rx8racer

The weather here finally cooled off a bit so I made a few more g-tech dyno tests on my car. The car made the highest horsepower I have seen on every pass. I feel that the G-tech dyno tests are more accurate than an actual dyno. The G-tech gives you the actual power that is converted into acceleration. I tried several different roads in case one was not completely level. All tests were done in 2nd gear. I didn't want to use 3rd gear because of increased wind resistence. At 40-50 mph the wind losses are minimal. All of the runs were amazingly consistent. I think Mazda's new rated horsepower number is still high. I am really disappointed in this engine. I have not idea how it made international engine of the year with the power and gas mileage the owners are seeing (17mpg average). I think the novelty factor must be what did it. I will probably be taking the buy-back option even though I love the car. At 24 mpg and 200 hp to the ground, I would have definitely kept the car.

rx8racer

If someone out there wants to do the math, you could calculate the actual dyno horesepower by determining the losses due to wind in 2nd gear at 8300 rpm. Use the car's coefficient of drag, it's frontal area, and the speed at this rpm. It would be intesesting to see if it matches other's actual dynos. My guess it that it will be very close.

daedelgt

I thought the G-Tech took the drag at speed into account (at least aprox).

TurboSE

Just to add one point, the g-tech gave very similar numbers (within 5%) to the dyno rwhp on both my rx7s. Yeah, don't believe the 238HP number either. THEY ARE STILL TRYING TO GET AWAY WITH DECEPTIVE MARKETING.

rx8racer

No the g-tech does not try to compensate for drag. The G-tech gives you the horsepower that you feel which is the most important number! Who cares if an engine can make 300hp if you only get the feeling of 100hp due to drive train losses, etc.

ProtoConVert

holy those are worse numbers than I've ever seen. Even considering "you liked it when you test drove it, so..." considerations this is unacceptable. This is worse than Ford's Mustang GT catastrophe just by the numbers.

It seems unlikely that MNAO will retract an earlier retraction, and going to numbers this low they might perceive as a suicidal corporate action... so given this what the hell can be done about this to force Mazda to come clean?

ProtoConVert

Let me backtrack for a sec... considering the member dyno runs, are these numbers typical decreases for G Tech vs controlled dyno comparisons?

babylou

LMAO! The G-Tech, while a nice tool, does not even measure power. It measures acceleration, for which there are many influences, such as:

1. Static mass.
2. Dynamic mass.
3. Atmospheric conditions affecting drag (temp, pressure, humidity, wind).
4. Atmoshphric conditions affecting traction.
5. Atmoshpheric conditions affecting power.
6. Gearing.
7. Drag properties of the body.
8. Driver skill.
9. Road surface conditions affecting traction.
10. Tire compound and construction affecting traction.

rx8racer

I've been out playing with the G-tech for the past couple days. The thing is so repeatable I decided to do an experiment. I'm fiarly sure that in very hot weather the higher octane gas would be needed to prevent detonation but it cooled off here over the last couple days into the low 70's and 60's at night. I decided to try lower octane gas and the results were exactly what I had expected. I'm sold on using the cheaper gas as long as the temps are in the 70's and lower. I think the mid range torque change is enough to feel the difference.

B-Nez

Quick question: Why did the 90-octane run add weight to the car?

Other observations between 93-octane and 88-octane runs

The main run had a quicker 60 ft. time AND 330 ft. time, yet resulted in a slower 0-60 and 1/4 mile. That's interesting indeed. Also, I'm wondering if you got much wheelspin on 1st and 2nd run. Looking at the HP graph, for run 3 it starts at like 2700 rpm, and the other 2 don't start until 2.9K. I'm not familiar with this program, but does that more or less indicate clutch-drop rpms? Do you think the differences in clutch drop/wheelspin might have had some influence on the results? I'm being genuinely inquisitive here, not trying to slant any of your numbers.

MrWigggles

B-Nez,

I think rx8racer is taking first and second gear very lightly so that he can do a nice long RPM sweep in 3rd gear. He is trying to get a complete Tq/HP curve not to go as fast as possible. On a serious 0-60 run, you would never be in the 3000 RPM range ever.

racer,

If you are doing the your testing in third gear, could you try 2nd or 1st gear instead? I don't think the Gtech from your graphs is properly taking out the effect of wind resistance in your HP and TQ calculations and that is why they are 15-20 HP lower than others. Since wind would be much less of a factor in second (or first) gear, could you test in those gears instead?

