Gtech - new pocket dyno on steroids

[jwdeeming]

I just got a flyer in the mail from Gtech, the makers of the pocket dyno. Their new "Competition" model looks pretty cool. Too many new goodies to list here but their website is www.gtechpro.com.



The big ones that jumped out at me are:

1. It now tracks rpms and plots your hp or torque on a graph over the 1/4 mile run. Could be useful for tuning shift points.

2. Enough memory to store multiple runs

3. A data cable and PC software for analysis work.



I don't need one, but you serious drag racers might get a kick out of it. More ways to spend your money...



JimD

 

[thejeepdude]

RPM?

Has anyone actually used the Pro with a Diesel? I've never seen one in action, but I was just reading their website and it says



"Engine RPMs are sensed directly from the cigarette lighter voltage. No installation required at all with this true plug and play feature. The unique RPM feature is used for anything from realtime torque measurements to shiftlights. "



Um... how does it sense RPM from the cigarette lighter?! I could see this possibly with a gas engine's electircal system, but what on a diesel could be running through the electrical system that could let the GTech sense RPM through the cig lighter?



Maybe I've overlooked something obvious...





Josh

 

[Groover]

rpm from the cig lighter?

Jeepdude I am with you.



Cigarette lighter voltage rpm detection could work as long as the lithium crystals don't overheat and the warp drive holds together. Of course if the clingons decide to attack the deflector shields might not hold.

 

[TxDieselKid]

It does pick up RPM, I have played with one, we have on up here at the shop. I couldn't believe it at first either, but whatever, it works.



Andrew

 

[CumminFast]

They have the competition g-tech on ebay for $250 and the other one for about $70. That comp is bad to the bone. I have heard they are pretty acurate. My friend has one, I guess I need to test it.

 

[thejeepdude]

wow

That's a trip... so anyone know HOW this works? I emailed GTech... we'll see what they say.

 

[Groover]

I would like to know how it works too. The electronic injector pulses would affect battery voltage like pee-ing in the ocean. The g-tech would have to be super sensitive to pick up on voltage fluctuations.



Follow me here... on a cummins at 3000RPM you would have 9000 injector pulses per minute (3 per rev) or 540,000 per second.



This sound right?

 

[thejeepdude]

Well, I don't know how many pulses there would be, but if there were 9000 per minute, that wouldn't be a higher number per second. It'd be more like 150/sec than 540000. Gotta divide by 60, not multiply.



Josh

 

[StakeMan]

Maybe they are using altenator noise.

 

[thejeepdude]

Using alternator noise... hmm at first that sounded far fetched, but perhaps this is indeed possible. By measure the electrical frequency and using that as a baseline, I suppose it would be possible to determine the RPM as the frequency went up, regardless of whether the frequency was at a 1:1 ratio with crankshaft rotation. Still not sure if that would actually work... I hope these guys reply to their email soon.

 

[mgonske]

I have one I used to take some baseline measurements on my '98 before I sold it; haven't tested the new truck yet.



The multi-run memory and PC interface are future upgrades--not included on the one I bought, but to be software upgradeable later.



The RPM detection looks at noise on the power bus, and you calibrate it by running up to two set RPM levels and 'marking' the readings--it then interpolates/extrapolates the relationship betwen the noise and the RPMs from there. There is certainly more noise available from an ignition system, but I suppose there may be other speed-relative (alternator?) noise to work with--we'll see.



I'll try to remember to post once I try it in the new truck.

 

[mschoenheider]

I have had and used the G-tech Pro comp for about 4 months now. I am still running one of their trial firmware versions which I will be upgrading in the future. Their software has not been out yet for PC graphs, but you can download the data, then put it into Excel to calculate your curves yourself. I have been happy with the product, and will be downloading the firmware updates tonight. I'll let you all know how the new setup works.

Mark

 

[thejeepdude]

Great, let us know how it goes with that Gtech Competition once you get the new firmware installed. I'm curious what functionality it adds, and if everything is cool, I may spring for one myself. It's not that I really need one, but it seems like it would be a fun toy to have, just for the 'cool' factor. And even if it's not as accurate as going to the strip, it seems like it would still be a good tool for developing a baseline to which you can compare the affects of any mods done to your truck... a lot more accurately than just the seat-of-the-pants gauge anyways.



Josh

 

[Groover]

Back to school

I will write on the board 100 times - "I will divide by 60 not multiply"



Jeepdude- all I was trying to say was 3 cylinders "fire" per revolution so... if at 3000 RPM there would be 9000 injector pulses per minute and perhaps the G-tech was picking up these pulses and somehow calculating RPM. After that my math skills got a little skewed. Thanks for the math lesson.



If it is picking up noise in the electrical system it might work but it seemed to imply "rpm picked up directly from the cigarette lighter voltage". I just cant see how voltage would vary in any consistent pattern to tell-tale RPM's.



Interesting stuff.

 

[drees1]

They probably are looking at the alternator noise to get the rpm. Remember how noise is transmitted into an aftermarket stereo system? Any way the alternator is 3 phase power that is rectified to DC. The DC is pretty dirty and has enough waveform in it that they can detect it. I'm just guessing, here.



I had a Dixco Diesel tach in my 6. 9 ford and it picked up inside the alternator. Worked fine, in fact, still working with 250,000 on it.

 

[mgonske]

Nope, the tach (and therefore, the shift lights) part doesn't work.



I dug it out before leaving for work this morning. The first problem is that the two reference RPM speeds it asks you to rev the engine up to in order to calibrate it are 2,000 and 4,000 RPM I tried just changing the scale, by using 1,000 and 2,000, and then doubling the shift redline that I entered, but the tach needle just jumps all over the place wildly. I guess that means it really is ignition noise it depends on, and alternator noise won't do it.



The constantly jumping around tach indication also meant the shift lights were constantly flashing (and they're *bright*!). By setting the shift redline to 15,000 RPM, I was able to keep them off, and use the instrument for the performance measurement functions, just without the tach.

 

[mschoenheider]

In the firmware version 1. 0, the tach calibration points were not adjustable, and were 2000 and 4000rpm. While using that version I used 1000 and 2000, and the rpm the Gtech recorded was twice my actual. The tach on the gtech was not very accurate, but always within about 15%. To get an accurate RPM value, I used my speed and gearing to calculate for use calculating torque numbers for the runs I downloaded to my laptop.

In the firmware version 2. 0, which just came out, the RPM calibration points are variable. The accuracy seems to be better also.

The unit uses variation in the output from the alternator. I am not sure if it is what you refer to as noise, or if it is just the variation in voltage. The owners manual states that you can turn on different accessories combinations to try to make the tach feature more accurate.

Mark