I have a question about rotary engine, It's like this I heard from my friend that if you
wish to overhaul the rotary engine, you will have to replace the engine. So, that mean
no overhauling or you can't overhaul the engine.....

I have doubts about this statement, Is this true or a stupid fact made by my friend....

What do you mean "overhaul"? :?

Well to me, "overhaul" means to re-build everything.

It makes no sense. :?

Well to me, "overhaul" means to re-build everything.

yeh...thats what i'm thinking at the moment...

Rotory means high HP/ low torque.

BTW....torque is what makes you move...not HP.

BUT with higher revs (-->high HP) you can use shorter gears, so more torque arrives at your wheels.

BUT with higher revs (-->high HP) you can use shorter gears, so more torque arrives at your wheels.

ive read that a few times and that makes little or no sense!

I don't know if this will help:
http://travel.howstuffworks.com/rotary-engine4.htm

BUT with higher revs (-->high HP) you can use shorter gears, so more torque arrives at your wheels.
ive read that a few times and that makes little or no sense!
If you knew better how gearboxes work then you would know why it makes sense.

Here, we have the facts:
1. The RX-8 rotary has little torque, approx. 20 kgm? Yes, I agree, it's a fact.
2. The redline of the RX-8 is at 9500 rpm, that is pretty high. This is a fact too.

Now, let's say that we have a car with 30 kgm of torque (that's decent) and a redline of 6500 rpm.
Suppose that the gear ratios for this car are set to a specific point:
1st gear: X km/h @ redline
2nd gear: Y km/h @ redline
3rd gear: Z km/h @ redline
etc...

The torque at THE WHEEL of this car will be a multiple of 30 kgm, let's say A*30.

Now think of the RX-8: 20 kgm, 9500 redline.
Suppose the RX-8 has the SAME gear ratios (as a function of speed) as the car above, i.e 1st gear at X km/h and so on. The torque arriving at the wheels will be a multiple of 20 kgm. To be exact, it will be B*20, where B = A*9500/6500 =~A*1.5 so the torque at THE WHEELS will be A*1.5*20 = A*30 kgm!!!
So the torque at the WHEELS will be almost the same as the 30kgm car! So the two cars will have exactly the same acceleration.

IMPORTANT NOTE: To simplify things, I've considered that the two engines produce the same amount of torque through the entire range of rpm, otherwise you would have to replace the torque number with the Riemann sum of the torque function over rpm (this is for math connoiseurs).

Anyways, what I'm trying to tell you is that when you have small torque - high rpm, you must use a gearbox with shorter ratios, and then you have the same result in acceleration as with some appropriate large torque - low redline engine.

If there is anyone who KNOWS stuff here then please tell me that you understand this.

yeah thats right - although youve made alot of simplifications.

ANd thats not what you said nor implied in your first statment - since high revs doesnt mean higher horsepower, and shorter gears doesnt mean MORE torque at wheels.

if just read that again - its all right what youve written but it is so inaccurate that you cant really on it. Only accounting for point torque at the redline. I mean what you have done is multiple the torque of a car by the ratio of redline rpms, to come out with a figure 1.5 times the original (i.e. 20* 9500/6500). Now that is not sufficent to explain torque values. ESPECIALLY when you are trying to compare 2 diffeerent types of engine (piston and Rotary). So the Riemann function for both engines are so so different that you simply cannot do a calulatino as basic as that.

Yeah, I know I've made alot of simplifications, but it was just meant as a simple analysis in order to understand what I wanted to say, and I didn't want to get all technical with differential or Riemann analysis etc.
I repeat that I've considered that both engines produce the same amount of torque throught the entire rpm range (flat torque curve like electrical engines). If we could roughly say that the torque curve is flat, then my calculation is correct.
BUT if you think about it, my calculation also works if the two engines have the same torque curves. (the 9500 rpm engine torque curve would just be "widened" to fit through the whole rpm range... ~1.5 times wider, but with the same relative peak points etc.).
Anyway, we're getting very advanced now, I think we should quit so that more members besides you and me can keep talking about stuff and can get back to topic. :lol:

If you needed to rev to 9500 rps everytime you wanted to get up and go, the life expectancy on that engine would be about a year.......

