For anyone who's curious, just how accurate IS that G-tech thing (and others)?

[Guest bastaad525]

Hey all... well I've asked this question numerous times myself, about the G-tech Pro performance meter. It seemed little more than an expensive novelty, and while very few people seem to have actually used one, it seems everyone knows someone who knows someone who's used one, and has various tales to tell ("HP figures were way off" "trap speed was way too high" etc.). I've always wondered, why no magazine or website has ever given a good review of these types of devices and really thoroughly tested them to see just how accurate they are. Well... I just found out that my wife has gone and ordered me a Gtech Pro RR as a gift for our 7 year anniversary *SWEET*... so I went looking for some real info on how well these things work.

 

Well... I finally found a review, at the Car and Driver website. And I was pretty surprised with what they found. Here's the link:

 

http://www.caranddriver.com/article.asp?section_id=4&article_id=9380&page_number=1

 

It's a pretty long article... for anyone not inclined to read some 10 pages here are the results for the 1/4 mile testing they did:

 

 

 

They tested them on two different vehicles, a G6 and an Envoy, and most of them were very accurate, within one or two tenths of a second, and most were within 1-2mph of the actual trap speed.

 

The G-tech, as you can see, actually IS pretty accurate, it was one of the most accurate ones tested, even w/o being calibrated, which is impressive. They ALL were pretty accurate... even the cheapest one (the $90 Tazzo VPC).

 

Unfortunately (and very oddly, IMO) they did NOT test out the HP and Torque measuring functions of the devices, which sucks... maybe because not all of them have this feature? It's too bad as that is the one thing I hear most about the G-tech is that it's HP numbers are usually way off, and it'd have been nice for them to test this on factory cars with given, known HP. They did however, test other functions such as skidpad G's and braking distance from 60-0, those results are on the last page of the article, and most of the units performed very accurately in those tests as well.

 

Needless to say, I'm VERY excited and really can't wait to try this thing out! Unfortunately, it looks like it might be like a week... the only reason my wife ended up spilling the beans about my gift is that she found out it wouldn't be here in time to give me on our actual anniversary (Wednesday), so wanted to let me know that I DID have a gift coming but that it would be late.

 

Well, just thought I'd pass along this info for anyone who is interested, and you'll definately be hearing what kind of results I get with my Z soon... man the anticipation is gonna kill me.....

[Afshin]

I used to have the old g-tech and it was fun, but prone to error if not leveled properly and so a little bit of a pain to use.... I then got the g-tech pro and it think it is great. Another magazine maybe grassroot motorsports (i'm not sure) had done a review as well and found them to be accurate. I find the results very consistent. Also, the HP and torque measure are not that reliable compare to dyno results in a non-moving car with no aerodynamic factors, but they are GREAT for comparing all modification made to your car both for HP/torque curves and max. values. I'm sure you will have a lot of fun using it.

[80LS1T]

I have a "G-Tech Pro Competition" and I have found it to very consistent as far as ET and MPH but I never really bothered with the HP/TQ because I couldnt get a consistent #. So Im a a little skeptical of those numbers but for the ET/MPH they are pretty much where I should be with my engine's estimated power. So I am faily confident that I should run mid 12's on street tires.

 

 

Guy

[Moridin]

I used to have the old g-tech and it was fun, but prone to error if not leveled properly and so a little bit of a pain to use.... I then got the g-tech pro and it think it is great. Another magazine maybe grassroot motorsports (i'm not sure) had done a review as well and found them to be accurate. I find the results very consistent. Also, the HP and torque measure are not that reliable compare to dyno results in a non-moving car with no aerodynamic factors, but they are GREAT for comparing all modification made to your car both for HP/torque curves and max. values. I'm sure you will have a lot of fun using it.

 

Best is to compare the numbers to a Mustang Dyno...I believe it compensates for aerofactors based on a table of basic car data. I remember hearing this somewhere, but I may not be entirely right.

[Guest bastaad525]

What I can't understand is how the HP WOULDN"T be accurate.

 

Considering that it's all just basic math to figure, knowing your cars weight and your trap speed, you should easily be able to arrive at your hp number to the wheels.

 

So if the Gtech can consistently measure trap speed and ET, why can't it do HP accurately?

[80LS1T]

You have to do it from a running start and then accelerate smoothly to get the HP functin to work......having said that........I tried it and came up with numbers from 230HP to 430HP. So yeah you would think it would be easy to figure out but apparenly its not.

