MrWigggles

A colleague of mine who has used in-car dynos for many years is very impressed with the new G-timer by Passport.

We did a tremendous number of calculations and calibration of the sensor itself to come up with an engine power of 212HP at 8250RPM.

We factored in a 10% drivetrain frictional losses (arbitrary) and a 15.6% inertial loss (calculated for run done in 2nd gear) for a total of 25.6% losses. FYI, the Passport only does frictional drive train loss and it is fixed regardless of gear so we had to do or own calculation for the interial loss.

I only went full throttle to 8250 RPM (I didn't mean to go that high, oops ) so if the torque curve is flat there could be another 6HP at 8500 RPM. Also, the car only had 160 miles on it so after a little more break-in I could be up 10HP more like other forum members. That would be a grand total of 228HP peak. Still short of the claims by Mazda, but within 5%.

When Passports software improves (graphing sucks currently), I will post graphs generated by the software. I will also also redo the testing when I get more miles on the car to see if I do infact get 10HP with a little more break-in.

-Mr. Wigggles

mdmaclean

I am considering getting one of these devices, either a Passport of a G-Tech pro.

What made you choose the Passport over the G-Tech? If you don't mind, I would also appreciate a PM with where you bought it.

jmanolov

Get a GTech Pro Competition. It is much much better device than the Passport.

MrWigggles

How did you come to that conclusion?

-Mr. Wigggles

RX8-TX

As I read before from another member, I don't really trust these GPS devices that much. I know they are excellent for comparo purposes on the same vehicle and different conditions. Or maybe even for the different vehicles, under the same conditions.
In other words, they probably offer a good quantitative comparissons. But I don't think they are very reliable for quality measurements. Anyone feel free to make me shut up and realize I'm wrong.

MrW. have you gotte the car on a dyno? it would help you (me) a lot to have those reference points in a future. How much does a wheel dyno spit out? how much does the G tells you?

Anyways, keep up the research going on! I wish I had the will to go through some of it....

Cheers!

Gord96BRG

I'll say that's arbitrary! How did you arrive at that figure? The absolute lowest number I've ever seen suggested is 17%, and a few people think it's closer to 20%. When you add back in the 7% additional loss that you neglected, your flywheel HP goes up by at least 10 - there you go!

Regards,
Gordon

MrWigggles

Hi Gord,

As I am sure you know there are both frictional drivetrain losses and interial drivetrain losses during an in-car dyno. Escort recommends using 15% total but that would be more appropriate for third gear or forth gear testing. Since I did testing in 2nd gear, I am using 25.6% total not the 10% if I wasn't clear earlier.

-Mr. Wigggles

MrWigggles

The acceleration of the car is not everything that is important it is the only thing. The actual power put down to the road was 158 HP based on the g data, period. The science is getting the 25.6% losses number which tells you the engine is actually doing 212 HP. But still ultimately the important thing is that the car is putting down 158HP to the road.

Having designed accelerometer systems for NASA and the military for the last 6 years I am very impressed with G-timer GT2. It is lightweight and has very good accuracy. (I have heard problem about the older G-techs but I haven't used the G-tech Pro)

-Mr. Wigggles

Blue 350z

I have the G-Timer 2.

Its defaulted to 15%, I am currently using 18% Drivertrain loss and getting 241.7HP

I can't think of 1 reason why you would use 10% as a DT loss. And fudging with numbers and estimating losses and your HP estimate is worth garbage.

As far as I know you set the speed where you want it to measure the HP and just run it hard as you can thru the gears and you get your HP.

Mine is set to 30-50MPH @ 18% = 241.7HP. It supposed to do all the math internally.

So set it to 18-20% for your car, set it to 30-50mph and just do basically a 0-60 run and you will get your output.

Also my best runs with my G-TImer 2 so far (only about 5 total runs) are.

0-60:
5.25s
5.27s
5.34s

Best 1/4:
13.82@102.3mph

MrWigggles

To repeat myself, I use a total of 25.6% drivetrain loss. 10% for frictional and 15.6% for intertial losses due to second gear.

