Hello all,

I have a 1969 Camaro which now has a 5.3 and a 4L60 transmission. It is currently geared at 2.73 and is extremely slow off the line. I'm only pulling about 1600 RPMs at 60mps (I will be driving to work about 80 mph routinely). I'd like to be able to have a little take off speed, be able to spin the tires and all that, but I also don't want to be at 3000 RPMs the entire drive to work.

With overdrive, would a 3.55 option still be too many RPMs at 70-80 mph? Thanks for any help you could provide.

 

3:42 is a great gear for a 4L60

you can use a calculator to see what RPM at X MPH

Engine RPM Calculator | Spicer Parts

 

Thanks for the tip! It's exactly what the guy at the transmission place recommended. Appreciate your advice!!

 

I think you'll be fine with anything over 3.25
I'd go with a 3.73

 

Appreciate the reply. My concern with the 3.73 is the amount of interstate driving I'll do here in the Atlanta area. I'll be driving 75-80 mph for a good 30-35 miles a few times a week. That's a lot of RPMs with a 3.73 even with overdrive, no?

 

You might be right
You could do the math
What size tire and all that
My old 69 Z-28 with a 15 inch tire and 3.73's was doing around 2400 rpm at 70 IIRR

 

With a 27" tire when I had 3:73, Fwy RPM's were to high and no better times at the 1/4 mi vs 3:42 when I had a 4L60.

 

During the restoration of my ’68 coupe, there came a point where we had to choose what ratio I would want for Ring & Pinion. I have a Muncie M20, and was set on rear tires. I found multiple sites on the web that allow you to plug in numbers to obtain an RPM for a set speed but I wanted a “big picture” view of RPMs across the speed spread and per gear, so built a spreadsheet to give me that, once I figured out the mathematical formula those websites were using. The printed picture might prove helpful in thinking about shift points vs available torque, as well.

While my spreadsheet was meant to be used to select a rear gear ratio, I allowed the user to plug in various gear ratios for each gear in a 4 speed, and on a second worksheet, for a 5 speed, as well as different rear wheel diameters in inches and tenths of an inch, plus of course, rear gear ratios. When done, the print area produces this view:



Note that the “bold” numbers are done manually, as I chose to hillite the RPM’s between 2K and 5K, pertinent to my build. Also note that the numbers in this example are for my Muncie M20, the final selection for rear gear that I made (3.42), and the actual tire diameter of my rear tires. All of these can be changed (the numbers at the top, in bold yellow), and when you hit enter, all RPM’s re-compute. Handy spreadsheet if you’re familiar with spreadsheets. Feel free to download, I claim no copyright.

 

Good job
Where's the "like" button?
Like in modern drag racing these days
The pro's figure out "each and every rev" down the 1320 foot track

 

IIRC the OD gear ratio on a 4L60 is .7

The Spicer calculator APP uses .7 in its formula for OD automatic transmission which is a good app to see what RPM will be at what MPH

This explains the APP

Engine RPM Calculator | Spicer Parts