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

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.

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

Originally posted by jmanolov
Get a GTech Pro Competition. It is much much better device than the Passport.

How did you come to that conclusion?

-Mr. Wigggles

Originally posted by 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

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!

Originally posted by MrWigggles
We factored in a 10% drivetrain frictional losses (arbitrary)

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

Originally posted by 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

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

Originally posted by RX8-TX


...

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!

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

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

Originally posted by Blue 350z
I have the G-Timer 2.

....

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.

...

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.

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

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.

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 [/B]

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

-Mr. Wigggles

Originally posted by RX8-TX
I don't really trust these GPS devices that much.

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. "

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

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

Originally posted by Spin9k


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


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) .

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

Originally posted by 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

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

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?)

Originally posted by Spin9k

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

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.

Nice work Blue!!!!!! That was silly!!!:)

Originally posted by 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.

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

Originally posted by Spin9k


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

LOL! I knew it..

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

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.

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

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

Originally posted by 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.

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

Originally posted by 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

Yes, they are the same units. A private investor owns Bel which owns Passport.

-Mr. Wigggles

Here's an idea just to see how the RX-8 compares on the numbers. Use the G-tech (or whichever device) and record 5 runs in a few different cars (brands, models, makes, etc...) then compare these numbers with the factory specs on these same cars for power and accleration. Then do the same for the RX-8 and figure out an average correction by using all the different vehicle's data. I know that different cars have different losses but this is just for comparison purposes. I bet that the losses for all the cars is actually pretty close to each other and that this number would be a good number to use for the RX-8. Just a thought.

Obviously that was too complicated for you.

So I'll put it simpler. You did not measure power at the flywheel. Instead you measured power at the wheels and infered the power at the flywheel by making certain assumptions. Some of the assumptions you made have a certain degree of error. In your case, the error caused by your assumptions renders your final conclusion inaccurate and, for the "mazda made up power figures" argument, useless.

Don't claim to have measured something when you think actually measuring it is too difficult.

What people should be comparing is Rear Wheel HP, like your 158, not flywheel horsepower, because no one has measured it. It's too bad Mazda didn't publish any RWHP numbers.

Here's the answer key:

Originally posted by 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.

1. The car is in its break-in period. There is no easy way to put a few thousand miles on the car. Other forum members have experienced and dynoed their car with about 10 extra horsepower from before and after break-in. (Do a search) So I added those 10HP in.

2. Because I am in the break-in phase I don't want to rev it to redline. Mazda's claimed RPM for peak horsepower is 8500, I got to 8250 RPM (and I didn't mean to even go that high). It is not that big of an assumption that more power would be available at 8500RPM. If it is 4, 6 or 8 HP, who cares? It is not that big of a deal either way.

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.

3. Where did I state otherwise? In the test the adjusted acceleration experienced passed 6500RPM to 8250RPM is fairly flat and consistent. That means the torque is constant as well. If that trend remains consistent to 8500 RPM, then there will be 3% more power at 8500.

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!.

4. Is an excl4mation point necessary? 1.58Hp is imperceptible. I made it perfectly clear that the 10% value was arbitrary. If it makes you happy use whatever value that puts a smile on your face. I really don't care.

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.

5. Is this a joke? You left out a ton of stuff. Go read the Yaw Power threads and you will see how hard it is to actually do an engine dyno for the Renesis. He has one on an engine dyno and can't get to work properly because the ECU (among many things) needs wheel speed from all of the wheels (which aren't there). He has resorted to doing in-car dynos as the only practical method to determine the power of the Renesis. Once again, do a search.

GoBeserk,

What I don't get are post like yours where you know nothing about the RX-8 and haven't taken the time to research. Plenty of newbies like yourself are just spewing ignorance without an once of thought or research. And for what reason? I very clearly stated what part of my measurements were from the G-timer and what I had derived. Do you think your post makes you look smart? Do you think you have solved a great mystery? You want a cookie? Wait, I have something better ... For the apprehension of one Mr. Wigggles, imposter Engineer, I hereby award you your very own Junior G-Man badge:

http://www.bairdco.com/bdgmelvinpurvisjrg-man.gif

Wear it with pride and I mean the following quite sincerely:

The World wouldn't be the same without people like you.

