StealthTL

iTrader: (1)

I don't even buy the fact that it is a high revving, low torque engine!
Let me tell you how I see it - it's a 3.9 litre motor, with six power pulses per complete cycle. (Like a six cylinder.)
To get the engine thru all it's phases and stokes, back to the starting point, takes three revolutions of the 'output' shaft and six intake volumes of 600+cc. I dont buy the high revs at all, the rotors are only rotating at 3000 revs when the 'output' shaft is at 9000, because of the internal 3:1 planetary gearset in each rotor.
It is a similar situation as if a V6 motor had its 'output' shaft to the gearbox from its overhead cam; not a true indication of 'actual' engine revs.
The planetary gear triples the output shaft speed to 9k, dividing the torque-per-cycle by three, which then is rectified immediately by the gearbox, back to a realistic 450 ft/lbs, at 3000 actual rotor revolutions! Now tell me that I am not DEEPLY in denial !!!!Can anyone deny that this motor has a 3:1 planetary gearset at it's center?
Then let us not get seriously upset at it lack of torque.... it is only a figment of your imagination- it is geared up by a factor of three before it ever sees daylight, then it is geared down, back o reality.... face it - those big lumps of triangular alloy could never get over four thousand revs, anyway! Embrace the JOY! 450 ft/lbs! How can anyone look at this design and ignore the planetary gearset?

Dazz

Dude you need some serious help!

So at what rpm (eccentric shaft) does it make 450ft/lbs?

wakeech

ahahaha... double post, so i will too

he's saying that AT THE ROTOR the engine is making a theoretical 450lbft force, which means it's making that at whatever rpm it's making 150 at the flywhell...

because this is force at the rotor, it's also the ROTOR rpm which counts, so if it was like 6000 for instance, it'd be 2000 rotor rpm, leaving you with exactly the same amount of horsepower, no matter what.

fun stuff Stealth

Dazz

but the engine has two rotors, so six faces, and makes 150ft/lbs total, or 450 Stealth/lbs, so isn't that then 225 Stealth/lbs per rotor or 75 Stealth/lbs per rotor face?

Why the hell am I even entering into this nonsense! :D

zoom44

now your getting it Dazz:D

wakeech

no Dazz, c'mon: even YOU know that there are only two combustion events per revolution, not six :p ahahaha...

vipeRX7

Somehow I dont think the torqueaholics will swallow that one ... :p Nice try though :D

StealthTL

iTrader: (1)

O.K. Dazz & Andrew, you can back off, just trying to get a little stimulated conversation going, after a little arm-wrestling match with a Mr. Samuel Adams....
I lost, big time - he had me convinced that a complete rotary cycle was from starting point of rotor 'one' to same point of next cycle. What was I thinking - great taste / less filling?
.......3.9 litres..... 450 ft/lbs.......it all made sense when I saw the evil planetary gears within.....I am so far in denial, I thought people would see the basic truth of '10% alcohol by volume"
........sorry, a little side bet with a heavy hitting dutch beer.
.....thought I might get some interesting responses from the Euro forum, distract them from their 'hope the government thinks it's a 1.3 litre four door' obsession. It really is "Americas Best Beer".
.............I like the new dyno-measure - ' stealth FT/LBS "

RacingDynamcs

. . . i/u wish

lefuton

you know, i could have sworn that it was 3:2, ie, 3 teeth on the outside gear and 2 teeth on the stationary gear (wait a sec...now i remember some weird blurb about the outside gear being the stationary gear?).

it should be 3:2 anyhow so that in one e-shaft revolution the outside gear rotates 1/3 of the way (rotor only spins 1/3 revolution per e-shaft revolution)

SlideWRX

Just a technicality, it isn't planetary gear set. With a planetary there is the sun gear, planet gears and the outer gear (inverted teeth to match up to the planetaries.) In the rotary we just have the sun gear and outer gear. Just a gear reduction that speeds up the output shaft.

I have a little toy rotary that shows the cycles, and it has a different gear ratio than what I've seen of the Renesis/Mazda rotaries. More like 3:1 or more instead of the 3:2 lefuton mentioned. I wonder how changing that gear ratio affects the performance of the engine.

Tom

lefuton

now that i think about it, it really has to be 3:2 otherwise the rotor won't spin correctly and ram into the rotor housing and/or the seals will break away from the housing as well. with a 3:2 gearset imagine the top is connected, if you wrap the outside gear all the way around and back up to the top that is one 3-shaft revolution and the outside gear loses 1/3 of the circumference which is 1/3 rotor revolution.

sparck

i have studied these engines in great detail.

the rotor revolution to e-shaft revolution gear ratio IS 3:1.
if it wasn't this the rotor would slam into the peripheral housing!

