View Single Post
Old 05-18-2020, 05:08 PM   #96 (permalink)
JulianEdgar
Master EcoModder
 
Join Date: Nov 2017
Location: Australia
Posts: 496
Thanks: 36
Thanked 528 Times in 291 Posts
Quote:
Originally Posted by MeteorGray View Post
I made a throttle-stop in a few minutes using materials in my possibles bag: a rectangular piece of plywood, a 6-inch-long bolt and a couple of nuts and washers.

It works!

It allowed me to hold the throttle consistently open every time.

For starters, I adjusted the bolt so that the accelerator-to-floorboard gap was set at 3.4 inches. I was shooting for a speed of about 60mph. Since I tested the unit on an undulating road with gusty winds, the speed varied, in this case from about 50mph to 70mph. This is exactly what I would expect: the speed to vary depending on load since the accelerator setting did not change.

I casually observed the TPS screen on my Scangauge during the test, and it ranged from maybe 20% to 30%, depending on whether I was going uphill or downhill or with or against the wind. I think the TPS showed 11% idling. So, obviously the TPS values change with the load like you would expect a cruise control to do, but the actual power output of the engine is not changing like it would with cruise control.

Having said all that, what is the problem with using the throttle stop in my drive-by-wire car to test aerodynamics as described in the first post? Even with a drive-by-wire design, my throttle is not moving and on a level highway, I think the speed would remain constant for the tests just as it would with a cable-controlled throttle.

What am I missing?
It would seem to me that the power output of the engine would be changing if the throttle position changed. Just not enough to keep a constant speed with the change in load (ie hills, etc).

However, the best test is windows up / windows down on a long, flat road and compare top speeds.
__________________
Modifying the Aerodynamics of Your Road Car

A really good book that should be added to the library of everyone working in automotive aerodynamics, as well as those making car aero modifications at home. - Rob Palin, former Tesla aerodynamicist
  Reply With Quote