Do I Have 3.73 Gearing?

5.0_H.O · December 19th, 2007, 09:56 AM

i have an 87 gt with 225/55r16 on the rear and a T-5 trany, i was wondering if anyone knew wat gears my car has? at 120KM my stang revs at about 2300 RPMs.

ryans88gt · December 19th, 2007, 10:09 AM

Maybe 3.55 gears?

Haggis13 · December 19th, 2007, 10:52 AM

Probably a stock 3.08.

nolife · December 19th, 2007, 12:03 PM

Originally Posted by 5.0_H.O

i have an 87 gt with 225/55r16 on the rear and a T-5 trany, i was wondering if anyone knew wat gears my car has? at 120KM my stang revs at about 2300 RPMs.

Well, assuming your tach and speedo are correct and you have a 0.62 fifth gear, mathematically, you have a 3.82 rear ratio which is close to 3.73.

If you have a .68 fifth gear, you have a 3.48 which is close to a 3.55.

If you do not know your 5th gear ratio, use 4th gear (which is 1:1) and plug the numbers into this equation:

axle ratio = RPM X Wheel_Circumference / trans_ratio X 1056 X mph

Wheel_circumference for a 225/55/16 is 80 inches
120 km/hr = 74.5 mph
trans_ratio in 4th gear is 1

Either way, speeds and tachs are no where near accurate and you will have to estimate. Do like the other recent thread states and turn your drive wheels and count the drift shaft turns, it will be right every time.

JONJON · December 19th, 2007, 12:58 PM

3.08

ryans88gt · December 19th, 2007, 02:21 PM

Originally Posted by nolife

Well, assuming your tach and speedo are correct and you have a 0.62 fifth gear, mathematically, you have a 3.82 rear ratio which is close to 3.73.

If you have a .68 fifth gear, you have a 3.48 which is close to a 3.55.

If you do not know your 5th gear ratio, use 4th gear (which is 1:1) and plug the numbers into this equation:

axle ratio = RPM X Wheel_Circumference / trans_ratio X 1056 X mph

Wheel_circumference for a 225/55/16 is 80 inches
120 km/hr = 74.5 mph
trans_ratio in 4th gear is 1

Either way, speeds and tachs are no where near accurate and you will have to estimate. Do like the other recent thread states and turn your drive wheels and count the drift shaft turns, it will be right every time.

yeah you are right, probably a 3.73 with the stock trans.
I miss calculated KM to MPH...somehow I got 67 mph

Also you are correct about the tach and speedo being off. My stock tach was off by 400 rpms at 3000.

5.0_H.O · January 2nd, 2008, 10:29 AM

thanx for the help sorry i'm canadian my cars in km lol

juggalowelder · January 2nd, 2008, 09:06 PM

It's relatively easy to find out another way. Mark the rear tire in a spot with chalk. Mark the driveshaft in a spot also. Start spinning the driveshaft. However many times you have to spin the driveshaft will give you your gear ratio. Unless you've owned the car from new, ya never know what gears are in the rear anymore.

Stangzilla · January 2nd, 2008, 10:05 PM

Originally Posted by juggalowelder

It's relatively easy to find out another way. Mark the rear tire in a spot with chalk. Mark the driveshaft in a spot also. Start spinning the driveshaft. However many times you have to spin the driveshaft will give you your gear ratio. Unless you've owned the car from new, ya never know what gears are in the rear anymore.

He has to count how many times the driveshaft goes around for 1 tire rotation and thats his ratio..

ChrisJ · January 2nd, 2008, 10:25 PM

Mark the drive shaft with chalk...

Mark the bottom of the tire with chalk...

Rotate the tire and count how many time the drive shaft turns per one full rotation of the tire...

3 1/4 rotations - 3.27
3 3/4 rotations - 3.73
4 1/10 rotations - 4.10

So on and so forth...

8t6gt · January 2nd, 2008, 11:25 PM

A little more than 3.08 I would think mine revs around 2500 and 70 MPH and thats like 120 kmh isnt it

White Thunder · January 2nd, 2008, 11:27 PM

120 kph is 74.57

30 19
50 31
60 37
80 50
100 62
120 75

1 mph = 1.609344

8t6gt · January 2nd, 2008, 11:29 PM

Thanks WT your a life saver

White Thunder · January 2nd, 2008, 11:33 PM

Find Out Your Gear Ratio - Brightcove

Iwannagofast · January 3rd, 2008, 02:48 AM

i have 2.76 gears and im doin around 83 mph at 2000 rpms according to the stock tach if that helps anything

nolife · January 3rd, 2008, 09:16 AM

Originally Posted by Iwannagofast

i have 2.76 gears and im doin around 83 mph at 2000 rpms according to the stock tach if that helps anything

My 91 has 2.73's. 1K rpm for every 40 mph. Nice for the long highway trips cruising at 2K going 80. Sucks for everything else though.

Iwannagofast · January 3rd, 2008, 10:53 AM

+1......everyone i tlk to is like i bet your car getts crappy gas mileage and then im just like actually i get about 27-28 on the highway and17-18 in town and they usually dont even believe me

tehdwarvenn · January 3rd, 2008, 06:27 PM

ok guys this is going to help much lol.. 3.73 gears, 4th gear at 2k rpm should be about 40 mph. test it out.

