Mazda MX-6 Forum banner
1 - 20 of 21 Posts

·
Registered
Joined
·
27 Posts
Discussion Starter · #1 ·
I'm looking for a device that will test my 0-60, 1/4 mile and breaking times. I have seen them in performance shops and they plug into the cig lighter. Does anyone know where I can find one that will mount in-dash?
 

·
Registered
Joined
·
312 Posts
Well I have used a G-tech thats my friends. He payed $100 i think. It said I ran a 15.7 at 94 mph. I think the mph is off by a little. If I did 94 mph my time would have been a little quicker. the horsepower is way off, if you go on a uphill I can get almost 400 hp, downhill not even 100 hp. It also tells 0-60 which seemed correct. Braking time I am not sure if it showed it.
 

·
Registered
Joined
·
1,858 Posts
The key to these devices is that they must be installed perfectly horizontally, and the runs must be on perfectly flat and horizontal roads. They can be somewhat accurate, but I still wouldn't bet on those numbers.

The uphill-increase is because the device thinks gravity is adding to your acceleration (which is, of course, not true). Downhill is the opposite... again not true. This is why the device can't be totally trusted. However, you can get close if you do two runs, in opposite directions, and average the values. This is what the car magazines do, in case you didn't know, since you can never find a perfectly flat, perfectly wind-less day.
 

·
Registered
Joined
·
1,112 Posts
They're usually .2 seconds faster than the actual 1/4 mile ET. Don't really know why...

I'm gonna guess it's because there's no "beam" to pass at the start or finish line.

At a real dragstrip, most cars have a 6-8" "rollout" from the start. That's when the car moves, but isn't actually being timed yet. The G-Tech times as soon as the weight is shifted to the rear of the car.

They're also usually 2-3 mph faster than the 1/4 mile. This is because the drag strip averages your speed from two beams at the end of the track.

The beams are 60ft apart, and the time it takes you to get from one to the other is used to determine your speed.

In order to stay consistant, the computer they use adds the two together, then divides by two. The result is your "average" speed over the last 60 ft.

Just to give you an reminder of what an "average" is...

Add each number to get a total, then divide by how many numbers you added together ...

64 + 36 = 100
100 / 2 = 50

38 + 42 + 20 = 100
100 / 3 = 33.333

The G-Tech displays your speed RIGHT AT the end of the 1/4 mile. So of course it reads a little faster.
 

·
Registered
Joined
·
1,858 Posts
Ahh... now I get to play some math!

So, you're saying that over those last 60 feet, I am still accelerating 2-3 mph, and that the GTech is "more accurate" because it's taking the speed at the end? I highly doubt that, so let's look at some numbers.

Let's take some "professional" numbers and use the August 1992 Car and Driver test of the MX6 LS. They claim a 1/4 mile time of 15.6 seconds at 88 mph. Start by converting to feet per second:

88 mph * (5280 feet/mile) * (1/60 hours/min) * (1/60 min/sec) = 129 feet per second.

So, at that speed, we travel the 60 feet in how many seconds?

60 feet / 129 fps = 0.465 seconds to travel 60 feet.

Your telling me that I am still accelerating over those 60 feet to result in a 2-3 mph speed increase. In other words, over those 0.465 seconds, I am accelerate 2-3 mph?

Let's put that in perspective. C&D shows that from 80-90 mph in the acceleration test took 16.5 - 12.6 or 3.9 seconds. This run is mostly in 3rd gear, which is where I end my 1/4 mile run (at just about 7krpm). So, for 10mph of acceleration in third gear, we take 3.9 seconds. To put it another way, we are accelerating an average of 2.6 mph per second.

Of course, over those 60 feet, as you recall, we only have 0.465 seconds to accelerate, so we can only possibly accelerate 1.2 mph over that distance. Not quite the 2-3mph that GTech claims to be gaining over that distance, now is it?

Sounds to me that Gtech is simply not perfect, as I stated before... so I stand by my original statement - don't bet on Gtech numbers.
 