think about it this way: there is one ignition per revolution of the output shaft for EACH ROTOR. you know this by looking at the dizzy. yet there are 3 faces on the rotor and each of them gets used once in every revolution of the rotor!
so, 9000 shaft RPM means 9000 ignitions per minute per rotor divide by 3 to get ignitions per face of rotor, thats 3000 ignitions per face. one ignition per face per rotor revolution means 3000 ROTOR RPM!

so, who knows the difference between torque and horsepower?
torque is the force output, and can be at whatever speed. if you rig up a bunch of gears, sure you're increasing torque lots! but you're not increasing horsepower.

the internal gearing steps up rotor revolutions (3000rpm) to shaft revolutions (9000rpm) but reduces torque by the same factor (3). so if the engine is outputting peak 150ft/lbs, the rotors are producing 450ft/lbs at 1/3 that speed. SIMPLE!
this also goes to show torque is meaningless and all the hicks who brag about how torque wins races are full of scheisse. USEABLE HORSEPOWER WINS RACES. if you have 1000ft/lbs of torque at 200rpm you might think you're a big man with a big V8 but unless that high torque extends so that most of your rev range has torque when you're going through the gears you're gonna get your **** kicked by a rota.

oh, and also, like 65% of torque in a renesis is available just above idle! can any other engine achieve this?

ok lets do a bit of a thought experiment.
we bung a 3:1 reduction gear on the end of a renesis.
normal renesis idle is what 900rpm? so, we have:
idle of 300rpm
redline of 3000rpm
torque at idle (WOT) of about 300ft/lbs
max torque of 450ft/lbs
what is this?? a massive diesel? No! its a renesis with a reduction gear! And it has anyway in the form of a gearbox with appropriate ratios!

this is why rotaries always kick the crap out of the supposedly muscle engines when they have such a small torque. its because torque means nothing on its own!! you need to find the FORCE AT THE WHEEL/ROAD to get anything meaningful! engine torque means nothing when you have a gearbox.

ok having said this if you still think torque is everything STAB YOURSELF IN THE EYE NOW :P

oh, another thing, just think what crawling gears do for 4wds. massive torque! not massive torque at engine!! ????

ok end flame now sorry if i've offended anyone lol

wakeech

...i think you've got your sums backwards.

the shaft spins at 3 times the rotor, so for each e-shaft spin the rotor turns 1/3.

the gearing is 3:2 (in fact, the tooth count in 13B's is 51:34 for inner: outer).

if you have any problems with this, i reference this link:
http://www.rotaryengineillustrated.c...mech-cycl.html

sparck

oops sorry yes that is correct, my bad.
thats what happens when you write stuff when you should be asleep

StealthTL

iTrader: (1)

Mr. Sparck said its 450stealth/lbs!!!
....I'm back in the game!
.........I must be drunk again!
..............Looking for trouble, and lots'o'torque!!!
Think I'll go over and annoy the Brits one last time!!
S

97gpGT

Torque is everything, if you still don't think so I'd like you to find me a machine that directly measures hp without having to use the (torque*rpm)/5252 equation :p... With that said, peak hp or peak torque mean nothing at all, it's the space under the torque curve that actually determines how fast a car is going to be.

rotarygod

Torque is what's important? Sounds like a V-8 guy here! You're welcome here too! Check out this article on the importance of HP vs. Torque. When you read it, the example is a little far fetched but it gets the point across very well. Yes the area under the curve (hp) is what matters.

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

For an explanation as to how the rotary works check out these articles I wrote on another, smaller forum. You have to read both together to answer some questions from the other.

http://www.performancescene.net/foru...=&threadid=172

http://www.performancescene.net/foru...=&threadid=173

Lots of good info.

Aw hell if you want to figure out how to calculate intake runner lengths go here:

http://www.rx8forum.com/showthread.p...5&pagenumber=2

Scroll down to the long reply.

97gpGT

I'm not really a V8 guy (although I wouldn't mind owning an LS1 powered car ) and I know how a rotary works, it's a great engine and I've been looking in to it for a while. I was just pointing out that torque is what actually moves the car, hp is just a product of torque and rpm divided by a constant. So, to improve hp output, you have to raise the engine's torque at a given rpm, whether that rpm be 1500 for torque down low or 9000 for a higher peak hp. But thanks for the welcome, it's nice to find a forum full of open minded people who really just want to talk about a common interest. And the intake runner post was pretty interesting, thanks for sharing that.

daedelgt

I love this thread! **** 4 stars!

It's so dumb The REN isn't 3.9L. Maybe you should come over to the rx7club forum and find the huge thread we had a few months ago.

StealthTL

iTrader: (1)

Thanks, DAEDELGT, and no, no-one is claiming 3.9L, it's just a (deep in denial) way of looking at the torque/output #s.
Could you add a link to your frum thread?
S

daedelgt

http://www.rx7club.com/forum/showthr...hreadid=165579

It goes back and forth forever, but you can reach your own conclusions.

rpm_pwr

Not quite right - torque AT THE WHEELS moves the car. Do you know the difference?

Hey whoah - why are we improving flywheel HP? isn't torque all-important?

