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?
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.
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!
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.
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.
If I was gonna switch from the 3.31 mine came with I'd go 3.55 or 3.73. I've driven both 2.73 and the 3.31 and the difference is big but I would go bigger.
I wonder if someone with 3.55's will let me test there car out on the spring cruise, or at least ride in it for a bit. I want to see/feel the difference in person before I drop the cash on gears. It is really something you should feel in person before jumping into them.
My Base Stang with 3:31 option runs 1750 @ 60 mph, 2000rpm @ 70mph and 2250 @ 80... I'm gonna have to guess its 2500 @ 90. Too much traffic today to find out. 17" tires btw and automatic.
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.
do you have a tuner? Just datalog and compare speed and rpm more accurately.
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