Changing gears in my 4T45-E....questions.

[gectek]

pulses per mile will stay the same as long as you stay with the same size tires i think, because the transmission internals that the output shaft sensor measures(the tone ring on the diff) still has 30 teeth, and itll still turn the same amount of of revs per rotation of the tire...

[sprucegagt]

y ru dividing by 1.12, it calculates the pulses as they are read right off the drive sproket which would be 32/33/35

Per the Parameter Description in Powrtuner:

"Defines the number of input speed sensor pulses as Input_Speed_Pulses_Per_Rev / KE_Drive_Sproket_Ratio."


As for pulses_per_mile I'm not sure if it uses the OSS or ISS for it's measurement. I agree it should be OSS. But I haven't done the math yet to confirm the stock spec of 25080. But double check that tooth number for the OSS sproket. I'm wondering if it's 31.

[gectek]

the way to calculate the ratio is driven over drive, but the stock measurement of 35 is the tooth count of the drive sprocket, so that is 1:1 ratio from the sprocket to the sensor...so it should be 32 for the 32 tooth drive gear, and 33 for the 33 drive gear. i thought it was 30, but i have a spare one, ill check tomorrow

and if the ring has 31 teeth then it would have to be revolutions in multiples of 10 in order to have a 0 as the end digit

[sprucegagt]

I'm only going by what Powrtuner says. It can be wrong, but the 32 and 33 tooth gear sets don't have a 1:1 drive set ratio.

[gectek]

no they dont, but the pulse is taken directly from the drive gear, so it should be a direct 1:1 no matter the gear ratio as long as you use the right sensor. but anyway, here is some info from the GM manual(whatever the heck it means wont know the actual count until i get the old ring i have)
4T40E
. .
. . 30 - Input Sensor . 24218077
. $22.82
Notes
. . Contact dealer for most current part and price information.
. .
. . 42 - Output Sensor . 24207507
. $22.58
Notes
.
. 4T45E
. .
. . 31 - Input Sensor . 10456546
. $21.85
Notes
. . Contact dealer for most current part and price information.
. .
. . 45 - Output Sensor . 24207507
. $22.58
Notes
and no they dont have 1:1 gear ratio, but the input gear has a 1:1 ratio to the sensor

[sprucegagt]

I get the feeling that the Calculated_Pulses_Per_Rev. table is really just a sanity check against the ISS sensor. If so then all of this may be for nothing. I take it you don't get any DTC's for ISS problems.

[gectek]

yah the transmission acts very funny...i tried it out, and you do get codes, namely p1870, and also it is 30 teeth on the reluctor wheel, i counted mine and double checked with GM on that one

the iss is there to logic check the oss to check for slippage, TC engagement and traction controls as well as monitor internal slippage and any parts just flying around inthere

[sprucegagt]

Here's what I've found about the Pulse_Per_Mile table off of the DHP forums. This sounds realistic and I'll try it out tonight, if I have time. It is V Day. Hopefully this will explain why the stock 25080 listing for pulses_per_mile reflects a stock tire diameter of 24.1" when the tire manufacturer spec'd diameter is 24.9".

For calculated pulses per mile, measure the actual roll0out of your tires with a piece of chalk and a tape measure. Mark the tire and a common point on the ground. Roll the car until the tire mark touches the ground again and mark the ground there, too. Now measure the distance b/t the two marks on the ground and THAT is your actual circumference taking tire pressure, tire depression and tread wear into consideration. Make sure the tires are inflated properly. Then do this, value T = roll-out (circumference) of the tire as measured:

CPPM = 63360 inches per mile / T inches * number of teeth on the VSS reluctor wheel. Using this method to find actual rollout and CPPM, I have stop watch tested my van over 10 mile stretches with the cc engaged and my calculated speed using the mile markers is less than .2mph from the observed speedo reading.

As for the Calculated_Pulses_Per_Rev table I found this:

calculated_pulses_per_revolution = InputSpeedSensorTeeth/DriveSprocketRatio

[mfuller]

Well, the gears, chain and Input Speed Sensor came in today. Already have the billet accumulator pistons.......now if the weather would warm up......

[gectek]

As for the Calculated_Pulses_Per_Rev table I found this:
calculated_pulses_per_revolution = InputSpeedSensorTeeth/DriveSprocketRatio

ok so the calculated pulses per rev would then be going from 35/35 1:1 ratio to the 32/38 1.1875ratio would be 32/1.1875 which is 26.947...if my car were running i would try that and see if that fixed a few probs but it isnt...so maybe someone else can try it

[sprucegagt]

Hopefully this will explain why the stock 25080 listing for pulses_per_mile reflects a stock tire diameter of 24.1" when the tire manufacturer spec'd diameter is 24.9".

Well to update my own post. I finally measured my tire circumference and found out that my tire diameter is 23.8". Considering I'm using tires that are slightly smaller than stock, I'd say the stock measurement is correct.

[1QUICKHATCH]

did you compleate this chain/gear swap? what are your results?

[gectek]

i ran it for a long time with a 3.91 and LSd from Ep. and a small stall (2700). all i do is burn the tires when i stop on it, either in 1st or downshifting at 40. it pulls sideways. this is normal street tires, some crappy wal mart specials. i think on anything sticky like a good summer tire, it would be more fun. im going with some rims that are 1" smaller than stock (15 instead of 16) and the same aspect ratio, but it will still be shorter, so im effectively giving myself more gear, somewhere to the tune of 4.xx. i also have BFG drag radials on them, and the only ones stickier than them are mickey thompsons. these will give good tread life, and will def get me below the 2.xx on my 60'. im hoping for a 1.9xx off the spray, and idk what to expect on it. to date with the gears, stock stall, and LSD with a poorly running engine, i ran a 2.2 best 60'. i may want to up my stall converter also, but that is prob later.

[mfuller]

Yes, I had the gears changed last fall. It took some trial and error with the PCM (threw incorrect gear ratio codes for a while), but it works well.
I still have some things to tweak in the tranny tables. First gear rips through so fast that I still bounce of the 6500rpm limiter if I'm at WOT. Otherwise, I'm pretty happy with it. Didn't really see a huge change in fuel mileage either.
I kept a stock-stall converter so as to retain driveability at low speeds, and I run on 17" street tires (needed to clear my 13" front brakes). I refuse to run DRs or slicks, so when all is said and done, that may still keep me from optimal launches.

[gectek]

Yah, i have to take my rev limiter to about 6800 to get anything out of it, i know the cam runs out of gas at 6200, but the gear helps out ALOT. my stall converter keeps stock drivability. i have no bad effects. i still keep 28+ on the mpg on the highway, in town i do good, if i can keep my foot out of it. its so fun to make the burn at the lights tho. esp when you take off like a freakin rocket, but i have had problems with the tuning a little bit, so sometimes itll hit the rev limiter at 7k+(stock gauge only goes that high lol) for a second or so until it goes into second gear.

mfuller, what do you have your gear ratio set as? 3.91 or 3.29. when i changed the gears in the 06 malibu, i went from a 3.69 to a 3.42. but i had to put the gear ratio at 3.05 because that is the differential i was using, and i noticed stock it had 3.29 instead of 3.69. when i put it to 3.42 like i though, it messed everything up. 3.05 is right on. its strange. i used HP tuners for that one though. i have tried to dial in trans settings with DHP PT, but its not as user friendly, and they use different tables from the comp for some reason. im going to try HPT when i get my grand am back up and running tho. and prob the DHP PT also. i like HPT trans tables better