coop

Can you tell me what the difference between the two of these are? Rotary are reasonably hight HP but what about torque?
If rotary engines are low in torque, what causes that?

JONSKI

Horsepower is based on work over time.
Torque is based on twisting force.

Here's a good article if that's not enough (and it shouldn't be ):
http://www.howstuffworks.com/horsepower.htm

noodle

torque gets you goin,
horsepower keeps you goin

RX7SV

torque is what an engine creates. Power is just a calculation based on the torque that the engine puts out at a given rpm. A rotor is a powerful engine because it revs high and produces it's maximum torque higher up in the rev range.
Probably one of the factors that causes a rotor to be low in torque is that it is only a 1.3l engine.

newRX7fan

iTrader: (1)

Mazda calls it 1.3L, but it's really 2.6L based on any reasonable definition.

The low torque might be due the geometry of how the force against the apex seal/rotor is applied to the eccentric shaft. Just a guess.

To add to what's been said above, acceleration is caused by the torque, so torque is what you feel. Horsepower is caused by good torque at high rpm.

The best explanation I've found that gives you an intuitive feel is here: http://www.vettenet.org/torquehp.html

Texas7

Go ask Riceracing this question, and duck!

JONSKI

I think it's more an issue of only 2 rotors. The torque that a rotor produces during its power stroke is a cubic curve that is strongest just after ignition. If you have more rotors, then you can maintain more of the high torque end of the power stroke. A 20B has noticably more torque, especially in the lower revs.

riffraff

i think i have heard this before, but why do you say that..

REVHED

It's because of the number of combustion events per revolution of the e-shaft.

A 13B actually displaces the same amount per revolution as a 2.6L 4 cyl. engine.

JONSKI

Describing a rotary engine in terms of a piston engine is like describing an apple in terms of an orange.

RICE RACING

We simply need to compare a Wankel as ALL other things that combust air and fuel to make power in terms of mass flow of air in a given time.

the given units of choice tend to relate crank shaft revolution (or eccentric shaft revolution) per minute.

When you measure how much air is consumed by a rotary or more simply measure how often the trailing spark plug is fired you will find that it in 13B two rotor form fires one time per crank rpm, a conventional piston engine fires once every two rpm, hence the rotary does DOUBLE the work of the 4stroke piston engine...simple as that.

It is a 2cycle 4stroke if you get what I mean? So yes it is only a 1.3lt engine is displacement in 13B form, but it has one power pulse per rotor per one crank revolution where as a 4stroke has 1/2 a power pulse per crank revolution. In short the Wankel does double the work of a 4stroke but still with the 4stroke principle of operation, it does this through unique design and the fact that the moving combustion chamber is geared differently to the eccentric shaft...hope this explains it for you?

NOW dont get me started on TALK (torque!) I have over 900 newton meters of torque in my arm but with only about 0.1horsepower, enough torque to shear a 1" diameter steel bolt clean in half ! but my arm does not have enough power to drag my 158lb frame up to 20miles an hour on a skateboard along a flat piece of road !

A 5hp go kart on the other hand does not have enough torque to snap a pencil but it can do some work i.e accelerate my body to 20mph no problem + the weight of the go kart. Torque is NOTHING without power, the two terms should not be looked at individualy but instead they are mutually inclusive.

Power is what makes the world go around, talk is just that...nothing on its own, you need to know the frequency with which it happens, then guess what YOU WILL KNOW THE POWER

RICE RACING

Why ?

newRX7fan

iTrader: (1)

No, its describing something that most people aren't familiar with in terms of something that people are familiar with And they are both four-cycle spark ignition gasoline engines. They accomplish the same thing in different ways.

JONSKI

That's not exactly what I meant. The point I was trying to make is that when describing a rotary in other terms facts will easily give way to opinions. When someone says something like, "Mazda calls it 1.3L, but it's really 2.6L based on any reasonable definition." I could argue that a more reasonable definition would be a 3.9L because there are 3 working chambers per rotor. There aren't as many factors involved, but perhaps you see what I'm getting at. People will deductively draw conclusions that differ from one-another's, but no one can claim to be the ultimate word, because they are equal in the sense that they don't all share the same logic. Also see: opinion. I see your point in trying to explain the rotary to those that are unfamiliar, but I feel that strategy would be more likely to confuse someone by having them picture a piston engine in their mind right off the bat. If you were to build a rotary engine from a piston engine you would take away valves, camshaft, crankshaft, crank case, piston heads, rods, piston rings, etc. You would only be left with a flywheel and an oil pan. I choose to explain it from scratch for this reason. A term like 2.6L 4cyl. has too many levels of indirection for a complete newbie. They first need to understand how the rotary gets a 270 degree power stroke and how the e-shaft spins three times for every complete turn of the rotor. The 2.6L 4cyl. analogy is only good enough for explaining the power that a rotary produces. Although, I'm sure for most piston driven people this is more knowledge than they care to know .

