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Gtech Results In
Well, my sorry slow *** 1987 GT turned in a 14.19@103.8mph. Shitty launches really hurt, stupid county roads have NO traction.
Here is my total combo. 1987 GT 5spd Hatch. 145k miles, clogged K&N, 10* timing, 87pump gas. T-5z (2.95:1 1st), 2.73's. BBK 2.5" hiflow cat H pipe, dynomax 2.5" super turbo cat back. I had 100lbs of crap in the back, and haven't tuned it for the last 32k miles. Looks to me like $100 of tune up 93oct and air filter cleaning would put me in the 13's easy. That's with 145k, 2.73's and a shitty 2.95 1st gear. Basically stock. Course, since all us old fox 5.0's get beat by stock Integra's my numbers must be off? |
Like usual with the Gtech trap speed is WAY off!!
My best time on gtech is 15.47 @ 94mph but I did not try it since I had 3000 km on the car! http://www.mustangworks.com/msgboard/biggrin.gif ------------------ 2000 Honda Civic SiR 15.368 @ 89.220 mph (stock) 1989 Ford Mustang LX Coupe 5.0L (RIP) 14.120 @ 98.126 mph |
Actually it's the dragstrip that is way off. http://www.mustangworks.com/msgboard/smile.gif
Tracks average your last 60 ft. rather than measure your exact mph as you cross the finish line. So at the track your trap speed is actually lower than your finish line mph. If you don't believe me, take a look at your speedo the next time you are crossing the finish line. Unit5302, I have tested my GTECH at the track and found that the GTECH will show almost a tenth of a secong slower than the track. This is because at the track the timer starts when you break the staging beams, not when the car starts to move. At the track you can pick up a tick if you stage very shallow. Just so the 2nd pre-stage light comes on. At the track you could very well see a 13.9 @ 100-101. |
G-TECH usualy is about 4-5mph off from the track because it measures the whole 1/4 mile where as the track does not just as xgmguy said, my car may pull 112+mph with the G-TECH but only 107+mph at the track but the ET is fairly close. http://www.mustangworks.com/msgboard/wink.gif
------------------ 98'Trans Am LS1 A4 273 gears Whisper lid,K&N,Flowmaster,Best ET on street tires 13.17 @ 106.49mph NEW MODS:3" Flowtech cutout,Magnecor wires,NGK TR55's |
Also the mph difference is greater the faster your car is.
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This is interesting info. I have heard some of this before, but I have one question: At the track, why do they AVERAGE your MPH for the last 60'?
I guess if all tracks do this then all of us comparing our track mph's are comparing apples to apples. E ------------------ 1991 5.0 LX Coupe - 38,000 miles 13.17 @ 106.14 mph w/ 2.138 60' |
The average at the strip because its a lot easier to have 2 beams a set distance apart, measure the time it takes you to get between them and divide then it would be to have a RADAR gun or similiar device to measure the actual speed.
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Cool, that seems logical. Thanks, 97snakedriver
E |
Upon consideration of the argument that the track is off by 3-4mph, I'd have to say that is totally false.
Both the Gtech and the track are off. Take a 100mph finish speed. We'll say it took 14sec to do the 1380. So 14.00@100.0. At 100mph = about 147ft/sec you'd be travelling the 60ft in about .4sec. Meaning at about 100mph you'd need to accelerate 3-4mph in .4 sec. Now the cars average acceleration from 0-60 could do that. We'll give the hypothetical car a 5.5 0-60. That's 10.9mph/s. Or about 4.4mph in the .4sec timeframe. That would be accurate, but the car doesn't accelerate anywhere near the same at 100 as it would during the 0-60. Since it took a full 14.00 to hit 100mph, that means it took the hypothetical car took 8.5sec to go from 60-100 or an average of about 5mph/s. That would be about 2mph over a given 60ft area at the end of the course. Now here is the fun part. We can acknowledge that the acceleration will be for all reality the same over that 60ft period, which means the average speed difference would then be half of the 2mph (actually, a little under 2) and that gives us a 1mph differential between what the Gtech should read, and the trap speed at the track. Math used behind this. 0-60 5.5sec 1/4 mile 14.00@100mph 0-60 average acceleration 10.91mph/s (60/5.5) 60-100 average acceleration 4.71mph/s (40/8.5) 40 comes from 100-60, 8.5 comes from 14.00-5.5. 3-4mph inconsistancy in Gtech vs track estimated. 60ft the last section of track where speed is averaged. ET for last 60ft .41 (60ft/147ft/s <100mph=147ft/s> ET for last 30ft .205 <since the acceleration can be rounded to even over the last 60ft, the speed given by the traps should be at 30ft before the end, cause that is exactly 1/2 way throught the 60ft> Now total acceleration over the last 30ft should be slightly under 4.71 x .205 = .96mph. That tell's me that the Gtech should be less than .96mph off what the track reading is. Since .96< 3 to 4, that means either the track is more inaccurate than we think, or the Gtech is also off slightly higher than real life. |
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------------------ 90 Honda CRX aka Project Mongoose Estimated Completion: 7/1/01 84 Toyota Supra High flow cat, two chamber flowmaster, custom 2.5" piping, msd 8.5mm wires. Will have boost before 2002. |
No I didn't.
