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Discussion Starter #1
Hey wowfactr,


Craig here.I just ordered a G-tech SS acellerometer I think just like the one you showed me at McDonalds last spring on our OC run.
The purpose of this is so I can get before/after test results before i install the supercharge kit.I didn't ask you what kind of numbers you were getting form your setup.Are there any setup tricks that I need to know? I see that it seems to be important to set the unit level on the windsheild to prevent accuracy problems.
 

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53wanab: The G-Tech is sophisticated enuogh that absolute levelness is not required. Because it has a 3-dimensional solid state accelerometer, it notes the starting orientation no matter what it is, and calculates from there.

However, there are MANY other critical setup issues in order to get data that is truly accurate. Some I have covered on this board in lengthy, previous postings, and you can find them by doing a search with "G-Tech" as the search word. My book provides a full 13 pages of content on how to do G-Tech based testing, and how to analyze the data.

Just four examples of the critical control factors that many people never even think about are

1. FLAT road: Establishing that the road surface is truly zero percent gradient. If it is even 1% slope, the results are badly skewed. 2% makes the results virtually useless. Slope is a problem whether downward (makes your vehicle artificially quicker) or upward (makes your vehicle artifically slower). This is why dragstrips have to be zero percent gradient. Good analysts can detect slope by looking at the resulting data. Depending on human eyesight to detect slope is a bad idea, and counting on the vehicle to "roll" in neutral if there is a slope is similarly bad (a typical production vehicle won't roll until the slope is at least 1.5%, and that slope is enough to be a big inaccuracy). In the absence of topo maps or laser level, try running both directions. If EVERYTHING is right, the results in BOTH directions will overlap each other PRECISELY with a G-Tech. Of course multiple runs in each direction over the same stretch of road tend to attract unwanted and expensive attention. Try a drag strip, using BOTH timing light and G-Tech. Your reaction time will be bad, but the data will be accurate.

2. Wind: ANY wind is a problem. A 5 MPH tailwind makes the results artifically quick. A headwind OR crosswind makes them artifically slow.

3. Ambient conditions: The precise combination of air temperature, % humidity, and air pressure (inches of mercury) is critical. Otherwise, engine power is affected upward or downward by up to 10%!

Use

http://www.wunderground.com/

as an easy way to get the ambient conditions for your testing (not home) zip code, and use an ambient conditions power correction factor calculator like the drag racer and dyno guys do. Test only when the factor is close to 1.000, as the impacts of many improvements are greatly masked by changes in ambient conditions. (See
http://www.land-and-sea.com/dyno-tech-talk/corrected-horsepower.htm
)

4. Unless you have an engineering degree, disregard the horsepower and torque numbers generated by the G-Tech, for reasons explained in my book.

My book goes into lots of other important factors.

Using a G-Tech is superficially easy, but nobody said ACCURACY was easy! :)

Jim G
 

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Discussion Starter #3
Flat Road

Thanks Jim,

I know that ther are some real time problems with wind, road conditionsand lets not forget Jhonny law.I', eally only doing this to get a comarison on the same road, level or not before and after the supercharger install.There is however, a road down here in the country that is reasonable level and straight for at least 1/4 mile.Nuthin but cows and tractors.Ive' checked it with my sight level and it shows about 30" of fall to the landmark that is about 1/8 mile away.This should be good enough to get a good comparison.....I hope
 

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A 30 inch elevation drop in 1/8 mile is only a 0.38 % "downhill" in that 1/8 mile.

Yet, it changes the time and terminal speed for a stock 03 / 04 SSR as follows:
0 to 60: 0.1 second quicker
1/8 mile: 0.1 second quicker and fraction of a mph higher
1/4 mile: 0.1 second quicker and 1 mph higher

A 1% downhill (only 6.6 feet in 1/8 mile or 13.2 feet in 1/4 mile) does the following:
0 to 60: 0.2 second quicker
1/8 mile: 0.15 second quicker and 1 mph higher
1/4 mile: 0.2 second quicker and 2 mph higher

A 2% downhill (13.2 feet in 1/8 mile or 26.4 feet in 1/4 mile), which would be the lowest gradient potentially detectable by letting the vehicle try to roll in neutral, does the following:
0 to 60: over 0.4 second quicker
1/8 mile: almost 0.3 second quicker and 2 mph higher
1/4 mile: over 0.4 second quicker and 3 mph higher

You can see why I say that a 1% grade is already a problem for any accuracy, and a 2% grade makes the results useless.

Because Austin, Texas is in a climate where normally no ice can form on a road, we allow high grades here. In fact, one of the commuting highways here, FM 2222, has a 16% grade on it. When it does snow once very year or two, no one goes out on the roads.

Jim G
 

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What Jim said.....

I couldn't have given all that information :D

I have mounted mine on the silver bar across the dash so as not to block my view in anyway.

Have fun...
 

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Discussion Starter #6
thanks

WOWFACTR&JIM,

thanks for the info, I'll apply those numbers to my data when I get back home.So, WOW, the unit doesn't have to be in the windsheild for rececption or anything?
 

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The G-Tech doe not "receive" anything, except the tachometer siganl from the cigarette lighter, which comes via a coiled cord.

The most important thing is that its mounting be absolutely rigid. Any movement under than that caused by pure acceleration will also be misinterpreted by the unit as "acceleration".

This is why G-Tech provides that "solid" mount which can be bolted onto a consolte or other rigid surface. It makes it unnecessary to depend upon suction cup stability.

It is important that the unit be easily accessible so that you can hit the "start" button without doing gymnastics. However, the unit does not actually start timing until the vehicle "moves", so you have plenty of time after hitting the button to start the action.

Jim G
 

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Again what Jim said....(I wonder why he always beats me to the answers :lol )

I think that most people just mount it on the windshield because it's just a common, convinient, solid spot to mount it. I started out there, but I wanted to test my SSR out under a bunch of conditions on a bunch of roads, so I stuck it to the silver piece going across the dash and left it there for days. Anytime I found a flat (or so it seemed) road with no traffic and a good speed limit, I would do another run.

As Jim has pointed out in other threads that just because a road looks flat, doesn't mean it doesn't have a tilt that will affect your measurement. If you want an exact measurement, you should run the same road in both directions and if you come out with the same time then you probably weren't affected by tilt or wind factors. My times varied by .5 secs on most of my original runs and averaged about 6.5 sec 0-60 (which is all I ever ran). If you remember, GM stated a 7.5 0-60 for the 2003's, so I felt good about that right off the bat without having done anything to mine.
 

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Wowfctr: If you control the variables correctly, the difference between runs will be measured in hundreds of a second. A variation of 0.1 to 0.2 sec on a 0-60 mph run is about as much as you should get if everything is correctly controlled.

My graphs lines of multiple runs, and the matching tables, are often "right on top pf each other" EXCEPT when you can see a trend of "getting better" as the PCM learns from a series of runs and optimizes its lookup trim tables.

As for why I often "get here first", it might be because I spend altogether too much time on this board . . . :)

Vehicle physics is a passion for me, and therefore "fun" . . .

Jim G
 

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Even though I knew I wasn't controlling everything correctly, I still made the runs....just to see what happens.

And I did find out that many things affect your time....loose gravel, up hill slope, down hill slope, slight curve in the road, mashing the pedal down, pushing the pedal down, pushing the pedal half way down, wind.... just reiterating the fact that there are many things that can affect your time and may cause you to believe that something you did to your vehicle improved or adversely affected you when it may actually be some other condition.
 
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