-Mr. Wigggles

ProtoConVert

also, how many trials were made per octane?

rx8racer

Wiggles, you are correct. I never had any wheel spin. I slowly got the car in motion in first gear and immediately shifted to second. All of the tests were done in 2nd gear not 3rd. 3rd would produce too much wind resistence and skew the high rpm results. The times that you see for the 60ft and 330 ft do not matter at all for the horsepower tests.

The weigt difference in the 90 octane run is because my 120# girlfriend was in the car. That is why if you look at the accereration times they look slightly slower but the horsepower in in line with the rest of the runs.

I had tried a couple 1st gear runs in the past but got lower horsepower even though there is less wind. The engine must not have enough load on it to get peak power in this gear. 3rd gear would definitely be lower due to wind. 2nd gear has proved to be amazingly consistent. I have done many runs using 93 octane. When the air temps are constant, the runs are within about 1-2 horsepower of each other. That is why I feel this data has some statistical significance showing a gain of 3hp and 3ft-lbs of torque.

If it cools off a little later this week I will give the car some 86 octane gas to see if the trend continues. The weather will be in the 80's today. I may try the remaining 88 or so octane in this heat to see if the power drops.

BillK

Do you really want to see what MPG you're capable of reaching? Want to try an experiment? Do this for one tankful:

1) Shift at 3K RPM, 3500 RPM at most. Never exceed that unless you have no choice (e.g. to go at 60 MPH in sixth gear you have to exceed 3500 RPM.)

2) Shift into sixth as soon as possible in most situations and skip gears. For example, a trip from stop to sixth at around 40 MPH shouldn't take you much longer than 10-15 seconds. Don't shift out of sixth unless you absolutely need the power. If you're going much slower than 35 you can use fifth, otherwise always use sixth.

3) Accelerate as if there's an egg on the pedal. If there's a Kia next to you and it begins to pass you as you're pulling away from a light, good. Pretend you're driving an econobox.

I'm convinced that if you drive that way you will meet or exceed the EPA estimates for the car.

rx8daniel

While good ideas, I think shifting at 3K-3500 AND skipping gears will lower the engine speed too much for any kind of normal driving. i.e. at 3500 in 3rd, you are going very close to 35; in 2nd at 3500 it will be...26.44 - had to open calculator. 1st will be about 15MPH. So a shift in 1st to 3rd at 15 MPH will drop to 1500RPM in 3rd. reduce that by 1/7 for 3K shifts +/-. I'd say one or the other perhaps. I'm convinced that nobody will get more than 24MPG on an everyday basis using anything close to normal driving habits. By comparison, my Miata can easily get 28-32MPG.

wakeech

thanks for all the effort racer.

don't mind me, just merging the threads.

*MERGE*

have a nice day.

...although i've not yet driven the car, and am used to driving a true econobox (and thus wouldn't be worried about the slower-than-minivan acceleration) these shift points and driving style doesn't seem unreasonable to me.

Lensman

Isn't this REALLY BAD!!!
No.. hold on.. that was in Ghostbusters.

rx8racer

No problem with the merge in the thread. I just started a new thread because I wanted to get the keyword "octane" in the subject.

wakeech

...no, that's CROSSING the "threads"... i was simply merging. enormous difference in terms of spelling, number of letters, pronunciation, etc.

Wing

Back ISH on topic.

The way folks drive in this town I am consistently left in their dust at lights shifting at 5K! NO JOKE!

If I shift at 3k it's rather funny how the guy behind get peeved off.

I'm not sure what is with people around here, but seriously in my tiburon if I didn't FLOOR it out of lights 2 or 3 cars would pass me in the next lane.

Other cities are different, I know in my home town it's the opposite of this. It sounds like a racetrack out on the streets here, GREEN = ROOOOAAAARR.

Heck I see people doing this from the stop sign at the end of THEIR street to 5 houses from it, FLOOR IT, stop, FLOOR it, stop. Annoying!

rx8racer

I did some more tests tonight. This time with 88 octane and some nice hot muggy weather. I found what I had expected. The car lost some power. 88 octane in cool weather gave the most power but 88 octane in hot weather gave the least power.

BillK

Of course the appropriate response is, "Who cares?"

I had kids in econoboxes fly by me on the left in my Audi TT all the time. I just figured the joke's on them when they have to fill up twice as often as I do...

AnthonyS

Well I have some bad news for you. While the Dynojet is a nice tool, it too does not measure horsepower. It measures the acceleration of a weighted drum of a known diameter and converts it to power. As a matter of fact, there is no horsepower measuring device. Horsepower is always calculated. On an engine dyno (best device for measure hp), you measure torque and rpm and calculate power. While a chassis dyno is probably better than a G-Tech, they aren't fool proof.