December 19th, 2007, 09:56 AM	#1
5.0_H.O Newbie Join Date: Oct 2006 Posts: 20	Do I Have 3.73 Gearing? i have an 87 gt with 225/55r16 on the rear and a T-5 trany, i was wondering if anyone knew wat gears my car has? at 120KM my stang revs at about 2300 RPMs. __________________ !987 Mustang Gt (Summer Car) - Ford Racing Headers, Flowmaster American Thunder Exhaust Without Cats, Flowmaster Hushpower 2 Mufflers, March Performace Ram Air Kit And Pullies, BBK Short Throw Shifter. 1997 Ford Taurus SHO (Winter Car)

December 19th, 2007, 10:09 AM	#2
ryans88gt MM Fanatic Join Date: May 2007 Location: Bloomington, IL Posts: 3,288	Maybe 3.55 gears? __________________ 89 LX 515 hp 497 ftlbs 88 GT 11.4 @ 118

December 19th, 2007, 10:52 AM	#3
Haggis13 Regular 1993 Mustang GT Join Date: Sep 2006 Location: Ottawa, Ontario, Canada Posts: 391	Probably a stock 3.08. __________________ Bart 93 Black on Black GT Kenne Bell S/C 3.73 Gears Tremec 3550 5 spd with Pro 5.0 Shifter BBK Catted X Pipe/2 Chamber Flowmasters

December 19th, 2007, 12:58 PM	#5
JONJON Regular 1988 Ford Mustang GT 8.372@82.8 1/8mile w/1.825 60' Join Date: Sep 2007 Location: Miami,FL Posts: 357	3.08 __________________ I never thought I would own a mustang!!!

January 2nd, 2008, 10:29 AM	#7
5.0_H.O Newbie Join Date: Oct 2006 Posts: 20	thanx for the help sorry i'm canadian my cars in km lol __________________ !987 Mustang Gt (Summer Car) - Ford Racing Headers, Flowmaster American Thunder Exhaust Without Cats, Flowmaster Hushpower 2 Mufflers, March Performace Ram Air Kit And Pullies, BBK Short Throw Shifter. 1997 Ford Taurus SHO (Winter Car)

January 2nd, 2008, 09:06 PM	#8
juggalowelder Newbie Join Date: Dec 2007 Posts: 18	It's relatively easy to find out another way. Mark the rear tire in a spot with chalk. Mark the driveshaft in a spot also. Start spinning the driveshaft. However many times you have to spin the driveshaft will give you your gear ratio. Unless you've owned the car from new, ya never know what gears are in the rear anymore.

January 2nd, 2008, 10:25 PM	#10
ChrisJ MM Ninjas! 2002 Mustang GT SLOW Join Date: Jun 2006 Location: Williamsburg, Virginia Posts: 14,711	Mark the drive shaft with chalk... Mark the bottom of the tire with chalk... Rotate the tire and count how many time the drive shaft turns per one full rotation of the tire... 3 1/4 rotations - 3.27 3 3/4 rotations - 3.73 4 1/10 rotations - 4.10 So on and so forth... __________________ My Junk www.myspace.com/cjobe

January 2nd, 2008, 11:27 PM	#12
White Thunder Hardcore Enthusiast 2005 skittle low 13's Join Date: Sep 2007 Location: roanoke va Posts: 2,043	120 kph is 74.57 30 19 50 31 60 37 80 50 100 62 120 75 1 mph = 1.609344 __________________ 2005 - one fast ass black skittle TURBO HO MILITARY CREW BM3

January 2nd, 2008, 11:33 PM	#14
White Thunder Hardcore Enthusiast 2005 skittle low 13's Join Date: Sep 2007 Location: roanoke va Posts: 2,043	Find Out Your Gear Ratio - Brightcove __________________ 2005 - one fast ass black skittle TURBO HO MILITARY CREW BM3

January 3rd, 2008, 02:48 AM	#15
Iwannagofast Hardcore Enthusiast 1990 Mustang GT 9.39@76.09----1/8th mile Join Date: Feb 2007 Location: Arkansas Posts: 1,767	i have 2.76 gears and im doin around 83 mph at 2000 rpms according to the stock tach if that helps anything

January 3rd, 2008, 10:53 AM	#17
Iwannagofast Hardcore Enthusiast 1990 Mustang GT 9.39@76.09----1/8th mile Join Date: Feb 2007 Location: Arkansas Posts: 1,767	+1......everyone i tlk to is like i bet your car getts crappy gas mileage and then im just like actually i get about 27-28 on the highway and17-18 in town and they usually dont even believe me

January 3rd, 2008, 06:27 PM	#18
tehdwarvenn Regular Join Date: May 2007 Location: Columbia SC Posts: 273	ok guys this is going to help much lol.. 3.73 gears, 4th gear at 2k rpm should be about 40 mph. test it out. __________________ 1993 Mustang GT, catless h-pipe, bbk shorties, 40 series flows, bbk rear suspension, edelbrock front suspension, AUTOLITES!!! =), k&n, underdrives, 3.73's

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