Mark Booth

A member in one of the Miata clubs posted a link to an article regarding the relationship between torque and horsepower. I thought it might be of interest to some here:

http://personal.riverusers.com/~yawpower/tqvshp.html

Mark

Genom

Then they get sued by a few hundred pissed off people who feel betrayed, lose a ton of money from the horrible publicity and probably suffer a huge pullback from Ford.

Jeez, isnt that obvious? Again, why worry about it right this very second?

ggreen29

I think the MPG will be a bigger turn-off than the HP. I can't see too many families ponying up 30k for a 15-18mpg car. I'm more concerned with the low MPG that I'm still getting (17-18s) as I was expecting abot 22 to 25.

Elak

The tech highlights CD talks about the variable fresh air duct (not ports, they come after the duct) being an "important distinction between the high power and low power engines". According to the same CD the variable duct opens above 5500rpm. So maybe there is some amount of inertial ram-air going on to achieve the full effect. Thus more power is developed at higher vehicle velocity. With a dyno setup that doesn't force air into the ducting at 40-100 mph this would result in lower performance.

Indeed yawpower pointed out earlier in this thread that the car runs rich after about 5000rpm, now couldn't that be a result of not ramming in enough air?

The above theory fits both with the dyno results and my own observation that the car does have more power above 7200rpm when I drive it.

/Elak

1stRX8

I doubt Mazda is blowing 100mph+ air at the intake during tests to make the 247hp. That would insure that any 3rd party measurement of power would always indicate lower power.

Mazda would have to respond to all of us with something like..."Our new Renesis engine is capable of producing 247hp....but only at 100mph or greater. For those of you intending to autocross and such, your cars are only 210hp. Sorry."

Elak

Ok, 1stRX8 - so take the lower number instead, 40mph. That is what you're doing at 8500rpm in first. Maybe 40mph air force is what is required?

Mazda doesn't promise 247bhp on a dyno, so I don't see why that would prevent them from quoting a higher, Ram-Air effect dependent number.

Just out of curiosity, when you red-line your car in 1'st and 2'nd, does it feel like the acceleration diminish after 7250rpm?

/Elak

1stRX8

Elak -

It does seem to diminish a bit after 7250. Could be psychological because I am looking for it. I don't even dream of having senses so keen that I would really know. I would like to get a G-tech or similar device to confirm what I feel because I certainly feel good driving the car.

I won't feel as good when a S2000 shows me his rear plates. I guess if that happens I could just yell "MAZDA OVERSTATED MY F***ING HORSEPOWER - TRY AGAIN IN 20,000 MILES AND I'LL BLOW YOUR DOORS OFF!!"

Half the fun the RX-8 is talking about it.

TurboSE

elak,
the 247 bhp number is what the renesis should make on an engine dyno at the crank. Why would it be a ram-air dependent number? You just can't put a 5000 cfm fan in front of the intake and then do the sae bhp test to inflate the number. All manufacturers would do that now wouldn't they?

Elak

From what you are saying SAE guidelines ban any velocity related forced induction, even if it is real? Ok, that does shoot down my argument.

I guess on the positive side that means that the engine will actually have more than 247bhp at speed;D.

/Elak

1stRX8

We can only wish for such luck. Besides "Ram Air" reminds me of pontiac [I know the p is not capitalized, it doen't deserve it]

5Gen_Prelude

The poor showing of the dyno's have been backed up by racing the 210 and 247 HP versions of the cars against each other. The 247 BARELY beat out the 210. Imagine buying a 330 and barely beating a 320 and you'll understand why this is not just about numbers.

gettingan8

I looked through out this thread and cannot find any mention of the 207 and the 247 being very close in performance. Can you point me at your source of this info? Thanks

Elak

Look here:

http://www.artex.co.jp/Pages/Car/RX-...03_6-26_03.jpg

As far as I know nobody has translated the article in this forum, so the circumstances are unknown.

/Elak

BillK

Do you drive exclusively highway miles? Given the released car's EPA estimates, that seems a rather high expectaton to me...

OdinGuru

According to my understanding of the variable duct system in the high power RX-8, "ram-air" has nothing to do with it. The variable ducts are designed to resonate at complementry frequencies to the engine RPM, and are variable to match a wider range of RPMs. Effectively they are turning the intake into a Helmholtz resonator, and tuning it much like a trumpet (with different lengths of intake pipe that they switch in and out). This is also the same technique that is used to design base ports for speakers, as well as a whole host of other applications.

But long story stort, I seriously doubt forced air is required for the variable tuned intake sytem. The sucking intake pulses from the engine should be more than enough to excite the resonances.

Skyline Maniac

I'll do the honor and translate the article for the forum the best I can. (just hope I don't get flamed by some A-hole for taking my time doing this)

The top of the article states: Performance Test: Acceleration times of 250hp and 210hp models not much difference!

250hp 1/4 mile 14.97s 0-100km/h 7.04s
210hp 1/4 mile 15.02s 0-100km/h 7.10s

Then the article gives some 0-100km/h time for other Japanese sport cars. I'll just list a few:
4.6s WRX STi
4.8s Evo8
5.8s 350Z
5.9s Q45
6.2s S2000
6.4s SC430
7.0s IS200
7.04s RX8 6MT 250hp
7.10s RX8 5MT 210hp

Now onto the summary of the article:

Article states naturally most people assume high power version to be significantly faster than normal version. In the case of the RX-8, the JDM spec 210hp (22.6 kgm) yields a slightly better torque curve compared to the 250hp (22.0 kgm)model due to intake design. Under normal driving, the 210hp version has more torque up to 6000rpm than the high power version. Despite the advertised spec difference on the two models, does the high power version actually feel more powerful?

