does it work? has anyone tried this before?



http://cgi.ebay.com/ebaymotors/ws/eB...tem=2416970564

 

yeah, it works

What works well is the 1/4 miles, reaction time, 0-60 time, shift light, rpm reading, lateral acceleration warning.

The hp and torque reading is less accurate. It takes into account a lot of factors, even more than a dyno.

I was very dissappointed with the HP reading from my Celica GT though.

 

It's accurate withen 5% of the rwhp. Meaning suppose you really have 240rwhp, it's range would be 228rwhp to 252rwhp.

I use to own a celica gt.. they are low hp cars, but light as hell, so it's pretty nice. 140hp, 1.8l vvti engine, with about 15% loss, your looking at about 119fwhp?

 

uhhh, much lower

plus it's an auto

and had extra weight in it

anycase all the reviews I've seen showed the hp/torque estimates are way off

 

I dunno about HP / TRQ Estimates...but it works great as a mod difference tool. Test it out then add say a K&N FIPK then run again to see the difference... Otherwise mine was always 2~3 tenths off in the 1/4 and 6~7 mph higher than my traps. Verified at the track on more than one occasion.

 

its like the difference between accurate and precise?

cant remember which is which, but it is consistant, it will tell you the difference between 2 setups very well. but it wont tell you the ACTUAL time quite as well. if that makes any sense, if it says 14.1 and then 14.0, you know that the second time you were faster, but neither run was nescesarrily a 14.1. or 14.0.

 

I borrowed the newer GTech Pro Competition from a friend of mine and tried it out on my Z. At the time I tried it out, I was bone stock. For what its worth, the thing is consistent. My 1/4 times were in the 13.7-13.9 range trapping rather high. I did back to back runs, on the same street, in both directions. I've never taken my car to the track, So I cannot comment on how accurate it is in relation to actual 1/4 track times.

I have dynoed my car, so I can safely say that the HP/TQ #s were off (below actual RWHP) by like 10-15 hp, but I guess that might be due to me inputting the incorrect vehicle weight (I guesstimated). Nevertheless, it can be a useful, if not fun, tool to use in your tuning.

Would I buy one? Probably... if it were less than its MSRP... say in the neighborhood of $100-$150.

Regards,

iboost

 

I have one and its pretty much accurate. I was running a 14.2-14.3 with just a Injen intake. 0-60 was 5.7-5.8 seconds.

 

By what I remember, percise is when you do something over and over again (for example, quater mile runs), and get the same time all times. Of course maybe out of 100 runs, you'll get a few, but it's a very low percentage.

Accurate is when it's in a "ball-park" range of each of the trials.. such as maybe 13.9,14.0,14.1,14.0,14.0,14.0... you could said "14.0" is an accurate number.

 

I have one also except I did take it to the track to see how accurate it was. At the end of the run I did a 13.88 @ 105 mph with a 0-60 time of 5.3 and sure enough, the gtech was spot on with the exception of the trap speed which is alway 2-3 mph high.

 

trap speed at the track is an average of I think the last 60 feet/time it takes to travel it, meaning its an average of your speed over that 60 feet, not your real final speed.

gtech gives final speed, hence why it should be a bit higher than your "trap speed"

 

You guys are all close.

Accurate is how far away you are from the "actual" value.

Precise is the level of resolution you are able to measure.

Repeatability is how close you can get to the same value on multiple attemts.

Lets say for instance that you run a time of 14.05 seconds exactly.

A measured time 14.069002 is very precise (measured down to the nanosecond), but not very accurate (off by .019 seconds).

A different measurement device gives you 14.06 . This number is less precise, since you are measuring only to the hundreths of a second, but actually more accurate since it is off by only .01 seconds.

I have no first hand experience with the G-Tech, but based on its name, I would guess that it is accelerometer based. Therefore it is measuring the amound of acceleration the G-Tech is experiencing over a given increment of time. Since the car's velocity is simply a*t, the G-Tech can calculate the speed by multiplying the measured acceleration by the time period. It can then add up all the samples to find the total velocity. Also, distance is equal to 1/2*a*t^2, so the G-Tech should also be able to calculate your distance travelled (probably how it determines 1/4 mile times, maybe comparing it's numbers with your Odometer if it plugs into the car somehow). If the G-Tech uses a single axis accelerometer, then it would need to be placed in a specific orientation so that accelerometer is acting inline with the direction of travel. Also, it would only be able to measure in a straight line. With a 2 or 3 axis accelerometer it could measure lateral g's as well as hills and valleys.

