I thought I had 3.73's... maybe I don't?

colemanitis

Member

Apr 1, 2003

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16

Panama City, FL

Oct 7, 2004

#1

• Oct 7, 2004

• #1

I went out yesterday to confirm my gear ratio using my new C2 tach and one of those signs along the road that tells you how fast you're driving. I don't have a speedo right now, it's at Brother's Performance being calibrated for my new 140mph face. Anyway, I was told my car has 3.73's, but after running the numbers it seems as though I may have 4.10's. Here's the results from yesterday's test:

Here's the gear ration calculator I used: http://www.corral.net/tech/gearcalc.html

2nd gear: 30mph: 3,000rpm: 4.096 gear ratio
3rd gear: 38mph: 2,500rpm: 4.032 gear ratio
4th gear: 50mph: 2,500rpm: 3.952 gear ratio

What do you guys think? Do I have 4.10's, or should I jack up the car and count the driveshaft revolutions to be sure?

 

Look Its Aaron

Your car looks like it came straight from Mexico.

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Nov 18, 2001

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Fontana, Cali

Oct 7, 2004

#2

• Oct 7, 2004

• #2

colemanitis said:

or should I jack up the car and count the driveshaft revolutions to be sure?

Click to expand...

Should have just done that in the first place. Would have saved you a lot of time...

 

PhLoBuS

New Member

Aug 15, 2004

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Beverly, MA

Oct 7, 2004

#3

• Oct 7, 2004

• #3

sounds like 4.10s

 

colemanitis

Member

Apr 1, 2003

145

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16

Panama City, FL

Oct 7, 2004

#4

• Oct 7, 2004

• #4

 

colemanitis

Member

Apr 1, 2003

145

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16

Panama City, FL

Oct 7, 2004

#5

• Oct 7, 2004

• #5

Look Its Aaron said:

Should have just done that in the first place. Would have saved you a lot of time...

Click to expand...

My floor jack is broken... that's why I used the calculator first. I guess it's time to buy a new one.

 

Michael Yount

Mustang Master

Apr 10, 2002

9,039

6

79

Charlotte, NC

Oct 7, 2004

#6

• Oct 7, 2004

• #6

Counting revolutions is the only way to be certain. Tachs and speedos aren't always accurate, tire sizes may be changed, and ID tags/serial number disemination fails if the rear end has been swapped, or the gears changed. Counting shaft revs to tire revs always works though.

 

colemanitis

Member

Apr 1, 2003

145

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16

Panama City, FL

Oct 7, 2004

#7

• Oct 7, 2004

• #7

I'm gonna borrow a floor jack from a friend after work today. I guess I'll jack it up from the rear differential. Do I need to put anything in front of the front tires... will the car try to roll forward when I jack the rear up?

 

Michael Yount

Mustang Master

Apr 10, 2002

9,039

6

79

Charlotte, NC

Oct 7, 2004

#8

• Oct 7, 2004

• #8

ALWAYS chock in front of and behind the tires that are on the ground; ALWAYS use jack stands before you crawl under something that's heavier than you mind falling on you (one end of a car qualifies for most people). Mark/count carefully. The difference between 3.55's and 3.73's or 3.73's and 4.10's is only about a 1/4 of a driveshaft turn.

 

cevtv

Founding Member

Sep 15, 2002

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Massachusetts

Oct 7, 2004

#9

• Oct 7, 2004

• #9

colemanitis said:

I went out yesterday to confirm my gear ratio using my new C2 tach and one of those signs along the road that tells you how fast you're driving. I don't have a speedo right now, it's at Brother's Performance being calibrated for my new 140mph face. Anyway, I was told my car has 3.73's, but after running the numbers it seems as though I may have 4.10's. Here's the results from yesterday's test:

Here's the gear ration calculator I used: http://www.corral.net/tech/gearcalc.html

2nd gear: 30mph: 3,000rpm: 4.096 gear ratio
3rd gear: 38mph: 2,500rpm: 4.032 gear ratio
4th gear: 50mph: 2,500rpm: 3.952 gear ratio

What do you guys think? Do I have 4.10's, or should I jack up the car and count the driveshaft revolutions to be sure?

Click to expand...

Aren't you running 245/60/15 tires? If so, they are about 1 inch taller than the stock tires, and that will effectively change the gearing......






.

 

colemanitis

Member

Apr 1, 2003

145

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16

Panama City, FL

Oct 7, 2004

#10

• Oct 7, 2004

• #10

cevtv said:

Aren't you running 245/60/15 tires? If so, they are about 1 inch taller than the stock tires, and that will effectively change the gearing......

Click to expand...

Yes, i'm running 245/60/15's. I entered this into the gear ratio calculator.

 

cevtv

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Sep 15, 2002

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Massachusetts

Oct 7, 2004

#11

• Oct 7, 2004

• #11

colemanitis said:

Yes, i'm running 245/60/15's. I entered this into the gear ratio calculator.

Click to expand...

Ooops - I should have looked at the calculator brfoe I posted.......

 

Michael Yount

Mustang Master

Apr 10, 2002

9,039

6

79

Charlotte, NC

Oct 7, 2004

#12

• Oct 7, 2004

• #12

25.7" stock vs. 26.5" for the 245/60/15 - only about a 3% difference. That tire would make 4.10's act like a 3.98 gear; 3.73's act like 3.62's.

 

colemanitis

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Apr 1, 2003

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16

Panama City, FL

Oct 7, 2004

#13

• Oct 7, 2004

• #13

UPDATE: They're definitely 3.73's. I jacked up the rear and spun the tires. The driveshaft spun exactly 3 3/4 turns. Thanks everyone for the help and advice!