3.90 gear questions
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LI98GTStang
Founding Member
I've got my hands up with 3:90s from motive and like them. I think I would have been disappointed with 3:73s and 4:10s might have been too much for me personally, so it was a good choice for me. Note that I have not driven (only driven in) a 3:73 or 4:10 geared stang before, so I don't have anything to compare it to. Shop did a great install job and speedcal has a setting to fix the speedo. I've said this before, but talk to the install shop prior to purchasing to make sure they are OK with going with non-FRPP gears. A lot of shops will not install/guarantee the install going non-FRPP.
I haven't noticed a difference in gas mileage, just shifting at earlier speeds than before and think I'm driving a little slower on the long highway runs - 75 compared to 80 with stock 3.27 gears as the revs are higher now in 5th. Definately feel 2nd, 3rd and 4th gears kickin' it more. No 1/4 mile runs prior to the gears, but feel they helped me get down the track better.
I haven't noticed a difference in gas mileage, just shifting at earlier speeds than before and think I'm driving a little slower on the long highway runs - 75 compared to 80 with stock 3.27 gears as the revs are higher now in 5th. Definately feel 2nd, 3rd and 4th gears kickin' it more. No 1/4 mile runs prior to the gears, but feel they helped me get down the track better.
whyask
New Member
Had them when I was running NOS (150 shot) they are awesome, get you in the powerband quick and the rpms arnt as high as 4:10... I have 4:10s now just because Im not running NOS and its a garage and weekend queen only.. so no long drives anymore !
SaleenGT2001
Well-Known Member
i have them in my car. they are great for a n/a or low hp s/c car. i will be swapping mine out for some 3.73's when the new engine goes in. i'm already hitting the rev limiter in the 1/4. all around they are a great street gear and they dont kill mileage too badly.
chrisconsin
Member
Whats your top speed in 4th gear with 3.90's and whats your tire size.
I just got back from the drag strip and need gears, my top speed was 106MPH in the 1/4 mile and I was JUST shifting in to 4th right before I went into the traps.
I just got back from the drag strip and need gears, my top speed was 106MPH in the 1/4 mile and I was JUST shifting in to 4th right before I went into the traps.
billfisher
Active Member
i have 3.90's, and i'm changing them. they work fine, but i need more mph in 3rd. i will try 3.73's and see id i get through the light before shift tine to o/d. if not 3.55's.
chrisconsin
Member
billfisher
Active Member
i an an auto. it shifts at 5200 and 97mph. WOT 3 - O/D shifts with an auto is asking to blow the tranny up. when i get it programmed i am sure it will fix that. but until then i need a few more mph
Loud 3.90's
I recently bought a set of 3.90 (may have been 3.89's I forget) from Richmond Gears with a motive install kit. The installation wasn't too bad if you know what you are doing and take your time. My only problem was that after installing them they are loud. I know for a fact the pinion checking distance and backlash are dead on. I worked with a friend who owns a shop working on cars and big rig trucks alike and he has been doing it for years. He basically showed me what to do every step of the way and took extra time to make sure things were perfect. After the installation both he and I drove it and concluded that it was too loud. I spoke with Richmond and they basically said that with more teeth you are going to get more noise. Unfortunately Ford Racing doesn't make a 3.90 set otherwise I would have gone with them. In terms of performance gains I love them. For me they are a perfect middle ground between 3.73's and 4.10's although your mileage definitely still suffers. But hey if I was worried about that I would own a Prius.
I recently bought a set of 3.90 (may have been 3.89's I forget) from Richmond Gears with a motive install kit. The installation wasn't too bad if you know what you are doing and take your time. My only problem was that after installing them they are loud. I know for a fact the pinion checking distance and backlash are dead on. I worked with a friend who owns a shop working on cars and big rig trucks alike and he has been doing it for years. He basically showed me what to do every step of the way and took extra time to make sure things were perfect. After the installation both he and I drove it and concluded that it was too loud. I spoke with Richmond and they basically said that with more teeth you are going to get more noise. Unfortunately Ford Racing doesn't make a 3.90 set otherwise I would have gone with them. In terms of performance gains I love them. For me they are a perfect middle ground between 3.73's and 4.10's although your mileage definitely still suffers. But hey if I was worried about that I would own a Prius.
Crzyhrse
Active Member
When Saleen GT posted I thought it was strange, since he does'nt have that car anymore.
chrisconsin
Member
three year old thread is valid information
I know this is an old thread, but it still gets read. I am a newer Mustang owner, I bought a 2000 GT convertible last year, and all of this information is new to me. So... I appreciate being able to search the old threads and find info.
I am looking to switch to the 3:90 gears as well, I am looking for a gear table that shows the rpm vs. mph per gear with an automatic.
I am not a racer, more of a cruiser, but I am doing some mods. I want some upgrades, the gear set is next in line.
Anyone out there with 3:90s in an automatic wish to comment?
Thanks
I know this is an old thread, but it still gets read. I am a newer Mustang owner, I bought a 2000 GT convertible last year, and all of this information is new to me. So... I appreciate being able to search the old threads and find info.
I am looking to switch to the 3:90 gears as well, I am looking for a gear table that shows the rpm vs. mph per gear with an automatic.
I am not a racer, more of a cruiser, but I am doing some mods. I want some upgrades, the gear set is next in line.
Anyone out there with 3:90s in an automatic wish to comment?
Thanks
Dark_Horse
Member
Not to thread hijack, but what mods are you running to trap 106mph chriscousin? Your sig run was awesome.
I have read many threads about the 3.90s making noise. My personal opinion is: if you are concerned about mpg then stick with FRPP 3.73s. Otherwise FRPP 4.10s all the way!
390's are great for an N/A Mustang. My advice only, but if you trap more than 120mph, 390's are too much, unless you want to get into the whole tire diameter change, etc. I have 373's on my SC Mustang and she redlines at about 123mph in 4th gear, perfect for the 1/4 mile, since I hit in the area of 114-117 et.
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