The Stovebolt Site Forums The Shop Area Engine Shop Ratios, gear boxes and rpms

I've finally gotten around to doing some research on my truck. A while ago I picked up a 3.73 limited slip rear (disk brakes) for it and hooked it up to a T-5 tranny that I got for not too much money. Driving the truck was enjoyable, but I never got out on the road to really push it.

Yesterday I finally found a place on the web that told me exactly what gearing I have in the tranny. T-5 gear ratios

Turns out my T-5 is from a 83 Firebird V6 2.8L car. The gears are 3.50, 2.14, 1.39, 1.1, 0.78.

So, I went to one of the online RPM calculators and figured out that my top speed at 3000RPM was 46MPH???? Another one said it was 71MPH.

Anybody know of a site that accurately determines speed based upon rpms and gearing?

Never mind. I figured out what I was doing wrong. My tire size is 205/70/15, so my diameter is 26.29 inches. I should run 65 at about 2500 RPMS.

Aww, nuts. And I was gonna run inside and get the book (Auto Math, exellent book! ) to get the formula for ya!
BTW, I figured mine once after a run to see how it did wound up a bit, ran about 3300 rpm, speedo said 80-ish. Ran the #s, came out that I was actually doing 109!!!! Needless to say, I haven't done that again!

I like this one

http://www.drivetraindirect.com/t_gear_calculator.htm

i use, www.randysringandpinion.com. ron BTW i run a nova rearend with a 2.73. a little low in town in first.

You might try:

http://csgnetwork.com/multirpmcalc.html

I like the bottom calculator as it let's you dial in your exact values. According to this calculator, you should be turning 2417 rpms@65mph. Just another tool for your toolbox.

IMHO you've got a pretty sweet setup....the 3.50 1st gear is going to let you stay in first a little longer than the S10 3.76 1st gear and the .78 is a bit lower than the S10 .72. You'll be able to zip around town in 4th gear and still stay within your torque band.

I'm running a 3.42 with a .72 and a 29" tall tire and 2000 rpm's at 65-70mph (with corrected speedometer). I can drop down to 45 mph in 5th and accelerate back up with traffic without a downshift. The cruise at 70 mph is effortless, vacuum gauge hovers at 14-16" at cruise and 20" at idle. There's plenty left with my tweaked 235 but I'm most comfortable at the 65-70 as I'm running the stock straight axle. The aero on these old trucks wasn't really designed for high speeds, and the air noise in the cab at 75-80 is annoying. Your setup should be a real hoot to drive!!! Have fun!!!

Dave

I'm running the stock front axle as well. Don't see any reason to change. I replaced the front springs, which were broken, with a set of Patrick's monoleafs. They cost me no more than replacement spring would have, and they lowered the front end 4" and stiffened it up. With hydraulic shocks, it rides real nice.

see

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=010819#000014
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http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=23;t=000654;p=1#000007