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Discussion Starter #1 (Edited)
Hi,
So, here is a small problem to wrap your brain around during the Covid doldrums -- any help will be appreciated.

I bought a set of Vorblade brand vortex generators and I want to test them carefully to see what the MPG gain (if any) is.

I know there are lots of strong opinions on how beautiful these will make my van look and how little or large the gain is, but I'm really only interested here in working out a good test procedure that will nail down the MPG gain (if any).

I've mounted the the Vorblades on strips of sheet aluminum so that they can be temporarily attached to the van and easily removed. I did this because it makes it easy to do A-B-A testing (see below) and because I don't want them permanently mounted on the van if they don't work.

This is approximately what they will look like on the van. I do plan to spray them white if I keep them. There is also a strip of vortex gens that go across the roof. I will duct tape down the full leading and trailing edges of the sheet metal for the test.

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I've been looking around for a good test method that will be able to pick up the small change the vortex gens will give.

There is one test procedure developed by the SAE that seems very airtight and involves a control vehicle and a test vehicle simultaneously driving a 50 or so mile test section of highway multiple times. It seems very good, but pretty time consuming and expensive with two vehicles.

The ecomodder.com site recommends what the call the A-B-A procedure. In this procedure, the baseline vehicle (no vortex gens) is run around a closed loop a couple times with MPG measured, then the vortex gens would be added and the vehicle run around the same closed loop a couple times with MPG noted, then the VGs would be removed and the baseline vehicle run around the same course 2 more times. In some of their examples, this method seems to be able to find differences in the 0.5% area (about 0.1 MPG on the PM).

So, if the VGs work, you would expect the before and after A runs (the baseline vehicle) to all be pretty close and consistent on MPG, and that both of the B runs (with VGs) to show better MPG. The idea of doing the 2nd set of A runs is that it reduces the possibility that changing conditions just randomly make the run with VGs look better (or worse) than they are.

In my case, I would use a section of I90 between exit 305 (Bozeman, MT) and exit 288 (Manhatten, MT) for the test loop -- its 17 miles one way and 34 miles for the full loop. I would do the A-B-A in one continuous test and pick a day with stable weather and low wind. I will try to pick a time with low traffic so I can maintain a constant speed (this may have to be at night). I will use cruise control and try not to reset it for the whole test. I would do the whole test on the same tank of gas.
There is an about 500 ft elevation drop from the start of loop to the turnaround point, but you have to regain this on the return trip.
The plan is to track the MPG for each of the six 34 mile trips around the loop using the MPG computer on the PM.

My biggest doubt about this is using the PM MPG computer. We all know it tends to read a bit high. But, as long as its consistent, it seems like it should still give a valid increment between VGs and no VGs?
An alternative would be to fill the gas tank at the end of each run, but its hard to fill the tank to exactly the same level and we are only talking about around 2 gallons per run -- so not much room for error.
Another alternative would be to have a 5 gallon gas tank and fill the main tank from it after each run while weighing the 5 gallon tank before and after the fillup to get the gas used. I do have scale that will weigh the 5 gallon tank to within a couple grams. I would have to fill the main tank almost to the lip to be able to make sure it was filled to exactly the same level each time. So, this seems somewhat workable, but a lot more work than getting the numbers from the computer.

Anyone have any ideas to improve the procedure? See any problems in the procedure? Any suggestions?

I realize this is a crazy amount of work to nail down a small MPG gain, but engineering tests are a hobby with me and I really enjoy doing them.

Edit: forgot to mention that if this method works for the VGs, will try some other changes, like with and without solar panels, different tire pressures, different speeds, wheel skirts, ...

Gary
 

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I feel the computer, while not giving the exact mpg will at least give good comparative values. Remember to add weight to adjust for the decreasing fuel weight. That you can know within a few oz by calculation. It might be the weight of a few gallons won't change the mpg values but JIC.
 
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I keep an MPG spreadsheet which includes both the hand calculated vs computer MPG. In over 150 fill-ups the average difference shows computer MPG being about .78MPG higher. However there is a lot of variation with the computer MPG being higher by as much as 4.64MPG to being lower by as much as 3.69MPG. So more than 8MPG range between high and low variations.
 

