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Discussion Starter · #1 · (Edited)
How to Measure Horsepower and Torque with the Gtech

By "Torqued"

Introduction
Use of the Tesla Electronics Gtech instrument is an easy and useful way to get accurate indications of your car tuning results. This device has been around for a few years now, but the newer editions of this product have provided a lot of usability enhancements and advanced features.

The Gtech works by using precision accelerometers to measure acceleration. The device can also calculate vehicle speed and distance which are computed by performing subsequent mathematical integrations of the acceleration data. Accelerometers today are usually constructed with precision ICs using MEMs technology. This means there is repeatability and decent accuracy associated with the device. If you follow the techniques described here you will find the Gtech provides incredible results in repeatability – better than the differences you will find between different dyno machines and as good as the run to run variances you will find on the same dyno.

Don’t get hung up on dynos being the last word in accuracy. If you have ever done dyno runs or looked at a pile of runs from machine to machine you will see variances, sometimes huge differences. Dynos are convenient for shops, and consumers can get their cars measured without breaking speed limits!

The Gtech will always give you numbers lower than that obtained on dynos due to wind and rolling resistance and you must correctly set up your car and correct the measured numbers if you want to normalize your results to that of a roller dyno. If you want to get as close to SAE compliancy as possible, you will need to do even more corrections – this is where a spreadsheet is handy.

Why use a Gtech?
* A Gtech is accurate, and the measured results can be normalized and compared to other results easily

* A Gtech is convenient. When you tune something on your car you can immediately take out the Gtech and measure the results. No waiting for dyno appointments, and no driving long distances to find a shop with a dyno.

* A Gtech is cost effective. For $300 you are set. You can measure as many times as you want, and many different cars as you want, and you won't go broke paying for dyno time everytime you twesk your car.

* A Gtech has advanced features. You can measure 0-60 and
 

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Excellent work Chris.

My only concern is that most people won't be able to setup an Excel spreadsheet given your info. You don't say specifically how those equations relate to horsepower and torque. Also, most people won't know the Cd or frontal area of the car. I frankly wouldn't even know how my bodykit might affect Cd. Listings of the equations for converting HP to torque and the SAE corrections would be nice.

Its also a bit unclear how many 2-way runs you think are necessary. In one spot you say two 2-way runs averaged seems to be consistent, but in another spot you talk about tossing out the highest and lowest 2-way runs and being left with two.
 

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Jesse IL said:
Excellent work Chris.

My only concern is that most people won't be able to setup an Excel spreadsheet given your info. You don't say specifically how those equations relate to horsepower and torque. Also, most people won't know the Cd or frontal area of the car. I frankly wouldn't even know how my bodykit might affect Cd. Listings of the equations for converting HP to torque and the SAE corrections would be nice.

Its also a bit unclear how many 2-way runs you think are necessary. In one spot you say two 2-way runs averaged seems to be consistent, but in another spot you talk about tossing out the highest and lowest 2-way runs and being left with two.

i think it's pretty clear that for consistency, he recommends 4 pairs of runs.

i agree with you on the first part. his next write-up should be setting up excel correctly, and how to calculate the numbers needed to plug into his formulas.
 

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Discussion Starter · #4 ·
Jesse IL said:
Excellent work Chris.

My only concern is that most people won't be able to setup an Excel spreadsheet given your info. You don't say specifically how those equations relate to horsepower and torque. Also, most people won't know the Cd or frontal area of the car. I frankly wouldn't even know how my bodykit might affect Cd. Listings of the equations for converting HP to torque and the SAE corrections would be nice.

Its also a bit unclear how many 2-way runs you think are necessary. In one spot you say two 2-way runs averaged seems to be consistent, but in another spot you talk about tossing out the highest and lowest 2-way runs and being left with two.
OK I think I can help. For the first part I'm going to make it way easy. I am going to clean up a spreadsheet template and figure out how to post it here. All the equations and run templates will be set up. All you will have to do is put in the raw Gtech data and you are ready to go. Unfortunately, this will not help people who don't know how to work spreadsheets. For these individuals, they will need to rely on the raw data. Do you all think a Gtech template would facilitate things and encourage Gtech use, or is this still beyond the scope of the capabilities of most tuners?

On the second question I recommend (2) two way runs at a minimum for averaging and correcting the data - this is after you have tossed out the high and low data pairs. This means (4) pairs of runs at a minimum - you can do more if you want. Also, you can do less runs if you are gross tuning your car, because the gross tuning effects will show up from tun to run. I found the technique described in the write up provides the best repeatability and consistency which you will want if you are fine tuning your car.

Hope this helps - feel free to ask any other questions.
 

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Torqued said:
OK I think I can help. For the first part I'm going to make it way easy. I am going to clean up a spreadsheet template and figure out how to post it here. All the equations and run templates will be set up. All you will have to do is put in the raw Gtech data and you are ready to go. Unfortunately, this will not help people who don't know how to work spreadsheets. For these individuals, they will need to rely on the raw data. Do you all think a Gtech template would facilitate things and encourage Gtech use, or is this still beyond the scope of the capabilities of most tuners?

Have you gotten around to putting this MS Excel template together yet? I just bought a GTECH RR for a great price and have decided to try this tuning method. Dyno tuning is getting way too expensive...
 

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I purchased an RR recently myself. I'm looking forward to tuning mine. Chris has a history of being shall we say "slow" on the progress :chuckles:
 

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Jesse IL said:
I purchased an RR recently myself. I'm looking forward to tuning mine. Chris has a history of being shall we say "slow" on the progress :chuckles:
:violin: Its been like 6 months...

