Hey, I was just wondering if there was any way of figure out how much torque one would get with a rotary at different levels of horsepower. Is there any kind of ratio that would give me a rough answer or some kind of equation?
Thanks guys!

 

HP = (torque x rpm)/5252

Therefore if you know what hp you are producing at a certain rpm then you can figure out the torque.

Torque = (HP x 5252)/rpm

 

Spank u berry mooch, thats exactly what I was lookin for

 

No, there isn't a simple ratio.

The torque is defined by displacement and volumetric efficiency (for the most part) and the HP is defined by how much torque you have AND where the torque curve is.

Some rotaries have more torque than HP because they make their power low down in the RPM curve. Others have over twice as much HP as torque.

 

How would you build a rotary engine that would have considerably more hp than torque?
Is it something to do with the seals that you use? like 3mm or something?
Im going to be building an engine this winter and would prefer it to have more hp than torque.
Thanks guys!

 

Shift the powerband higher up in the RPM range.

 

but how is that done? build a strong ported motor that will rev to like 10k? have the peak hp up there so that the torque curve is very gradual or something?

 

Most porting will decrease torque and increase Hp and the more radical the port the more Hp and less torque. There are other ways to do this (carbon apex seals, lightening rotor assembly, etc) But porting is the most profound of all. The ports are timing just like a cam and you have heard of ricers putting radical cams on that increase high end power same deal with the ports.

they you seem to want it either a extreme extenda street port or a mild bridge port.

 

Without getting too technical, the formula I gave is theoretical but is the correct formula for calculating HP. Torque is defined as the amount of rotational force produced by the engine when HP is just a function of torque and engine speed.

When you take you car to the dyno, what the dyno is actually measuring is the resistance (torque) created by the rolling drum trying to decelerate the vehicle. HP is ONLY CALCULATED from the measured torque figures.

HP is never a ratio of torque but a function of it.

 

coolio, I was plannin on doing a pretty wild street port anyways
And thanks HEVNSNT, I was testing out that formula on some of the dyno sheets here on the forum and its pretty darn accruate thanks.

 

Your formula is correct. Peejay is just on crack and trying to go off on some type of MEP tangent.

If your formula isn't correct, then I've been working on my psychic abilities. Try this out - find a dyno chart in which the units are in horsepower and torque lbs-ft. It can be a dyno chart of a rotary, Chevy 350, Honda 4cyl, or whatever, so just go with the first one you see. OK, now for my amazing powers of perception - I predict that the HP and Torque curves meet right at 5252 rpm. How did I do?

 

lol, you do good I just checked 3 dyno sheets on the forum and they all crossed around 5200-5300rpm Thats rather cool if you ask me

 

It's not psychic ability dammit! It's the laws of physics All dyno curves, if their power is in HP and torque is in ft-lbs, will have torque = power at 5252 RPM. If it doesn't then the dyno curve is bogus. And Peejay is not on crack...or maybe he is, but if he is on crack, he is still right Depending on what rev range your engine was designed to run, the peak torque will vary, even for the same HP levels.

As an aside, remember not to get so hung up on the peak torque figure. The important thing is not the peak torque figure, but rather the area under the torque curve. An engine that makes 150 lb-ft over a 4000 RPM range has more torque than an engine that makes 200 lb-ft over a 2000 RPM range. That's a fact. If you build a low-peak-torque, high-revving, high-hp engine, but the torque curve of that engine is long and flat, then that engine will be just as fast as a high-peak-torque, lower revving engine with the same HP.

 

totally unrelated question RED ROTARY ROCKET

you get your name off that one south park episode??
haah i laughed very much in that episode

 

No way, you are just jealous mon!


Do you need guidance on what to do with your 6-ports? You wonderin' when the RX-7 will be exported to the US again? Does Felix Wankel's ghost approve of your mods? CALL ME NOW!

 

Hmm, let's try using that "wrong" formula then, solving for rpm = 5252:

HP = (torque x rpm)/5252
HP = (torque x 5252)/5252
HP = torque

Drat, the secret to my psychic ability is out! Maybe nobody will believe that formula is correct (even though it has been a standard since before anybody on this forum was born) and then I can make a lot of money by claiming psychic ability!

 

All porting will INCREASE torque due to increased VE at all RPMs. HP is increased due to the increased torque and also due to the extended RPM range.

 

Just trying to answer the question He wanted to know if there was a general ratio of HP to torque (like say 2:3, so an engine with 100lb-ft has 150hp) and the answer is "No there isn't".

I mean, some PP engines have 175lb-ft of torque peak and 350hp peak, that's a 1:2 ratio... other engines have 135lb-ft peak and only 110hp for a less than 1:1 ratio... there is no "rule of thumb" as it is entirely dependent on the torque curve's shape and placement relative to RPM.

 

Porting increases torque, but it lifts it up the RPM range, which is how it raises the HP, You will have slightly less torque at very low RPM, thats all

 

Your right...I am jealous of your psychic ability...I'm just in denial that I don't have the same abilities

 

Note that the 5252 thing only is when you are measuring power in horsepower (aka lift 550lb one foot in one second = 1 HP) and measuring torque in pound-feet (one pound of force on a 1 foot long lever = 1 ft/lb).

Start measuring things in PS, or kilowatts, or newton-meters or kilogram-meters and you have to calculate differently, and so the "crossover" point is different.

That's why I get irked when people say HP and TQ. HP is a unit of measurement, while "TQ" is just a concept.. That's like saying the car weighs 1500. (What unit of measure?)