 

Guy

[Z Driver]

I have the original G-tech. It's pretty fun and accurate. I've found the HP function just too hard to work. I don't know the exacts weights of any of my cars either, so that doesn't help. It's a good too to see how well modifications affected your car. Even if it wasn't accurate, you are at least using the same method of gathering data so it's valid. Be sure the surface out are testing on is perfectly flat too.

[rudypoochris]

well i dont know about everyone else but i got my 25 dollar gtech (1994 edition pro) off ebay and it works great. My ford explorer with t5 and stock everying puts 130 hp to the wheels + aerodrag in first gear (can floor it with out spinning them on normal flat pavement). The crank hp is rated at 160hp so 130hp seems acctually just right. Few things to make sure of...

1. drive on a flat surface, durrr

2. make sure it reads 0 g's when your stopped (which means device must be flat/not broken)

3. the tires CANNOT spin

4. No clutch slippage/or autotrans whatever its called, so its best used on a stick... also if you use an auto remember to limit it to a certain gear, swithcing gears will destroy the readings (if i remember correctly)

5. The faster the speed the less accurate wheel hp will be.

[Guest bastaad525]

One thing about making sure the Gtech is absolutely flat and level, this isn't necessary with the newest model. It's sensor setup is a bit different, and can be mounted at an angle, oriented sideways, any way you can imagine, and still function properly.

 

Well I already know approximately how much HP my car puts down thanks to numerous dyno visits

 

Then again, I have fiddled with the boost a bit since my last pull, due to a funky boost controller that had boost falling 1psi every 1000rpm... I would like to verify how much HP I gained by fixing that.

 

I'm thinking... since the G-tech isn't 'smart enough' to figure HP the 'normal' way (i.e., taking your trap speed and/or ET and figuring it against your cars weight), then I'll just have to do it for myself

 

By the way can someone clarify for 100% sure if the HP number the Gtech gives is supposed to be RWHP or HP at the flywheel? I was under the impression it was estimated flywheel HP?

[rudypoochris]

neither. it is rear wheel hp + aerodynamic drag atleast its that way ont he earlier models.

[Guest bastaad525]

........

 

funky... well I was hoping the newest model would be more accurate there but it sounds like it's not... too bad.

[Pop N Wood]

I don't see how any of those devices could reliably predict horsepower. The basic math is simple enough, but there are too many things that could vary to produce an inaccurate result. The slightest wheel spin and all bets are off. Everyone knows driver technique and how well your car hooks up has as much to do with your ¼ mile time as engine HP. The HP estimates can’t be any more accurate or consistent than the measured ¼ times.

 

The time, distance, speed and acceleration measurements could be very accurate depending on how well made the units are. Hard to believe they only use inertial accelerometers with no GPS aiding. Inertial devices, even the ones military aircraft use, are much much more accurate when combined with a GPS signal. GPS by itself is pretty good. In fact, I have seen commercial differential GPS equipment yield better velocity and position measurements than a full blown, GPS aided IMU used in the B1 bomber.

 

Data latencies with an inertial unit like that mean they have to use some type of time averaging. That would mean they can only guestimate an average HP over a range of RPMS and not an exact value like a dyno can. I can see where shifting would cause a data hiccup that would throw off the averaging.

 

I was looking at OBDII code scanners the other day and saw several PC and PDA based devices that predict HP using only engine computer outputs. Seems like a more versatile way to get probably similar accuracy. IMO the ultimate device would be a PDA being fed with an external GPS signal and engine computer data. That way you could correct for wheel spin by comparing engine RPM to speed, then do the same math as the Gtech units to guess at HP.

[Guest bastaad525]

Got my G-tech today... so far a bit of a mixed bag, but it's fun, and doesn't seem to be too far off with anything.

 

Right off the bat I had a minor issue, getting the thing to properly calibrate my RPM, the end result would always be like 200rpm lower than what my tach was showing (even though I'm calibrating it to the tach). Odd thing is it also did the same thing on my Sentra. So I 'tricked' it during calibration, and now the G-tech tach matches up perfectly with my autometer tach.

