Gear

[BAD67FUN]

Man, I just can't make up my mind. Maybe I'm PMSing. I took about an hour to read thru posts on gears and I still am nit-picking on whether to go with the 3.55 or the 3.80. I know they're close, but I can only pick one. I'm going to be stuck with my C4 at least another 2 to 3 years. My rubber in back is 275-40 (25.6" tall). The car is strictly a toy. Hardly any freeway. And I'm planning on autocrossing again. Well, which one... and why? Thanks.

 

[Edbert]

Check this out...

http://www.edbert.net/rpm_chart.htm

Use the "3rd" gear portion for C4, the "4th" is for the AOD (duh!).

 

[BAD67FUN]

I got all that from a different calculator...

I'm just bored today and looking for opinions though.

 

[ratio411]

Your sig tells very little about your engine combo.
It doesn't make much difference since those gears are so close, but I could give reasons one way or another if I knew more about your cam and intake.
As it stands, I lean 3.80.
Reason being that the auto tranny has a fairly high first gear ratio. If you had a manual tranny I would lean to the 3.55.
Either gear you choose will seem like a huge difference from what you have now. If you switched a 3.55 for a 3.80, or vice-versa, you would probably not see a noticeable difference.
I did work under the assumption that your car is a small block, then judging weight, tire, intended use, and tranny... I like the 3.80.
Dave

 

[BAD67FUN]

Thanks Dave. I leave out the specific engine detail because that will all change eventually. The only thing I can assure anyone of is that it will be a small block.

 

[HistoricMustang]

3.73 - 3.80 is fine for your situation.

HistoricMustang
www.historicmustang.com