The 350z has taller gears so 18% is probably close, but I bet you are actually about 20% or more total in second gear, which would bring your total closer to the 250HP range.

Forget HP, those acceleration numbers are the important ones. The 350z is definitely a quick car.

-Mr. Wigggles

Spin9k

FYI, none of these devices have anything to do with GPS, which is short for Global Positioning System.

these devices use this method for calculation (from gtechpro web site) and they are extremely accurate if correct setup info is fed to them:

"At the heart of G-TECH/Pro is a precision 3-axis accelerometer.

The G-Tech measures your speed and distance travelled by integrating forward (the forward direction is chosen automatically) acceleration over time. Basically, if you know how fast you are accelerating for a certain time period you'll know how much your speed changed after that time period. So if you start off from zero speed then you'll know what your speed is after every time period. These time periods are very small (a few thousandths of a second) and that's how G-Tech maintains its accuracy. "

Dugless

Sorry for this, but what the heck are these devices you guys are talking about??

Spin9k

...for what these are (amazing for starters) try www.gtechpro.com :D

Blue 350z

2-axis accelerometer actually, not sure its possible to have 3 axis since it measures Acceleration and decelleration (Y axis) and lateral G forces (X axis) .

MrWigggles

The G-timer GT2 is a 2-axis accelerometer while the G-tech Pro uses a three-axis.

With proper callibration and installation, all that is needed is the two-axis.

-Mr. Wigggles

Blue 350z

Ahh, just checked that link. Never even knew about the pro model. It looks pretty silly!

Spin9k

The 3 axis GTECHPRO Comp needs NO calibration at all... a major, major improvement IMO.

I don't understand what is 'silly' about a pro model? (or any model?)

Blue 350z

I guess Spin2k is way out of the "Generation X" age where sometimes people use strange words to describe something.

The way I used "silly" in that sentence was to explain "awe" or to describe it as high tech or having many features. So let me rephrase the sentence for the older folk or the "un-hip" folk that cannot figure out simple things.

So here I go for Spin9k:

Golly gee, that G-Tech Pro is wonderful, so many nice and useful features were included into the design. To think that no calibration is needed is super duper!

Better??

Spin9k, are you an accountant or a librarian? Because everytime I have a chance to speak with either its like talking to a robot with no sense of humor, emotion or even 1 hip bone in their body.

Dugless

Nice work Blue!!!!!! That was silly!!!

Spin9k

Here's some words of wizdom from an old fart esp. for you Blue 350Z ---- just because you're an ***, no need to talk **** to your elders.

Blue 350z

LOL! I knew it..

BTW- Its spelt wisdom, not wizdom. Stop trying to make a hip new word :p

GoBerserk

The point of a measurement device is remove uncertainty. When you assume 10% drivetrain losses, and 10 hp for break-in and 6 for the fact you didn't rev it to max power, you add uncertainty and your "measurement" is total garbage.

You didnt' even rev it to max power, you just assumed the torque curve is flat. But in fact, max power come AFTER max torque, so the torque curve is actually going to be sloping downward at max power.

And you assume a random 10% drivetrain loss? And then use 15.6 for inertia. That's a whole magnitude greater accuracy! For every 1% off you are on your guess of 10% the car would gain 1.58hp!.

Get a real flywheel power measurement tool, like an engine dyno, rip a renesis out on an RX8, test the actual flywheel power, and then post your results. Until then stop saying the car doesn't make the power Mazda says it does. You don't know the flywheel power because you've never measured it.

synthtk

Is the Passport Gtimer the same unit as the Beltronics Vector?

http://www.beltronics.com/fx.html

http://www.escortstore.com/gtimer.htm

The copy on the sites look identical and do does the display... just different casings?

-Chris

Dugless

You two are both right and are both wrong. Hell, keep it going!!!!

MrWigggles

Let's make this a game.

Each paragraph contains one or more incorrect assertion and/or calls for something that is totally impractical. Can you spot them?

I wish I could make this game more difficult. Finding the "Waldos" should be very easy.

-Mr. Wigggles