Deslock

The RX8 6-speed is no CVT, but it's fairly close ratio... it's not like we're running 3 speeds like many older cars used to have. As I wrote, having more engine torque is useful in some situations, but power is generally the more important attribute for acceleration. No one has offered any specifics that dispute that.

I have a degree in mechanical engineering (which meant taking several physics, statics, and dynamics courses). This stuff is basic... some here are making it more complicated than it needs to be.

Deslock

Nothing I wrote implies that power is doing all the work. This discussion is becoming circular, so let's just lay it all out and be done with it:

• force = mass * acceleration
• torque = force * distance
• work = force * distance
• power = work / time
• power = force * velocity = torque * angular velocity

By approaching this in terms of work, your argument has become convoluted (perhaps there is some confusion because work and torque have the same units, though there is a conceptual difference). In this context, it's simpler to think of power in terms of force and velocity. For a car, acceleration for any given situation is increased if force at the wheels is increased (which is increased if wheel torque is increased):

1. engine power * system efficiency = wheel power (this is a standard input/output relationship)
2. wheel power = wheel torque * wheel speed
3. engine power * system efficiency = wheel torque * wheel speed
4. wheel torque = engine power * system efficiency / wheel speed

It's worth noting that

• Peak power isn't the only important attribute because we don't always drive at the RPM corresponding to it
• More torque is needed to make high power at low RPM
• Many drivers prefer not to have to shift a lot or to keep it in a high-RPM power band and there are some competitive situations when it's disadvantageous to have to shift a lot
• Wheel torque is proportional to engine torque in any fixed gear... this is why you don't accelerate harder in a fixed gear as your power increases with speed in a vehicle with a flat torque curve (which may be what usually gets people so confused about torque vs power)

As those last few bullets show, engine torque is relevant. But for any given vehicle speed, you increase your wheel torque if you increase your engine power (from eq 4 above) regardless of your engine torque (and as I wrote previously, you can make more wheel torque even if you decrease engine torque). That's why power is more important... it tells us how much mechanical advantage we can get from gearing. It's that simple.

I seem to remember there being an illustrative problem in my old physics text about a car accelerating up a hill against significant wind resistance (which is a cubic function, if memory serves). I'll be happy to dig it out and post it if anyone wants.

therm8

I gave up. You weren't understanding what I was trying to say. I wasn't understanding what you were trying to say. I was leaving gearing out of it and approaching it from the engine side. That is why I hate the hp vs tq discussions, because it is too complicated to argue effectively. Power is only more important as a concept, not as a physical analysis. That's why the units of horsepower and watts were invented, they provide a conceptually easier way of looking at work capability. When it comes to engines, however I still maintain that one is not more important than the other. Regardless my end of this discussion is now finished.

globi

I actually do think Deslock did a very good job in explaining it.

Japan8

That actually isn't what I was implying. I was implying that although it does shift faster and pro racers can turn slightly better times (which can mean the difference between winning and losing), that doesn't account for feel and "fun to drive" factor.

I know what the mechanical differences are between a SMG/DSG and a manu-shift auto. I have the auto in my current car. I've played with the shifter. I don't like it. I've had the car 3 years. I still don't like it, can't get used to it. I've driven BMW's with it too. Full auto is just more comfortable. I hate the +/-. I LIKE clutching. I like to skip shift sometimes. You can't argue this... this is personal preference. And there are others who feel this way. You like SMG... so good... get one in your car. Just don't tell the manufacturers to drop regular manual transmissions in favor of SMG, because there are plenty of us who hate them.

See this post... https://www.rx8club.com/showpost.php...&postcount=154

globi

No one said to get rid of manual transmissions. Auto, CVT, SMG and DSG has been an option so far and it will be an option in the future.
(Actually DSG seems to have more potential than SMG, due to the double clutch system there's no need for a power interrupt at all.)

Deslock

1. You need to consider gearing (either directly or indirectly - through speed) when looking at an engine.
2. Too complicated to argue effectively? This isn't philophy... I don't mean to sound arrogant, but either you understand it or you don't. If you don't, you can learn it if you choose to.
3. Hogwash. Just because power is "calculated" doesn't mean that it's important only as a concept. In a sense, torque is also calculated (dynos have to be calibrated to measure force and multiply it by a distance).
4. Please don't take this as an insult because that's not my intention, but you've misunderstood some key concepts. If you want to figure this stuff out, you have several choices:
   • Google it (though you run the risk of finding misinformation).
   • Read some physics/engineering texts.
   • Ask a teacher/professor about it. Feel free to show them my posts (I'll be happy to elaborate on anything).
5. On that note, sorry to everyone else for perpetuating this off-topic tangent. Also, thanks for the kind words globi.

hedgecore

Deslock, your write ups have been thurough. But they will never support your generalized claims.

