Gears again
 

OK don't everyone scream at once. I have a 98 Cobra - tube headers, X-pipe, Star Clutch, pully's. Shows 281 at the wheels on the dyno. I have 3.27 gears. I want to go to 3.55 or 3.73. I drive highway a lot. Can anyone give me the difference (rpm) between the gear ratio's at 60 and 80 mph? I have stock Cobra wheels and 245/45 - 17 tires. I would really appreciate as I have to make a decision soon. I realize many people use 4.10's and higher but I really think for where i am and what I do 3.55 or 3.73 would be better. Much appreciate.

There is a tool on here that will give you that information in 4th gear. Since 5th is OD, there is no system that can give you that information. You should be able to calculate it based on your gearing info, and go that way.

My thoughts is there is twice as much 'new gear' in the 3.73's, so it wouldn't be worth the money to go with 3.55's.

3.73's rpm range at 60=around 1900 in 5th
3.73's rpm range at 80=around 2200 in 5th

3.55's rpm range at 60=1500 in 5th
3.55's rpm range at 80=2000 in 5th

I'd go with 3.73's

I don't have a cobra, but I do have a 98' w/ 3.73's. My 80mph rpm's are around 2600-2800.

I personally think that going from 3.27 to 3.55 is a waste, and not worth the cost. I have 3.73 gears on my car, and I have a 35 mile commute on the freeway every day. 3.73 is not bad at all for highway driving, and this is what I would recommend.

Hi Lopez;
If you have a calculator handy this is the most accurate way I have found to do this .

For RPM's @ speed

Gear x 336 x speed (mph) divided by tire diameter x .68 ( overdrive)

Using this formula you can play with any speed or any gear ratio.Hope it helps you

There's no way...according to that, I run 3409 rpms @ 80 mph. That's way high...maybe low 3's...but not mids.

Hi again Lopez;
I think you've made a math error there. Let's try your 3.27 at 80 mph

3.27 x336 = 1098.72 x 80 mph=87897.6 divided by your 26' tire=3380.6769 x.68 (overdrive) = 2298.8602 rpm which is bang on what I run with my stock 3.27's


3.73 x336 =1253.28 x 80mph =100262.4divided by your 26' tire=3856.2461x .68=2622.2473 rpm

3.55 x 336 =1192.8 x 80 = 95424 divided by 26' = 3670.1538x.68 (overdrive) =2495.7045 rpm

After you play with it for awhile you get familiar with it.BTW it looks like 3.73 is the way to go.I 'm hoping to convert over the winter!

your tire diameter is 26 feet? Wow...even if that was inches, that's a big tire. I have a 17" rim and low profile tires, so that would make my total diameter just over 20"--not 26.

26 inches which is the stock diameter for 245/45 - 17 tires