·
Registered
Joined
·
1,974 Posts
My friend ran a few runs with his Gtech on while at the track. The GTech tmies were consistently lower and the trap speeds higher. I'll see if he still has the time slips scanned. If he does Ill post em.

Slips not scanned, but times:
GTech: 14.37 @ 102 mph
Track: 14.663 @ 95.29mph

Bear in mind the GTech measure trap speed at the last second versus the track using the average over the last 60 feet. Still though, even mounted properly on a flat surface the results were not the best.
 

·
Registered
Joined
·
1,112 Posts
schwinn said:
Ahh... now I get to play some math!......Sounds to me that Gtech is simply not perfect, as I stated before... so I stand by my original statement - don't bet on Gtech numbers.
I never said it was perfect, nor to "bet" on it. :rolleyes:

I simply explained why it's not 100% accurate. These are my own claims, not G-Tech's.

And actually, it may be the last 100ft of the track. I don't recall exactly since I don't own a dragstrip, yet.

Even so, the division you used was for an average rate of speed without acceleration.

And all you did was prove that the MX6 is slow to accelerate from 80-90 mph. That has nearly nothing to do with a 1/4 mile run because the momentum isn't there when cruising at 80 mph, then accelerating up to 90 mph. There's a slight "lag" (for lack of a better word.)

You've shown that you can add, subtract, multiply, and divide pretty well, but that's about it. There's a lot more math involved.

Damn... and you were SO CLOSE to showing me up. :rolleyes:
 

·
Registered
Joined
·
1,112 Posts
I'd just like to add something rather interesting...

You stated that Car & Driver magazine did the 80-90 mph test in 3rd gear. I have to call BS!!!

Right after I posted I had to travel 6 miles on a 2 lane highway to go pick up a few things. During my travel I experimented a little. I left my MX6 in 5th gear and sat at 80 mph for ~10 seconds. I then floored it until I reached 90 mph. It took me ~ 4 seconds according to the elapsed time counter on my Blaupunkt CD player.

I then did it in 3rd gear I was at REDLINE right at 90 mph, but it took me a mere 3 seconds.

I'd say that's rather interesting... Oh wait. I already did. :lol:
 

·
Registered
Joined
·
1,858 Posts
I confirmed your 60-foot statement with some other websites. Coincidentally enough, at least one other site was also questioning the GTech's accuracy, and a similar argument as yours was presented for the speed difference.

The division I used was for average rate of speed without acceleration because, as the numbers showed, the acceleration was minimal relative to the speed at the first 60-foot mark. Besides which, this is counter to your argument, as any addition of acceleration during those 60-feet would decrease the time to travel it, and therefore the actual speed increase would be slightly less. I didn't want to get that deep into the numbers, so I simplified and made the calculation conservative.

The acceleration time was given by C&D as part of their single run acceleration test. In other words, they do a full speed accel test, and the data logger captures the entire run, and breaks down the speed ranges as provided. That being said, they would obviously be driving the car at its best acceleration rate, ie mostly in 3rd gear for 80-90 (as the car comes to 88mph at 7krpm). Therefore, the 80-90 acceleration was not during any lag-event, nor would it be in the top gear, as they have a seperate test for top-gear accel.

Yeah, I can add, subtract, etc quite well. Being an engineer helps.

Now as for you calling BS, you claim to take 4 seconds to accelerate from 80-90 in 5th gear? Did you, by chance, repeat the run in the opposite direction, to cancel out wind and hill-effects? And you used a little counter on your radio to do this? You'll pardon me if I trust the accuracy of C&D's test equipment over your radio's clock. Nevertheless, being the open-minded science-geek that I am, I will perform the exact same test in my area, using a stopwatch... just for information's sake.

Lastly, you say you performed the test in 3rd gear and you were redlined at 90. As I said before, I chose 80-90 because it was within the trap-speed range of the 1/4 mile times for our cars, and it was mostly within a single gear, 3rd gear, which is where you would be during the 1/4 mile run. Again, I will confirm your clock-radio timings, just for information's sake.