That's either wrong or misleading depending on how you read it. If you're talking about peak power, boosting low-rpm torque won't do a thing. It will boost low RPM power though. But yes, at the end of the day you have to get more oxygen into the engine to make more power.

This is because you cant trade anything for HP. BUT you can trade RPM for torque. By using more agressive gearing you can dramatically increase RWTQ without changing anything to do with the engine. Because of this high-revving engines can run gear ratios that give them more torque at the wheels than a tractor whilst still maintaining the driveability of a normal engine.

Ever wonder why F1 motors are built for short-stroke (low torque) configurations? Why are they always chasing higher RPMs? Why not just build a narrow bore F1 motor - surely that could tow a boat? Because F1 engineers think in terms of torque at the wheels, because that's what actually accelerates.

hehe I love torque threads!

-pete

97gpGT

Yes, I do know the difference, but it's assumed that if you improve the torque output at the flywheel that the torque output at the wheels also increases. Kinda hard to imagine how it would be different, don't you think?

How is that wrong or misleading at all? I clearly stated when I was talking about torque down low and when I was talking about peak power.

What I should have said is "...1500 for power down low..." but I think the meaning is still pretty clear. I'm still not quite sure how you missed that, but hey, whatever.

Torque is important because it is what actually moves the car. Horsepower is a measure of torque with engine speed taken into consideration. The higher the horsepower, the faster the car will be. The higher the torque at a given rpm, the higher the horsepower at this rpm . Therefore, using simple logic, the higher the torque at a given rpm, the faster the car will be at this point in its powerband. I'm not one of the types of people who believes that torque is everything and that high powered, low torque cars are slow as it may seem from reading my first few posts, and I'm sorry that I gave that impression.

This part of your post I completely agree with. But, unfortunately, most of the cars that we drive are street cars, not all out race cars, and their designers have to take things like fuel efficiency and engine longevity into consideration. This limits the extent to which it can be aggressively geared. Take an S2000 and a C5 Corvette as examples of a high revving, low torque, aggressively geared car and a high torque, lower revving, long geared car, respectively. Neither are race cars, so both were geared with driveability and fuel efficiency in mind. Despite having an engine nearly 3 times the size of the Stook's and that puts out more than twice the torque and half again the power, the Corvette gets similar gas mileage as the smaller, more aggressively geared roadster. This is an important consideration to most people when buying a car (unless they're loaded), whether it be an econobox or a even a sports car that will be used in the real world.

An F1 car is not limited by fuel efficiency concerns (well, it is, but not as much as a production, street-legal car is, especially one built by Honda) and also revs much, much higher than any street car can. This allows it to be geared incredibly short to dramatically increase the amount of torque put down to the wheels while not limiting its speed in each gear by too much. Let's say that the top gear in an F1 car allows 15mph/1000 rpm. If this car redlines at 16,000 rpm, this means that it's theoretical top speed is 240 mph. Now, if this same transmission was put into an S2000 to achieve the same torque multiplication factors to make the S2000 even faster, the S2k's top speed (redline: 9000rpm) would only be 135. This also means that, at 75 mph, the engine would be spinning at 5000 rpm, not only causing a considerable drop in fuel efficiency but also greatly increasing wear and tear on an engine that is not going to be rebuilt after every time it is used, as F1 engines are. It's hard to compare racing cars with street cars, especially using a racing car so purely designed for racing as F1 cars, and though the theory remains the same behind their basic components (engine, transmission, drivetrain, suspension) the application and the reasons for implementation are considerably different so it's hard to say "Look at F1 cars, if they're built in this way then a street car would obviously benefit by having the same things done to it." It's comparing apples to oranges, sure it can be done, but it's really not a wholly valid comparison, now is it?

Sorry for the long post, but I enjoy debating and it's too late at night to distill my thoughts down any further. This thread is pretty interesting, I hope it doesn't die too quickly...

Buger

Hi 97gpGT,

Hmm...

To play devil's advocate... What would you think of a poster who said "RPMs are everything" .

They could then follow that up with the clever "... if you still don't think so, I'd like you to find me a machine that directly measures hp without having to use the (torque*rpm)/5252 equation :p... "

Whether one prefers higher flywheel torque or higher rpms as the means to get more hp, it is obvious that neither is the only factor in the equation.

Since you are aware that the area under the torque curve is important, I'm sure you're also aware of the flatness of the renesis torque curve by now, yes?

Remember, hp is just a product of rpm and torque divided by a constant. So, to improve hp output, you have to raise the rpm at a given engine's torque.

BTW, what if another poster said "weight is everything"?

They could then follow that up with a clever line about how lower weight would improve the rwhp/weight ratio, the rwtrq/weight ratio, the braking, the handling, etc.

Just playing devil's advocate of course. I'm mainly a lurker now and I don't post very much. This thread is pretty interesting, I hope it doesn't die too quickly...

Brian