Mustang Evolution Forum banner

3.31 gears info?

6K views 25 replies 15 participants last post by  Midnight2012 
#1 ·
I am trying to find my new mod to make my stang better so im going with the gears and a tuner. I am not sure which gears to get, the 3.31 or the 3.55. I commute to college and drive to work every day, live near DC so traffic is a big factor. could someone give me some insight please?
 
#6 ·
I went with 3.31 and love it. The RPM is about 2k when you cruise at 70 MPH on 6th gear. Just perfect.
 
#10 ·
How many RPM can you tolerate at cruising speed? I have the stock 3.31 (Performance Package) and as Liv4spd pointed out, it runs just over 2k (2100) at 70. My math says that with the same tires, 3.55 = 2250 RPM @ 70, and 3.73 = 2366 RPM... hopefully the guys with those gears can confirm or correct my math. I don't know how fast you like to cruise, but at 100 MPH (just for a nice round number - not that I would run that fast) those RPM's go to 3000, 3200 & 3400 respectively. Take your car out, shift to a lower gear and cruise at your target RPM... see how it feels. It's worth doing a little experimenting so you can live with the new gears on your commutes, as well as through the 1/4 mile.
 
#12 ·
DD....3.31. Mines a toy 3.73 are really fun (great hole shot), little much on the interstate. 2 lane road cruising at 65 is fun. At 80 I'm hitting 2500 rpms...other posts acknowledge gas mileage dips on the 3.73's from 65 to 70 mph considerably. Again mines a toy not transportation!


Sent from my iPhone using Mustang Evolution
 
#13 ·
Speed vs RPM Calculator

Here's an excellent little calc table that makes it easy to calculate RPM at a selected speed.
Speedometer, Gear Ratio, and Tire Size Calculator

Notes:
When using the Tire Circumference Calculator be sure to enter the tire ratio as a 2 digit number with no decimal points.
When using the speed calculator...
6th Gear Ratio in a manual trans. = 0.7
6th Gear Ratio in an auto trans.= 0.69
When looking for RPM at a specific speed simply try different RPMs until you get the speed you're looking for.
 
#14 ·
Have 3.55 on my MT82 equipped V6. Perfect all round gear for mpg & fun. Runs about 100-110rpm lower than 3.73's when it comes to highway speed. The reality is you're giving up probably 1.5-3mpg over the 2.73's at 70+ mph depending if you go 3.55 or 3.73, but it's completely worth it IMO.
 
#18 ·
I know this is an old post but just noticed it.
Based on your first 3 "RPM vs speed" tests you shouldn't have to guess. However, those 3 test were obviously slightly off, in that they don't agree exactly with each other. If a ratio is set between those results to what the RPM should be at 90mph, it comes out to 2531RPM, 2571RPM or 2625RPM.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top