Throttle stop testing on a diesel
 

Today, while I was waiting for the Tesla to arrive for tuft and pressure testing, I did some throttle stop testing in our W212 Mercedes.

Using a Scangage to monitor throttle position, I was able to hold a constant throttle (ie I didn't use a 'stop' as such - it's not too hard to hold a constant throttle once you get used to it.)

On the same test road that I've been using for my Insight, I recorded the following at TPS = 52 (not 52 per cent obviously, but a constant throttle).

Windows closed: 101 km/h
Windows open: 97 km/h

That calculates to an 8 per cent increase in drag - a bit lower than the change with the Insight (12 per cent) and well under the change quoted in Katz (2016) that has it at 16 per cent for a notchback.

I might do a few more tests with weird rear spoilers.

I put a throttle stop on my alh beetle years back, have one on my bew golf now, but have it screwed way down to like 80%. started trying to contrive some means to have a 2 stage stop. one for regular driving, but more of a detent that can be pushed through when more is really needed like, "right now full emergency thrust" situations.
original experimental intent was like 55%, worked for several days till it didn't. short version is that i thought i was about to die. "at your own risk" for sure.

have been thinking that a smarter cruise control might be better than trying to continue to improve the nut holding my steering wheel. PID maybe?

Just so that you're aware, the throttle stop testing I am talking about is to test for changes in aerodynamic drag, with the stop used only during the testing process.

Bad news for US (North America)
 

I followed the original Throttle Stop thread and assumed it would not work on the TDI since it is both drive-by-wire and turbocharged. I saw this thread and hoped it might give us another option besides A-B-A that Darrin has suggested for years. Alas, I tried it today without success.

I had the car mostly warmed up on a flat, straight road, at 70 mph, 16 degrees F with zero wind and speed and elevation measured by a Garmin on the dash. First, the Throttle Position Sensor on the ScanGuage (TPS) was useless as it just read 95 all the time unless I really stood on the throttle. I tried Load (LOD) but it was all over the place even with my right foot braced tightly on the footwell. I finally tried Gallons Per Hour (GPH) and was able to hold a fairly steady 1.66 @ 70 mph. However the windows up or down did not show a consistent difference in top speed.

I would say that for the most common small diesels in North America (Volkswagen Audi Group TDI) Throttle Stop testing may not be a viable option.

If anyone would like more info about A-B-A testing on my Golf TDI check out my Heresy thread.

EDIT: I just read a note from Julian that suggested that the test distance needed to be over the course of a kilometer. I may have to repeat the test under better conditions in the future. If anyone is attempting this with the TDI I still suggest bracing your right foot and using GPH on the ScanGuage

Small “thread hijack” for a shameless plug for my How to Ecodrive the TDI thread, specifically the Driving With Load (DWL) post. In hilly Colorado it doesn’t work well for me for optimum mpg. Besides why would anyone ever want to limit the power of the TDI? That is the fun of this vehicle, acceleration of a sports car but can be hypermiled like a 3 cylinder Geo Metro. :thumbup:

https://ecomodder.com/forum/showthre...sel-38306.html

Hijack over. Apologies Julian.

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?

Sounds good! Got some test results that you can share with us?

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.

What does this show when you do it windows up / windows down?

I also do this testing only on a dry road as I found that a road with sporadic puddles gave immediate inconsistencies in the results.

early baseline speed is constant load & MAF flow are variables
 

yes
2 of the initial baseline screen caps
with VCDS you can dial in the values , upper and lower for each parameter id or PID selected up to 10 PIDS , better to use fewer when you can collect what you need from just a few
less noise on the graph

instead of graphing , VCDS would log the data as csv and you could store longer samples and fuss with them using whatever office type software you are using

this is with Generic OBD2 not with VW KWP using measuring value blocks , engine data would be in address word 01

since i was / are only looking for change in in load OR MAF flow at a constant speed 3 PIDS in generic data was enough

my way is right for me , julian 's way is right for him
and what ever way YOU choose
will be right for you as long as what you choose has one constant that is repeatable
the variable will show improvement or lack thereof





Attachment 29914Attachment 29915

Yes I had VCDS on my Skoda Roomster, so I am familiar with it. But I was hoping for some comparisons of your different results with aero mods?

Good point. I did the testing using cruise control over my flat test road of roughly 2 miles (3K?) in my wheel cover test, before I saw the windows up/windows down idea. I may be able to test my testing method in the next few days. I will report back.