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Discussion Starter #5
I keep an MPG spreadsheet which includes both the hand calculated vs computer MPG. In over 150 fill-ups the average difference shows computer MPG being about .78MPG higher. However there is a lot of variation with the computer MPG being higher by as much as 4.64MPG to being lower by as much as 3.69MPG. So more than 8MPG range between high and low variations.
Hi,
Thanks for the data!
I'm wondering how much of the variation is due to filling the tank to a consistent level and how much due to MPG computer variation?
Do you feel you have a way to consistently fill the tank to the same level? What do you do to get a consistent fill level?

Gary
 

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I start by having a sense as to how many gallons it should take. If the hose clicks off close to that, I will top off by hand until it clicks off again. Probably not exactly to the same level each time, but I think it is reasonably close. If it is off by as much as half a gallon (probably not that much), over 300+ miles, I think that would contribute about .5MPG to the variation.

300 miles/17gallons = 17.65MPG

vs.

300 miles/17.5 galloons = 17.14MPG

Obviously, if I fill up with fewer miles on the tank, the variation due to inconsistent fill level would be greater.
 

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Gary, my only suggestion is that you make certain the cruise control is set identically because even a tiny variation in speed will likely offset results. I’m not sure how PM cruise works, but on my old Ford I’d have to keep engine running and then use resume in order to use same exact speed. PM may be all digital so 60 MPH (as an example) may be exactly right on 60 (calculated — not actual).

In the data you linked, going from two readings of 30 MPG, to two readings of 35 MPG, back to 30 MPG would convince me of actual improvement. But that’s 17% change with variations in A or B readings far less than that.

In my opinion, a difference of 0.5%, or about 0.1 MPG for a ProMaster, would not be significant with the test procedure you’ve outlined. You would need more readings to be statistically significant, and also have A, B, and second A readings closer that the difference. And it’s highly unlikely in my opinion that you will get all four A readings much closer than 0.1 MPG.

Unless Vortex generators give you at least 0.5 to 1.0 MPG improvement, I expect test accuracy won’t be able to detect the change with enough accuracy to confirm results.
 

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Is this what you are looking for you do not need to record all and this is a sheet with all. The zeros are what FCA does not send. And if your device has gps you can map and chart your trip.
 

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I really appreciate that you are doing this experiment and look forward to the results. I think it would make sense to go to the same gas station and fill up completely at the end of each run, taking note of exactly how far in you put the fuel dispenser nozzle and making sure to pull up to the same pump. Then you would have the same equipment, minimizing differences due to the fuel dispenser's measurement and automatic cutoff. Problem there is whether or not you can GET to that pump w/out idling, etc. But at least you'd be using equipment consistently. I wonder if you did the test at night if you'd run in to less traffic, less chance of the pump you need being blocked, and therefore less variety introduced into the tests.

One interesting note on the PM computer readout for mpg: Usually when we calculate mpgs, our calculation is lower than the computer's by 1.2 - 1.8 mpgs (working from memory here). But on two occasions we've run the tank almost to empty. Both times our hand calculations were only about .2 less than the computer's. Since then, I've just been trusting the computer, because we've accepted that this vehicle burns more gas than we wish, and we use mpgs as a way of monitoring the kind of driving we've been doing and looking for any potential mechanical issues. For those goals, change in mpg is more important than the mpg itself.

Good luck! Excited to find out what you learn.
 

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Awesome plan, look forward to seeing the results. Couple of notes:

1) I'm worried that the aluminum might flutter . . . maybe tape the leading edge the full length.

2) The VGs should make their best improvement for a given speed in a certain position. Does the manufacturer specify the distance?

3) The fuel computer knows how much fuel is being sent to the engine based on totaling the injector open time. This assumes that the injector flow rate and fuel pressure is constant. In your case, you are using exactly the same injectors and fuel pump, so I would expect the PM's fuel usage (and therefore MPG) to be repeatable. Using an OBDI tool like @KilWerBzz mentioned would be a good idea.

