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Old 01-02-2021, 11:18 AM   #9 (permalink)
Aero Wannabe
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Join Date: Dec 2007
Location: NW Colo
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TDi - '04 VW Golf
90 day: 51.96 mpg (US)
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Originally Posted by JulianEdgar View Post
I just want to confirm the approach you took.

1. Work out throttle position that holds car at chosen test speed.

2. Enter test section at that speed and then hold foot constant at that previously determined throttle position (as confirmed by whatever factor you're looking at on scangauge).

3. Wait until speed settles - might be 1km or more. Need to read speed to a resolution of at least 1 per cent.

4. Repeat with windows open, using exactly the same steps 1-3 above.

Is that how you did it?
Not exactly. My test was done hastily and under less than optimal conditions. It is cold and snowy here at this time of year. I was going from memory and I forgot I needed to do this over a level kilometer or more. I did not have a test section of over 1 kilometer without a slight change in grade.

That said, I found it difficult to hold a steady GPH reading even with my my foot jammed as hard as I could against the “trans tunnel”. I was hoping for a quick go/no go test system. If I need a long, level test track I think I will go back to setting the cruise control, leaving the car idling between runs while I make mods to hold the cruise setting in the car computer, and using the ScanGuage reset to current mpg to measure the change in aero drag.

I do want to try Throttle Stop testing on a ‘90 minivan I have as it is pre OBD, good old fashioned cable throttle and no cruise control. That will have to wait till spring as I do not have snow tires on it and it is parked for the winter.
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun

Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.

Last edited by COcyclist; 01-03-2021 at 10:25 AM..
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