turbo times 2 theory

[Polygon]

Originally Posted by CBFryman

I wasnt saying it was amazing because it was sequincial...i was saying it was amazing that you get over 150HP per litre OEM from ANY internal Combustion engine...the amazing thing to me is that the 13B has ben known to sustain 700+ hp...try getting 700 semistable HP out of even an H22a... KABLOOMEY

Well, you can't look at the 13B as a 1.3L engine, it is more like a 2.6L engine.

[CBFryman]

ok you lost me...lol...

[Sluttypatton]

Okay, here is the reasoning behind comparing a rotary motor to a piston motor with double it's displacement.

A piston motor's crankshaft rotates 720 degrees (two rotations) for every cycle. Since a piston will only have one power stroke in a single cycle, we can say that each piston will have one power stroke per 720 degrees of crankshaft rotation.

A rotary motor drives an eccentric shaft, however it is essentially the same thing as a crankshaft so I will refer to it as the crankshaft from here on. The rotary motor's crankshaft rotates 1080 degrees (three rotations) for every cycle. However, each rotor has three faces, each in a distinctly different phase of the cycle at any given moment. Each face is beginning the "stroke" that the face ahead just finished, so we can say that each face is one "stroke" behind the face in front of it.

This chart illustrates this.


Here is a diagram stolen from howstuffworks.com to help the visualization.
http://static.howstuffworks.com/flas...-animation.swf

So, since we know that each cycle includes 1080 degrees, we can see in the chart that there will be three power strokes in 1080 degrees of rotation. Thus 3 power strokes / 1080 degrees = 1 power stroke / 360 degrees. So we can see that the rotary motor has one power stroke every 360 degrees, or two in 720 degrees (per rotor). Compare that 2 Power strokes per 720 degrees to the piston motors 1 power stroke per 720 degrees and we can see that the rotary motor is having twice as many power strokes in the same time period and therefore should produce very roughly twice as much power as a piston engine of equivalent volume.

So in order to compare the two types of motors on a level playing field, we double the rotary motors actual displacement to see the volume of a piston engine that would produce the same amount of power. It isn't exact, as there are many differences between the two motors, but it can be used as a rule of thumb when comparing a rotary motor to a piston motor.

[Reed]

makes sense, now give us something on power to weight of a 13b (as 1.3 or 2.6) vs similarly sized recip motors.

please

[CBFryman]

^^i knew how a rotary worked...but saying that a 13B rotary it like a 2.6L engine is like saying a 2 stroke 300cc motor is a 600cc motor..but yes it does make sence. thanks for clearing that up for el stupido me but here are some comparisons for rotary to recip motors....

'87 CRX HF 1342cc
60bhp @ 5,500RPM
73ft/lbs @ 3,500RPM

'86-'88 RX-7 2nd generation Series IV 1308cc
NA
146bhp @ 6500RPM
138ft/lbs @ 3500RPM

Turbo II
182bhp @ 6500RPM
182ft/lbs @ 4000RPM

[Sluttypatton]

Yes, you are right, I agree that it is incorrect to do so. It just happens to be a convenient way of explaining the power produced by a rotary in terms of a piston engine.

[Neutrino]

We had this discussion before and personally i do consider the 13b to be a 2.6L engine. And internationally that is what is rated at. It entered and won the international engine of the year in the 2.5L to 3.0L category.

Originally Posted by Reed

makes sense, now give us something on power to weight of a 13b (as 1.3 or 2.6) vs similarly sized recip motors.

please

Its true that is were its main advantage lays. Lots of power out of a small a light package. However; it has plenty of drawbacks: mainly bad thermodynamic effciency and lack of tq. Eg. it eats more gas than a 350Z and it has way less hp and a fraction of its tq.