There was just no way I could accurately gauge that inconsistancy into the equation without getting very technical and doing some seriously ridiculous amounts of math. The acceleration for the said 14.00@100 car I'll submit is a 1987 GT with 2.73's. For your non-seemless acceleration I'd submit this car shifted 1-2 at 35mph, and 2-3 at 65mph and finished the 1/4 in 3rd. For all practical purposes the negligable amount of time lost in shifting would basically balance out. Obviously the Gforces in 3rd would be smaller than in 2nd, but since the car only spends 5mph in second gear I can pretty much rule your idea that I need to examine that factor out the window, inferno, and instead say with a high degree of certainty that a 5.0 Mustang will not accelerate faster at 100mph in 3rd than it would over the average of a 60-100mph run. Would you argue with that? You don't own the hypothetical car, or any Mustang 5.0 for that matter, so in this case, I think you should hold that information correct. Now if you look at my post, you'll see that I said the average acceleration over the last 60ft would be less than .96mph different than the terminal speed at the end of the 1/4 mile. The reason I said "less than" was because I took into consideration the fact the acceleration curve of the Mustang 5.0 would be weaker in 3rd at 100mph than it would be over the entire 60-100mph range. Now if you'd like I can give you the G-force of my particular car at 100mph vs the average based on say a number averaged from a sample every .5 sec from 60-100mph, but I'm extremely confident it will back up my original assumption based on the kind of rpm the 5.0 would be turning at 100mph in 3rd. |
Blah blah blah blah blah.
The G-tech runs 3-4mph fast. Everyone knows that no need to agrue. ET's are almost dead on. Skyler ------------------ -1989 Saleen Mustang #406- TFS Heads, E-303, edelbrock intake,70MM TB, 73mm MAF, off road H, headers and 3chamber flows. 12.55@107mph Runs on 87 Octane and gets 24mpg! |
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------------------ 90 Honda CRX aka Project Mongoose Estimated Completion: 7/1/01 84 Toyota Supra High flow cat, two chamber flowmaster, custom 2.5" piping, msd 8.5mm wires. Will have boost before 2002. |
I have a program , Drag Analyzer by Performance Trends, That gives a pretty good mathmatical model of a track run. With my car that runs very high 13's at about 100, The purported difference between the last 60' average times of the time slip and actual trap speed is about 1.5 seconds. We all know that the G-Tech is about 5-6 MPH fast for this speed. Unit is right about this. They are both off to some degree.
There was a time in the distant past, not sure how long, that they had the speed measured as an average between the traps and 60' AFTER the finish line. That encouraged all drag racers to stay in the throttle way after the finish line to inflate their time slip trap speeds. It didn't change E.T. or the winner of the race, but it did raise time slip speeds. It was for that reason that they changed the average to 60' before and finish line. Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi. |
Oops, I meant to say 1.5 MPH, not 1.5 seconds as the speed differnce between time slip and actual.
Rev |
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I didn't make a blanket statement about the accuracy of the Gtech, all I said was it reads 3-4mph higher than the track, and all of that difference cannot be made up for by the track averaging the speed. Since there is still a 2-3mph+ discrepancy in the mph, even after taking into account the averaging by the track, either the track is even more inaccurate than the averaging or the Gtech is inaccurate. |
Unit, I am not trying to argue about this. I was just saying that your initial estimate isn't exactly true. It could be true, but not neccesarily. Sorry if you took offense.
