Rear end ratio's with FMS T-56 - Ford Mustang Forums : Mustang Forum
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post #1 of 4 Old 01-29-2016, 07:51 PM Thread Starter
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Rear end ratio's with FMS T-56

If any of you guys have the FMS one with the weird wide ratio 1-3 and close 4-6 gear sets what rear end gears do you like out at the track/autox? I usually do 1/4 mile twice a year without slicks now and could care less about my "hole shot"

I feel like 1-3 are so insanely short with my setup. After going from the TR-3550.

I'm thinking about going to 3.31's in the rear because I'm sick of extending past 6000 multiple places at my track (its pretty fast) to grab 4th just for literally one or two seconds.

Current speeds with my tire size at 6000 is.
2.97 43mph
2.07 62mph
1.43 90mph
1 129mph
.80 161mph
.62 208mph

Thinking of going to 3.31's

The gap between 3rd and 4th though just sucks. I hate to make it bigger. In a perfect world I'd swap Cobra 1-3 gears in but that will be way more costly than just swapping out the rear end gears. Going to 3.31's also would only change my cruising RPM at 70 to 1900 from 2000. I think my cam will be OK with that.

Matt, 90' GT 347, 6037 heads, V1 Si-trim, 11psi, B31 Cam, T56, SV Intake, BE/Tweecer Tuned. 550rwhp 513tq
Bonneville 130 club member. (139.993) [email protected] in the 1/4.
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post #2 of 4 Old 02-02-2016, 08:57 AM
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what gears do you have currently? to gain 8 mph in 3rd i wouldn't even waste the time/money to swap gears. personally, i would just shift into 4th earlier and not wait until i topped out 3rd. id imagine your torque is almost identical in the top of 3rd/mid 4th anyway so the loss would be minimal on shifting earlier. unless you run solely 1 track you run into the issue in another gear at another track.

but in my current car i run a Jerico 4 spd with 2.94/1.91/1.72?/1 ratio with 3.08s which gives me a top speed of 168. running a 423whp motor

in the roush when i tracked that i ran a viper spec T56 with 2.66, 1.78, 1.30, 1.00, .74, .50 ratios and 3.73's 4th gear topped out at 135ish

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post #3 of 4 Old 02-02-2016, 10:51 AM Thread Starter
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Currently the car has 3.55's. The problem with short shifting into 4th is the car will substantially drop RPM because of the huge gap between 3-4. If I had the close ratio viper gear set like you posted I would be a happy camper with my current rears. Mine is

At Miller Motorsports Park if I do either of the smaller courses I'm in 3-4th the entire time. If I do the outer or full I'm 3-4-5th. The front straight is beyond fun with the close 5th to nail 150+.
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post #4 of 4 Old 02-02-2016, 10:52 AM
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I'm running the same trans gear ratios as you in my T56 with 3.55 rear gears and I like the ratios. Most of the autocross stuff I do are tight so I'm mostly in second and occasionally third but I also shift earlier at 5700-5800.
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