I've read some threads where it is stated that the 1.3L Renesis engine should really be considered a 2.6L engine when compared to a conventional piston engine. The logic (I guess) is that each rotor generates two power pulses for each crankshaft rotation. I find this odd when thinking that 2-stroke engines have been compared straight across the board to 4-stroke engines in terms of displacement. That is to say, I've never heard of a 175cc 2-stroke called a 350, either by the manufacturer or 4-stroke competition.

In my simplistic thinking, displacement is displacement. Why should crankshaft rotation have anything to do with it? I say, Kudos to the engineers who figured out a way to get more bang with less movement.

1.3L

 

I would think the only way to confirm that is to put a 2.6 L engine in the RX-8 and compare the two.

 

On the mazda website, it says "654cc x 2" for displacement. So, that adds upto 1308cc ~ 1.3L.
Now, why would someone compare this with a 2.6L?

I dont get it
:

 

It is 1.3l per rotor...they each displace 1.3l....it would kind of be like saying 1.3l per piston (i think)

 

oh god.

 

In countries where certain car taxes/duties are based on the engine displacement, it is common to apply the x2 multiplier to a rotary. That's how they calculate the fee to be paid.

 

I don't get it either, but I have seen it discussed somewhere else on this forum. Also, I found the following link that might explain the reasoning better than I can:

http://www.rx7.com/techarticles_displacement.html

1.3L

 

To understand why the rotary displacement is equal to twice the piston engine displacement, it helps to think of the piston engine as having half the displacement of the rotary.

Think of what happens in the rotary as the eccentric (output) shaft rotates. For each rotation, the rotor rotates 1/3 of a turn. So, one complete rotation of the rotor results in three rotations of the eccentric shaft. Since the rotor has three faces, and each one sees one power stroke for each rotation of the rotor, we have three power strokes for each rotation of the rotors, which results in three rotations of the output shaft. Three power strokes per three output shaft rotations is the same thing as one power stroke for one eccentric shaft rotation. The displacement of each side of the rotor is 654cc, so you get 654cc worth of power, for every rotation, for every rotor. With two rotors, you get 1.3L of worth of power per eccentric shaft rotation.

In a piston engine, the piston moves once through its range of motion (bottom to top and back again) for each rotation of the crankshaft. However, only once every two rotations does this involve a combustion event. So really, whatever the displacement of the piston is, you only get that displacement worth of power stroke every two rotations. Which means you can also think of it as half the displacement worth of power per crankshaft revolution, on average. Then you multiply by the number of pistons to end up with the total "working" displacement per revolution. In other words, if you have 2.6L of engine displacement, you only get 1.3L of that working for you per crankshaft rotation. The other 1.3L is doing the exhaust/intake stroke rather than delivering power.

 

In my country (Cyprus) we have duties and yearly road tax based on engine displacement and its defenitly considered as a 1.3L (the lowest category). That is why they are so popular here and great value for money.

1300cc X 0.86cent = 1,118 Cyprus pounds import tax ( US$2,000)
3000cc X 8.02 cent = 24,060 Cyprus pounds import tax (US $47,000!)

Its the goverment's way of getting people to buy small and economical cars (just like the RX8 ).

 

I wish my insurance company was that naive. I've read quite a few times that insurance is low for an 8 because it's a 4 door 1.3L. I have a 2 door 2.6L now and if I get the 8 it's going to go up. I guess some countries and insurance companies don't do enough research to know that the 8 is a gas guzzling sports car. Great break for you!

 

It has been said the Renesis has:

The size of a 4 cylinder piston engine (1.3 ltr)
The power of a 6 cylinder piston engine (2.6 ltr)
The gas consumption of an 8 cylinder piston engine (3.9 ltr)

Try searching the site for more info.

 

you just don't wanna have to change your screen name

 

Let me add:
The smoothness of a V12

 

I read a whole thread here that claimed that it should be considered 2.6, because of having to count two spins of the shaft. I came away unconvinced, based on the fact that nobody does the same thing for 2-stroke engines.

 

Same here. 1.3 liters is 1.3 liters. Displacement is displacement. It has nothing to do with output shafts or detonations per rotation. The equalizer comes in when the engines get classed for competition (as it does for 2-strokes in motorcycles). The RX-8 with its measly 1.3 liter engine competes against much higher displacement motors.

 

Nobody is argueing that it's not a 1.3L engine. The other thread started because someone was comparing specific outputs of piston engines vs the rotary engine using 1.3L. Which doesn't make sense. for that type of comparison, you use 2.6L for the rotary as expalined dozens of times.

 

Oh gawd not this again...

Displacement is the amount of volume swept which will be combusted. That means moving the crankshaft (but how many revolutions is where people mistake it). It has everything to do with revolutiions as a point of reference. Do you double count a 2 stroke motor? I don't think so.

In going along with Mark GS, the reason for 2.6L is that in 2 revolutions of the 13b's crankshaft it will have COMBUSTED 2.6L of air (read that's 4 rotor faces and consequently 4 power pulses if you will). A 4 stroke 2.0L 4 cyclinder engine will have combusted all it's cyclinders in 2 revolutions and 2.0L of air producting 4 power phases. See the similarities?

Apples to apples, this is why it's 2.6L when compared to how 4 stroke piston engines are measured. Do you not see the logic in measureing by crankshaft rotations? It's all about frame of reference.

Heck the world could start to rate their 4 stroke piston's displacement by 1 crankshaft revolution (the same way the rotary and 2 strokes are) and that would really put shame on an NA 13b, but they don't and everybody seems to get giddy with their 1.3L powerplant and yet confused on how 1.3L is derived and getting the gas mileage anything far from 1.3L.

It would be like measuring 365 days around the sun and yet another country measures their celebration in double the days (2x around the sun). You can still derive a comparison.

 

my insurance was 1/4 of my 5 year old honda civic...

 

IIRC, back in the Rx-2, 3, 4 days, FIA declared it a 2.2 or 2.6, right after they started showing their sexy little round tail lights to the darling roadracers of the day *cough*porsche*cough*

Then they got forced to run with ballast, and when *that* wasn't enough, they got banned outright, moved to IMSA, and totally tore up IMSA... then LeMans. bwahahah.

Then again, that was a long time ago, and I could be confusing fact with my hatred of FIA for banning the wankel in the first place

(that, and their constant attempts at trying to put a leash on F1... the engineers ALWAYS find a way around it...)

 

Umm. You've seen that I'm the first to admit that 1.3L rotary is not equivalent to 1.3L piston engine. But comparing apples to apples, the Renesis has nothing to be ashamed of. If you consider it to be a 2.6L, putting out 238 hp, that's 91.5 hp/L. That is a pretty good specific output. The Renesis is also lighter than any 2.6L piston engine that I know of. Definitely, there are a lot of engines putting out more HP/L NA, but all of these are great engines. Who cares if some other engine beats the Renesis in specific output - there is always someone better, and if not, just wait a while. In my opinion, any (street car) engine that puts out 90 hp/L or more is a well engineered lump. And, if it makes you in particular feel better, the S2k engines are particularly good engines by this measure.

 

Bully for you, but you can't tell me that someone didn't fall asleep at the wheel over at that insurance company.

People that are glad they're getting good rates is great -- I would be too. But people who think they've "beaten the system" by getting the 4 door 1.3L engine RX-8 are out of their minds. No insurance company is sitting there thinking "curses, we know it's a sports car, we just can't do anything about it." If they knew what they were doing they'd charge you more IMO. That was my only point.

BTW, what insurance company do you use?