I love the concept of the rotory engine, but realisticlly, torque is what makes a car move.

Maybe a forced induction rotory might produce enough torque to be attractive, I don't know.... something to consider........

If you needed to rev to 9500 rps everytime you wanted to get up and go, the life expectancy on that engine would be about a year.......
That's a reasonable point, however high-revving engines are usually very resistant to wear and tear. So running all day long up to ~5000 rpm (in normal driving) in a RX-8 wouldn't be a problem, and reserve 5000-9500 rpm only for rare racing conditions when full performance is needed.
Anyways we're getting seriously off-topic, matt-x just asked about info on rotaries...

Yeah, I know I've made alot of simplifications, but it was just meant as a simple analysis in order to understand what I wanted to say, and I didn't want to get all technical with differential or Riemann analysis etc.
I repeat that I've considered that both engines produce the same amount of torque throught the entire rpm range (flat torque curve like electrical engines). If we could roughly say that the torque curve is flat, then my calculation is correct.
BUT if you think about it, my calculation also works if the two engines have the same torque curves. (the 9500 rpm engine torque curve would just be "widened" to fit through the whole rpm range... ~1.5 times wider, but with the same relative peak points etc.).
Anyway, we're getting very advanced now, I think we should quit so that more members besides you and me can keep talking about stuff and can get back to topic. :lol:

but thats one of my points jim. Roatary and Piston torque curve arent a) flat b) similar shape.
Your calcualtion proves nothing - all you have done is scaled up torque in ratio with max revs. - that is not good/accurate/useable data.

If you needed to rev to 9500 rps everytime you wanted to get up and go, the life expectancy on that engine would be about a year.......
That's a reasonable point, however high-revving engines are usually very resistant to wear and tear. So running all day long up to ~5000 rpm (in normal driving) in a RX-8 wouldn't be a problem, and reserve 5000-9500 rpm only for rare racing conditions when full performance is needed.
Anyways we're getting seriously off-topic, matt-x just asked about info on rotaries...

My only argument against that is that rotory engines is something that only Mazda will do, and even they had to tackle many problems with them. They had seals blowing out of them, and with any newer design, you gotta get the bugs out of them, and get a little time under the belt, before poeple would consider them reliable...

OMFG...
I drop it... I'm bored and tired.

OMFG...
I drop it... I'm bored and tired.

because you aint talking much sense :D

Dude what I needed/wanted to say, I said it earlier... I hope at least someone got my point... I aint gonna be sad cause some ppl don't understand. And anyway, we are OFF TOPIC, and I try to think of this as well.

Dude what I needed/wanted to say, I said it earlier... I hope at least someone got my point... I aint gonna be sad cause some ppl don't understand. And anyway, we are OFF TOPIC, and I try to think of this as well.

Although I mostly agree with everything you say jim I think your statement on wear and tear is inaccurate. Even with larger displacement or "slow revving" (talking peak RPM not HP) engines wear and tear isnt bad at all. Its more up to the individual who maintains any given motor to keep it alive. Even then we're dealing with extreme variables here. You might buy a Honda such as I did at one point and well before it hits 100k it grenades the distributor. You might buy a Ford Bronco II with the crap 2.8 and it may last 300k for you. I believe it to be more operator maintenance on the vehicle then any other factor.
With the torque equation everything looks great but you're missing some important things that you need to consider. First off an engine spinning high RPM's has to be precisely toleranced. Ok so nowadays we've got that down. Next would be the rotating assembly on the outside of the motor. We're talking about all the front accessories running off of a crank (or eccentric shaft) thats rotating over 9,000 rpms now. Then consider clutch assembly. Input shaft speed on the transmission, and a dozen other factors.
Torque. Torque on a larger displacement engine will be a lot broader whereas on the "revver" you're talking about you're addressing a very small portion of the powerband.Think about it this way. 2 cars of at least near equal weight. One has a B18C5 in it making near 200 hp, but only 140 ft lbs of torque. Now the other one has a 302 or 289 small block in it making 300 ft lbs of torque, and 225hp. Consider the car with the 302 will pull harder across the entire powerband from 600rpm's all the way to 6000 rpms then that revver ever will. It has not only more rpm to use, but more power at any given point. No amount of gearing could change that. (unless you had 30 gears in some sort of automatic shift configuration or something hypothetically insane like that).
Whats this have to do with the wankels you ask? Not a lot to be honest. Yes it burns fuel just the same as a regular ICE does. The rotary is a very different animal, although the rules of HP and Torque still apply. The thing is, is that the rotary with its simplicity of moving parts isnt likely to have massive high rpm related failures. I have in fact on occasion seen them rev to over 20k rpm's. Yes you read that right. We're talking Titanium Apex Seals, 30+ psi etc. Only on drag or sand rail applications I might add as well. Still though thats pretty awesome. Now if it could succesfully provide over 5000 rpm of serious motivation instead of your typical 3000 or so rpm window, whether it was at 18,000rpm's or not, I'd be impressed. Problem is right now its barely competitive with standard ICE engines in its own class. Given more time and development who knows. Due to simplicity of its design though there isnt a whole lot to improve upon.