ScanGuage aero testing checks out
 

I had a few minutes today and dry roads before the storm coming in tonight so I decided to test my testing method. At Julian’s suggestion I did a total of 4 runs on my reasonably flat, straight 2 mile test road. 30 degrees F and winds calm (3 mph from the west according to the weather radio from the airport next to the road). I did an east and west run with the windows up and repeated the procedure with all the windows down and the cruise control set to 65 mph (63 on the GPS) for all runs. There was no other traffic on the road during the testing.

I averaged the windows-up runs and got 51.05 mpg.
I averaged the windows-down runs and got 48.05 mpg.

That is almost a 6% difference so I feel pretty good about the ScanGuage current mpg test model.

Yes, that's a great result.

Diesel fuel rack stop on a mechanical pump.
 

The adjustable fuel rack screw on my diesel rabbit reduces the fuel when I back it out. Would that work for "throttle stop" testing?
Or would a mechanical stop on top of the injector pump work better?
I do not know if there is a internal governor that can introduce variation at full rack.
I do know fuel temperature must be controlled from past testing.

OXYMORON: 'diesel / throttle'
 

I wasn't aware that this thread existed, and just stumbled across it while digging into the past here at the Aerodynamics Forum, page-10.
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1) It would be technically improper to associate 'throttle stop' testing with any diesel vehicle.
2) Diesel-powered vehicles have an 'accelerator' pedal, not a 'throttle' pedal.
3) As, diesel engines do not have 'throttles.'
4) Diesel engines have no restriction of any kind in their inlet tract.
5) The diesel's pedal is associated with the Robert Bosch fuel injection pump, whether by direct mechanical means, or drive-by-wire, which modulates the 'racking' function of the pump, as mentioned in the most recent post.
6) What might be referred to as 'wide-open-throttle' on a gasoline-powered ICE engine might be compared to 'full-rack' on a diesel.
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7) Any discussion of a 'TPS', or its signal, on a diesel would also constitute an oxymoron, for the same reason as above.
8) A ScanGauge cannot intercept a TPS signal, as one doesn't exist.
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9) Testing, and interpreting data for a supercharged, or turbo-intercooled diesel would be a massive challenge, even in the absence of a ' stopped-rack.'
10) Data collected under 'logic death,' thermal non-equilibrium conditions, and uncorrected to SAE Standard 60-F, 29.92-inches Mercury, would essentially be 'meaningless'.
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11) One current proponent of the' technique', according to the 'math', allowed a 4.39% rpm excursion ( 123-rpms ) as acceptable on his 1991 Toyota DLX 4WD pickup's 2.4-liter IL-4 engine.
* On a 2022 Genesis G80 3.5 AWD, this would allow a 57-rpm allowable test window.
* On a 2023 Lamborghini Huraca'n Technia, an excursion of 285-rpm would be the limit.
Thought I'd mention it.

Didn't know they are diesel. Learn something every day.

diesel vs gasoline
 

I'm just pointing out rpm constraints inferred but never specified by Mr. Edgar, nor VMAN 455.
VMAN455 was 'comfortable' with a delta-4.3928% rpm 'window' on his 1991 Toyota.
If this were to hold for the Genesis, only a 57rpm engine change would be tolerated during testing.
Mr. Edgar never provided any rpm parameters for Gasoline ICE, nor additional parameters for diesel ICE.
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TDI issues are self-explanatory.

I left off the [/jk]

I thought I'd found someone to characterize my Lexus electrric axle. On the condition that if they liked it they could buy it, but if they didn't they'd tell me why.

All I got was that it wouldn't deliver power above 35MPH. I asked for your attention at Hot-rodding the Toyota MGR #406. Does it seem reasonable that an SUV AWD axle would only provide power at parking lot speeds, if it has a external oil cooler for trailer towing option?

GrayRaceCat gave it a shot at #407. They admitted they didn't try to spin it.

Do we have to beat a dead stick with a horse?

As long as we understand, do we really need such perfeccionism?

The other day I got called out for saying I charged my 12V battery with a trickle charger. I was told it wasn't a trickle charger and I should never use a trickle charger on a car battery, even though the charger says "Trickle Charger" right on it and on the box it came in from Wal-Mart.

I don't like the term "battery pack" when referred to BEV's since a "battery" is already a series of individual cells put together. "Battery pack" sounds like what AA's and AAA's come in. But I usually don't even mention that I dislike the term when others mention it in referrence to BEV's.

'characterize'
 

I ran the numbers for the RX 450h and will post them at the 'Hot-Rodding' thread @ Fossil Fuels.