The testers also stated much lighter 16' wheels on the 210hp model and 5MT transmission might help the lower power model achieve better time. (on top of the better torque curve)

On a side note, Japanese testers and drivers do not like to drop clutch from high rpm due to the obvious potential damage to the engine/tranny/clutch. This type of suicide driving is often frawn upon in the JDM world. Maybe that would explain why the RX-8 time from oriental magazines have been lacking behind the optimistic projections from preproduction models in US. Then again, how many of you will actually do 8000rpm clutch drops on your brand new RX-8?

Hercules

Thanks Skyline..

It's signifigantly lower than the 5.9s gotten by the US mags, so.... *shrug*.

I think we will have to see... I've noticed a top-end deficiency and I'm hoping it will get remedied but I dunno... we'll see...

Elak

Those are the engine valves (ssv,vdi) you are talking about? The variable fresh air duct sits before them. At least this is my understanding from the CD-ROM.

/Elak

5Gen_Prelude

Nice job Skyline,

One would think this would be an even bigger problem in Japan then since they have a choice between a 6sp 250 and a 5sp 210, with the former costing more presumeably

Skyline Maniac

btw: I forgot there is also a second page on that article. I don't want to go into all the shifting details and such. Seems that they drooped or sliped the clutch from 5000rpm, and shift at 8000rpm. The testers noted the smooth Renesis engine and its signiture tone. They were very impressed with the performance of the acceleration in quarter mile until they saw the numbers. (Apparently the car felt much faster than what the stop watch says) They also mentioned the acceleration tapered off after shifting into 3rd gear.. The 250hp model feels slightly faster than the 210hp model, which is confirmed by the data. (but not by much) Amazed by the closeness of the quarter mile performance between the two models, the testers arranged to line up the 210hp and 250hp side by side and gave them a go. The result was quite shocking as the 250hp model beat out the 210hp by nose length. 14.97s vs 15.05 sec.

Article indicated factors that yield these surprising results included 1) Better torque curve for the 210hp model, lighter wheels and tires, and 3) Final gear ratio.

Here is the break down of specs.

250ps @ 8500rpm
22.0kgm @ 5500rpm

210ps @ 7200rpm (Redline of Type E is 8000rpm only?)
22.6kgm @ 5000rpm

Gear Ratio
--------250hp--------210hp----
1 ----- 3.760 ----- 3.483
2 ----- 2.269 ----- 2.015
3 ----- 1.539 ----- 1.391
4 ----- 1.187 ----- 1.000
5 ----- 1.000 ----- 0.806
6 ----- 0.843 -----
F ----- 4.444 ----- 4.300

Now for another piece of info that will likely tick some of you off - The tested both 210ps and 250ps models in a AutoX type course that included 5 slalom turns, 1 hairpin and one sweeper. The 210ps beat out the 250ps model 3 times on the course. They were comparing the sport suspension on the Type S and Type E. I'll read more about it later, but the result is rather....... insane IMO. This begs the question why would anyone buy the 250ps Type S RX-8 in Japan over the cheaper, lighter, more agile 210ps Type E.

Elak

They shift both cars at 8000rpm? That seems strange, since the high power engine only will deliver 220-240hp in that interval, rather than the 240-247hp in the 8000-9000rpm.

Do they say anything about the max speed for the two cars? That could be an argument to buy the higher powered one.

/Elak

Skyline Maniac

The 210ps model has a redline of only 8000rpm. Thus they did shift at the redline for the 210ps model. They said both cars will accelerated to redline. There is no reason to believe they would shift the 250hp model at 8000rpm instead of 9000. On a side note, the torque curve of the 210ps is higher than the 250ps model up to 6000rpm. At the 7000rpm range, both models yields about the same power.

Skyline Maniac

Minor correction here, it seems that Type E is only offered in automatic trim. So when I said 210ps Type E I actually meant the 210hp 5MT base model.

6MT 250ps Type S 18" wheels Bose upgraded brakes + sports suspension

5MT 250ps Base - 16" wheels base everything, but standard DSC and LSD. This model retails for 2400000yen, which is a tad less than $20,000 USD.


What gives? Mazda! bring over the base 5MT RX-8 over and just forget about the 6MT since it doesn't perform that much better anyhow. (maybe on paper it sounds better with 247ps. However most people buying the RX-8 aren't interested in high horsepower to begin with. The 210hp gets better torque curve (more practical), better gas milage (cheaper) handles better (according to the article data from the AutoX course) and can accelerate just as good as the high power model. The JDM 5MT retails for around $3k cheaper than the Type S (US 6MT model) I'll bet a whole lot of people would be interested in a 5MT 210hp base RX-8 with a base around $24,500. Now THAT would be a reasonable and attractable price and packaging. Mazda need to realize they are only digging themselves a hole with high profit margin and low volume sales. They need to lower the price on the car and sell more of them to increase revenue.

Edge

so does anyone else take issue with the idea of being sold a car that limits its performance for the first 20,000 miles? that's like 20% of it's life (assuming a 100K turn over)! even if you're going to go for 200K+ it's still 10%.

in other words i'm getting 8% less car for up to 20% of it's perceived lifetime. i don't like that without being told up front that's the situation. i also don't like wasting a bunch of gas just to blacken my exhaust. i don't find the "it'll be okay after 20K" to be an okay answer.

am i crazy?

BillK

Why were you expecting that? The EPA sticker on the window says 18 city, 24 highway. Are all your miles highway miles?