I know, I know... you're mostly correct on what you say too.
And I know that torquey engines are more suitable for everyday driving and normal conditions etc, whereas high revvers are successful in racing. Yet you must admit they have their own unique charm...

About the rotary, it indeed has increased fuel consumption. It still has some (minor) problems too, but I'm confident that, given some years, it will ultimately be really competitive against pistons. Btw, 20k rpm???? WOW. :shock:

I was also wondering at which point do you guys change gears. I mostly change at 3500-4000 rpm under normal driving, but I go up to 5000-6000 when I want extra acceleration (e.g. when I'm pissed off with someone going slow in front of me :P ). Redline is at 6500.

Rotory means high HP/ low torque.

BTW....torque is what makes you move...not HP.

its also got high rpm..higher than s2000

I know, I know... you're mostly correct on what you say too.
And I know that torquey engines are more suitable for everyday driving and normal conditions etc, whereas high revvers are successful in racing. Yet you must admit they have their own unique charm...

About the rotary, it indeed has increased fuel consumption. It still has some (minor) problems too, but I'm confident that, given some years, it will ultimately be really competitive against pistons. Btw, 20k rpm???? WOW. :shock:

I was also wondering at which point do you guys change gears. I mostly change at 3500-4000 rpm under normal driving, but I go up to 5000-6000 when I want extra acceleration (e.g. when I'm pissed off with someone going slow in front of me :P ). Redline is at 6500.

In my 5.0 I dont have to go past 1300-1500 rpms for normal driving/acceleration. Usually around 55mph my car is loping along at about 1500 rpms exactly in 5th gear. At 140mph 5th gear is around 3500 rpms although it wont pull. 4th gear is 6000 rpms at 140mph which is right under the fuel cut off. Anywhere above 2000 rpms it starts pulling hard with a major jump around 4500 rpms.

I have a question about rotary engine, It's like this I heard from my friend that if you
wish to overhaul the rotary engine, you will have to replace the engine. So, that mean
no overhauling or you can't overhaul the engine.....

I have doubts about this statement, Is this true or a stupid fact made by my friend....

Well, :-k if your engine doesn't have any internal damage you can rebuild it. Problem is [-X that for the cost of new rebuilding parts and service you can just buy a used low mileage JDM spec engine and replace your old one and get on the go easier. :smt023

New Rotary engine = about 500 bucks......

So if your engine goes..

buy a new one..
and swap over any parts you wanted to keep..
simple as that.

jimkk29, I agree that you can gear an engine towards torque.

For torque at the tires, multiply the tranmission gear ratio X rear end gear X engine torque. For example:

Engine Torque = 300 ft-lb
1st gear ratio = 3.27
rear end gear = 3.50

Wheel torque = 300 x 3.27 x 3.5 = 3434 ft-lb

Make sense? Use this formula to go backward to calculate the engine torque knowing the wheel torque.

I think the torque halved at the differential assuming both wheels have grip so 3434/2=1717 ft-lbs.

It looks funny though, even how I just picked some numbers. I could be wrong.