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Discussion Starter · #1 ·
OK, so I pick up a Droid X yesterday, then I remember all the cool threads about phone-based dyno software (software that uses the built-in accelerometer to measure acceleration and g-forces, etc.).

So naturally download one (dinodyno in this case).

To get all the results (derived horsepower and torque, etc.), I need to enter some info, including:

Weight, frontal area, coefficient of drag, and drivetrain loss.

I think I've found a good number for weight (from someone with the same model, and same weight as me): 3,571 pounds (sounds reasonable).

I found a couple numbers for coefficient of drag, between 0.29 and 0.31.

Anyone out there have the "accepted numbers" for the 330i (preferably ZHP)?
 

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OK, so I pick up a Droid X yesterday, then I remember all the cool threads about phone-based dyno software (software that uses the built-in accelerometer to measure acceleration and g-forces, etc.).

So naturally download one (dinodyno in this case).

To get all the results (derived horsepower and torque, etc.), I need to enter some info, including:

Weight, frontal area, coefficient of drag, and drivetrain loss.

I think I've found a good number for weight (from someone with the same model, and same weight as me): 3,571 pounds (sounds reasonable).

I found a couple numbers for coefficient of drag, between 0.29 and 0.31.

Anyone out there have the "accepted numbers" for the 330i (preferably ZHP)?
The curb weight listed by most sources for the manual 330i zhp is 3285lbs and the Cd is 0.31. I am not sure about the frontal area, but I am sure that you could roughly calculate it using only two planes. Probably around 20 sq ft. I would use between 13% and 15% drivetrain loss.
 

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Discussion Starter · #3 · (Edited)
The curb weight listed by most sources for the manual 330i zhp is 3285lbs and the Cd is 0.31. I am not sure about the frontal area, but I am sure that you could roughly calculate it using only two planes. Probably around 20 sq ft. I would use between 13% and 15% drivetrain loss.
I think you're right on the weight - but the program is looking for "as-run weight", so my previous guesstimate includes a tank of gas and my 155 pound self (which makes the two numbers look pretty close).

The frontal area on the car has to be more than 20 sq. ft. though... (maybe you're factoring in coefficient of drag?).

On the drivetrain losses... that seems to be as good a place to start as any, I suppose... I guess I could peruse some "real dyno threads" and compare the measured HP with the theoretical HP for that model (which would force me to assume that the cars were in good tune, and that's always dangerous).
 

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Discussion Starter · #5 ·
I found a website that listed the frontal area of a 2000 E46 330i as 2.09 sq. meters, which sounds a whole lot like DangerousMind's number (converted to metric, of course). Still seems awfully low, somehow...
 

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I found a website that listed the frontal area of a 2000 E46 330i as 2.09 sq. meters, which sounds a whole lot like DangerousMind's number (converted to metric, of course). Still seems awfully low, somehow...
I just did a very simple calc using the dimensions listed for the e46 53.9"h x 69.2"w), an estimated ground clearance of 6", and a 6 inch taper on each side of the top over 24" 53.9" = 4.491' tall. 69.2" = 5.766' wide. Take the 0.5 feet away for ground clearance = 5.266' wide. 4.491 x 5.266 = 23.649'^2 You then take away the area of the taper. 6" = .5' x 2' = 1. 1 x 2 = 2'^2. 23.649 - 2 = 21.649 sq ft

Please know that those were Very rough calculations and the mirrors and tires would be ~ 1- 1.5 sq ft of additional frontal area, so maybe 22.5-23 sq ft.

My car calculated to a 14.5% drivetrain loss assuming 230 crank hp on a 330ci with Dinan Cai and Software.

I am curious as to how accurate your app will be.
 

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The AutoEnginuity "speed tracer" application has a default of 20 sq ft for the frontal area for a 330i, drag coefficient of 32.
 

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Discussion Starter · #8 ·
Thanks for the input. I have no idea how accurate this app will be. One thing I did notice is that on my particular Droid phone, I have to hold it at about 30 degrees from flat to get the accelerometer zero'd out. The dinodyno instructions tell you to lay the phone flat, but also that the accelerometer should be reading zero in both planes. I'm not sure whether the phone I have (Droid X) has a "feature" that cants the accelerometer a little to make it easier to read/use, or whether something's wrong with it. I have a car mount on the way for it, so I should be able to get the phone aligned any way I need to...

Unfortunately, I don't have a baseline quarter mile time (or dyno data) for my car. Either would certainly make it easier to check the results.
 
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