CAUTION: throttle-stop testing

[JulianEdgar]

I was just going to post a detailed discussion of throttle stop testing (especially versus other amateur testing techniques for drag) but I just watched this video for the first time since I made it 9 months ago.

https://www.youtube.com/watch?v=tVAokIdaXm0

It the longest I have done but it covers quite clearly:

- how throttle stop testing is done

- what its advantages and disadvantages are

- and gives examples of its use with aerodynamic changes that are going to give clear changes in drag (eg ride height, windows up /down, wing in air brake position).

Very obviously Aerohead either never watched the video, didn't understand it, or watched it and forgot its contents. (And that's OK, but you'd think he'd ask for details of the testing if he didn't get it.)

The other video that is germane is this one, which includes reverting to standard aero configuration no less than three times during the test session to ensure the results in this form were consistent.

This video also shows the step-by-step of the development of the Edgarwit external air curtains' position and their tuning. (And I must have been enthusiastic. I did a lot of testing in the one session!)

Note that the 8 per cent reduction in drag with the Edgarwits was only in dead-calm conditions. It was about 4-5 per cent in windier conditions (and again, note that the throttle stop testing shows this degree of variation).

https://www.youtube.com/watch?v=I4O2Bp2RnoA

[aerohead]

Having reviewed the video of the throttle-stop testing, I've spent, since Wednesday, going over my archive, looking at official SAE, MIRA, and EPA road test protocols. References are ( and yes. they are all dated ) :
* Internal Combustion Engines and Air Pollution, Professor Edward E. Obert, Harper & Row Publishers, 1973.
* Automotive Fuel Economy, Progress in Technology Series, Number 15 & 18, Selected SAE Papers, 1965-1979, Volumes 1 & 2, SAE, 1976, 1979:
1) SAE Paper 770844
2) SAE Paper 780346
3) SAE Paper 760187
4) SAE Paper 730790
5) SAE Paper 740969
6) SAE Paper 740594
7) SAE Paper 750956
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8) SAE J-1082, ' Fuel Economy Measurement - Road Test Procedure '
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9) SAE Paper 830384

[aerohead]

The following are gleaned from the aforementioned literature:
1) Pre-testing requires approximately 30-miles @ 50-mph,thermal ambient condition equilibrium stabilization for:
* Tire temperature-related R-R variability
* Temperature / viscosity - related hydrodynamic tribological mpg- variability to guaranty repeatability.
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2) constant grade test course ( coast-up / coast-down ) prevention
3) wind less than 15-km/h ( 9.3- mph )
4) peak wind speed less than 20-km/h ( 12.4-mph )
5) continuous data-logging of :
- ambient temperature
- barometric pressure
- relative humidity
- road temperature
6) Reid Vapor Pressure ( RVP ) of fuel
7) Distillation temperature of fuel
8) No accessories allowed ( HVAC or Blower fan ) [alternator loading]
9) Recommended 68-F through 86-F ambient temperature window
10) 1/10th-gallon, graduated Burette fuel supply
11) Fuel mass, thermal - expansion compensation factoring
12) Instantaneous fuel rate by mass
13) Ambient, environmental, axial and crosswind aerodynamic loading
14) Uniform pavement surface
15) Straight course
16) Dry course

[aerohead]

From Donald L. Stivender, Engine Research Department, General Motors Research Laboratory, General Motors Corp, SAE Paper 780346
1) At a given constant throttle, essentially constant airflow is experienced.
2) At any given constant throttle position, the engine will exhibit a parametric BSFC ' fishhook', based upon F/A ratio ( oxygen balance ).
3) Engine torque = BMEP
4) Mechanical efficiency = BSFC
5) BSFC is inversely proportional to thermal efficiency
6) Optimum torque occurs @ ' Minimum Best Torque' - Spark Timing
7) BMEP is highly dependent upon A/F ratio
8) Minimum BSFC is defined by all throttle settings tangent to the throttle-stop fishhook
9) Fuel consumption- load characteristics generally apply at all engine rpm
10) Torque - A/F - efficiency, are all interrelated characteristics ( BMEP - BSFC - A/F )
11) Maximum torque occurs @ approx. A/F = 13:1 ( 'best power mixture' )
12) BMEP decreases with fuel flow at throttle - stop, torque per unit fuel increases to a maximum as fuel flow is reduced ( A/F = 18:1 )
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13) Throttle position is the only link between engine operation and the CPU
14) Any change in road load is unrecognized by the CPU, as it's 'eyes' have been removed, via the Vernier Rheostat in the throttle position sensor fixed position.
15 The CPU cannot detect 'driver intent'.
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16 Reduction in Road Load Horsepower forces the engine to shift it's BSFC map island, to that of a higher BSFC island, as friction effects now represent a larger fraction, increasing overall pumping losses.
17) A/F ratio experiences an excursion, taking BSFC with it, for overall lower mpg.
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18) Aerodynamic drag reduction will precipitate the excursion, unless the original engine-map load is maintained ( gear-matching ).
19) Failure to maintain original engine load is the setup for the 'influence factors' reported by Gino Sovran, introducing 'hidden' losses within the vehicle's internal fuel management system. It's flying blind.
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20) Any mpg attribution to an add-on aerodynamic appliance cannot be completely valid, by default.
Causality is indeterminant .
21) An 'observed' mpg improvement of say 0.6-mpg could actually be 1.0-mpg, only if the gear-matching is accomplished.
I've experienced this as a first-order-reality experience with 'Spirit.'
The highest mpgs ever returned were with 'rubber gearing', which reduced revolutions per mile, from 766, to 698. A $ 290 exercise.
A 'sixth-gear' would no doubt have helped even more. They don't make those.
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I like the throttle-stop testing technique!
It covers so many of the published variables that, I'd be surprised if it didn't indicate aerodynamic trends.
As to the degree of precision we can expect, with respect to quantifying the actual aerodynamic performance of any given modification, Julian has already adequately addressed that issue.
The information I've presented is just to add some seasoning to a fairly tasty recipe.

