ALDL based accelerometer/dyno... - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-13-2007, 10:29 PM   #1
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Default ALDL based accelerometer/dyno...

Forgive me, just thinking out loud...

It strikes me that there is enough data in the ALDL data stream to compute the power output of the motor.

My physics memory is a little rusty, but given a known mass of the car, you should be able to compute power from just a capture of the data from a WOT pass through the gears. In other words, look at the dV/dt from frame to frame to get the acceleration of the vehicle. Use the mass of the vehicle to compute the force being used to accelerate it. You also have the engine rpm and transmission gear data..so you should be able to compute HP and torque at the crank.

About the only thing that cannot be accounted for is wheel slip if you spin the tires off the line.

Anybody tried this?
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Old 03-13-2007, 10:44 PM   #2
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No but you have me intrigued... Very interesting...

I saw the tool you were using on the car... I have that one also..

But I also have the CP9110... The one thing I like about the 9110 is that it will do a capture... I forget if it will record for 15 or 30 seconds at a shot... It will record all parameters for that length of time .. Would that give you the data you are loking for to be able to do the equations..

Other than this I am not much help here.. Math was never really a strong point

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Old 03-14-2007, 11:00 AM   #3
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I'm going to try a new one out later this week,

Pickup up a Moates ALDL to USB converter. Going to try out some of the PC based scanner tools to see if they will do a reasonable job reading the data stream. I like using the hand-held scanner tool, but the capture is non-existant on it..(Well, it'* as good as my ability to jot numbers down on paper and pad.)

With a ALDL to PC cable, I can record the frames to the laptop and write some conversion software for it to compute power output. (I think, I've got to crack open the old textbooks to refresh my memory... The basic F=MA is pretty easy...it'* converting all the units..I think.
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Old 03-14-2007, 11:15 AM   #4
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the new MSD dashhawk does this, but it only works with 05/06 and newer cars..
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Old 03-14-2007, 11:43 AM   #5
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I have done this with the Jetta. If you can log speed, RPM and, time stamp, I have a spreadsheet you should be able to adapt.

It is actually easy to do if you can get the data. You know mass and speed so you can calculate kinetic energy. Using the time stamp to determine the time between speed readings you can calculate the change in kinetic energy over time. (Hp) With Hp and RPM you can calculate torque.

The Spread sheet can be found here:
http://forums.audiworld.com/vag/msgs/457.phtml
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Old 03-14-2007, 12:17 PM   #6
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Cool, I took a look at the calculations behind the spreadsheet cells.

Don't really care about the absolute accuracy of the numbers it generates..I'm more interested in using this for comparison purposes on the same vehicle after each change is made.
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Old 03-20-2007, 10:34 AM   #7
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Ok, got through the first step this morning. Went up to the local truck stop and got the car weighed:



Gross weight of 3760lbs with a full load of fuel, me, and roughly 75 lbs of gear (tonight I have to unload the car and weight all my gear to get down to the base weight of the car. Fuel is pretty easy to back out at 6lbs per gallon (81 lbs for the 13.5gallons usable)

That gives me a rough empty weight of 3379lbs (for the moment, I can refine that after weighing everything removable from the car.
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Old 03-20-2007, 01:59 PM   #8
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Curt what is the GVWR on the door? Would be interesting to see the differences..



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Old 03-20-2007, 05:10 PM   #9
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Quote:
Originally Posted by jr's3800
Curt what is the GVWR on the door? Would be interesting to see the differences..

GVWR from the door sticker is 4434 lb. Useful load from the tire pressure tag on the door frame is 1067 lb. Subtract it from the GVWR number and you get 3367lbs...pretty darn close to the empty weight I calculated from the actual weight of the car less fuel, gear and me.

So, I guess if all you have is the door stickers, take GVWR, subtract the Useful load number to get the empty weight of the car, then add the weight of driver, cargo, and fuel to get the weight of the car at any given time.
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Old 03-20-2007, 05:23 PM   #10
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Quote:
Originally Posted by toastedoats
the new MSD dashhawk does this, but it only works with 05/06 and newer cars..
Not ALL 05/06. Only CAN bus enabled vehicles. Bonnevilles, even in 05 don't have CAN.
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