Random Question
Random Question Didn't quite know where to post this, maybe gearing would have been a better forum, but I guarentee it'll get more attention in this one...anyways.....I was reading a thread the other day where some guy was asking how to tell what kind of gearing he had in his rear-end. I believe it was Super Mario who said that at 89mph a 3.42 car should read exactly 2000rpm in 6th gear. Well I tried that out today for ***** and giggles and my tach hit 2000rpm at 77mph in 6th gear. WTF?? So either its three things.
1) Super Mario (or whoever it was) was wrong
2) My tach is messed up (it does read 1100rpm at idle, so that could be a possibility)
3) Or somehow, someway my car had a different gear ratio put in it. I bought it used with 40K on it two years ago, and it was bone stock (as far as I can see at least)
Whattya guys think??
1) Super Mario (or whoever it was) was wrong
2) My tach is messed up (it does read 1100rpm at idle, so that could be a possibility)
3) Or somehow, someway my car had a different gear ratio put in it. I bought it used with 40K on it two years ago, and it was bone stock (as far as I can see at least)
Whattya guys think??
I'm guessing my tach might just be off. When my car is idleing it sounds absolutely fine, as if anything lower and it would be sputtering. How in the world could my tach be off by like 500RPM though?? and is there anyway to tell besides hooking A-TAP on to the car? That would be damn cool though if I had 4.10s and didn't even freakin' know it 
TECH Senior Member
Joined: Nov 2001
Posts: 9,246
Likes: 3
From: Troy, AL
Any diagnostic scanner will tell the tale. You could go to the dealership and hook it up to a Tech II.
Or, you could do this. Pick the rearend off the ground. Put a mark on the driveshaft and a mark on a tire. With the tranny in N, turn the tire exactly one revolution (make sure both tires turn the same direction.) If you have 4.10 gears then the driveshaft should turn 4.1 times for every turn of the tire. If it's 3.42s then it should turn 3.42 times for every turn of the tire. Etc...
Or, you could do this. Pick the rearend off the ground. Put a mark on the driveshaft and a mark on a tire. With the tranny in N, turn the tire exactly one revolution (make sure both tires turn the same direction.) If you have 4.10 gears then the driveshaft should turn 4.1 times for every turn of the tire. If it's 3.42s then it should turn 3.42 times for every turn of the tire. Etc...
I dunno, It must be a tach issue. The fact that it reads 1100rpm at idle and the fact that I actually get a little bit of traction when punching it in first gear would clue me in to that. As much as I'd like to think that somehow 4.10 gears made its way into that car. I just can't imagine what would cause the tach to be off by that much. Oh well....time to go and find a diagnostic tool now.
Just pick the rear end off the ground and do what the colonel said ... far easier then finding a tool ...
SuperMario was perfectly correct btw ... 2000rpms with stock gearing = 89mph
With 4.10's ... 2000 rpms = 74 mph
(granted you have stock tire size)
SuperMario was perfectly correct btw ... 2000rpms with stock gearing = 89mph
With 4.10's ... 2000 rpms = 74 mph
(granted you have stock tire size)
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Originally Posted by ta12sec
at 75 mph in 4th gear (6 speed) your tach should display your rear end ratio (or very vey close to it) mine reads like 3300, I have stock 342s