------------------ 90 Honda CRX aka Project Mongoose Estimated Completion: 7/1/01 84 Toyota Supra High flow cat, two chamber flowmaster, custom 2.5" piping, msd 8.5mm wires. Will have boost before 2002. |
Dudes,
I don't like the GTec. It said I pulled a 14.65@97MPH to beat a 2001 911 Carrera 4 this weekend???? Mind you I don't think the weight of my car was entered.... WHAT THE HELL? ------------------ Lizard King, Bone Stock; 13.69 at 101MPH • Extreme Burnout •2000GT VS LS1 • Quartermile run •2000GT vs LX Stang |
Instead of using G-techs for ET's and MPH's, use the track! Nearly everyone on this site and countless others use the track to compare a car's status/potential. Barring any runs in Denver, most track times are comparable.
The "track" is definately an apples to apples comparison that I think we can all live with given its consistency among measurements. Unit - You should get track times for your Stang to put all this to bed once and for all - sounds like your ET may actually improve given the rough roads you were on. E ------------------ 1991 5.0 LX Coupe - 38,000 miles 13.17 @ 106.14 mph w/ 2.138 60' |
Eric, the track is not always quite as available as the G-Tech. Mine stays in the glove compartment. My G-Tech is .3 seconds and 5-6 mph optimistic for the 1/4 mile. It is dead consistent though. All I ever really use mine for is to see if my car is running up to snuff. Good for seeing if mods (timing, jets, etc) have hurt or helped. or how bad my fried Traction-Lock was hurting me. Stuff like that. Gives you a chance to take it out and toast the tires occasionally as well.
Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi. |
Good points,Rev
I guess if the G-tech is consistent, then it would be good for monitoring items mentioned in your post. E |
We used the Gtech at the track and it always came within about .1 of a sec, sure the MPH measuring is different. Like rev said it is a great tunning tool.
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I usually try to get a cop to get my MPH ... hehehe
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I have one real quick question, but it doesn't really have anything to do with a GTech, at all. But anyways...If I beat a car by about 3-3.5 car lengths in a 1/4 mile, about how much difference would be in our times? I know this changes with your speed, but a rough estimate would be nice. Thanks in advance.
------------------ '69 Coupe with 351W ========================= Edelbrock Performer-RPM intake manifold, Edelbrock Performer-RPM cam, Edelbrock lifters, Edelbrock 750 cfm carb, Accel coil, Moroso Blue-Max spark plug wires, Hedman headers, 2 1/2" pipe, glasspacks, Edelbrock double roller timing chain, Edelbrock valve springs, Flex fan, C4, Lakewood traction bars, 3:1 open rear-9" 3.89:1 posi coming this summer ========================= |
If yor trap speed is around 100mph, each car length will be about .1 second.
Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi. |
I agree with Rev my G-Tech is a great tuning tool, because the track is so far away. It is nice to go out and let her eat after small mods: tires whatever then you know if it's any better. Just my .02.
------------------ John Welch 86 GT, 3.73's, H-pipe w/ 2-chamber Flows, No smog pump or A/C, crank pulley, K&N in stock box, adj. FPR, bypassed EGR(coolant) Best Run 14.34 @100.0 MPH (on G-Tech) |
Is the Gtech worth the money or not?
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Sorry to be ignorant on this subject but what is GTech? A software program, timing trap lights, what? Approximate cost? I'm new to this but trying to educate myself. Thanks.