As for betting on the GTech, at least you realize it's not that accurate. But that is the point I am making... it's not accurate, and so it should not be used for presenting time-slip quality data. I was simply trying to explain away the "2-3 mph" difference as an error in GTech's device, rather than "better accuracy".
 

·
Premium Member
Joined
·
7,196 Posts
schwinn said:


The division I used was for average rate of speed without acceleration because, as the numbers showed, the acceleration was minimal relative to the speed at the first 60-foot mark. Besides which, this is counter to your argument, as any addition of acceleration during those 60-feet would decrease the time to travel it, and therefore the actual speed increase would be slightly less. I didn't want to get that deep into the numbers, so I simplified and made the calculation conservative.


As for betting on the GTech, at least you realize it's not that accurate. But that is the point I am making... it's not accurate, and so it should not be used for presenting time-slip quality data. I was simply trying to explain away the "2-3 mph" difference as an error in GTech's device, rather than "better accuracy".
Keep in mind, as you get higher in the gear, you don't necessarily have a faster acceleration rate. The KL03's performance is known to drop off around 6200 or so...Because of this, it's going to get better acceleration in some parts of third gear than others. I'm sure it is possible to gain 2-3 mph if you're right in the heart of your powerband over a half second interval. Afterall, it takes ~7 seconds to get to 60, giving you 8-9 per second. Obviously, first gear will have a little better acceleration than third, but it's still very possible to gain 6 mph in a second.

I know Gtech times are off, but being an engineering student also, I had to think about the math and some other factors involved:) I don't think my logic is off anywhere, but point it out if I am.
 

·
Registered
Joined
·
169 Posts
is there any way i could get my hands on that C&D issue? do they have a deal or something that i could buy that year?
 

·
Registered
Joined
·
1,858 Posts
Mavric03 said:
Keep in mind, as you get higher in the gear, you don't necessarily have a faster acceleration rate. The KL03's performance is known to drop off around 6200 or so...Because of this, it's going to get better acceleration in some parts of third gear than others. I'm sure it is possible to gain 2-3 mph if you're right in the heart of your powerband over a half second interval. Afterall, it takes ~7 seconds to get to 60, giving you 8-9 per second. Obviously, first gear will have a little better acceleration than third, but it's still very possible to gain 6 mph in a second.

I know Gtech times are off, but being an engineering student also, I had to think about the math and some other factors involved:) I don't think my logic is off anywhere, but point it out if I am.
Normally I would agree with you, Mavric, but our redline is at 7k, and I know that after 6250, the last VRIS point clicks over and I certainly see improvement in my acceleration immediately thereafter.

Secondly, as an engineering student, you should certainly be aware of gear ratios, correct? Well, in 1st gear, you have a much lower gear ratio than in 3rd, so therefore, it's a physical fact that you will get much more acceleration in 1st rather than 3rd - you're simply not putting down the power in 3rd that you are in 1st.
 

·
Premium Member
Joined
·
7,196 Posts
I know about the ratios, and you're not getting the same amount of power in third. I'm just saying that it would not be out of the realm of this world to see 2-3 mph increase in the 60 ft. Even if you're getting only half the acceleration as first gear, that would still give you a good 5 mph gain within a second, especially in the heart of the power band.

Of course, when I finish out a quarter mile track, I'm always in fourth gear. I figure I'll get better times using fourth right at 4500 rpm then 3rd going into redline
 

·
Registered
Joined
·
1,858 Posts
I'm not so sure that it's not out of the realm. I don't have the gear ratios in front of me right now, but I believe there is a difference of about 4:1 between 1st and 3rd. No matter, this is the reason I looked at the accel numbers from C&D since they represent reality, and what is actually happening.

At this point, I think the discussion has left the intents of the original post. I would be happy to continue this mathematical exploration, but I don't want to bore everyone.

Suffice it to say that I still do not believe a 2-3 mph increase in the last 60-feet.

The GTech is useful for comparing performance from one run to another, but it cannot be used to compare directly with a true 1/4-mile track run.
 