4) Engine temperature should be constant once the PM is at operating temp. Make sure the first run is not cold.

5) Tire temperature changes a lot between parked and rolling down the road, and with that change the tire pressure, so you would want to start with a known good pressure in all the tires then make sure the tests are such that the tires are heated fully for all the runs.

Can't wait to see the data !
 

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Discussion Starter #11
Gary, my only suggestion is that you make certain the cruise control is set identically because even a tiny variation in speed will likely offset results. I’m not sure how PM cruise works, but on my old Ford I’d have to keep engine running and then use resume in order to use same exact speed. PM may be all digital so 60 MPH (as an example) may be exactly right on 60 (calculated — not actual).

In the data you linked, going from two readings of 30 MPG, to two readings of 35 MPG, back to 30 MPG would convince me of actual improvement. But that’s 17% change with variations in A or B readings far less than that.

In my opinion, a difference of 0.5%, or about 0.1 MPG for a ProMaster, would not be significant with the test procedure you’ve outlined. You would need more readings to be statistically significant, and also have A, B, and second A readings closer that the difference. And it’s highly unlikely in my opinion that you will get all four A readings much closer than 0.1 MPG.

Unless Vortex generators give you at least 0.5 to 1.0 MPG improvement, I expect test accuracy won’t be able to detect the change with enough accuracy to confirm results.
Hi Chance,
I do plan to try to set the cruise control at the start of the first run and then try to never reset it for the whole A-B-A. This does require keeping the engine running, but as long as I can use the computer for the MPG calc, the transition from VGs to no VGs should take less than 5 minutes, so I can just keep the engine running.

Agree that detecting 0.1 MPG is probably a bit optimistic. Will have to look at the consistency of the data I guess. I can look at the first two A runs and maybe decide to do 3 A, 3B and 3A if needed. I suppose that if the gain is less than 0.5 MPG, not very many people would be interested -- maybe not even me :)

The very extensive test that Vorblade did on semi trailer trucks using the SAE procedure was significant and I think would be easily detectable by the ABA method, but our vans might be a different animal.



Gary
 

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Discussion Starter #12
I really appreciate that you are doing this experiment and look forward to the results. I think it would make sense to go to the same gas station and fill up completely at the end of each run, taking note of exactly how far in you put the fuel dispenser nozzle and making sure to pull up to the same pump. Then you would have the same equipment, minimizing differences due to the fuel dispenser's measurement and automatic cutoff. Problem there is whether or not you can GET to that pump w/out idling, etc. But at least you'd be using equipment consistently. I wonder if you did the test at night if you'd run in to less traffic, less chance of the pump you need being blocked, and therefore less variety introduced into the tests.

One interesting note on the PM computer readout for mpg: Usually when we calculate mpgs, our calculation is lower than the computer's by 1.2 - 1.8 mpgs (working from memory here). But on two occasions we've run the tank almost to empty. Both times our hand calculations were only about .2 less than the computer's. Since then, I've just been trusting the computer, because we've accepted that this vehicle burns more gas than we wish, and we use mpgs as a way of monitoring the kind of driving we've been doing and looking for any potential mechanical issues. For those goals, change in mpg is more important than the mpg itself.

Good luck! Excited to find out what you learn.
Hi and thanks,

If I could figure out a way to fill the tank to a consistent level, I'd definitely go that way. There is a gas station right at the start of the loop, so no problem there.
The problem I've had with the PM is that (at least on mine) if I just let it fill to the point where the nozzle clicks off, and then give it one more shot until it clicks off a 2nd time, the result is highly variable -- sometimes the tank will only end up about 3/4 full.
If anyone has figured out a consistent way to fill the tank to the top, I'm all ears.

Gary
 

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Discussion Starter #13
Awesome plan, look forward to seeing the results. Couple of notes:

1) I'm worried that the aluminum might flutter . . . maybe tape the leading edge the full length.

2) The VGs should make their best improvement for a given speed in a certain position. Does the manufacturer specify the distance?