-Mr. Wigggles

Originally posted by rotarygod
Here's an idea just to see how the RX-8 compares on the numbers. Use the G-tech (or whichever device) and record 5 runs in a few different cars (brands, models, makes, etc...) then compare these numbers with the factory specs on these same cars for power and accleration. Then do the same for the RX-8 and figure out an average correction by using all the different vehicle's data. I know that different cars have different losses but this is just for comparison purposes. I bet that the losses for all the cars is actually pretty close to each other and that this number would be a good number to use for the RX-8. Just a thought.

That is a great idea.

If anyone in the Houston area wants to compare the G-timer to the Gtech Pro, let me know.

The important thing is that the G's measured between the two units are the same. Everything beyond that is calculations.

-Mr. Wigggles

we are still on this hp thing...............did you bother reading the info on the reason the car has issues being dyno'd............they put out a release...........a client who owns a garage, made a comment to me about newer cars and the ECU's underneath...............they have advanced like your desktop computer the last 5yrs, and it is very difficult to have someone other than the dealership that knows the sytem and all the variables to get an accurate reading...............god you guys, this is getting to the point of being humorous...........stop looking for cover-ups when there is none......but if that is what entertains you, then by all means.......

Originally posted by MrWigggles
Here's the answer key:
1. The car is in its break-in period. There is no easy way to put a few thousand miles on the car. Other forum members have experienced and dynoed their car with about 10 extra horsepower from before and after break-in. (Do a search) So I added those 10HP in.


So you say no one has flywheel dynoed the renesis. That's fine. So the 10 ponies everyone is claiming to have gained are from the RW not the Flywheel. So you need to add them to your 159, and then take your 25.6% -there's two more horsepower.

Originally posted by MrWigggles
2. Because I am in the break-in phase I don't want to rev it to redline. Mazda's claimed RPM for peak horsepower is 8500, I got to 8250 RPM (and I didn't mean to even go that high). It is not that big of an assumption that more power would be available at 8500RPM. If it is 4, 6 or 8 HP, who cares? It is not that big of a deal either way.
[/B]

The peak power is at 8500 (according to Mazda). I agree that more power will be available above 8250. But you're claiming 212, that's only 26 less than mazda. And now you say 8 isn't a big deal? That's 31% of the amount you claim to be missing.

Originally posted by MrWigggles
3. Where did I state otherwise? In the test the adjusted acceleration experienced passed 6500RPM to 8250RPM is fairly flat and consistent. That means the torque is constant as well. If that trend remains consistent to 8500 RPM, then there will be 3% more power at 8500.
[/B]

Again, past the peak torque (in the revs, 5500rpm) the amount of torque will be decreasing. Unless it has two torque peaks. I've seen that weird case before. However, as with most engines even though the torque is dropping off the power will be increasing because the revs increase.

Originally posted by MrWigggles
4. Is an excl4mation point necessary? 1.58Hp is imperceptible. I made it perfectly clear that the 10% value was arbitrary. If it makes you happy use whatever value that puts a smile on your face. I really don't care.
[/B]

Yes, it is. Do you think any car company anywhere, or any race team doesn't try to squeeze every horsepower they can out of an engine? Are you for real? Actually the engineers at Mazda probably got 238 and called it a day. I mean why spend the time to be able to increase power and not increase weight. 1.58 per 1% wrong your guess is. Say it's 4% (pretty small) wrong, that's another 6.32 hp. Actually it's 6.72 because you forgot the 10 that should be added to the wheels not the flywheel. And if I can use any value I choose 21% that whay when I multiply it all out I get 238.