[JulianEdgar]

Originally Posted by aerohead

The information I've presented is just to add some seasoning to a fairly tasty recipe.

No, as always, the information you've added a mish-mash of irrelevancies, misunderstandings, confusion and weird theories.

In addition, again as always, you are quoting material that shows you have a poor / zero understanding of the topic. There are so many mistakes in what you have written that it would be far easier to pick out the one or two correct points than address all the errors.

I must remember to take a copy of some of these posts so I can use them in a book one day about how much rubbish is disseminated on automotive discussion groups. But to be honest, I don't think readers would believe me. (I'll just use "Maximum torque occurs @ approx. A/F = 13:1" - that will cause anyone who has ever done any dyno tuning to just fall over laughing.)

If you want to write about engine management, I suggest that you actually learn something about the subject first. This will help you, it starts at the very basics and then goes right through to Bosch Motronic, etc. (The version that's just been published in Korean on the left.)

[aerohead]

Nice reward for dedicating the last two days of my time off to your thread.
If you'd like to parse out your points of contention, we're all ears ( eyes ).
I'm uncertain how the physics of internal combustion engines and electronic fuel injection has changed since 1979, however it must be astonishing, and I'm very anxious to hear all there is about it.
Thanks in advance.

[JulianEdgar]

Originally Posted by aerohead

Nice reward for dedicating the last two days of my time off to your thread.
If you'd like to parse out your points of contention, we're all ears ( eyes ).
I'm uncertain how the physics of internal combustion engines and electronic fuel injection has changed since 1979, however it must be astonishing, and I'm very anxious to hear all there is about it.
Thanks in advance.

There's honestly no point. I wasn't joking when I said far more of what you have written is wrong than right. Your knowledge of engine management is obviously very poor, so the first step would be to learn something about it.

If you could then add some practical experience (eg in engine management modification or tuning) that would again help your understanding a great deal. It certainly helped mine.

(And, pretty darn obviously, there have been huge changes in engine management in the last 42 years!)

[aerohead]

Allegedly, two capacitors in the T-100's mother board ultimately gave up the ghost, leaking acid, and eating away two traces of the printed circuit board.
The computer was sent off for repair. When it was returned and installed, the truck failed to start.
Presuming the computer was 'fixed' I went on a month's spree, chasing through the entire engine management system before coming to the realization that, the computer had not been repaired at all.
After sending the computer back, I got a call from the technician, apologizing for having missed two additional dead caps, and dissolved circuit board traces.
I got the CPU back, installed it, and the truck fired right up.
Over the course of all that, I got a pretty intimate look at all the logic and hardware from Toyota's official training manual.
The vernier-rheostat inside the throttle-position-sensor, and its variable resistance signal is a vital component of, and the CPU hasn't a clue what's happening without it's signal.
That may not be germane to your cars.

[JulianEdgar]

Originally Posted by aerohead

.
The vernier-rheostat inside the throttle-position-sensor, and its variable resistance signal is a vital component of, and the CPU hasn't a clue what's happening without it's signal.

1. No car uses a rheostat as the throttle position sensor (TPS). They use a potentiometer. Different device, three wires versus two, with a different output (voltage versus current). There is no 'varying resistance signal', there is a varying voltage signal.

2. In cars without electronic throttle, and excluding the earliest L-Jetronic systems that used a full-load throttle switch and the 'carby-like' Bosch Mono-Jetronic system, the TPS is not used to indicate load to the Electronic Control Unit (ECU).

3. Engine load is determined by either:

- the combination of a MAP (Manifold Absolute Pressure), engine RPM and look-up tables that correlate these with engine volumetric efficiency

or

- the output of the airflow meter

The main function of the TPS is to control transients - eg fuel enrichment / enleanment on throttle increase / decrease, and the same for ignition timing advance / retard.

Note that in throttle stop testing, the throttle is not moved.

As I said, you obviously don't have much understanding of engine management systems. That's OK, but it makes criticism of the throttle stop method based on your misunderstandings pretty problematic.

[aerohead]

Originally Posted by JulianEdgar

1. No car uses a rheostat as the throttle position sensor (TPS). They use a potentiometer. Different device, three wires versus two, with a different output (voltage versus current). There is no 'varying resistance signal', there is a varying voltage signal.

2. In cars without electronic throttle, and excluding the earliest L-Jetronic systems that used a full-load throttle switch and the 'carby-like' Bosch Mono-Jetronic system, the TPS is not used to indicate load to the Electronic Control Unit (ECU).

3. Engine load is determined by either:

- the combination of a MAP (Manifold Absolute Pressure), engine RPM and look-up tables that correlate these with engine volumetric efficiency

or

- the output of the airflow meter

The main function of the TPS is to control transients - eg fuel enrichment / enleanment on throttle increase / decrease, and the same for ignition timing advance / retard.

Note that in throttle stop testing, the throttle is not moved.

As I said, you obviously don't have much understanding of engine management systems. That's OK, but it makes criticism of the throttle stop method based on your misunderstandings pretty problematic.

You may read all the listed papers and find out for yourself what they knew.
You may re-read my remarks. Obviously you never have, or you wouldn't be making the asinine remarks that you are.