Lou. |
A GTech is a small electronic accelerometer that mounts in your car (on the windshield like a radar detector) and measures acceleration and elapsed time to come up with a 1/4 time. They are only as accurate as the accelerometer used in their circuit. The math they use is very accurate so like I said they are only as accurate as their accelerometer and timer can be. As far as GTechs or track times being more accurate, Unit, your math makes sense, but every car is different, that is why people say their GTechs are consistantly off. Every engine has a different torque curve and therefore a different HP curve. So, when you say that a car in 3rd gear will accelerate at a lower rate than the car in 2nd gear, you're correct, assuming that the torque curve of the engine is flat (a constant) This is only true for electric motors, hardly ever for a gasoline internal combustion engine. So, the mph change in the last 60 feet would be different for a car crossing the traps in it's power band and a car not in it's powerband, for instance, with my gears, I shift into 4th about 300 feet in front of the 1/4 mile. So I am crossing the traps at about 4000 rpm, I would accelerate differently in the 60' in front of the line than a car crossing at 6000 rpm. Therefore the difference between average speed over the 60' and instantaneous speed at the end of the track will be different for every car. In other words, the track will be off by a different amount for every car. Now, I feel that I must make a statement about somthing that someone else said. Something about being able to get actual speed with a radar gun at the end of the track. Did you mean instantaneous speed? speed is defined as the (change in distance)/(change in time). Instantaneous speed is defined as the speed when the change in time = 0. Everyone knows you can't divide by 0 so it is impossible to measure instantaneous velocity, unless you use calculus which is what a GTech uses. When the GTech integrates to get velocity the margin of error becomes exponentially greater, so if the accelerometer is off by a small bit, the velocity will be off by a lot. Anyway, like I was saying, even with a radar gun, you are by no means measuring instantaneous velocity. The radar gun measures doppler shift. The change in frequency of a wave when it hits a moving object (listen to a car horn as the car is moving towards and then away from you, it's higher and it gets lower as it goes by right?) doppler shift. Anyway, the radar gun knows the wavelength of it's sent signal, it measures the wavelength of the received signal, and subtracts them. Which is still measuring a distance over time. So anyway, even though a radar gun is more accurate than a 60' average, it is still an average. My main point here is, nothing is 100% accurate, and all of this is for fun anyway guys, so GTech times, track E/Ts whatever, believe what you want about accuracy, it's all relative.
Oh yeah, Lizard King, what does the weight of your car have to do with a GTech measuring a 1/4 mile time? [This message has been edited by QuantumMotorsports (edited 04-24-2001).] |
Thanks Quantum,
I found their website: http://www.gtechpro.com Price is $139.95 for the new (pro) model. Will upgrade origional for $40.00 Unit mounts to windshield and plugs into cigarette lighter. As long as it stays consistant seems like a great tool to have despite all this controversy. Lou |
The proper shift into the next gear should hold your acceleration curve nearly perfect, Quantum.
Sure your car will be making more torque at 4000rpms than 5500rpms, but I'm willing to bet the loss of torque multiplication due to a higher gear in the tranny will offset this. If you are shifting properly, it most certainly will. From everything I've seen the Gtech's seem to be a pretty consistant 3-4mph off. |
So you're trying to tell me that in each individual gear your acceration is a constant? Even though engine RPM is changing and when engine RPM changes your torque changes. Then why not run each gear to the rev limiter even on a stock motor? After you pass peak HP you will reach a point where your acceleration will be greater in a higher gear. My whole point is, the track times will be off by a different number for every car. And since the track times won't have a consistent error for every car, neither will the GTechs. I'm sure that there is some car that could run the 1/4 with a GTech in the car and the GTeck would match the ET and MPH exactly. It depends on the car. And given the amount of variables that are present when running a car down a track, you're never going to be able to accurately calculate acceleration. And using an average is not helpful because the range is so large and you are making a calculation of error using one end of the range (the end of the track)
About the change in RPM and difference in gear ratio. Not all engines make more torque at 4000 RPM than they do at 5500. My whole point is, without knowing the torque and power curves of the engine, you cannot accurately calculate acceleration. ------------------ Michael Black Quantum Motorsports Norman, Oklahoma 1988 Merc Cougar 5.0 HO, Ported and Polished E7TEs, 2.25" duals w/ 2 chamber flowmasters, T5 tranny New E/T!!! 14.626 @ 94.94mph, 2.194 60' time, a little better than last time. Keep in mind this thang is heavy (3590lbs) Finally 14s!!!! |
The G-Tech claims to check G force about 100 times a second. From these numerous samples, it calculates speed at any given instant. Since time is determined by a pretty accurate clock, the mph and distace can be pretty accuretly determined at any given instant. These "averages" are from one 1/00 second to another. That's the only reason these gadgets work as well as they do. The fact is that the G force meter works pretty well due I think to space exploration developement.
Rev Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi. |
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