Originally posted by MrWigggles
5. Is this a joke? You left out a ton of stuff. Go read the Yaw Power threads and you will see how hard it is to actually do an engine dyno for the Renesis. He has one on an engine dyno and can't get to work properly because the ECU (among many things) needs wheel speed from all of the wheels (which aren't there). He has resorted to doing in-car dynos as the only practical method to determine the power of the Renesis. Once again, do a search.
[/B]

That is unfortunate. Perhaps Yaw should try a LabView system to fake the wheel speeds. Or run the renesis with an aftermarket ECU to see what it's capable of.

Originally posted by MrWigggles
GoBeserk,
[/B]

Learn to spell. I mean it's right there in the margin.

Originally posted by MrWigggles
For the apprehension of one Mr. Wigggles, imposter Engineer, I hereby award you your very own Junior G-Man badge:
[/B]

Thanks, I graduate from Cornell this spring with a Mechanical Engineering degree with a concentration in vehicular engineering. I've worked personally with an SR20DET on an engine dyno and know first hand how hard it is to get things to work outside of thier donor cars.

Learn to spell. I mean it's right there in the margin.

...And if I can use any value I choose 21% that whay when I multiply it all out I get 238....

...how hard it is to get things to work outside of thier donor cars. ...

Accidents happen...

-Mr. Wigggles

Originally posted by Broker73
we are still on this hp thing...............did you bother reading the info on the reason the car has issues being dyno'd............they put out a release...........a client who owns a garage, made a comment to me about newer cars and the ECU's underneath...............they have advanced like your desktop computer the last 5yrs, and it is very difficult to have someone other than the dealership that knows the sytem and all the variables to get an accurate reading...............god you guys, this is getting to the point of being humorous...........stop looking for cover-ups when there is none......but if that is what entertains you, then by all means.......

Where did I say Mazda was a lying bunch of bastards. If you think accelerometers (i.e. in-car dynos) are a waste of time, start a thread stating so.

This is an information thread. Despite GoBerserk's claim:

In your case, the error caused by your assumptions renders your final conclusion inaccurate and, for the "mazda made up power figures" argument, useless.

I have not made that assertion at all. I don't know where he got that. I said in my first post that after break-in and if I went to redline that it is conceivable that my HP would be within 5% of Mazda's claim.

People act like I called their girlfriend ugly. I am reporting what I experienced.

-Mr. Wigggles

Originally posted by MrWigggles


Where did I say Mazda was a lying bunch of bastards. If you think accelerometers (i.e. in-car dynos) are a waste of time, start a thread stating so.

This is an information thread. despite GoBerserk's claim:

In your case, the error caused by your assumptions renders your final conclusion inaccurate and, for the "mazda made up power figures" argument, useless.

I have not made that assertion at all. I don't know where he got that. I said in my first post that after break-in and if I went to redline that it is concievable that my HP would be within 5% of Mazda's claim.

People act like I called their girlfriend ugly. I am reporting what I experienced.

-Mr. Wigggles

So I came to this forum because I'm looking at cars to decide what I want to get when I graduate and I was sold on the RX8 based on my experience with Mazda, Mazda's history, everything I'd read about the 8, and the renesis. Then a friend of mine told me that there were some major issues with the 8, something like the A/C was busted and it didn't make any power.

So I thought I'd check it out. What I found was a lot of people making the most retarded, unscientific claims I'd ever seen. So when I saw Wigggles' post I set out to correct some of his errors in order to make the information he supplied more usefull.

I erred in my judgement, however, assuming he was one of those people out there pushing the idea that there is some huge power conspiracy. I should have offered my corrections in a more civil mannrr. I do stand by the corrections I suggested. I think they can help to make his numbers more accurate.

Wigggles,
And yes, it sounded at first like you were calling Mazda ugly, but no ( I reread your orig post) that is not that case. I apologize.

Oh yeah, I can't wait to go to work so I can get my own 8. My protege is still alive with 203k miles. go Mazda!