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-   -   Throttle-Stop Test, a granular look (https://ecomodder.com/forum/showthread.php/throttle-stop-test-granular-look-39042.html)

aerohead 01-20-2021 12:02 PM

Throttle-Stop Test, a granular look
 
Some points to ponder:
* Axle lube viscosity can vary 95% during 'warmup'
* Axle mechanical efficiency can vary 14% during 'warmup'
* Axle-related power absorption can vary by 0.8- kW during 'warmup'
* Low-temperature testing in the past has revealed 8-mpg @ 4-miles range
.................................................. ..................... 11-mpg @ 15-miles range
.................................................. ..................... 13-mpg @ 30-miles range
* An 18-mph headwind has shown a 16.4% mpg penalty @ 50-mph
* An 18-mph crosswind has shown a 2.15% mpg penalty @ 50-mph
* A 10-degree-yaw crosswind increases drag by Cd 0.055
* A 12-degree-yaw crosswind lowered the Cd of the Arrivett Brother's NHRA Top Fuel Streamliner dragster, from 0.20, to 0.18
* An 18-mph tailwind has shown a 19.42% mpg improvement @ 50-mph
* An 18-mph quartering wind is an unknown quantity
* Pumping losses are higher @ light load
* Pumping losses vary as the square of engine rpm
* 45- minutes @ 55-mph warmup has demonstrated data 'repeatability' for the USEPA
* 'Cold' tires, @ ambient temperature demonstrate 40% higher rolling-resistance than when fully-warmed
* Electronic engine management relies upon ALL 'normal', real-time sensor signal participation in order for the ECU to perform minute, asynchronous EFI and ESA optimization commands, otherwise, A/F ratio and Spark advance will experience excursions, even precipitating loss of 'closed-loop' function, allowing the engine BSFC map to fall to a less efficient island of operation, sacrificing optimum performance.
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* Any 'assumption' of steady-state performance is extremely dubious.
* Without baseline testing, which happens to capture performance spectra at any 'new' velocity experienced during the course of testing after aerodynamic modifications are accomplished, any success in parsing out the actual contribution of a specific aerodynamic modification could be lost in the signal-to-noise of the uncontrolled engine, and performance variability of an 'un-warmed' test vehicle; easily exceeding any 'signal' from the aerodynamics.
Simply allowing engine speed to increase from 2,400-rpm, to 2,450-rpm introduces a 4.2% increase in pumping losses.

AeroMcAeroFace 01-21-2021 06:18 AM

Julian isn't here to defend this, throttle stop testing is like coast down testing, susceptible to environmental effects. Doing multiple consecutive A-B runs a few minutes apart will mean that the wind is likely to be the same for all tests or at least averaged.

So from your data, we can say that multiple consecutive A-B runs on a warmed up car has no issues other than pumping losses.

Pumping losses depend on the engine, a six cylinder has virtually no pumping losses due to constant crankcase volume. But even if the pumping loss increase is there, it is a very small, virtually insignificant amount increase of the total drag and even then you need to have a reduction in aero/rolling drag to get the engine speed to increase. So it may not be accurate to 1% but I think it is more reliable than coast down tests.

aerohead 01-22-2021 12:28 PM

So from your
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641218)
Julian isn't here to defend this, throttle stop testing is like coast down testing, susceptible to environmental effects. Doing multiple consecutive A-B runs a few minutes apart will mean that the wind is likely to be the same for all tests or at least averaged.

So from your data, we can say that multiple consecutive A-B runs on a warmed up car has no issues other than pumping losses.

Pumping losses depend on the engine, a six cylinder has virtually no pumping losses due to constant crankcase volume. But even if the pumping loss increase is there, it is a very small, virtually insignificant amount increase of the total drag and even then you need to have a reduction in aero/rolling drag to get the engine speed to increase. So it may not be accurate to 1% but I think it is more reliable than coast down tests.

1) I've identified eleven ( 11 ) unknowns.
2) Pre-conditioning the test vehicle to achieve thermal equilibrium at any given ambient temperature will certainly whittle away at this list.
------------------------------------------------------------------------------------
Beyond the warmup, the following issues remain:
3) Asynchronous A/F ratio optimization signals are rendered impossible. The BSFC can drift.
4) Asynchrounous ignition timing optimization ( best torque spark advance ) signals are rendered impossible. BSFC can drift.
5) Asynchronous EFI frequency and duration optimization signals are rendered impossible, due to drifting Oxygen sensor voltage signals being over-ridden by a non-participating TPS prompt. The ECU may default to 'Open-Loop', power-enrichment without veto from the TPS.
6) Any presumption as to 'constant torque' is a presumption.
7) Powertrain mechanical efficiency is predicated upon ' transferred power' and is not a constant.
8) No provision for knowing vehicle performance at velocity-2, is available for comparison the the baseline velocity-1. They're all unknown quantities.
* Rolling resistance road-load power
* Engine accessory loads which vary arithmetically with velocity
* Pumping-losses are non-linear, having to do with hydrodynamic, tribological losses, which vary with lubrication viscosity, as the square of engine rpm, oil pump, and with water pump hydrodynamic drag, which also varies geometrically. If say, the Insight develops it's maximum Bhp @ 6,000 rpm, and we choose 2400-rpm as our test velocity, even a 50-rpm increase at velocity-2 will create a 4.2% rise in pumping losses alone.
* BSFC
------------------------------------------------------------------------------------
It can be a setup for false-positives, or false-negatives.
Any 'true' effect from an aerodynamic modification could be lost in the 'noise' of the unknowns.
And we know that, typically, a smaller load-load fraction leads to a higher BSFC, even when all engine management components are 'communicating.'
-------------------------------------------------------------------------------------
Hucho tried to inform us in his 2nd-Edition, and it is he would cited Sovran's SAE Paper 830304 for those interested enough to check it out.
Why the 'select panel of experts' went into the ditch is beyond me.