3) The fuel computer knows how much fuel is being sent to the engine based on totaling the injector open time. This assumes that the injector flow rate and fuel pressure is constant. In your case, you are using exactly the same injectors and fuel pump, so I would expect the PM's fuel usage (and therefore MPG) to be repeatable. Using an OBDI tool like @KilWerBzz mentioned would be a good idea.

4) Engine temperature should be constant once the PM is at operating temp. Make sure the first run is not cold.

5) Tire temperature changes a lot between parked and rolling down the road, and with that change the tire pressure, so you would want to start with a known good pressure in all the tires then make sure the tests are such that the tires are heated fully for all the runs.

Can't wait to see the data !
Thanks Baxsie,

I'm going to tape that metal strip down along the full length of the leading and trailing edge -- don't want to be leaving my pricey vortex generators along the freeway :)
I think I should still be able to do the change over in 5 minutes.

I will look into a better OBD2 device than the simple one I have now. One that would log and allow me to mark the start and end of each run would be great.

Agree that the tire pressure is a thing. I'll set all the tire pressures at 60 psi at home, then I'll drive the van before the first run to warm up the tires and drive train -- maybe 10 miles at freeway speed?
Maybe check the tire pressure a few times during the runs to see how much its changing.

Gary
 

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Been waiting for the premier of this thread for months!
Please drive the van on a dusty road with and without the VGs.
You don't have to remove and weigh the dust collected or anything.
Just a visual comparison will do.
?
 

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Discussion Starter #15 (Edited)
"Is this what you are looking for you do not need to record all and this is a sheet with all. The zeros are what FCA does not send. And if your device has gps you can map and chart your trip.
"

Thanks -- Ordered one.

Gary
 

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Discussion Starter #16
Been waiting for the premier of this thread for months!
Please drive the van on a dusty road with and without the VGs.
You don't have to remove and weigh the dust collected or anything.
Just a visual comparison will do.
?
Hi RNR,
I'll see what I can do -- plenty of gravel around here :)

Gary
 

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I vote for the 5 gallon can fill up . And suggest at least 50 mile loop , or longer .
The Mythbusters busted the pick up truck tonneau cover myth with a 50 mile loop or one way (don't membr) and the gas can . The tailgate creates an "air bubble" in the bed. And we all know air is very slick ( boundary layer ) . Getting that boundary layer onto the rear doors is what we want .
Gary , if your still having fun after the VG tests try folding the outside mirrors in tests .
 

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Even if you stretch each loop from 34 to around 50 miles, you’re still looking at only burning 2 to 3 gallons of gas. And if fuel economy improvements were in the 1% range, you’d have to be able to measure .02 to .03 gallons accurately. In my opinion this is never going to happen because of variability in headspace inside fuel tank.

By using the same gas pump, or by measuring gas out of a can and weighing usage down to the gram is completely meaningless if the amount that goes into tank varies by much more than that. It will only take a couple of fluid ounces of volume change in a 25-gallon fuel tank to completely ruin the test — unless aero improvement is far more than 1%.

I’d personally use the van’s computer as the first A-B-A test and see just how much variability there is between all the readings. This first test will not only tell you if there is any chance of vortex generators working, but will also tell you if the computer’s MPG reading is accurate enough for what you’re trying to measure.

In chart below from article the readings varied by 1 MPG, but was good enough to confirm a +/- 5 MPG improvement. That’s the best type of data you can expect in my opinion.



5E87179C-6F8C-4941-9332-49761DFC48A6.jpeg
 

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P.S. — I’m only sharing my technical opinion on the test itself, as you requested, and not suggesting that I expect an actual improvement. While almost anything is possible, I seriously doubt they will make much difference, and not enough to measure accurately.

I think your questioning the testing itself shows why there are so many bad conclusions on the Internet. If a guy drove his van 100 miles, then added something, and drove another 100 miles, it would be extremely easy to get a few percent difference just from inaccuracy. Those who got lower MPGs will move on, and the ones who get better fuel economy will convince themselves it actually works.
 

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Don't forget to factor in barometric pressure, the Earth's rotation and the gravity of the moon.
And stool samples from before and after.
 
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