scathcart

Try:
HP= (torque * rpm)/5252
HP is simply a derivative of torque values.
Since the rotary has such a flat torque curve (due to lack of valves), the the above equation is linear, it explains why rotary engines have such a linear hp curve.
Thus, [hp(5252)]/rpm = torque.

Your eg would mean an engine making 200 hp at 7000 rpm would have 108527 ft.lbs of torque. Such is not the case.

Sean Cathcart

REVHED

The statement I made was 100% correct. It was simply an answer to the question on why rotaries are often refered to as having twice their displacement. Stop trying to make things complicated.

JONSKI

Yes, but going back to the 2.6L analogy... Would that be an I4 or a V4? :P: j/k. Now I understand what you are saying.

sinfestboy

oh my god. I swear to god this is the fourth time I have encountered this question today.

Mom asked me this morning.
friend asked me on the way to the movie.
I was browsing t04r.com and saw an article about this.
and now this thread.
You guys explain it. and from my experience, when the argument is over (I didnt read all the replies, but there is always an argument) make a summery for the person who asked. It will make their lives alot easier.

peejay

Torque is what slams you in the seat! It is what is the driving force.

So why do we have horsepower figures? Because horsepower is how much work can be done. An engine with half as much torque only exerts half as much twisting force, however if it is spinning twice as fast, then you can use gear reduction to make up the torque. Because of that, both engines are making the same amount of POWER because they can do the same amount of WORK.

When people talk about "torque motors" what they really mean is the engine has lots of torque down low in the RPM range. Because it's low in the RPM range, the HP will be lower. However, see above- torque is what shoves you into the seat. A high torque engine will accelerate harder, however it has to upshift sooner to trade off gear reduction for speed. Low torque high winding engines can stay in a lower gear longer and take advantage of greater gear reduction.

Confused yet?

RICE RACING

**** me ! I hope this post never comes up again !

PLEASE READ

Torque means nothing ! You can multiply torque by a factor of 1000 through gearboxes and differential ratios, but at the END OF THE DAY the power measured at the crank or the rear wheels will STILL BE THE SAME (near enough)

That is why when you buy a truck it is rated on the amount of POWER it has not on the torque !

What is important is that you have HIGH average power over your rpm range to match your gear ratios and the rev range you use during driving...PERIOD.

For me because I use my car the way it was designed to be used HIGH average power from 5000 to 8500rpm is paramount, the average power at 3000rpm is LOW compared to the power I make up high. If you want low down power you either need a larger displacement engine or supercharging to get a 13B to have good low down "instant" power comparable to a large displacement engine like a V8.

Power is what it is ALL about, look at the power in the rpm ranges you are interested in, **** the torque ! It is ONLY one component, you need the power @ relevant RPM to know what an engine can do, TALK is only one component. When someone asks me or tells me how much TALK they have, I ask them at what RPM it is made at and over what range, SO I CAN CALCULATE OUT THE POWER, because without knowing the POWER.....YOU DO NOT KNOW **** !!!!!!!!

RICE RACING

The rate of change in POWER is what slams you in the seat, the constant application of power over a large rpm range is what keeps you pressed into the seat, as the power drops of the acceleration drops of and the G loading drops of, and you do not get pressed into the seat as much.

G forces are caused by power applied to a mass, not a torque applied to a mass !

RICE RACING

To prove to yourself how pointless the torque v's Horsepower argument is, just go stick your car on a chassis dyno.

Test it in 1st gear ! The torque will blow you away !

Test it in 5th gear......The torque will be low in compared to first.

The power will be around about the same (depending on gearing losses).