 

Well... the first thing this thing has taught me is that I suck at driving my car (as I expected!). But at least I suck consistently . A few 1/4 mile runs netted me mid 13's at a consistent 106-108mph, with horrible 2.7 sec or worse 60' times (I SUCK at launching with this turbo! Bog or spin bog or spin... I can't seem to pull it off right.). 0-60 were consistent low 5's. It was pretty consistent with hp, showing 200-210hp after every run... Though, having dynoed on a Dynapack dyno and several Dynojet dyno's, I say the G-tech is lowballing me on the HP, as in it's current state of tune, I've never put down less than 225rwhp on any dyno. I guess it's that dang aerodrag I didn't actually do a proper HP run with the thing the way the manual says to do it, so maybe the HP will show up a bit higher if I do. Or maybe it will get lower who knows

 

As far as the 1/4 times... driven perfectly, shifted quickly at just the right times, and with no wheelspin (very hard for me on 190/60/14 crappy $25 all season radials) at 2600lbs with me and half a tank of gas in it, and averaging my whp from my dyno runs, I would expect a 13 flat or better.

 

But as I said, I'm a sucky driver averaging 2.7 second 60' times, and 'granny shifting' it as I don't want to shred my transmission banging gears (I didn't even chirp the tires once), best run was a 13.36 at 108, average runs were 13.5 to 13.7.

 

So... If I could drop my 60' to a more reasonable 2.0-2.2 seconds, how much would that shave off the 1/4 time?

 

Well... seems to me just knowing what I know about my car and the horrible way I'm driving it, that the G-tech seems to indeed pretty accurate, no surprising seeing the results Car and Driver got with it.

 

Definatley a fun little toy... wish I had a better place to really use it (live very near L.A.). As it were, testing in the industrial area near my job (a ghost town at night), I quickly found just how useless my stock brakes really are... and how lovely they smell when I roast them! :D Maybe the thing will make me a better driver... practicing my launching til I melt the clutch or something I dunno.. I have a feeling I'll bore of it pretty quickly, then I'll put it up for sale and buy what I wish my wife had REALLY gotten me, a WB O2!

 

EDIT: no s**t... I really DID fry the brakes! Front driver side pads are worn down to the metal.....

[wheelman]

Bastaad525,

Thanks for the feedback on the G-Tech.

 

BTW: Congratulations on the 7th anniversary and keep up the good work.

 

Wheelman

[Guest bastaad525]

Bastaad525' date='

Thanks for the feedback on the G-Tech.

 

BTW: Congratulations on the 7th anniversary and keep up the good work.

 

Wheelman[/quote']

 

thanks She's been great to me, I couldn't ask for better.

 

Well about the G-tech, I've gotten about as much as I'm going to get out of it, and it's actually gotten me in some trouble, and I started a new thread to put it up for sale.

 

But it was fun and again, definately seems to be pretty accurate. I only tried a couple more 1/4 mile runs, and fiddled with the calibration a bit to compensate for my cars relatively stiff suspension, based on some suggestions from their tech support people. Though it didn't really seem to make much difference. I never was able to duplicate or better the 13.3, or 0-60 in less than a low 5 seconds, though my trap speeds stayed a consistent 106-108. Given the accuracy of Car and Driver's test unit, I'd like to think mine is working as well as theirs. If anything, their tests showed that when run at the factory calibration setting (as I did for the most part), the G-tech consistently gave SLOWER results than the track lights did. At any rate, if the trap speeds it's giving me are at all accurate, it's indicative that the car could do much better, and should easily be able to pull a high 12, were I not such a crappy driver

 

Also, the trap speed seems to confirm what I've been speculating all along. As noted in my sig below, last time I dynoed I put down a decent 233 rwhp and 303 ftlbs of torque, but was having problems with my boost controller, where boost wasn't holding steady from onset to redline, but would gradually fall off. It would fall about 1psi per 1000rpm. This was cutting my power peak short of the usual 5000rpm to about 4000rpm.

 

I finally solved the problem, and now boost is steady to redline. I had always speculated that this must have resulted in a modest gain in HP, maybe 5-10 hp. Well plugging my cars weight and the G-tech's average ET into the HP calculators strewn all over the web seem to agree with me, putting power right at about 245 rwhp, 10hp over what I dynoed last. And thankfully, right where I wanted to be when I started this turbo conversion 2 years ago. Well technically I'm still 5hp short of my original goal but who's counting

 

It also seems to confirm that Dynojet dyno's, at least the one I went to, aren't TOO 'optimistic' since the power rating I got there and the G-tech's trap speeds are matched up VERY well.

 

With all that in mind then, I still don't get how the G-tech is figuring hp. I plugged some numbers into their equations for how to figure for aero drag and it still wasn't matching up, giving me way low numbers. They should just set it up to calculate the HP the same way as they do at the track and avoid all the confusion and unhappy customers.