G-Tech Pro Competition

[jgparker]

Per the suggestion in the rebuild book, I got the new G-Tech Pro Competion (at PP). From what I've seen so far, it's a really useful tool. Here is a HP vs RPM plot from the PC application:



My question is, has anyone done baseline runs of the G-Tech vs a chassis dyno or flywheel dyno? Does anyone have a guess on the correction factor from crank to road HP? From what I can tell, I'm loosing 50 hp from the flywheel to the road. The plot is of my 140 hp '96 Miyata (Sorry, my new 2.8 is not quite broken in yet, those plot to follow.)

I don't think this is OT, since this board is about wayne's new book, but I'm open to move it if it is.

Thanks,

JP

[dd74]

What's the hp reading on the G-tech? 90 hp? Multiply that by .015, which is standard drivetrain loss in percentage, and you get 13.5. Add that to 90 hp, and it's 103.5 hp at the flywheel.

The '96 Miata made 133 hp at the flywheel, correct? The G-tech has shorted you 32.5 hp.

I wouldn't call that "accurate."

I'm sorry if you spent $250 or so on the G-tech, but if I were you, I'd take both the Miata and the 2.8 engine to a real dyno.

[jgparker]

The closest "real dyno" is an hour and a half away from me, and runs $100 for 3 runs and $150 per hour after that for tuning. This is not a practical solution for me for the amount of runs I want to do. As far as accuracy goes, the run to run consistancy of the G-tech appeare to be as good as the chassis dynos I've used. (See how close the 4 runs line-up on the above graph, and compair to your old chassis runs)

I agree that the aerodynamic and road losses for the miyata example appears to be around 40-50hp. My question is, is this reasonable for a small car at 50 mph.

Thanks,

JP

[aigel]

Don't you have to factor in the weight of the vehicle? Don't forget that it means WITH you in it!

I am only familiar with the old G tech that gives you max hp, and 1/4 mile times etc.

I think you may have entered the wrong weight.

Don't bash teh G tech. It is a great tool for TUNING your car. While the absolute numbers may not be dead nuts on, the relative changes in performance will be very well visible with every change you make. This will avoid that you drill holes in your air box and feel the car being more 'powerful'. And it also allows you to fiddle with settings for days, weeks and years. Nothing a dyno run can give you. The tuner may set things up for you, but after the next mod, you are at the dyno again....

Just my two cents.

George

[jgparker]

George,

I'm fairly sure the weight I entered is correct. There is a vehicle scale next to my office, and I weighed the car with me in it right before the runs (2410 lbs). The thing I hated about the old G-tech was that you had to re-enter the weight every time you started the car. Being able to download the runs to a PC for analysis is great too.

This is where I think the discrepancy in HP might be coming from:

Crank HP: 140 (132 hp stock Miyazda +8 hp timing mod)
Transmission loss: ~14 hp (10%)
Aerodynamic loss: ~35 hp (at 55 mph)

I believe that the 90 hp reading is an accurate measure of the amount of HP left to accelerate the car at this speed, after all the losses. I'll concede that you can not get accurate crank HP reading with the G-tech, but you can't actually get that from a chassis dyno either. The HP vs. RPM curves make it a bit more useful to me for tuning than the single peak HP readings from the old version, and the convenience make it much more useful than a chassis dyno. If only it had a lamda input too...

Thanks,

JP

[aigel]

Stupid question: Have you considered the fact that Mazda may have overstated the power?

With the old G tech that I had borrowed from a friend, I got pretty good readings on my wife's pickup truck. Comes with 200 hp, IIRC and I read 165 at the 'wheels'. Automatic.

On my 71 Olds 442 it was a bit more problematic to get anywhere close to the estimated 390 hp because it goes along with about 500 ft-lb of torque. After it finally stops roasting the tires shifting into second gear, right on that shift I measured 270 rw hp.

As I said, the biggest value in the thing is that you can compare before and after mod performance. And it is a buch of fun too. Just make sure you find a quiet spot to drive!

George

[jgparker]

Yup, Mazda may have overstated their HP, but my car runs well, and is in good tune, so I'm assuming it's still in the 130 to 140 range. I found a source that said the wind resistance for a sports car eats around 40 hp at 60 mph, so I'm starting to trust my loss line-up a little more. I'll need to do a side-by-side comparison to really know though.

Here is something else the old G-tech would not do, hp and torque vs RPM curves right on the display:

[Jeff Alton]

I used to own a rather tricked out Miata. I had all the mods. We did some before and after testing on a dyno jet at a shop specialising in Miatas. Believe it or not, A miata looses about 22% of the flywheel hp through the drivetrain!!! That was backed up my car and about a half dozen or so other stock Miatas that they had dynoed.

Jeff

[Jeff Alton]

Oh ya, one more thing, I think the miata weighs right around 2400lbs with a little fuel and NO driver. Do you know how accurate that scale was?

Jeff

[jgparker]

Wow, 30 hp loss in the trans! That seems high, but does help explain the low readings. I did a number of runs to measure the aerodynaic loss on the car at 60 MPH and only came up with 20 hp. That does get me above the stock HP though.

I think the weight I used is fairly accurate. I weighed the car at a certified freight scale with one of thoes state inspection stickers on the read-out. The Miata measured 2220 empty and 2410 with me in it. I found the spec for the '96 miata at 2293, so it did measure lighter than spec by a few lbs.

[Jeff Alton]

Actulally, I guess your weight is probably accurate. I had a four point roll bar, bigger wheels and tires, larger brakes, etc. Mine also was a 97 so there could be a difference there as well. Afew pounds here, and a few pounds there start to add up quicky though!

Jeff