·
Registered
Joined
·
1,112 Posts
schwinn said:
The GTech is useful for comparing performance from one run to another, but it cannot be used to compare directly with a true 1/4-mile track run.
No sh!t Sherlock, as I've already pointed that out AND explained why...

yet you continue to argue. :rolleyes:

Some people have nothing better to do with their time :shrug:
 

·
Registered
Joined
·
1,858 Posts
drvITlîkUstôlIT said:
No sh!t Sherlock, as I've already pointed that out AND explained why...
I fail to see where you explained why. I said it's not possible to show 2-3 mph increase over 60 feet at or near redline. You have said nothing to "explain" it otherwise.

yet you continue to argue. :rolleyes:
I don't see where I was "arguing"... I was simply discussing, and hoping that you, or someone else, would have an explanation.

Some people have nothing better to do with their time :shrug:
You're right, I have nothing better to do than to ask for reasons for statements which don't make sense. If you can't explain your reasons, then don't complain when someone can refute your unsupported statements.

Anyway, I don't want to drag this out anymore. Seems like some people can't take a healthy discusson on a discussion board :shrug:
 

·
Registered
Joined
·
1,112 Posts
This is one of those things that you just have to bite your lip and accept. :shrug:

If you don't know how to figure out the math, like an accelerometer can, then don't try. That's why they sell them.

I'll be the first to admit, I don't know how. But then again, I don't really care to. I'm not in the market to make these things so why do I care? I suppose if I set my mind to it, I could find out how, but again, why?

Plus... You make it sound as if every pass at a dragstrip is etched in gold. Well, there are great margins of error there also. If you know about deep, shallow and side staging, roll out (which I've explained), as well as low staging then you'll see there are many ways to fool the beems at a dragstrip.

I can go to the dragstrip right now, and without changing my launch or shift RPM, I can make a 2-3 different changes from one run to the other and shave or add 1-2 tenths to my 1/4 time.

Since you're a engineering student you should easily be able to figure out what I'm talking about.

BTW, if it helps in your quest... I found out for a fact that it's the last 66' of the track.
 

·
Registered
Joined
·
1,858 Posts
Understood... and thanks for your input.

I like to analyze things deeply, being the engineer that I am. Sometimes that gets me in trouble :p

The concept behind the Gtech is a good one, however if you ask me, it's not well implemented. Leveling the device is critical to its accuracy, but when you jump off the line, the car tips back, hence changing the leveling and adding to the inaccuracy. It just bugs me that they don't see this problem and don't seem to want to resolve it. Instead, they'll just "fudge factor" it out. To me, that's piss poor engineering.

Anyway, I am off the box now.... :)
 

·
Registered
Joined
·
1,974 Posts
schwinn said:
Understood... and thanks for your input.

I like to analyze things deeply, being the engineer that I am. Sometimes that gets me in trouble :p

The concept behind the Gtech is a good one, however if you ask me, it's not well implemented. Leveling the device is critical to its accuracy, but when you jump off the line, the car tips back, hence changing the leveling and adding to the inaccuracy. It just bugs me that they don't see this problem and don't seem to want to resolve it. Instead, they'll just "fudge factor" it out. To me, that's piss poor engineering.

Anyway, I am off the box now.... :)
Though it may seem like an easy task, building a perfect accelerometer (sp?). is a pain in the ass. I helped some friends design one as a senior project. They spent WAY too much money. Used parts that are far more advanced then you'd ever find in a GTech. (Wish I'd had a near neverending bankroll for my senior project.) And they were smart guys on top of it. And all said and done their results were very similar to a GTech, with a mere 800 bucks in parts. In the end, a perfect accelerometer is no easy task. To think there's an easy solution to keep the thing level during acceleration is far fetched. Piss poor engineering. :shrug: I don't think so. It has a great market. If it were more accurate but cost 10 times as much who would buy it? That's where engineering meets marketting. Maybe it's not as good as it COULD be, but it's good enough for people to buy it, and still cheap enough for people to afford it.
 
1 - 20 of 21 Posts
Top