you have an eff. launch gearing of about 9.46 vs my M-20 at 8.34!!

BUT if you want better you might consider either the 3.23's, (9.88 to 1), or 3.42's, (10.46 to 1), b/c I don't think 3.31's are even made for any rearend anymore..

But 3.73's are going to give you a way too short first gear IMHO of 11.41!! Lower then I think the about 10 to 1 the guys talk about as being ideal with good tires in a drag situation.

pdq67

PS., I haven't gotten hardcore here and factored in the about 1/2" diff. in tire dia......

thanks for the input.For now i will try too get some more accel by working with the governersprings.Right now it will shift almost at once thruhe 1,2 and third.Maybe that is a factor that makes the car feeel tired.I know that the first gear is maybe too low with 3,73 but i am a little lost what makes the best uppgrade for the buck.
Have a nice day.

I would adjust your TV cable 1st so it shifts better. If you do want lower gears, make sure your overdrive Rpm is not too low. I have 4.11's with a 700r4 and they are too low. (1st gear is like Lo Lock on a 4x4). I have played with RPM calculators and 3:42 seems about right, for me. I'm not sure if 3.42's are available for your application or not. I would suggest about 2200 Cruising Rpm's.

I will do that.First the TV cable and then the gouvernersprings and then the final gear.

I have the 3.73's but with a th350 and had 26.5" tall tires. I will say its like driving in 2nd all the time cruising (65 mph = 3300rpm in drive 1:1). My car is leaning more and more toward strip so the gears work great. I did go with a 27.4" tall tire for a little less rpm. If your more street I would go with a mid 3.xx gear like a 3.42 as stated above. Launch will be fine due to the lower 1st gear and still cruise the hiway with ease.

I really like the 3.55's I'm running with the 700r4. I think 3.42's would be a good choice as well.