There are many variable that contribute to the characteristics of a sports car. Ignoring torque is foolish.

Would you drive a car that has a constant 10ft-lbs of torque that redlines at ~157,000RPM with a max 300HP?

No, no you wouldn't...

Would you drive a car that has a constant 300ft-lbs of torque that redlines at ~175RPM with a max of 10HP?

No, no you wouldn't...

An car that yeilds good performance can come in different flavors...and current engineering doesn't give us any clear "Best way" of doing things. The smart engine designers know the limitations of their resources and abilities...these limitations are defined by the realities of things outside of you simplistic text-book explinations.

These two things are tied together...neither is nay more important than the other.

The best production cars on earth have engines that neglect neither torque or HP.

HP is not more important than Torque...this statement is much to general to be true.

*BOTTOM LINE*

If forced to trade one for the other...there is no clear answer without taking many factors into consideration.

If Power was more important, then you could blindly use it as your answer in all cases.

Japan8

You have to admit that auto makers would kill for a 1 transmission setup across all their lines of cars. Imagine the profit savings from no more auto AND manual. I am more than willing to bet that automakers will jump on this boat if given the chance. Be sure to continually remind them of what we REALLY like...

therm8

I guess I'm not done, since I must now defend myself...

1. gearing can be ignored in the original context of the discussion, since I was originally talking about 2 different engines for the same car. Therefore with the same gearing. The discussion got carried beyond that original context.

2. I don't feel I've misunderstood anything. I was just talking about a different aspect of the topic than you. When 2 people narrow their focus to different parts of the system, the topic cannot be discussed effectively.

3. In that case, everything is calculated. Since everything is calibrated to some prime standard.

4. I have a heavy background in physics. Newtonian to nuclear. But perhaps my internet arguement capabilities are not up to par enought to get my point across effectively.


No offense taken, and now let's get back to the topic at hand, if there is one any longer.

Deslock

1. My original response to you was to your post containing, "Apply x torque for some amount of time and you get power." (see post 227). It's worth noting that even with two cars with identical gearing, you still must consider what that gearing is (post 254) because if the two engines have different redlines, there may be vehicle speeds at which the two cars are in different gears.
2. It appears you have either misunderstood a few things or there are some typos in your posts. You wrote:
   • "Apply x torque for some amount of time and you get power." (this is not necessarily true... if you apply torque at some angular speed and you get power... to be fair, when questioned about it you mentioned that your statement was elaborated on in a subsequent post, but what you wrote is still misleading, even in this context)
   • "I was leaving gearing out of it and approaching it from the engine side." (if you're looking at acceleration, you really can't do that)
   • "Power is only more important as a concept, not as a physical analysis." (this is false)
3. My response was really for those who think power is esoteric because you don't "feel" it directly. In any fixed gear force at the wheels is *proportional* to engine torque, but you don't feel the engine torque directly either (it goes through the transmission first).
4. My cousin is a brilliant guy with a physics PHD who is working on some pretty wild stuff (involving - I kid you not - teleportation). But if I asked him what makes a car accelerate, he probably wouldn't be able to explain it and would stumble over a few concepts as some have done in this thread. Then again, he's not a sports car enthusiast and he doesn't spend his free time in online torque vs power discussions.

Ultimately, I agree with many of the things in your other posts (the ones I didn't reply to). My beef is with a few things you wrote above (summarized under my bullet 2) and with your statement that I was implying that "power was doing all the work" (see post 235) when I never wrote anything to suggest that. And I think there are a few gaps in your logic in order for you to think that power is not more important than engine torque when it comes to acceleration. Again, as I wrote previously, engine torque is *also* relevant but it's not *as* important in most situations (which I detailed in post 254).

Anyway, thanks for keeping it cordial.

Deslock

1. What generalized claims have I made that are unsupported by my write ups? I've qualified my statements and I have not advocated ignoring engine torque outright, but rather I've explained why power is ultimately more important.
2. Obviously not. But what you wrote partly illustrates why power is more important. I would drive CarA with a constant 150 ftlbs that redlines at 10500 yielding ~300 hp peak hp rather than CarB that has a constant 300 ftlbs of torque with a peak 150 hp that redlines at 2600 RPM (since CarA will have more wheel torque in most situations).
3. Often, engineering does provide a clear "best way" of doing things (depending on the application). There are always compromises, and for everyday sports car drivability that sometimes means lowering peak power in order to increase low-end power (usually done by increasing peak torque). I never wrote anything that suggested otherwise (and in fact touched on this in post 254).
4. I believe I covered real world situations in my posts before. However, since you believe otherwise, please show me a real world example that my simplistic text-book explanations do not cover.
5. I find it a little ironic that your beef with my posts is that I'm being too general with my claims when I thoroughly explained why power is more important while mentioning why torque also needs to be considered.
6. Nonsense. Just because attributeA is more important than attributeB, doesn't mean we can ignore attributeB.

