Selecting a Final Drive Ratio

Midlife Crises

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I have a full weight 2010 GT with a 2.66 first gear T56 mag. 3.73 differential gears and something over 500HP. Using 28X10.5 MT ET Drags the diff. gears need to be changed. I see 4.10s are very popular and Ford brand gears are an easy choice. On the other hand, 4.30s are doable within my RPM range and could help the car out of the hole. I have set up Ford Performance and Yukon brand gears before but nether list 4.30. Any recommendation on ratio or brand for the 8.8 will be appreciated. Please don’t tell me to change the tranny.
 

Juice

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I would calculate the ratio bassd on your trap speed, in 4th, to just shy of redline.
I usually just go with Ford racing brand gears. i did install a set of Summit racing "unbranded" gears, they are fine.
 

Midlife Crises

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Playing with a calculator I like what I see running 4.30s. Ford Racing doesn’t offer that gear set so are there any brands to avoid?
 

Juice

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Don't know if there is one brand to avoid.
I was looking at the Richmond "lightened" gears to try, but since I've decided to leave the 3.73s for now.
 

Dino Dino Bambino

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I would calculate the ratio based on your trap speed, in 4th, to just shy of redline.

What he said.
Assuming you have 500rwhp and a race weight of 3750lb, I'd anticipate a 1/4 trap speed of ~126mph.
Your 28" tires will rotate 720 revolutions per mile. At 126mph in 4th, your engine would be at 6200rpm with 4.10 axle gears, and 6500rpm with 4.30s.
 

WNYGT5-0

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Run the Richmond 4.30s
You should be able to find Ford Performance 4.30s tho... here is the pet number
FRP-M-4209-G430M
 

RED09GT

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I had a set of Richmond 3.73's in a fox body and they were quiet.
I bought the rear end complete so I can't comment on the install difficulty.
 

Midlife Crises

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Thanks for the input you have offered. I will be going with 4.30s, maybe 4.33s.
 

07 Boss

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I've been using Richmond gears for over 30 years. Never broke one set and I have broken a lot of cars. My latest rear end (Ford 9") I had built by Strange and I'm not sure if they use their own gears or someone else's, but it's my first non-Richmond set in forever.
 

GriffX

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I used a Ford 3.73 gear set and had a gear noise first which disappeared within 3000 miles. Worst part in the Ford kit was the shims from Ratech, not enough thin shims, had to file some off.
 

Juice

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I've been using Richmond gears for over 30 years. Never broke one set and I have broken a lot of cars. My latest rear end (Ford 9") I had built by Strange and I'm not sure if they use their own gears or someone else's, but it's my first non-Richmond set in forever.

I just installed my first set of Richmond gears. Been an FRPP or nothing guy, but I will and have installed used gears without issues. I went to 3.89s from jegs, $165 for the set.
Easiest install ever. Using the original 3 shims in their original locations came out perfect. 006" backlash (on the tight side of rec. spec) with good pattern. Has a little decel whine, that I cannot really hear unless the windows are closed. I expect it will quiet down with some miles.
 

GlassTop09

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I've been using Richmond gears for over 30 years. Never broke one set and I have broken a lot of cars. My latest rear end (Ford 9") I had built by Strange and I'm not sure if they use their own gears or someone else's, but it's my first non-Richmond set in forever.
I just installed my first set of Richmond gears. Been an FRPP or nothing guy, but I will and have installed used gears without issues. I went to 3.89s from jegs, $165 for the set.
Easiest install ever. Using the original 3 shims in their original locations came out perfect. 006" backlash (on the tight side of rec. spec) with good pattern. Has a little decel whine, that I cannot really hear unless the windows are closed. I expect it will quiet down with some miles.
I'm going the Richmond route as well.....been gathering together all associated parts to do the swap. Was gonna go w\ 4.10's but when I ran them thru a calculator w\ my running tire dia size (26") I saw that the cruising engine RPM's were gonna be a little higher than what I wanted to tolerate on the street so I thought that since most who ran 4.10's on the street also mostly ran either OEM 27" or 28" dia tires so I used 4.10's\27" (RPM's were 2,430 in 5th @ 70 MPH, top of 4th at 6,350 @ 124 MPH) as a template to see what would come the closest using 26" dia tires & it spit out 3.90's (RPM's were 2,391 in 5th @ 70 MPH & top of 4th at 6,350 @ 126 MPH) so I picked up a set of Richmond Excel 3.90 gears
 

RED09GT

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Which version of the tru-trac did u get, the normal version with 3 x helical gears on each side...or the HD version, with 4 x helical gears on each side ?
Where have you heard about this alternative version? Eaton's catalogue only lists 3 part numbers, one for 28 spline, one for 31 spline, and one for 33 spline.
Are you sure this isn't just due to the different makeups required for different differential sizes?
 

Pentalab

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Where have you heard about this alternative version? Eaton's catalogue only lists 3 part numbers, one for 28 spline, one for 31 spline, and one for 33 spline.
Are you sure this isn't just due to the different makeups required for different differential sizes?
VMP lists 2 x versions of the tru-trac...for the 05-14 cars..with the 8.8" rear end.

This is the HD version, 33 spline, for the 8.8" rear end, (05-14 cars). Comes with 4 pinion gears on EACH side. Steel box it comes in is heavier. Recommended when ur 60' times are 1.4 secs...or less. Requires 33 spline axles...from strange engineering, or Moser. https://www.vmpperformance.com/Eaton-33-Spline-TrueTrac-Differential-for-05-14-8.8-BUILT-solid-axle



This is the lighter duty, 31 spline, for the 8.8" rear end, (05-14 cars). Comes with 3 pinion gears on each side. Plug and play, uses oem 31 spline axles. https://www.vmpperformance.com/Eaton-31-Spline-TrueTrac-Differential-for-05-14-8.8-solid-axle
 

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