I have a 1992 vert. 6sp with 3.45 rear gears, all stock. I think I want to go to 4.10's, but I have a few questions like, what the top speed is now and what it will be? what does it do to the 1st-2nd shift and 2nd-3rd shift, how quickly do you go through the gears? what rpm are you doing at say 70mph in 6th? where to buy the diff. assy set up to just swap with my 3rd member? and price? and anything else I should be aware of good or bad please let me know, thanks

 

Sounds like my spreadsheet here can answer most of your questions.
Just plug in all the appropriate information and go to town.

I believe you'll be suprised at how little it changes things. Top speed will still be well faster than you would ever need to go anyway.

http://www.wku.edu/~nathan.plemons/calc.xls

 

The 4.10's will be alot of fun. As for top speed, who cares. Do you really want to do 170mph in a vert. and where would you do it? You can get 4.10 gear sets from Toms differential and he also has an install kit that includes new bearings and stuff for $100 more. They bolt right in to your Dana 44 carrier. Just need to find a good shop you can trust to do it. With the 4.10 in 6th gear at 70mph is around 1900rpm.

 

Wind resistance would limit your top speed with either gear ratio (notice that 5800 RPM is over 250 mph on Nathan's calculator). We're stuck around 140-150 until we get a lot more HP.

I like the idea of the 4.10's, but I worry that 1st would run out on a short auto-x course.

 

4.10'S make 6th gear alot more useable! I had mine installed when I was pretty stock still and I think the car should have came from the factory like that!

 

Tom's Diff are good folks. You do have to get used to hittin' redline quicker. I can actually accelerate up a steep incline in 6th now!

 

In my fbody, I went from 3.42's to 4.10's and it was probably the best bang for the buck I ever put into the car. If you don't mind shifting (hopefully you don't), you'll only be shifting a little bit sooner is all.

I'll be doing 4.10s very soon in mine

 

Thanks for the replys guys, I think that I will be doing this soon (1-3 months) . One other question, what about speedo corection? Can you just change the drive gear in the trans.? Any more input or comments from people who have done this would be great. thanks again every one.

 

ZFdoc.com has the speedo gear change. I have heard this to be a tough one. I still searching for someone I trust to install the gears for me. Its pretty tough to find around here.

 

I went the "tough" route and dropped the back of the tranny to get at the tailshaft. You have to remove the sensor and install a new drive gear on the shaft and new driven gear in the sensor cavity. Everything went well until I busted the sensor. Turns out it's a discontinued GM part and there's only a couple left in the country. I believe you can also buy a "black box" that will make the change electronically. I would go that route if I were you.

 

I hated my 4.10 gears. i dont mind it now because the motor revvs to 7700 rpm so it makes up for it. i used to get annoyed shifting so quickly driving in the city that i used to use 2nd gear to start and go to fourth. 6th gear shouldnt be used anyways as it shares the same syncro as reverse... something ZF says themselves (that 6th shouldnt be used under load). I believe 5th gear at redline was around 245 k/hr or maybe 249 so say around 155 or so would be your top speed.

Why i think 4.10s are too steep is because our motors especially modified have lots of tourque. longer gears are better suited for torquey motors and for higher speed runs. The viper is a good example of this. slap 4.10s in a viper and you have wheelspin in the first 3 gears. sure its fun if you have slicks and you're 1/4 mileing steep gears are great... but at the most id reccomend 3.73s for a stock motor.

 

Well I know that my car can do 155mph, and still had a ton more to go. I agree with DieL, 4.10's a just to high, 3.73's or close would be a much better gear choice.

I have always wondered about if you are supposed to run hard in 6th gear if you have 4.10's, I know in the T-56 and most other tranny with overdrives, the overdrive gears are to weak to take sustainted beatings at WOT. I figured you could get away with it since you end up using such little mechanical advantage.

I still have the stock 3.45's, and the only thing I think I would switch them for is 3.73's. 4.10's wouldn't be so bad if you could hook with 'em.

 

Yes, your LT4 has more horsepower than the standard LT1/L98, and your mods probably help your top end a lot (lowering may help your drag too). So, yeah, I can see you hitting 165-170, no problem.

You need 330 HP to counteract wind resistance at 197.5 MPH, so that is your theoretical limit, even though you'd only be at about 3700 RPM in 6th. Of course, that gives zero power to accessories and assumes no other frictions.

P.S. My calculations for wind resistance are borrowed from the text at http://www.pelicanparts.com/techarti...hysics_racing/

 

ttt

 

Assuming that your top speed is limited to 5th gear at 5800 rpm, your max currently is 144 mph, with 4.10 it would be 121 mph (you should be producing enough hp at 5800 rpm to counteract the wind resistance).

If you want to live on the edge and use 6th, we'll assume your top speed there is 150. That puts you at 3390 rpm, and ~195 hp rwhp*, roughly 145 of those are going toward wind resistance. With the 4.10 at 150 mph you'd right around 4000 rpm, which produces more hp (remember, hp increases linerarly with rpm as long as your torque curve is flat, and corvette's are generally flat between 3 and 5k). So now you're pushing about 225 hp, holy cow, you have 30 more hp than you did with the 3.45, you can actually go faster in 6th! Turns out, if you do the math on multiple linear equations, or just use excel with trial and error, your top speed will jump to 168 mph*.

Here are the shift points (in mph) at 5800 rpm.
gear: 3.45 / 4.10
1: 48 / 40
2: 71 / 60
3: 98 / 82
4: 128 / 108
5: 144 / 121

The gears will feel noticably shorter.

The price should be $200-$300. Try calling Precision Gear, they would know exactly what you need (or Tom's Diffs, since they got a lot of recommendations). Installation should cost about $500.

I'd also recommend reprogramming the computer to calculate the correct speed, or you could just memorize a few key speeds using Nathan's calculator... but I'd feel sorry for anyone who borrowed your car.

*I got my rpm/hp reference from Nathan's first dino of his car, which is close to stock, refer to his web page to double check me. I also verified them against Mr. Mojo's stock dino, so that's my basis.

**Please note that 6th gear may not be suitable for high speed applications, consult someone who knows something about it before you try to hit 170 on a track, I worked through the math because it was an interesting problem (you make the gears shorter but your top speed increases), please obey all speed limit laws, and for the love of god, wear your seatbelt.

 

JCD, that was a beautiful post.