Gears and gas mileage... Yes this again

[Cronus]

With the ever increasing prices of gasoline I've been questioning the impact 4.10s would have on my wallet. I'm looking to put gears in a 99gt, basically stock and is currently a daily driver, good amount of Highway...

I tried looking back through the pages here to find the answers to my questions since I know this has been beat to death but I just couldn't find what I was looking for. I'm basically asking what RPMS I will be pulling with stock rims and tires at around 70mph with both 3.73s and 4.10s. How did the gears impact your gas mileage and such? I have plans to eventually get myself a blower but cannot see that happening for the next few years. Not sure if I want to go with the 4.10s for the fun now or just stick with the 3.73s saving myself some money in the long run.

Sorry to ask questions that have been posted here more time than can by counted but with only being able to go back 3 pages of history I just couldn't find the info. If anyone wants to slap me around and point me in the direction of a thread that already touches on this, I could handle that. Thanks.

 

[Go HoTO!]

4.10s on my car run around 2800 rpms at 75 mph. In theory, you should loose gas mileage with higher gears. about 1-3 mpg. But, you can drive in a higher gear at lower speeds and some guys claim better mileage with them.

I have 4.10's, but I really don't pay attention. I believe that 4.10's will get better mileage in the city, but lower on the highway compared to stock gears.

 

[YallarStang]

Gear, speed and RPM calculator:

http://www.tchracing.com/tech/gearcalc.php

 

[GTvert01]

I get better mileage now than i did stock.On the highway especially.I can get between 24-25 mpg @ around 80mph with my 4.10s.My gas mileage in town has suffered more, because it's more fun to drive.

There will be about a 200 rpm difference between the two assuming you have the t-45 tranny.est.(2300 vs.2500)

 

[Cronus]

YallarStang you are the man...

So we are only talking around an addition 600 rpm @ 75mpg in 5th with the 4.10s over the 3.27s...interesting.

 

[GTvert01]

How are you planning on getting 75mpg?

 

[cmb91LX]

I do not get anywhere near 20-25 MPG on the highway. with the 410s at @ 70 I am over 3k RPM. I get much better mileage in the city. On the highway forget about it. Put your foot in it, forget about it. I dont see 373s being much better either. Car feels much stronger but gas mileage went to Hell.

 

[GTvert01]

I do not get anywhere near 20-25 MPG on the highway. with the 410s at @ 70 I am over 3k RPM. I get much better mileage in the city. On the highway forget about it. Put your foot in it, forget about it. I dont see 373s being much better either. Car feels much stronger but gas mileage went to Hell.

Have you changed tire sizes?If not, I wouldn't think that you would be at 3k rpm @ 70.

 

[tjm73]

...with the 410s at @ 70 I am over 3k RPM.

This is mathematically impossible with stock size tires, unless you are not using overdrive.

4.10's with stock size tires will turn 2550 rpm at 70 mph in 5th gear. About 2600 with the 4R70W automatic.

If you want to know what the gas mileage will be like, drive around without using 5th gear for a tank of fuel. Figure out your gas mileage. This will be about what you can expect...give or take a little.

 

[Rocketman]

I find this to be one of the best gear calculators out there. It gives you RPM's for all tranny types.
http://www.differentials.com/calc.html

 

[Cronus]

ha 75mpg..... That would be nice without sacraficing any power...



I've never really been worried about gas mileage but with the way prices are its starting to become a factor. How do you guys think the 4.10s would compare to 1990 GT with 3.73s and a T5?

 

[tjm73]

I find this to be one of the best gear calculators out there. It gives you RPM's for all tranny types.
http://www.differentials.com/calc.html

or here's the formula.....

gear ratio X mph / tire height X 336 X overdrive gear ratio ( 0.68 in 5 speed)

 

[GTvert01]

ha 75mpg..... That would be nice without sacraficing any power...



I've never really been worried about gas mileage but with the way prices are its starting to become a factor. How do you guys think the 4.10s would compare to 1990 GT with 3.73s and a T5?

All the 5.0s I've owned, I put 3.73s in, and never got anywhere near what I am getting with my 4.6 with 4.10s.Maybe it was just my luck, or the way I drove, or the fact that I have more money now ,but none of the 5.0s could catch this car at the strip, or match it for gas mileage.

 

[tjm73]

How do you guys think the 4.10s would compare to 1990 GT with 3.73s and a T5?

I have a 90 Mustang GT convertible with 3.73's and a full exhaust, B303 cam, roller rockers CAI kit, underdrive pulleys, 275/50R15 tires. I get 18-20 mpg at 70-72 mph highway speeds with normal driving habits.

 

[1stmust02]

Cronus,
Get the 4.10 gears. I have had them in my 2002 GT for about 2 months. My gas mileage has a range of 20.2 (worse) to my last fill up of 22.8, not much different when I had the 3.27's. I drive my stang to work every day, 50 miles round trip with 40 of them on 295 at 70 mph.
My rpm at 70 is 2200 with the 4.10's (and with FRPP aluminum drive shaft) and was 1800 with the 3.27's. That is not much of a difference but the performance increase is amazing. It acts like an entirely different car.

 

[4.6_02_Black_GT]

...

Gas mileage threads are aways fun. My 4.10 are going in on Thursday. Just a reminder we all own Mustangs...do we really care what our gas mileage is????

With 75%/25% city/hwy miles I rarely see anything over 18 mpg. My driving style is to putt around town 45-60mph in 4th gear alot.. rpms in the 2000-2200 range, so this certainly kills my mileage...I see 5th gear rarely. So for me I really dont expect any change in my mileage since I already tend to ride around at higher rpms already.