Now if torque were the almighty thing by which we measured performance then you would imagine that cause your car has over 3 times the torque it should be "yo mad quick" It is not, you see the measured power is what determines how fast a car will be, not the torque the car makes as the torque varies ALOT depending on which gear you are in and what final drive ratio you are running....but the power (rear wheel or engine power) does not vary.

What I am getting at is you need to look at the whole picture, the whole picture is the POWER you make, not the torque, as when people mention torque it is rarley mentioned together with the corresponding rpm at which it was made (as this would give the power!) IT IS EVEN MORE USELESS WITH CHASSIS DYNOS as you have gear ratios and final drives which ALL change the torque you measure at the rear wheels !!!!!

THIS IS WHY ENGINE or REAR WHEEL POWER, combined with the rpm range is the KEY MEASURE of engine performance, IT IS THE ONLY WAY TO COMPARE ENGINES IN CARS ON CHASSIS DYNOS.

RICE RACING

Read above for your first answer.

The reason rotaries are low in low rev power is because of their displacement, in general people try to compare my 550+BHP 13B to a 350chev making the same power and say that "mate your engine has no torque!"

My engine has no low down power like the 350 because I do not have the air mass flow rate at 2000rpm ! I am only breathing in 2.6lt of air v's 5.8lt from the chev, combine this with the lower compression of my engine and it is impossible to make even half the amount of power (TALK) that the chev will make at 2000rpm.........HENCE I AM NOT ABLE TO TOW BOATS

But I make almost 500nm of torque at 8000rpm, the chev on the other hand cannot match the torque my engine makes in the upper rpm range when tunned for high torque in the low rpm range, hence it's power is dropping or staying flat where as in my rotary it is rising.

At the end of the day it is all about matching the power your engine makes to the gearing you have to utilise the power. If you average 400bhp across your gear ratio spread and the weight you are accelerating is the SAME it does not matter if you have 200 times the torque of the other engine you will both achieve the same time to accelerate from point A to point B.

This is fundamental physics you learn in high school. You do not need to be qualified in mechanical engineering like me to follow this

BlackDragon

Don't you mean to say "G forces are caused by a FORCE applied to a mass" thus the rate of change in the velocity (since it now has speed and direction) is what is actually pushing you back in your seat. The rate of change in power is simply what causes the change in velocity (because that power is being used to turn a crank/eccentric -shaft that works its way through the driveline towards the wheels. And through torque, turning the wheels to change this velocity). So this statement would also be incorrect :-p

Because I tell you what, you push in the clutch and rev that engine up to 10 grand for all I care. That rate of change in power can be IMMENSE! But it still wont push you back in your seat :-D

hehehe I'm just playin with ya Rice Racing. I just wanted to split hairs. You're one of the few people in this topic that really knows what it's all about. Interestingly enough I just asked my dad that same question not more than 4 nights ago and learned all the physics of why what you're saying is true and all that. Great to know. Good question by the way coop. Much better than "Which body kit?!?!?!?!" hehehe. One thing you forgot to mention is that the power under the curve is one of the most important things for determining how good an engine is at doing its job. I mean one of the things I find so hilarious is when someone is like "Yeah this engine makes 600hp. Come to find out that the RPM - HP put out goes something like this:

(Not actual figures just an exagurated make believe engine)

RPM HP

1000 150
2000 175
2250 400
2500 600
2750 400
3000 300
3500 175
4000 = Redline


Yeah wooohooo. So long as your between a 500 rpm increment you make great power. But unless you've got 12 gears and a fancy tranny....you're screwed. Thats why the Rotary engine makes such a great road racing engine. You go into a turn at 7000rpm and you've got 400hp. You come out of the turn (you've slowed down but you're not ready to downshift) and your rpm has dropped to 5000rpm and your engine is still producing a good 350hp. Whereas my friends camaro (with a 2k rpm drop) would lose LOTS of its horsepower (If he were at a corresponding point in his power curve). Great stuff these rotaries. Although, in drag racing, the old adage "There's no replacement for displacement" holds pretty true. The big blocks are better suited to the drag racing environment as they can get moving quicker (most of your time in the 1/4 is lost in the start). So the rotaries and short strokers have to make up for it by gaining high end speed REALLY REALLY quickly. Oh well, give me a mountain, a twisty road, and I'll hand you a big block's *** on a platter

Great discussion guys! Lates