Kawi

Just dyno'd my car this afternoon. I think I'm pretty pleased with the results:



I apologize if it's hard to read. Since it's hard to read I'll list out the data here.


*Run 001 - 4th gear
Max HP - 186.7 Max Torque - 136.8
*Run 003 - 5th gear
Max HP - 190.2 Max Torque - 138.9
*Run 004 - 3rd gear
Max HP - 185.0 Max Torque - 130.2

More info:
*run on a Dynojet
*2023 miles on the odometer
*87 octane
*half tank
*DSC AND traction control off
*about 90 degrees at the time of the test
*high humidity

Did five runs total. The first two were fourth gear pulls. But Arthur (the shop manager who did the tests) wanted to be sure we were getting a 1:1 gear ratio pull. So we did a check both in the owners manual (no luck) and then on the web. There we saw fifth gear was closest to 1:1 so we did the next two in fifth and got the best numbers. Not all of the runs are listed here because the third and fourth gear runs were only off by about .5 HP. Then we ran the fifth run as a third gear pull because my understanding is that's how most people were doing their test. From what we can see, those tests are off. Fifth gear looks like the best to check on a dyno.

If you're wondering what the little warble at the beginning of the pull is, it was just me not putting my foot into it all the way at the start like I should have. But nothing for real concern.

So: 238 HP at the flywheel - 20% drive train = 47.6 HP lost
238 - 47.6 = 190.4. My best was 190.2, but I think I could have eeked out that extra .2 if I had kicked it down at the beginning.

And to anyone in the Atlanta area who wants to do a dyno, check with Arthur over at Dynolab in Marietta. A real nice guy and let me do the two extra runs to be sure that we were getting accurate results.

[edit]
Oh forgot to add, the car topped out at 144 mph on the fifth gear runs.

Wing

Sweet, this is nice!

Now I just have one observation.

I have read so many people complaining that you can't drive this car unless you floor it all the time or it won't keep up with traffic. etc.

This is ridiculous! I know this is not true because I drive the car. But this graph proves it, come on, the car produces close to 75Hp at 3000rpm!

Some cars don't produce that at 6000RPM! You can toot this car around at 2500rpm all the time with no issues..... except the always nagging urge to POUND IT! :D

ChurchAutoTest

The 1:1 gear ratio thing being important is a fallacy - gear train losses vary by less than 1% between 1st and 4th gear. But what does happen is that the taller the gear you pull, the longer the load time. The longer the load time, the more power you'll show unless the car heat soaks.

If you look at your data disk, you'll note that the 5th gear run probably took at least 3-4 seconds longer than the 3rd gear run (maybe even longer). That's why the numbers were higher in that gear. I don't think you can posit that the lower runs were off, they are just different.

BTW, Arthur is a nice guy. We used him when we tested an Accord V6 6MT Coupe in Atlanta (217 whp !!)

SC

Kawi

That's correct. They were longer.
So do the fifth gear pulls get tossed out completely?

NashuaCLS

looking better, I think you should have no more than 17% loss to the wheels. The RX-8 should dyno at 200-205 WHP stock!...



Nashua.

ChurchAutoTest

No, just make sure that as you make mods, etc. that you stay consistent and use the same gear each time. A dyno is but a tool. If you wish to make comparisons to other cars, just make sure that you do so with a similar load time.

SC

rotarygod

5th gear is 1:1 so that is where you should do it. Not enough of a difference between all the others to really matter though.

eclps0

i said that over a month ago and i got flamed whos laughing now
ha ha ha ha
i was right the dynos should have all been done in 5th gear 1.1.

4thGen

Could the fact that he used 87 octane gasoline affected the results?

Wing

So if we believe mazda that anything below 91 octane would result in reduced performance, we should see MORE power at 91

I wonder if by performance they mean gas mileage?

KyngNothing

Out of curiousity, how many miles do you have on your car???

ChurchAutoTest

I really wish people would stop saying this. What if you changed the rear diff ratio from 4.44 to 3.33? Is 5th gear still the right gear?

Its load time, not gear that matters.

SC

Gord96BRG

So you're saying that the RX-8 dyno runs would show even more power if done in 6th gear? Everybody is freaking out about the data from the private dyno runs, and you now say that (essentially) "of course you'll see more power from a 5th gear run"... , which implies that the 3rd gear runs that have been reported have been fundamentally under-rating the rwhp?

Just curious!

Regards,
Gordon

Kawi

I guess that's what I'm confused about too.

ChurchAutoTest

Yes, you would potentially see even more power in higher gears if the engine didn't get too hot and heat soak (pull out timing, etc.).

This same thing would apply to any car though (within reason). So, if you took a 350Z, or S2000, or TSX, or Mustang, etc. and ran them in higher gears, you'd see more hp.

On a dynojet, this can make comparisons between cars a little tougher unless you monitor load times and try to make sure they're close. On something like my Dynapack, we _set_ a load time and this allows us very high consistency (BTW, we tested in 5th gear, but that really doesn't matter on the Dynapack, just made it easier to calculate total gear reduction).

