Why not 3.90s???

PSCBrenden · Jul 31, 2004

Well all i hear on this site is people saying 4.10s are they way to go with the Mustang and i even see posts of people wishing they went with 4.30s. But everyone over at my local speed shop says dont get the 4.10s the best gear for the Mustang is 3.90s i hear the same thing from several of my Mustang friends. Now im about to order gears and i cant decide between Motive 3.90s or FRPP 4.10s i trust both the forums opinion and my friends opinion...so tell me again why i should go with the 4.10s over the 3.90s

1tirefire · Jul 31, 2004

go ahead, there isn't much differance between the two. think of it this way 4.10 axle turns to one turn of the wheels vs 3.90. not much differnce. either one is fine and better than stock.

54life · Jul 31, 2004

the 4.10's are just a slight bit more of gear....all a personal preferance.....it is a good gear though

98SteedaStang · Jul 31, 2004

Well its better then a 3.73!

StangFreak32 · Jul 31, 2004

see i was always told 3.73 for 5spd and 4.10 for autos (daily drivers)

crew_dawg16 · Jul 31, 2004

the 4.10s will give you a slightly better mechanical advantage, but the 3.90s will not drop your rpms a lot from the 4.10s... I say 4.10

281Ponies · Jul 31, 2004

Just had Motive 3.90s installed yesterday, made a 50 mile trip to have it done. On the way over I set the cruise on 75mph for a comparison later and was turning 2000rpms according to the tach needle. After the install I used the predator to calibrate the speedo for 3.90s and did a bit of heat cycling the new gears. Later I set the cruise on 75mph for the trip back home and was turning 2450rpms according to the tach needle.
Looking at the Engine, Gear, & Tire Calculator at http://www.wcfords.com/stuff/calcs/EGTcalc/egtcalc.php I should be turning 2150rpms with the factory 3.27s at 75mph and 2565rpms with 3.90s which seems to match what I was seeing looking at the tach needle (not the digital tach readout). According to this calculator with 4.10s you should be turning 2696rpms at 75mph, which is a 131rpm difference.
I should add, when I made my gear selection I was not concerned with tenths out at the track. I just wanted to give the car some kick off the line and make it feel a bit lighter. 3.90s have done a good job doing this and I’m very happy with the choice I’ve made.

BTW I haven't changed tire sizes, these speeds and rpms were in 5th gear on 245/45/17s.

-Cale

twogts4us · Jul 31, 2004

My shop told me definately 3.73s for the street. (And I'm OK with with that, except when I drive the 01 with 4.10s) I think the reason more people don't go with 3.90s is because FRPP doesn't make them. Any of these gears will be a big improvement over stock. I really think the 3.90 would be a perfect fit, right in the middle.
I drive both cars listed in my sig...my 02 pulls better thru 3rd and 4th, but my wife's 01 is better off the line. Both are a blast to drive.
If your shop supports and installs the 3.90s, I'd say go for it. I think you'll be very happy with these.

DJsZincGT · Jul 31, 2004

PSCBrenden said:
Well all i hear on this site is people saying 4.10s are they way to go with the Mustang and i even see posts of people wishing they went with 4.30s. But everyone over at my local speed shop says dont get the 4.10s the best gear for the Mustang is 3.90s i hear the same thing from several of my Mustang friends. Now im about to order gears and i cant decide between Motive 3.90s or FRPP 4.10s i trust both the forums opinion and my friends opinion...so tell me again why i should go with the 4.10s over the 3.90s

I just had 3.73's installed yesterday (3.73 because I'm supercharging my car). The car definately accelerates harder than it did when it was stock. It's much more fun to drive. However if I was staying N/A I would've done the 3.90's or 4.10's (most likely the 4.10's) and I have a 100 mile round trip to work everyday. The 4.10's are just more fun. Don't fear the gear!!!!

SonicBlueBabe · Jul 31, 2004

I love my 3.90's. There is a slight difference between the 3.73's and 3.90's. Should be about the same between the 3.90's and the 4.10's. I was goin to go with either the 3.73's or the 4.10's and then I saw the 3.90's came out and ended up with those. They are great! Even with the nitrous, it's not too much gear. I say the 3.90's are perfect for a car that's gonna stay n/a or if you're gonna go with a power adder.

GoBabyVroommm · Jul 31, 2004

Well 390 vs 373/410 you have to customize to get in and work. Most shop don't even know how to install a simple Ford Racing gear let a lone a 390.

I'm gettin a 390 as my next gear but its going to come with the 9inch i order. My friend talked me out of gettin the 390 just because of the fact its not a easy bolt-on.

Ghostface · Jul 31, 2004

281Ponies said:
Just had Motive 3.90s installed yesterday, made a 50 mile trip to have it done. On the way over I set the cruise on 75mph for a comparison later and was turning 2000rpms according to the tach needle. After the install I used the predator to calibrate the speedo for 3.90s and did a bit of heat cycling the new gears. Later I set the cruise on 75mph for the trip back home and was turning 2450rpms according to the tach needle.
Looking at the Engine, Gear, & Tire Calculator at http://www.wcfords.com/stuff/calcs/EGTcalc/egtcalc.php I should be turning 2150rpms with the factory 3.27s at 75mph and 2565rpms with 3.90s which seems to match what I was seeing looking at the tach needle (not the digital tach readout). According to this calculator with 4.10s you should be turning 2696rpms at 75mph, which is a 131rpm difference.
I should add, when I made my gear selection I was not concerned with tenths out at the track. I just wanted to give the car some kick off the line and make it feel a bit lighter. 3.90s have done a good job doing this and I’m very happy with the choice I’ve made.

BTW I haven't changed tire sizes, these speeds and rpms were in 5th gear on 245/45/17s.

-Cale

Great review!

Defleshed · Jul 31, 2004

Please. 4.10s. Please.

vidmaster · Jul 31, 2004

Heh I went with 4.10's. When I'm ready to supercharge, I'm going to rebuild my whole rear end. It'll be at least a year before I s/c so I figured what the hell might as well have fun now while I wait.

damacman · Jul 31, 2004

awe, don't be a sissy, 5.14s would get 'er outadahole' quicker . . .

laser2kgt · Aug 1, 2004

Redfire03GT · Aug 1, 2004

Problem is, a lot of people still have the mentality towards our cars that they had for the 5.0's. It's not the same.

Generally speaking, 3.73's just doesn't cut it, 3.90's would be a tease, 4.10's are the accepted equalibrium, where as 4.30's or higher are usually meant for those who drag race only or simply don't give a damn.

Get 4.10's at least.

ronaldriske · Aug 3, 2004

I dont care! I'm running 4.30's and love them. Of course the way I judge mods are by how much they help me destroy tires, and 4.30's have been the best mod so far!

jmichalicek · Aug 3, 2004

ronaldriske said:
I dont care! I'm running 4.30's and love them. Of course the way I judge mods are by how much they help me destroy tires, and 4.30's have been the best mod so far!

Yep. I'm going 4.30 as soon as I've got another car to make the 80 mile round trip for work everyday or I get the chance to move closer to work.

billyfe390 · Aug 3, 2004

GoBabyVroommm said:
Well 390 vs 373/410 you have to customize to get in and work. Most shop don't even know how to install a simple Ford Racing gear let a lone a 390.

I'm gettin a 390 as my next gear but its going to come with the 9inch i order. My friend talked me out of gettin the 390 just because of the fact its not a easy bolt-on.

What in the world are you talking about.

Why not 3.90s???

PSCBrenden

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