Depending on the sampling rate and accuracy of the accelerometer, the results could either be quite close to real or very far off.

In order to translate back to HP, the G-tech would need to know the mass of the car with driver and gas, and perhaps some gear ratios, although I think those should factor out in the end. Anyway, I'm guessing that the main problem with calculating the HP is the variation in vehicle weight.

My Z with me inside and about 12 gallons of gas weighed 3400 lbs. I measured the car at our local dump where the scale has a resolution of 20lbs, and is accurate to +/- 20 lbs.

Anyhow, I thought it would be cool to hook up a 3 axis accelerometer to a laptop with a datalogger and a GPS system. Then you could map out a course as you drove and compare your lap times with lateral G's and stuff. Does G-Tech do something like that already? Basically a poor-mans telemetry system.

-D'oh!

 

[QUOTE]Originally posted by D'oh

I have no first hand experience with the G-Tech, but based on its name, I would guess that it is accelerometer based.


Yup.

Also, distance is equal to 1/2*a*t^2, so the G-Tech should also be able to calculate your distance travelled (probably how it determines 1/4 mile times, maybe comparing it's numbers with your Odometer if it plugs into the car somehow).

No interface with the car. It is indeed just calculating distance via acceleration and time, as you suggested above.


If the G-Tech uses a single axis accelerometer, then it would need to be placed in a specific orientation so that accelerometer is acting inline with the direction of travel.

The old version is indeed only a singal-axis unit. When you first suction-cup it to your wind shield, it has an "alignment" mode where you keep adjusting it's mount until it's perfectly even. It displays it's current angle in some unit... I'm assuming degrees, but it could just as easily be some arbitrary unit. You basically just adjust it's mount until you get it level and the display shows zero "units". (no positive, no negative)

Also, it would only be able to measure in a straight line. With a 2 or 3 axis accelerometer it could measure lateral g's as well as hills and valleys.


Exactly. The old version, being a single-axis unit, can only measure in straight lines. It will do braking tests, acceleration test, hp test, etc. But you can't turn, or it gets messed up. The new version (I believe it's the "Competition" model) is a multi-axes unit, so it is much more capable. Even has a serial interface for your computer so you can download results. I think it even will record longitudinal and lateral g's over time, and do a simulated course plot which you can download to your computer... or I might be thinking of a competing product on that feature. I know there is one out there which will do that. Can show you your braking, turn-in, and turn-out points on the course plot. Extremely cool.


In order to translate back to HP, the G-tech would need to know the mass of the car with driver and gas, and perhaps some gear ratios, although I think those should factor out in the end. Anyway, I'm guessing that the main problem with calculating the HP is the variation in vehicle weight.


Exactly. I believe most people just estimate their vehicle weight, which is inevitably wrong by many pounds, thus giving very inaccurate HP readings with the G-tech. I did like you, and weight my car at a vehicle scale, so I knew the weight of my car with me and a full tank of gas. When I entered this correct weight into the G-tech, it actually gave me surprisingly accurate HP results.



Anyhow, I thought it would be cool to hook up a 3 axis accelerometer to a laptop with a datalogger and a GPS system. Then you could map out a course as you drove and compare your lap times with lateral G's and stuff. Does G-Tech do something like that already? Basically a poor-mans telemetry system.

You should go here:
http://www.extremegeez.com/

There are others which are even more capable than the Extreme Geez unit, but I can't think of the names. They get extremely impressive as they get more expensive.

A neat feature of the new G-tech Pro Competition model is that it will give you a complete hp/tq graph over all rpms, as opposed to just the peak HP that the old model gave you. Once it knows your power graph, it will even tell you where you optimum shift point is. I believe the new model gets your RPM by reading some pulse from the cigarette lighter power. Not sure how that works exactly.

Check out:
http://www.gtechpro.com/

 

From the GTech FAQs...



Why is my G-TECH/Pro consistently 2-3 mph above the track?
G-TECH/Pro is a very accurate machine, and the trap speed result that you get from the G-TECH/Pro is actually more accurate than the racetrack. Reason is that the racetrack averages your speed over a 60 feet stretch between two beams and G-TECH/Pro measures your speed at the exact 1/4 mile point.

 

jreiter,

Thanks for the info and confirmation.

I'll have to check out those links.

-D'oh!