My Speedo is off my 15 mph @ 60mph. At 60 mph it reads 75mph. The pcm is tuned for 4/11 gears. Anyone got a rough guess as to what gears i would have in my car.

 

Sounds like you have a taller gear than what you are programmed for. Are you sure that you are programmed for a 4.11 gear? And not say running a 4.11 gear but programed for a 3.23 or 3.73?

 

I bought the PCM off a guy on this site and he said it was tuned to run on a 4/11 I know for sure that im running a higher gear i was just dont know how much higher. I have never had the rear diff apart and a lot of things were done to the car when i got it. I just didn't want to pull the diff cover just to count the gears.

 

My reasoning for that statement was how much higher than 4.11 did he go??? I had a 5 mph difference when mine was tuned for a 3.23 and i had 2.73.

 

I see what you are saying, im just going by what the guy said the PCM was tuned for. I really dont think i have lower than a 4/11 in my car. Maybe he didn't have the PCM programmed for 4/11's and just thought he did. I guess the only way to know for sure is to bust it open and take a look. Just trying to be lazy.

speedo reads 60 actual speed 45. There is no way in running lower than 4/11's i have had the car up to 150. Maybe he was wrong about what it is programmed for or maybe that explains why i can destroy a set of street tires in 1st and second with an automatic.

 

I went for a little drive during lunch and wrote down some numbers. At 60 real mph i am turning 2600RPM in OD and 3100RPM in Drive. At 45 MPH i am turning 2000RPM in OD and 3000RPM in D. Does that help any. I have never owned or driven a camaro with an Auto until this one so i dont know where the stock RPM's would be. I do know that if i jump on the interstate in Drive it sounds like it is revving pretty high.

Looks like i will be getting dirty this weekend cause i have to know for sure. Any guesses on what gear it might be.

 

Judging from the #'s in your last post - I would guess you have 3:73's

 

Sounds like 3.23's . Well, going by your first couple posts, where 60 = 75, and 45 = 60 ...

60 x 4.11/3.23 = 76.3
45 x 4.11/3.23 = 57.2

Going by your last post, giving RPM's per speed ... that looks WAY off of anything?!?!

Anyway, to find out for sure WITHOUT GETTING TOO DIRTY, just jack up the back, and spin the wheels and/or driveshaft, and count how many turns of the driveshaft it takes to turn the wheels 1 revolution. If it's "around" ~3-1/4, you've got 3.23's, ~3-1/2, then 3.42's, or ~3-3/4, then 3.73's . OR, if it turns just over 4 full turns, then you've really got 4.11's!!

 

I am tired of wondering what the hells back there. If the speedometer says im doing 60 but im really doing 45 and the pcm is tuned for 4/11's that would mean i have a lower geared rearend like 4/56. I am sure im not geared that low. But i do know how to find out. I appreciate the help.

by the way what was the formula that you were using and where did you get the numbers you used to divide by? Those are pretty close because runnibg 60 MPH my speedometer reads pretty close to that.

 

I'm just doing basic mathematics, using the gear ratios in question .

What I'd like to know, is what are you using to verify your TRUE speed, vs. displayed speed? (pacing another car? GPS?)

 

okay i jacked the car up and put a piece of tape on a tire with a reference point on the body. From laying underneath the car i can spin the tire 1 complete turn and the drive shaft shaft turns a little over 3.75 revolutions. to get 4 complete revolutions from the drive shaft i have to go about 1 hour past a full turn on the wheel. it looks like more than 3:73 but les than 4:11 if im doing this right.

 

How about try turning the driveshaft, and watch the line on the tire come around ... may be a little more "accurate"? Does sound like you've got 3.73's though ... which makes sense, if you got the car with gears already installed, since MOST people switch to 3.73's when they put gears behind an A4 .

 

yeah, i think im gonna go with 3:73's that is close enough for me. thanks for all the help. i dont think i can get any closer without pullin the cover and counting.

 

what size tires are you running on the rear? if you know the tire diameter .. (which can be figured out through the tire size,) and the correct mph the car is running at whatever rpm in overdrive, you can use math to figure it out.

mph = ((tire dia * rpm)/(vor * 336))

vor is the vehicle overall ratio (trans x rear end) since the a4 has .7 in od, you can replace vor with .7x (x being the rear end ratio in question)

this math formula sure beats jacking up the car and counting revolutions