I agree 100%.

The G-tech is a tuning tool, with its data to be interpreted as any raw data.

No different from interpreting dyno data and standardizing your testing methods to achieve repeatable results.

Comparing the 2 is an apples/oranges proposition, but it is valid data nonetheless.

 

I've never been a fan of the $150-300 accelerometers. I played around with a G-tech both on an off the strip. I never found it to be terribly accurate. It always seemed to read .2-.3 too quick and 3-5mph too fast. The device seems to flake out really bad if you have a violent launch with wheelhop and such which a common issue with FWD. I know that the G-tech would say my Maxima was running 14.0-14.1@103mph+ when my slips said 14.3-14.4@99-100mph. I got bad wheelhop once and it said I ran a 13.8@104mph. Yeah right

To me, accurate means it's within .1 seconds. The G-Techs read 1/4 mile trapspeed 2+mph higher because it doesn't average MPH over the last 66' like a real track does.

 

And personally to me that's more accurate.
I've never understood why dragstrips "average" your speed
over the last 66' or whatever it is.
The point it see how fast your car can go in the 1/4 mile.
Not how fast your going over an "average" if the last 66'.

Why don't tracks just have radar guns located AT the 1/4 mile stripe
and read what you are ACTUALLY going when you cross the stripe?
They don't "average" your time, so why average your speed?

 

It doesn't matter how accurate it is. It's a question of consistency. If it's consistently off by the same margin, then it can still be used as a tool. For example, if you ran a 14.5@95 stock, and the accelerometer registered a 14.3@97, then you did x number of mods, yielding a 14.0@101 at the track, and the accelerometer measured a 13.8@103, it's consistent. The margin is known. Knowing the margin, the unit can still be used to measure the effectiveness of mods, etc.

And someone please correct me(as I don't have a gtech), but the newer models use 3 separate accelerometers to measure along 3 planes, correct? If so, with some "dialing-in" of the unit, it shouldn't be fooled by crazy launches.

 

sorry dont know, i only have the beltronics, i think it is consistent, and thats my point, not how accurate it really is, i will test it though at the track and see how off it is


i have done about 30 40 runs with it and it always says within a tenth and 1 mph, assuming i didnt spin like crazy or do anything that wasnt normal..

even at the track though you will get a difference of that on your runs, so i am taking the average of a lot of them

and to the people that are raggin on accelerometers, please dont comment or how off they are until you drive around with one in your car for a while and play with it for a while, that way you have the chance to see how it averages out...

 

I've never found them consistent nor accurate, even on the track. I'm usually a very consistent racer with ETs and MPHs usually within .1 less than 1mph. The G-Tech (1st generation) was horrible. It was all over place. If you have a violent launch, the consistency went out the window.

This is just my experience. I would never buy one mostly because it would be way to tempting to be trying it out on every lone stretch of road. That's simply too dangerous, risky, and expensive for me I look at at as, I could have gone to the track at least 10 times and made over 10 passes each time for the cost of the unit plus I would have been racing my car legally and with an ambulance 100 yards away. That's just me though.

 

i do agree with this, thats why i was only running it out where my dad lives in the country, still not legal on a road that has no traffic and a 55 mph speed limit, the only thing i ever do on the streets in orlando would be my 0 - 60, only on the streets without anyone on it. i agree though, it is rare when you have no traffic and a nice red light to hit the calibration button, it probably is a bad idea if you dont have any control over driving crazy or not...

 

Not being much of a drag racer, I can't tell you why tracks do it the way they do. But your question got me thinking. Car & Driver uses a device called the VBOX to collect all of the performance metrics; in other words, they do not go to a sanctioned track with sanctioned equipment. Does anyone know if the VBOX averages 1/4 trap speed, or is it a terminal speed at the 1/4 mile point?

 

Terminal speed and it is typically an average of ~10 runs in both directions. The cars are also fully loaded with fuel, spare, etc plus ~50lbs of test gear. ET/MPH is also corrected to standard conditions (sea level, 0% humidity, 29.5? baro pressure). Basically if you can get your car to run at least as good as a mag gets, consider yourself a halfway decent driver.

