3.31 and 3.55 gear question

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Randy 25

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Jun 29, 2008

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Nov 22, 2008

#1

• Nov 22, 2008

• #1

For those with 3.31, 3.55 and 3.73 gears and stock tires, what rpms are you doing at 70 MPH? Thanks.

 

SpartaPerformance

10 Year Member

Nov 5, 2006

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Long Island NY

Nov 22, 2008

#2

• Nov 22, 2008

• #2

Each gear step up is around 250 RPM.

 

ptfoxbdy89

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Aug 4, 2007

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Memphis Tn.

Nov 24, 2008

#3

• Nov 24, 2008

• #3

lol read my mind man like the answer!

 

Sparty92

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Jul 30, 2007

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Detroit Burbs

Nov 24, 2008

#4

• Nov 24, 2008

• #4

I have 3.55s on the stock 17" wheels.

70 mph is 2K rpm in 5th gear.

 

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Randy 25

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Jun 29, 2008

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Nov 24, 2008

#5

• Nov 24, 2008

• #5

Sparty92 thanks, that's what I was looking for. I maybe should make myself a little clearer. I'm looking at buying a GT and was looking at axle ratios. I've had from 2.72s to 4.11s in cars over the years. I have an 04 F150 with 3.55 and run around 2000 rpm at 70. I was hoping that with smaller tires on a stang, that the rpms would be a bit higher than what Sparty 92 is reporting. Maybe a good all around ratio is 3.73. I drove coast to coast a couple of times in a vette many many years ago with 4.11s and it bout did in the engine. Can anybody chime in with what 4.73s do rpm-wise at 70 mph in 5th gear? Tx.

 

SlideWRX

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Jan 8, 2007

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Westland, MI

Nov 25, 2008

#6

• Nov 25, 2008

• #6

At 70 mph, the 3.31 is 1,990-2,015 rpm, the 3.55 will be 2,135-2,160 rpm and the 3.73 will be 2,240-2,275. Pulled from a spreadsheet I threw together at one point. Assumes 768 rev/mile on the tire, pulled from the specs for the OEM 17" Pirelli on the tirerack.com site.

 

Sparty92

Member

Jul 30, 2007

430

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Detroit Burbs

Nov 25, 2008

#7

• Nov 25, 2008

• #7

SlideWRX said:

At 70 mph, the 3.31 is 1,990-2,015 rpm, the 3.55 will be 2,135-2,160 rpm and the 3.73 will be 2,240-2,275. Pulled from a spreadsheet I threw together at one point. Assumes 768 rev/mile on the tire, pulled from the specs for the OEM 17" Pirelli on the tirerack.com site.

Click to expand...

Since my tach (and probably yours) shows increments of 250 rpms, you can assume +/- 250 rpm for any of the aforementioned gear ratios.

I find the 3.55s and a 5-speed to be fairly zippy. Lots of guys that drive cough...automatics...cough....swear by 4.10s. I would think that 1st gear would be really short in a manual trans car. I drive my car daily, year round. If you're a drag strip freak, 4.10s would be something to consider. I would opt for 3.73s myself. If Ford can stuff them into a Bullitt, it HAS to be safe for freeway driving....right?

I "think" you can get 3.73s in the 2010 Mustang...as an option. If not, gear swaps are fairly cheap...I was quoted $500 parts and labor...which I find "do-able."

Good luck!

 

garbledwords

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Aug 28, 2007

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Nothern VA

Nov 25, 2008

#8

• Nov 25, 2008

• #8

Attached is a Excel spread sheet that I found on-line someplace that lets you calc the rpms for different gears. For both transmission and rear gears.

Hmm.. It would seem that I can't upload a .xls file. I simply renamed the file to have a .txt extension so just rename it gears.xls and you will be all set.

 

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• gears_xls.txt

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Randy 25

New Member

Jun 29, 2008

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Nov 30, 2008

#9

• Nov 30, 2008

• #9

GarbledWords Got it, thanks. Thanks all, just was I was looking for.

 

GreyDiesel

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Jul 26, 2008

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Denver, CO

Nov 30, 2008

#10

• Nov 30, 2008

• #10

That is genius Garbled, thanks for posting!

 

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oh9mustang

Banned

Jul 27, 2008

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Dec 1, 2008

#11

• Dec 1, 2008

• #11

gears

I have 331 Ihave had 355 373 and 410 , I like the 410s the best

Ron

 

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explrsport

Founding Member

Apr 26, 2002

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SoCA

Dec 1, 2008

#12

• Dec 1, 2008

• #12

Not to hijack this thread but...I have a set of original 3.55 gears with less than 3000 miles on 'em...will sell at 75% off the price new...send me an email if you're interested -
wallstwiz9@aol.com

 

08blueskunk

New Member

May 8, 2008

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Maine

Dec 2, 2008

#13

• Dec 2, 2008

• #13

my old 97 Cobra Had the 3.73's and it was all together different from my 3.31's now, very snappy it got about 19mpg and my 2008 bone stock gets about 23 MPG. That would be my daily driver choice i think...3.73's

 

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kevanp

New Member

Aug 23, 2008

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South Jersey

Dec 2, 2008

#14

• Dec 2, 2008

• #14

I run the 4.10s @ about 2400-2500 @ 70

I get 24ish mpg on "winter 87 octane" with heavy snowtires.

I have stock exhaust and get no drone.

I commute 100 miles/day and thought I might regret the 4.10s. I don't...lots of fun.