AeroMcAeroFace 01-22-2021 01:51 PM

But other than accessory losses, everything else is changing due to the increased engine speed.

I am not saying that a 5% increase in top speed means an exact 10% decrease in drag, there are too many variables at play to say absolutely. The error between measurements is perhaps 10%.


However you can say with absolute certainty that a fixed throttle position will give you a higher top speed if drag is reduced, there is no way you can argue against that.

At least a few mph difference, averaged over multiple readings, it can't all be down to the car suddenly becoming more fuel efficient or is that what you are saying?

aerohead 01-22-2021 02:17 PM

accessory and ................
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641366)
But other than accessory losses, everything else is changing due to the increased engine speed.

I am not saying that a 5% increase in top speed means an exact 10% decrease in drag, there are too many variables at play to say absolutely.
however you can say with absolute certainty that a fixed throttle position will give you a higher top speed if drag is reduced, there is no way you can argue against that.

1) Technically, if the accessories are belt-driven, hysteresis losses in the rubber of the serpentine or cog-belt will increase losses arithmetically with rpm, like the tires with velocity.
2) For drag versus top-speed, Hucho reported a 30% delta- Cd -to-10% delta- velocity relationship as of December, 1986. There may exist more contemporary reporting on this. Don't know.
3) Yeah, lots of variables, which Julian spells out many in the video. I've collected materials since 1974, and I may have some obscure data easily missed in all these intervening decades.
4) You're absolutely correct about expectations for a higher top speed. I don't think it could be argued otherwise. Top-speed testing is a form of ' throttle-stop' testing. Spirit picked up 19-mph ( 31- km/h ) that we know of. And that was with a 920-lb weight penalty ( 418 Kg ).

freebeard 01-22-2021 02:32 PM

Quote:

Julian isn't here to defend this...
And who does he have to blame for that? Probably me for provoking him.

Do we know if it is temporary? Wasn't there someone who was banned for like a week?

AeroMcAeroFace 01-22-2021 03:29 PM

So we can agree that it is possible to ascertain drag reduction from throttle stop testing?

That is of course assuming the following:
Accessory load is the same (no-air con, no extra lights, heating, etc.)
Tests are done back to back multiple times on the same day to average out any wind changes.
The vehicle is appropriately warmed
The fuel is the same

Whether it is safe to block your throttle, or accurate enough to measure a 1% or 0.5% drag reductions is yet to be decided/ascertained, I will not argue for or against either of those.

aerohead 01-22-2021 03:32 PM

isn't here
 
Quote:

Originally Posted by freebeard (Post 641372)
And who does he have to blame for that? Probably me for provoking him.

Do we know if it is temporary? Wasn't there someone who was banned for like a week?

He usually comes in later in the day. With the time difference, sometimes he's posting at 3:00 A.M. Texas time. He's gotta sleep at some point.:p

aerohead 01-22-2021 04:01 PM

can agree
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641376)
So we can agree that it is possible to ascertain drag reduction from throttle stop testing?

That is of course assuming the following:
Accessory load is the same (no-air con, no extra lights, heating, etc.)
Tests are done back to back multiple times on the same day to average out any wind changes.
The vehicle is appropriately warmed
The fuel is the same

Whether it is safe to block your throttle, or accurate enough to measure a 1% or 0.5% drag reductions is yet to be decided/ascertained, I will not argue for or against either of those.

1) I'm in total agreement that we can.
2) Accessory load will increase at the new, higher velocity, after the aero modification, and we have no baseline data for that.
3) Same for rolling resistance
4) Same for powertrain mechanical efficiency ( it's at a new rpm and lower load )
5) Same for BSFC as the engine is 'blind' to some former signal input
6) From the EPA, we know that A-B-A testing doesn't cancel wind effects, as the vehicle demonstrates different reactions to, say, headwind / tailwind.
7) If we're in 'quartering' winds, there's no available data for that, one way, or another. A complete unknown.
8) Fuel Btu content won't vary.
9) Fuel density ( coefficient of thermal expansion ) WILL vary with temperature, however, probably not, in the timeframes we're working with.
10) As to accuracy, one thing not mentioned, but of some assistance to us, would simply record the fuel economy for a spectra of higher velocities which happen to include the new, higher, velocity-2 with no modifications, to compare to the modified car at velocity-2. Some things could be reverse-engineered from that kind of data.
11) The more 'book-keeping' we can perform, the higher the resolution when attempting to isolate the aerodynamic effects.
12) Qualitatively, the throttle-stop test will demonstrate the trend, without countless hours and liters ( gallons ) of fuel going up in smoke. It's worth the fuss.

MeteorGray 01-24-2021 07:12 PM

Are these factors in conflict?

Post #9:

7) If we're in 'quartering' winds, there's no available data for that, one way, or another. A complete unknown.

vs Post #1:

* An 18-mph crosswind has shown a 2.15% mpg penalty @ 50-mph
* A 10-degree-yaw crosswind increases drag by Cd 0.055
* A 12-degree-yaw crosswind lowered the Cd of the Arrivett Brother's NHRA Top Fuel
Streamliner dragster, from 0.20, to 0.18

Or does "quartering wind" relate only to certain degree yaw angles implied by the term?

It seems that the direction of an angling wind will make a difference, just as it makes a difference whether a wind is a headwind or a tailwind. And that an angling headwind will be detrimental, but to a lesser degree; and that an angling tailwind will be beneficial, but to a lesser degree.


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