(My apologies for any typos or errors in the last couple posts... it's way past my bedtime)

pcimino

Doesn't really answer your question but suggests hydrogen injection could be a solution...

http://www.wired.com/news/autotech/0,2554,69529,00.html

hedgecore

Perhaps we're misunderstanding eachother..

You said "That's why power is more important... it tells us how much mechanical advantage we can get from gearing. It's that simple."

More important how?

If you are saying it's the most important factor in determining where a driver shifts from one gear to another...then i agree. By maximising the shift points to contain the most area under a power curve for a given car...you will achieve the best performance.

Or if you are saying that at any given instant, power is more important in determining what behavior the car will have...i agree again.

These are both highly conditioned statements...

Deslock

Are you pulling my leg? I explained it in several posts, including the one you quoted above!

Oh wait, I suddenly get the joke... you've been yanking my chain this whole time, replying to my posts as if you hadn't read them, goading me to explain myself over and over. Wow, you had me going there for a while. Bravo!

tuj

What we need is a better measure of a car's power-to-the-ground potential. I'd like to see a measurement that integrates (area under the curve) the actual wheel torque of a gear, starting at the rpm's you would land in that gear if shifting optimally, up to the point you would shift out of that gear (at max wheel torque). Average 2nd, 3rd, and 4th gears and you'd have a good measurement of how effectively the engine, gearbox, and differential can deliver power in the rpm ranges that matter most.

hedgecore

You are clearly my intellectual superior, i bow to you.

Umbra

Hmmm......

convert chemical energy to mechanical
vs.
convert chemical energy to mechanical to electrical to mechanical

Seem's pretty obvious which is more efficient. So I doubt the train idea is going anywhere, that is done simply to get max torque.

fatmarco

Does anyone know what potential direct injection technology has? Maybe this is the factor that has made bigger rotaries possible..re:2rotor 1.5litre.

rotarygod

It's not a fuel issue. It's an airflow issue.

neit_jnf

direct injection in a rotary (or piston engine for that matter) has the potential to allow high compression forced induction with NO knock, meaning better low end, faster spooling and high reliability!

Also the direct injetion system allows for leaner overall mixtures by creating a bubble of rich mixture near the spark plugs and ultra lean combustion in low load , i.e, cruising and idleing (some gdi engines run 40~50:1 afr's). This means lower emmisions and higher mileage.

Jyariten

In Japan, "17B" has heard the said rumor. However, the story of "15B" doesn't have the hearing kite.

BoosTED

iTrader: (2)

This website states that:"HFI's manufacturer guarantees 10 percent fuel savings"

For us that would mean close to 2 miles per gallon minus the cost of the distilled water that a person would need to produce or buy in order for the system to be able to pull hydrogen from the water it needs it.

Second of all Murphy's law states that there has to be some loss of energy from the conversion, so there can't be 100% efficiency from the conversion.

Third the cost of the HFI systems cost $4,000 and $14,000, depending on the size of the vehicle.

How much gasoline can a person buy for $4,000? IF gasoline was $3 per gallon that $4,000 could buy 24,000 miles worth of gas, averaging 18 MPG. That does not include the cost of distilled water. In order to reach the savings point the car would have to be driven 240,000 miles. How many people keep thier vehicles that long?

Does it sound worth it?

Truck drivers put a lot of miles on a vehicle. Most run them into the ground, I have heard of trucks with 1 million miles on them that is why it is worth it for some of them to invest in these units.

jeffe19007

Ok, I know it has been a while for this thread, and I just scanned it looking for someone else's mention of this idea and didn't see it...

But if you are widening the rotors (not saying they will) but that would involve a redesign of the crank, correct? If you are doing that, why not widen the center plate and put larger exhaust ports in? Get rid of the siamese ports, and allows some real breathing on each rotor.

That, with the better air flow velocities from the larger rotor may change the power picture.

Would this correct the flow issues that RotaryGod brings up?

When I read through the thread it seems the assumption that the center plate would remain the same.

There may be other benefits of a larger center plate too... crank shaft bearing stability, cooling, whatever.

These are just the thoughts of an amateur waking up in the middle of the night...

tuj

RG says the port area on the side housings is tapped out. Making the center housing wider won't help with a surface-area challenge. I'm not exactly convinced that there is no more flow to be had from the existing port; I haven't seen any explaination or proof of that. The key stat. is how much surface area do the ports have? Also, wider rotors definitely means a new e-shaft.