 

I know we've already discussed this portion of the mag's testing methodologies, but, I'm not too sure I believe it.

 

I've already tested this theory. Last time at the drag strip, my best run was 14.1 at 99 mph with a 2.1xx 60'. I then made a run with my girlfriend, who weighs 1xx lbs (she might read this), and ran a 14.4 with a 2.1xx 60' at 96 mph. My shifting was flawless in both cases and the weather condition, baro, elevation, etc was exactly the same. Weight does matter.

 

The tracks I have been to won't let you take passengers!

BTW, Has anyone tried the New GTech Pro SS or RR models. They are supposed to use 3 accelerometers and be more accurate.

Finnaly, I assume that Dragstrips use a 60' average for your trap speed because it is more reliabe and accurate. I t makes determining the MPH a very easy calculation of the basic formula...rate*time=distance. If the tracks were to use radar or something similar, there are too many chances for error.

 

Maybe I'm not following you. Are saying you're not sure if the mags really correct thier times? Well either way, this is taken directly from Car & Driver (April 05) (Motor Trend reads similiar) concerning their driving, correction for conditions, etc.

....test vehicle loaded with driver, full tank of fuel, and 10lbs of test instrustmentation (hey, it use to be 50lbs )

....with manual transmissions, wheel spin or clutch or both are used at the starting line to make the best of the engine's power characterisics...

....all upshifts are lift-throttle..

....with automatics, brake torquing is used when beneficial to produce the best launch..

...time, speed, and distance are measure using a Racelogic VBOX GPS-based velocity sensor...

...all performance results are corrected to standard atmospheric conditions...

 

Prior to 1989, there were three sets of timers near the end of the track. 66' short of the finish was the first trap speed box, right at the finish line was the ET box, and 66' past the finish was the last trap speed box. The trap speed was calculated from the average over 132'. Drivers had a tendency to stay in the gas longer than necessary and as the years progressed and cars got faster and faster, people simply started to overshoot the runout and wreck. In 1989, in order to stop the overshoots and wrecks, the NHRA mandated that the second trap speed box be pushed back 66' to the finish line and that trap speed would only be calculated over 66'. This gave drivers the ability to know the race was truely over at the finish line. There is about a 1% difference in MPH between the old way and new way of calculating trap speed.

Also, if you read about some car posting freakishly high MPHs, there is the possibility the track is using the old system. Only NHRA/IHRA tracks are required to use this system.

 

I'm sorry I wasn't clear. I understand that C&D claims to correct for atmo corrections. I've read the magazine's published testing procedures. I'm just not entirely confident that they actually follow the procedures.

For example, go back over the sports/lux sedan comparison of a few months back. The lexus IS350 was published as having a time of 13.7@104. The G on the other hand(6MT), was published as having a time of 14.6@9x(can't remember the exact speed).

Back then I questioned the times of the G. I, having never been to a track in my life, having driven my first and only manual transmission daily driver for a total of 3000 miles, put down a 14.7@95 in 98+ degree temps. That was with a 2.29 sixty foot, and horrid shifting. Now, compare that time with what C&D could wring ouf of the car. According to the magazine's own publish testing procedures, they try different launching techniques. They lift the throttle while shifting. And they supposedly correct for atmo conditions/elevation. Granted, the temps the day they tested the G were registering in the 115 range, and I don't know the elevation, but to have the magazine get a *corrected* time of 14.6? No way. Absolutely not. Maybe if they were running 87 octane and a spring was faulty on the throttle body allowing only 50% airflow, maybe I'd believe that.

I won't go into any more specifics, but I'm fed up with C&D. I'll read it for entertainment purposes in the future(still have almost 3 years left on my subscription), but I cannot take them seriously as any kind of authoritative source.

As for the IS350? 13.7 is on the low side of believable, but still doable. I doubted it earlier. But I can't believe they got a 104mph trap speed.

Here are a couple of times from dragtimes.com:
http://www.dragtimes.com/results.php...arch+DragTimes
One guy hit a 13.9, and another hit a 14.5. But both only trapped at 98. 98 to 104 is a *looonnng* way to go...

Oh, and for reference, here's the C&D comparo:
http://www.caranddriver.com/article....&page_number=8