The simple point is, pick a gear and stick with it. For the vast majority of cars, its usually 3rd or 4th gear. The more powerful the car, the higher the gear because otherwise the load times get too short.

SC

r0tor

iTrader: (1)

The rear diff gear has nothing to do with why we should be dynoing the cars in 5th gear.

5th gear on the RX8 is the gear where the tranny itself locks the input shaft directly to the output shaft, hence there is no power loss in the tranny (or very little), hence it has a 1:1 ratio! If your in 3rd or 4th, the input shaft turns a gear which turns another gear which turns the output shaft. Well lubricated straight tooth/helical gears are only 98% efficient (per SAE guidelines). 2-4% may not sound like much, but 2-4% is also almost 5-9 hp, which is clearly showing up here!

ChurchAutoTest

So Prober, what you're saying is that 5th gear is actually no gear at all, but a direct connection from the transmission input shaft to the driveshaft? Sorry, but that is incorrect.

5th gear still involves a mainshaft and countershaft gear intermeshing. There is no "direct drive". The only difference between 4th, 5th and 6th is that they are different ratios. The differences between the gears of various ratios are miniscule at best. I suggest checking your factory service manual for transmission diagrams, or even some general internet sites on how stuff works for some good animated examples.

As a further example, I can test cars in multiple gears on my dyno and hold the load time constant. The variance between runs is less than 1% when doing so.

SC

eccles

I know many transmissions work as pr0ber describes - in whichever gear is 1:1, the input and output shafts are indeed locked together by a sliding collar. Sure, the layshaft is still being turned because it's in constant mesh with the input shaft, so there is still some parasitic loss, but the power is not actually being transmitted through the layshaft.

Without having seen the insides of the RX-8 6-speed, I'll have to take your word for it that this is not the case on our cars, but I am surprised.

klegg

Why am I the only one who sees church for what he is? He may be polite, but he seems to go out of his way to attack mazda. Even with the 1/4 info they(mazda) just released, he still posted insisted that was "Just about right" for a car with less horsepower then mazda has now claimed. Unless he has opened up an rx8 tranny, why take his word for anything? He tested the car in the wrong gear, and now is backpeddeling. Frankly, he has zero credibility with me.

klegg

Why am I the only one who sees church for what he is? He may be polite, but he seems to go out of his way to attack mazda. Even with the 1/4 info they(mazda) just released, he still posted insisted that was "Just about right" for a car with less horsepower then mazda has now claimed. Unless he has opened up an rx8 tranny, why take his word for anything? He tested the car in the wrong gear, and now is backpeddeling. Frankly, he has zero credibility with me.

compaddict

Polite, knowledgeable and a good contributor is a good thing
around here I think.

Vince

ChurchAutoTest

Eccles, I'd ask you to find a modern automobile transmission that works as such. I'd certainly be interested in seeing it - just because I've never heard of one doesn't mean they don't exist.

Here's an excellent interactive example:

http://auto.howstuffworks.com/transmission3.htm

Notice that the mainshaft and countershaft are always engaged by the gears. You're simply selecting which gear is is being driven by the mainshaft and therefore drives the countershaft.

Someone has been perpetuating this 1:1 thing for a couple years now, long before the RX-8 came out. Maybe it was spawned from an experience with a tranny like you describe Eccles, but I do not know.

klegg, I don't know you, so I'll assume that perhaps you're having a bad day. However, I usually don't go out of my way to offer a _free_ dyno test to help clear up an issue as I did in this case. I did so because I believe that many dyno tests are done incorrectly and that the early low examples may have just been examples of poor test procedures - unfortunately they were not. And it doesn't hurt to support a new car community - that tends to be good for business (not "attacking" a car company).

That said, the data so far indicate pretty clearly that the RX8 is not producing 238 hp yet, let alone the 247 claimed at the time of testing. We have dyno data from multiple sources, multiple dyno types, etc. We have quarter mile times and trap speeds as well from Mazda. Trap speed combined with vehicle weight is a pretty accurate way to look at power. Both sources indicate about 220 hp give or take. As others have said, if you're happy with the performance, who cares? But some people do care about rated vs. actual power. Just the facts.

Oh, BTW, I tested the RX-8 in 5th gear - but such a piece of datum is largely irrelevant on my sort of dyno. It would suggest that you double check before jumping to conclusions.

SC

Digisan

I commend your efforts, thank you.

D-san

BRealistic

I have always heard that 1:1 ratio is the best for wheel dyno's- to minimize trans parasytic losses. But how does the output shaft (e-shat) turning at three times the rotor speed effect the crank(e-shaft) numbers?

brillo

Shawn's been nothing but helpful here, he's a car enthusiast like everyone else on this board, he's not trying to slam Mazda the 8 or anything else. We may yet see more power as the engine breaks in, but be thankful we have some dyno experts willing to share their opinions.