DJSensation

having trouble telling guys about the size of the engine, few guys persume is a 1.3L but on my reg docs it says 2.6L i no each rotor has cubic copasity of 1.3 x2 as 2 rotors correct ?

jasonrxeight

each rotor is 625cc, so two would be 1.3L, hence the 13B engine model.

DJSensation

ok well in uk on my reg doc its regesterd as 2.6 lol

warren(silver-roxy-8)

If it was 2.6, that means that you'd have a 26b, which means that you have a 4-rotor, which means that I would try to convince you to come state side so that I could....."borrow" your car

Chad D.

iTrader: (19)

They most likely register it as a 2.6 for insurance reasons.

jasonrxeight

well, if you consider firing order, its equivalent to 2.6L inline 4.

gwilliams6

By designating it as 2.6 in UK they can charge a higher fees. There was a RX8 club post this past year where a group of RX8 owners on the island of Crete, I think, won a year-long battle to defeat that island from raising the designation from 1.3l to 2.6l (the island wanted to raise the use fees and taxes to a higher category). The RX8 owners prevailed in court and it was correctly kept at 1.3l.

DJSensation

so it is 1.3 then lol i think ive got 2 rotors i got 4 plugs multi port lol
£250 road tax 04 plate 06 plate £450 thats yearly lol.

how can a 1.3l engine use so much god dam fuel then so strange

ken-x8

Probably because it has four spark plugs. Take two out and it won't use any.

FWIW, I had fun registering my 8 as having no cylinders. Property tax here in Virginia is by the book value of the car, so as long as they have the make and model, and a copy of KBB, they don't care about displacement.

Ken

warren(silver-roxy-8)

higher rate of operation compared to a 4 stroke reciporicating piston of equal size

usnidc

wasn't there some controversy over how Mazda figured the rotary displacement? In a piston engine it is easy because you add up the displacement of each cylinder. some argued that in a rotary, instead of the 2 "combustion chambers" mazda calculates (the displacement of one face of the rotorx2), you actually have 6 combustions chambers (the displacement of each face of each rotor), which would give youa 3.9 liter engine. which would explain our fuel economy.

ken-x8

But the rotor turns at 1/3 output shaft speed, which gets it back to 1.3 liters. You do get a power stroke every time, rather than every other time, but 2-strokes do that and AFAIK they don't multiply 2-stroke capacity by 2.

Fuel economy (or lack thereof) is explained by the shape of the combustion chamber and all the surface area involved through the strokes.

Ken

dznutzuk

625cc x 2 does not come out to 1308cc, 654cc x 2 does

Yup, Mazdz ELMA here in Greece won that battle, but I don't know if it holds in all of Europe. There was another guy in Cyprus with the same problem. Also when I registered my car there in Portsmouth, it indeed wrote 1.3l, problem was when I went to get the MOT, the book says 2.6l, which is wrong. Explain to them that there are 2 rotors, which are 654cc each, not 1.3l x 2. That's like saying someone who has a 2.0lx4cyl. has 8000cc...


Really? Think so? Cooooome on....

jasonrxeight

because its not an efficient engine. you turn more gas into heat.

Roaddemon

Because it produces so much hp and performance for it's displacement it is considered a very efficient engine in power to displacement ratio. For that reason I can forgive the fuel economy which is a little worse than a 265 hp piston 3x it's ci. The fun factor, comfort and handling easily make up for it. High performance engines use more gas. Some more than others. The greedy oil companies and the price at the pump are what bothers me. I hate giving into them, even filling my 90mpg scooter feels like I'm getting screwed by big oil.

jasonrxeight

you cant compare displacement vs power in different engine type. say if you have a 1.3L two stroke and a 1.3L four stroke, the two stroke will make twice as much power and burns twice as much gas at maximum load (assume same efficiency), because power comes from burning gas.
now a 1.3L rotary engine is equivalent to a 2.6L inline 4 four stroke engine looking at firing order, or 1.3L inline 4 two stroke engine AT maximum load.
so really, if you talk about power/displacement efficiency it all comes down to how they use the displacement.

Roaddemon

Please explain th 3.9 theory as posted below. Which is more correct yours or his?



some argued that in a rotary, instead of the 2 "combustion chambers" mazda calculates (the displacement of one face of the rotorx2), you actually have 6 combustions chambers (the displacement of each face of each rotor), which would give youa 3.9 liter engine. which would explain our fueleconomy.

jasonrxeight

ok, the combustion chambers are 654cc per rotor right? the eccentric shaft spins three times when the rotor spins once. when rotor spins one turn, three combustion stages occurr. Which means there is one combustion stage per eccentric shaft rotation per rotor. and two combustion stages per eccentric shaft rotation for two rotors.

now, we looking at a four stroke engine. it takes a single four stroke engine two crank shaft rotations to do a combustion, so two pistons give you one combustion per rotation. now a 654cc single rotary engine combusts 654cc per eccentric shaft rotation, for a twin cylinder engine to do the same, it needs TWO 654cc combustion chambers to satisfy combusting 654cc per crank shaft rotation. that gives you 1.3L. now two 654cc rotary engine, equals two 1.3L twin engines, that gives you a 2.6L inline 4.

usnidc

His is more correct as he explained above.

I threw that out as something I had seen discussed in various places a long time ago where some people were debating how to compare the rotary to other engines. the arguement was each rotor has 3 "combustion faces" so that is 6 x 650cc = 3.9L. But that doesn't go into the differences with how the rotary combustion cycle/eccentricshaft rotation works vs. a 4 stroke recip engine.

Roaddemon

i researched the engine a little more in regards to displacement. The displacement is 1.3 by volume but breaths like a 2.6 piston for the reasons you stated. So the rotary breaths twice as efficient as a piston engine the same displacement but also sucks more gas for the reasons stated. Insurance companies are wrong to call it a 2.6 for rate hikes. Here in wisconsin my 8 is rated as a 1.3 four cylinder familiy sedan by state farm. I love it. My insurance rates are lower than 4 banger accord I had 10 years ago. kinda makes up for the lower gas mileage.

jasonrxeight

2.6L FOUR stroke cylinder engine. two strokes breath as efficient as a rotary the same displacement.
lucky you. how come mine is listed 1.3L "sport" coupe and I am paying almost twice as much as I paid for a 3.5L four door sedan?
maybe cuz I totalled two motorcycles. oh well.

Roaddemon

And I have a clean record, and am an old codger.

wrightcomputing

iTrader: (5)

They do it because of the related power to a cylinder engine and for tax purposes. 1.3L cars are typically under 100 HP. So they classify the Rotary as a 2.6L so they can steal more money when the tax man comes. I agree though should be taxed as a 1.3L not our fault we bought a wankel engine.

8 Maniac

iTrader: (1)

I thought these taxes were typically more based on power, emissions and fuel consumption... If that's the case, you're just mad they thought about that potential loophole lol.

wrightcomputing

iTrader: (5)

I live in the US now so it does not affect me. Thats what my friend told me when he had one about 5 years ago. I think it helps to sell the car too. Who wants a car with a 1.3L engine? (Appart from everyone on this forum)