Which gear for A4
This is a discussion on Which gear for A4 within the Dyno Information forums, part of the Racing Forums category; Which gear do you run while on the dyno? I've read 3rd everywhere, but the local shop ran mine in ...
08-09-2008, 02:48 PM #1
- Join Date
- Oct 2005
- Pocola, OK
- 2000 TA
Which gear for A4
Which gear do you run while on the dyno? I've read 3rd everywhere, but the local shop ran mine in 2nd. Will this affect the reading?
08-09-2008, 05:23 PM #2
08-09-2008, 07:23 PM #3
yeah, with 3.73's thats still like 125 mph of wheelspeed.
with a load on it, it might take a while to get up there.......forget about it with 2.73's
I would do second gear pulls. isnt second gear like 1.68:1
thats like inbetween 2 and 3 on a manual car
08-10-2008, 09:35 PM #4
Well yes and no. I have a A4 with 1st,2nd,D1 and D2. Put it in first and it stays in 1st same thing with 2nd gear. D1 the drive without the square goes into 3rd. D2 the drive with the square goes into 4th and the only way to get it in 4th. When you dyno just put it in D1 and run past 1st and 2nd gear. Once in 3rd and they are ready run it to redline.
08-11-2008, 02:50 PM #5
When Im on the Dyno, I put the car in 3rd let it shift until its in third but dont let it fall below 1400 rpm can cause it to drop down a gear so stay around 2000 rpm than make your pull. I know this is correct cause when I take my track times verses my dyno Hp and weight, my 1/4 mile slip match my dyno Hp numbers. Hope that made sense.
08-13-2008, 05:31 AM #6
I would think you would have to go into the tune and change the downshift characteristics of 3-2 before you make a pull.
Since you start the pull around 2,500 rpms or so in 3rd gear,,,the computer will still try to downshift to second at anything below 70 mph. My 4th gen does anyway. As a matter of fact, I've tinkered with the tune to make the downshift even more sensitive. So I would think I would have to go back in the tune and completely disable the 3-2 downshift before a dyno session.
I had this issue with my 70 formula on a chassis dyno,,,a 400 turbo car with 3.31 gears,,,it will do 85 mph in second gear,,,,and starting the dyno pull at 2,500 rpms in third would cause a downshift,,,,,,so I had to pull the plug on the downshift switch at the gas pedal to force the trans to stay in 3rd gear.
08-17-2008, 05:18 PM #7
Khaotic's methods must be right. He dyno'd my car at 328rwhp before I ran the 12.82 quarter mile. The calculations based on my race weight and ET put me around 330 rwhp.
08-17-2008, 05:22 PM #8
I say 373s are good!
08-17-2008, 06:19 PM #9
I think he needs to elaborate a little more,,,because every 4L60E out there will downshift automatically when the pedal is floored at only 2,000 rpms,,,and will not give you accurate numbers. You have to consider that 2,000 rpms in 3rd gear is only MAYBE 40 mph or so,,,,passing gear (second gear) is enabled in the tunes on these cars as high as 72-73 mph on a stock tune,,,,so even having rpm high enough to go 65 mph in 3rd gear wouldn't be enough....Thats probably closer to 3,000 rpms or so even.
As I mentioned,,,going into the tune to eliminate the downshifting in the trans functions is the only way on a computer controlled transmission such as a 4L60E.
Last edited by Firebirdjones; 08-17-2008 at 06:21 PM.
08-18-2008, 02:14 PM #10
You have 3 table that the computer looks at one is Part throttle shift those tables define the shift speed under NON - WOT, for normal and performance shifts. Then you have WIDE Open Throttle (WOT) shift RPM this table defines the RPM at which the Trans will shift under WOT condition it will orveride the MPH table for shifting thats why it wont down shift to 2nd
Last You have the WOT shift table for TPS % this is the threshold at which the transmission uses for (WOT) shifting and Again overides Mph shifting so it wont down shift, its totally looking at RPM and how you have it setup before it will shift.
08-18-2008, 05:54 PM #11
- Join Date
- Oct 2005
- Pocola, OK
- 2000 TA
will the dyno read any different on a 2nd gear pull versus a 3rd gear pull?
08-18-2008, 07:02 PM #12
Using the VCM Controls window in the HPTuner Scanner you can command a specific gear with an A4.
08-19-2008, 07:53 AM #13
This is a good question. The answers are important to understand, if you want to have consistent and meaningful test results to compare with other pulls.
First, I am assuming you are talking about a chassis dynamometer having both accurately documented roll inertia and an absorber equipped with a properly calibrated torque transducer. Secondly, I will assume that all your dyno's setup, calibration, inertial, and parasitic loss values have been correctly entered into its software. In such cases, the dyno will accurately display the delivered power - in either gear.
Warning: the key word in the previous sentence is "delivered" power! Even though a properly configured dynamometer can measure the supplied power precisely, this is only one component of the answer to your question. In most cases the vehicle's engine and drive-train will not supply the same power to the wheels in both gears.
Here are some of the most significant reasons for seeing differences in the delivered power:
1) Tire surface speed and temperature affect rolling losses and traction. In lower gears, slippage increases; while at higher speeds, parasitic losses rise exponentially. Consequently, the delivered power can change a bit unpredictably between gears.
2) The engine's air and fuel delivery system may not deliver the same AFR during rapid acceleration as it does under near steady state conditions. Intake runner wetting, acceleration fuel maps or carb squirters, heat soak, etc. are just some of the items that can significantly alter power output between pulls at significantly different acceleration rates. Turbocharged engines show even more extreme changes as a test's sweep rate is altered.
3) Higher-gear testing take longer to complete a run. Engines which are significantly power sensitive to internal or under-hood temperature variations will experience more power/temperature change during longer pulls in taller gears.
4) Transmission and rear-end drive-train losses vary with changes in the reduction ratios or the applied torque/speed. Again, this means the power applied to the dyno's rollers will be slightly different in each gear.
5) The accuracy of the user entered inertia values, for the engine's rotating components and those in the vehicle's drive-line, become more critical for lower gear testing. This is because the acceleration rates will be quicker, and therefore those components' inertial contribution to the calculated power increases. If you accelerate these items twice as fast, any error you make in estimating their inertia has twice the effect on the data.
The best way to sort all this out is to understand the above pit-falls and comparison test in both gears. Compare the results and you can more intelligently decide how much attention you want to give to mitigating any of the problem areas.
Tip: In most cases the higher gear testing delivers more accurate and consistent data.
08-19-2008, 01:56 PM #14
here's one from my car 2nd gear and 3rd gear both red lines
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