What rear gear?


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By Butch Lawson - 16 Years Ago
I'm putting an AOD behind a 292 with Mummert's 265S cam (224* at .050, 110* lobe separation, .435 lift). I'm trying to determine what gear ratio to use in the rear.  My question is what rpm should I be looking for at 65 mph to keep the engine from lugging or over reving?  Is 2100 rpm a goal to shoot for with this cam, or could I go lower and still have power?  I plan to drive the car a lot and want it to run well at cruise speeds.

Butch Lawson

Manchester, TN

By miker - 16 Years Ago
I'm running the 270 cam, with a 2.95 first, a .8 od, a 3:31 rear end and a 25-26 inch rear tire. You're looking at a little less (not much) cam.

I'm good starting on a hill, fine at 60-70 mph, in a 3300 lb or so 'bird. Try using this calculator, and plugging in the numbers.



http://www.csgnetwork.com/multirpmcalc.html
By Butch Lawson - 16 Years Ago
Thanks Miker.  I did my math and found this:

3.70 rear    27" tire    .70 transmission final drive    70 mph      turns 2250 rpm  (2100 rpm at 65 mph)

I guess my question is, can I go with a 3.50 rear and drop a couple hundred rpm and  not lug the engine and still have enough pep to pass someone if I need to.    Thanks.

I did the math on your combo and this is what I found:

3.31 rear    26" tire    .80 transmission final drive    65 mph    turns 2250 rpm  (2400 rpm at 70 mph)

I will be doing this in a '54 Customline and am hoping for some decent gas mileage along with a little grunt when I need it.

All thoughts, ideas, or advice is appreciated.  Thanks.

Butch Lawson

Manchester, TN

By Butch Lawson - 16 Years Ago
When I re-read this, I realized that I still am not asking this question correctly.  Old age and mad cow disease I guess.  Old people like me shouldn't be up this late.

My question should have been, what rpm range should I be looking for at 65-70 mph to get optimum performance with the 292 and cam that I have along with the AOD?  There, I think I'll go to bed and check for answers tomorrow.

By pcmenten - 16 Years Ago
John Mummert lists the cam's range as 1800-5500. I suppose you'd want to shoot for 2000 at 65 to give the engine a little extra grunt on slight grades.
By LON - 16 Years Ago
Butch ,

Try this . http://www.f-body.org/gears/.

It sure take the guess work out .Hope this helps .

Lon

By Ted - 16 Years Ago
Anywhere between 2100-2300 is a good cruise rpm.  If you’ve an automatic, then reduce your calculation rpms by 5% to compensate for converter slippage.
By Butch Lawson - 16 Years Ago
Looks like the 3.70 is going to be right in the range that Ted recommended.  Thanks to everybody.

Butch Lawson

Manchester, TN

By ejstith - 16 Years Ago
You can go to this site and plug in all kinds of scenarios ..



http://www.angelfire.com/fl/procrastination/rear.html
By Unibodyguy - 16 Years Ago
Butch, if you have any other questions on what RPM your running at what speed, look up Richmond Gear and look under the "stret calculator" and just plug the numbers in. Worked great for me to figure things out on my trucks.

                                            Michael

By Butch Lawson - 16 Years Ago
Thanks Michael and ejstith.  I have been playing with the angelfire site.  It's great!!

Butch