Finding current gear ratio?

rdharper02

like kicking myself in the junk

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May 8, 2006

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May 16, 2010

#1

• May 16, 2010

• #1

Anyone know a way to determine gear ratio without pulling the diff cover? I finally put some milage on the car and found the speedo to be off (much like the speedo gear for my 3:55s). I suspected as much, because someone put some money into superior axles and a trick flow diff cover.

 

trinity_gt

10 Year Member

Jan 31, 2003

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May 16, 2010

#2

• May 16, 2010

• #2

Jack the rear of the car up and support it on jackstands. Mark the driveshaft with a piece of chalk. Put the trans in neutral.

Rotate (or have a buddy do it) the rear wheels 10 times and count the number of times the driveshaft turns.

If it turns nearly 33 times, you're 3.27:1 If it turns 35-1/2 times, 3.55:1. ~37 times is 3.73:1 and 41 times is 4.10.

If the speedo is off, you can also do some math. Find a car with an accurate speedo. Follow him at, say, 70MPH and note your own speedo reading. Assuming your speedo is calibrated for 3.27s, the error in the speed reading can be used as a multiplier to get the error in the gear ratio. For instance, if your speedo read 80 while the car was ding 70 (as indicated by the other guy's speedo reading 70), then your error is 80/70 or ~1.14. Take the stock 3.27 gear that the speedo is calibrated for and multiply by 1.14 to get the rear gear. In this case, 3.27x1.14 is ~3.727 giving a rear gear of 3.73:1.

EDIT: FWIW, if you're talking about the 97 then 3.27 may not be the applicable gear ratio to start with...

 

rdharper02

like kicking myself in the junk

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May 17, 2010

#3

• May 17, 2010

• #3

I am talking about the 97. Right on, I'll let you know what I get.

 

Maxpowers

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Sep 9, 2009

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Pittsburgh, Pa

May 17, 2010

#4

• May 17, 2010

• #4

rdharper02 said:

Anyone know a way to determine gear ratio without pulling the diff cover? I finally put some milage on the car and found the speedo to be off (much like the speedo gear for my 3:55s). I suspected as much, because someone put some money into superior axles and a trick flow diff cover.

Click to expand...

I assume the previous owner didn't tell you or didn't know?

What size tires are on the car? Could be as simple as different tires sending the speedo off.

 

patman0911

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Jun 5, 2002

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May 17, 2010

#5

• May 17, 2010

• #5

2.73:1 are a possibility for a '97 also.

Just jack it up and count per Trinity's directions, that's the simplest and most accurate way to figure it out short of pulling the cover off and actually counting teeth on the ring and pinion gears.

What size are the tires? If they're close to the overall stock diameter, ~25.5", then they'll only make a couple of percent difference in speedo error at most anyway but if they're significantly taller then you'll need to factor them into any correction you make.

 

rispoli_23

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Jul 7, 2008

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May 17, 2010

#6

• May 17, 2010

• #6

if u have a sct tuner u can go in there and change the gears to diff choices and find someone to drive along with u till u get it right ... just a shot bro

 

rdharper02

like kicking myself in the junk

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May 18, 2010

#7

• May 18, 2010

• #7

Didnt get a chance to get under it yet, and the way its looking it will have to wait until tomorrow.

To answer your question, no the previous owner really didnt know anything about it. He blew it up (maf injector mixed) and I felt the need to save it. Actually a hell of alot of fun, now that she's running, because everyday I find some new part. Its like an easter egg hunt. Do have to say that someone put some love and time into her.

 

rdharper02

like kicking myself in the junk

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May 19, 2010

#8

• May 19, 2010

• #8

Trinity,
thanks for the help. Went through it today (twice) and found out I have 3.73s. I was really hoping for 3.55, but at least its not another set of 4.10s. Thanks again.

For the rest of the guys with input, definitely appreciate the support.

 

trinity_gt

10 Year Member

Jan 31, 2003

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May 19, 2010

#9

• May 19, 2010

• #9

3.73 is a good ratio. I've got that in mine and love 'em.

 

J

Jagerbeast

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Mar 7, 2010

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Virginia

May 20, 2010

#10

• May 20, 2010

• #10

Just curious what your beef is with 4.10's? I'm looking at getting gears installed in the next month or so and am not 100% what to go with yet.

rdharper02 said:

Trinity,
thanks for the help. Went through it today (twice) and found out I have 3.73s. I was really hoping for 3.55, but at least its not another set of 4.10s. Thanks again.

For the rest of the guys with input, definitely appreciate the support.

Click to expand...

 

rdharper02

like kicking myself in the junk

10 Year Member

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May 21, 2010

#11

• May 21, 2010

• #11

4.10s can be an absolute blast on a NA car. I personally dont do a ton of track time and like to drive to local events. It tends to be one of those trade off scenarios where the car feels wicked fast (and may actually be) but overall driveability suffers from high cruising RPM and fuel consumption. I'm a big fan of the 3.55s in my 93 (even before the turbo), but am definitely starting to warm up to the 3.73s in my 97. Then again, the 4.6 in the 97 seems to enjoy the RPMs a bit more and I am new to the 2V scene.

Best recommendation I can give you is to shoot a post and talk with the guys running your potential gear. Dont forget to mention your tire/rim combo and your future intentions (NA, Turbo, diffrent tire setup..). The best thing about these sight is the experience. Guys readily share whats worked and what hasnt.