Well, it all goes back to the standard deviations of the before and after situations. If you can narrow down a set of conditions that give you the same SG results on the same segment of your drive, then make your change, and then measure again, you might be able to see it. It depends how consistent you were before, how consistent you are after, and how small of a difference you are trying to see.

If you are very reliable before, and are looking for a large change, then one sample might be enough. For example, running on 4 donuts vs 4 regular tires.

But the improvement of something like a mirror delete might not be possible to prove statistically. Doesn't mean it didn't help, just that you can't statistically prove it.

>>But the improvement of something like a mirror delete
>>might not be possible to prove statistically. Doesn't mean it
>>didn't help, just that you can't statistically prove it.

Your right on the mark there. Many theories are right but cannot be proven experimentally because of precision. General Ralativity wasn't verified for years, until there was an eclipse with a know star position close to it... only then could the bending of light be experimentally measured with enough magnitude to draw a decent conclusion.

So I finally ran the numbers.
Example #1 (Bill's real data)
My tank fills for the last year had a std deviation of 1.3 mpg.

I added an air dam to my car. If I want to see a difference of .5 mpg, I need to collect 85 more samples. That's more than 3 years worth of data. In my opinion, there would be too many outside factors during those three years to say that anything was really valid.

Example #2 (made up example for "Bob")
Bob uses a SGII and on a particular trip segment he thinks he is pretty repeatable. He records data and finds that his std deviation is 0.3 mpg.

If Bob wants to see a change of 0.5 mpg, then he only needs to collect 6 samples, which would probably take just a week or two. This seems like a reasonable time period.

Example #3 (Bill's real data again)
I have heard that Acetone will bump my mileage by 10%. This is ~2.7 mpg for me. How many tanks would I need to confirm or refute the claim?

I would need 4 samples. During the two months required to get those 4 fills, there would be a lot of outside influence, but I might be okay with it if the weather and my driving patterns didn't change TOO much. Plus, for a 10% adjustment, I'm willing to put up with a little more hassle.

To confirm or refute a 5% improvement, I would need 13 samples. Too long of a time period.

Anyway, hopefully those examples were helpful. And again, something might help you, but not necessarily be statistically provable. Don't let the statistics get in the way of trying.

Bill it looks like this is pretty simple but I'm simpler still. How would this work as far as how we try to test things here. Tank to tank is out of the question IMHO.

How would this work as far as testing goes. When we test things with the SG we usually do 4-6 runs without the mod, then do the same with and then without in different directions. Most of the time in my experience the fuel results are with in .2 mpg or less when in the same direction. So what percentage would increase would you have to have to say it was a good result. Keeping in mind that most mods give somewhere around 2-3%.

I know it not that easy.

Post a data set and I'll run the stats and tell you if the A and B are statistically significantly different.

And once I have a typical set I'll poke around a little and see what the smallest difference we could prove would be.

It needs to be something with lots of runs, though. I know that already. 4 might work if you are looking at a big change and are dead-on in repeatability. Having more runs is always better, of course.

It will be tomorrow before I get to do any analysis.

No I don't have any thing with lots of runs and the % increase on the SG on most mods is around 2-3% so It won't fit the criteria. This has been an interesting thread. thanks

Okay, if anyone else has a set they want analyzed Friday, let me know.

I just read through this thread. My conclusion is that fill data and the scangauge will not convince any sceptics about the effectiveness of the Somender grooves in the combustion chamber. On the other hand I can go on believing in them no matter what the results are ;) .

Convincing skeptics is a waste of time? It's easy to be a skeptic, you just have to doubt and come up with some excuses to justify it...it's more difficult to go ahead and improve your mileage.

In the real world (at least I THINK that's where it is) I use a 3 tank avg (at least a 3/4 refill). This allows seeing some results in a reasonable amount of time and is...I believe.... an accurate reflection of mpg.

This is called a simple moving avg. When plotted...IF you are seeing real increases in mpg...you will see the plot go up and stay there RELATIVE to the time of year and so forth.

You do need to drive consistently and be accurate at fillups.

My next vehicle will probably be a Saturn...and I hope to duplicate the results others have managed. Plagiarism? :eek:

good thread clencher.

i think it's really difficult to test accounting for variables. weather/climate changes from 1 year to the next, increase in traffic, new roads and traffic lights, the tune status of tested car, etc...

stats and studies have the human error as well. i'd say it's imperfect, so do the best testing possible over a years time. the beauty is we can continue to achieve better FE w/out the worry of job security or funding to depend on.