Nah I'm just kidding, I dont mind waiting it it can save me wasted time and money. My last experience at my regular dyno kind of pissed me off. I'm going to try and stay away from there for as long as possible. I need to get the cam angle maps done for this damn header.
 

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Discussion Starter · #9 ·
I get the hint

I didn't see much pull on the thread, so I didn't want to assemble a spreadsheet if no one was going to use it. Looks like I have two takers, so I'll commit to assembling the spreadsheet by next week end and sending it to Jesse to host somewhere. I am flying out of town this weekend and won't be back until next Friday.
 

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Awesome. I haven't read your method in a while but was going to try and work my way through it. If you can provide a sheet, that would be great. I'm sure both Dan and I can give some good feedback once we actually get a chance to try the method.
 

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I just recieved my Gtech today. I cant wait to try out this method.

*EDIT* How do you get the raw data from the PASS software into spreadsheet format?
 

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Discussion Starter · #12 ·
New Template Ready

Hey all,

I updated the template and sent it to Jesse for hosting. I'm not quite sure how to post the spreadsheet otherwise. If anybody needs a copy of the template you can PM me for additional contact information and I'll be happy to send it to you.

-Torqued
 

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Torqued said:
Hey all,

I updated the template and sent it to Jesse for hosting. I'm not quite sure how to post the spreadsheet otherwise. If anybody needs a copy of the template you can PM me for additional contact information and I'll be happy to send it to you.

-Torqued
Your PM inbox is full.
 

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OK after looking at the spreadsheet template and reading the notes at the top of the sheet it says to enter the data by hand. I cannot figure out for the life of me how to get the exact raw data numbers at the set datapoints you have setup in the spreadsheet using the PASS software. You have the datapoints spaced every 100 rpm with HP and TQ figures to the tenth. The PASS software, as far as I know, doesnt give you those numbers.
 

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Discussion Starter · #16 ·
Unfortunately, this is a manual data transfer. I basically enter the data in directly from the Gtech display. I use the numbers in the Gtech display closest to the RPM setting in the spreadsheet.

As I eluded to, the reason why it's done this way is because we will want to average the results for at least (4) different runs (2 runs in each direction) not counting the high run and low run you may throw out. If we don't fix the RPM it becomes another independent variable and it won't graph properly in Excel. I suppose I could write up some macros that could extract the data taken from a raw database, but I have not done that. On the plus side it doesn't take to long to transcribe the data into the spreadsheet, and once you do that everything is set up and calculated automatically.

Let me know if you have any more questions or if you want to take a peak at some of the data I have taken - either Gtech logs or speadsheet data.

Also, I think I explained in the write-up that the spreadsheet does not do SAE corrections. This requires knowing the temperature and air pressure, the later being influenced by weather and altitude. If you are consisent and do runs at 70 - 75 deg ish temperatures, you won't have much variation and you'll be close to SAE unless you live in Colorado or something.
 

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Discussion Starter · #17 ·
DYI01 said:
Your PM inbox is full.
Thanks for the heads up - I'll go clean that sucker out.
 

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I have no possibility to make a drag strip since here in Italy there are no dragstrip points in which I could compare the track speed of the Gtech with the one of the ticket so..... is there another way to get the appropriate "Pitching"?
The default is 2.0 but I have Koni Sport shocks with Eibach Prokit springs. The konis are setted front to 450
 

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Hi guys I just found this post... Sorry for not coming up with this before!

There is a guy from The Netherlands who entirly tuned Is Subaru WRX with a gtech and he did an Excel Spreadsheet wich he updated a lot of times (last june 2006)

There is a lot of info you can enter on the sheet to correct the HP/torque numbers

-You can import the .csv from gtech.
-You can switch from metric and US unit.
-You can apply drivetrain loss correction.
-You can apply atmospheric correction (there is also a weblink where you can find the temperature in your region. You can also go back in time).
-You can apply aerodynamic correction.
-There is a toolbar with some option and much more

You'll need to lower your macro security to enable them and be warn the the file will start in Dutch language, you need to switch to english from the TAAL button in the tool bar

Here is the file --> http://members.chello.nl/~r.herweyer/software/gtech.zip

Here is his website --> http://members.chello.nl/~r.herweyer/
 

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Discussion Starter · #20 ·
NeXuS-GT said:
Hi guys I just found this post... Sorry for not coming up with this before!

There is a guy from The Netherlands who entirly tuned Is Subaru WRX with a gtech and he did an Excel Spreadsheet wich he updated a lot of times (last june 2006)

There is a lot of info you can enter on the sheet to correct the HP/torque numbers

-You can import the .csv from gtech.
-You can switch from metric and US unit.
-You can apply drivetrain loss correction.
-You can apply atmospheric correction (there is also a weblink where you can find the temperature in your region. You can also go back in time).
-You can apply aerodynamic correction.
-There is a toolbar with some option and much more

You'll need to lower your macro security to enable them and be warn the the file will start in Dutch language, you need to switch to english from the TAAL button in the tool bar

Here is the file --> http://members.chello.nl/~r.herweyer/software/gtech.zip

Here is his website --> http://members.chello.nl/~r.herweyer/

Yeah - you can go crazy with spreadsheets. You can also use the Datalogit output to get a rough idea of your HP/torque by using the time vs RPM data, gearing, and the rough weight of the car. The important thing in tuning to realize is that no measurement is perfect. If you can be consistent in what you do and look at the relative changes before and after you tune something, then you are golden.
 
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