Hi Guys,

Not sure about in the US but in the UK the RX7 FD is registered as a 2.6 despite being a 1.3
This sucks when it comes to paying for insurance or road tax especially.

Maybe I'm stupid and this is a simple to answer question but I would love to know why this is so.

Thanks for any info guys, hope everyone is having a nice weekend.

 

when a piston engine is at top dead center, it is either on the compression stroke or the exhaust stroke. When a rotary engine is at top dead center, it is always on the compression stroke. So to make the two engines comparable, a lot of people double the displacement of the rotary. Swept volume of the chamber is still 1.3 liter

Pull the head off a boinger and turn it over by hand using the crank bolt; you'll see what I mean. Or with head installed and the manifolds off, turn it over by hand and listen for compression sounds. On a rotary you can do the same thing--turn it over with the front bolt and listen for compression sounds. You'll hear compression sounds twice as often on the rotary.

 

my insurance doesn't have a classification for the rotary engine so i told them it was a 4 cylinder even tough the engine is supposed to perform like a v6

 

UK model. 2.6ltr. JDM 650cc early import (my dads is 650cc). JDM 1300cc import. UK cars was just a rip off for taxation.

 

For insurance they're listed as 2.3-2.6 (2.6 for type r). Its just so they fit into the correct insurance category. For tax they're still 1300.

If I put in my plates it comes back with a Mazda 121.........

 

1.3 per rotor. 13-BREW = 2 rotors x 1.3 = 2.6

your country is correct.

 

well mine is a JDM import and it's in the 2.6 category.


It just sucks doesn't it, so is a Mazda 121 a 2.6ltr aswell? or do you tell them it's 2.6ltr.

 

Send your log book to dvla and put engine size as 1300.

 

would that work you think?

 

My apologies to arghx, who explained it quite well, but here is a somewhat more technical explanation:

Since the combustion volume is used twice as often as a 4-cycle piston engine, i.e., similar to a 2-stroke engine, it is usually thought of as a 2.6L even though the physical measurements give 1.3L.

Here's a quote from an article linked below the quote:

"For comparison purposes between a Wankel Rotary engine and a piston engine, displacement (and thus power output) can more accurately be compared on a displacement per revolution (of the eccentric shaft) basis. This dictates that a two rotor Wankel displacing 654cc per face will have a displacement of 1.3 liters per every rotation of the eccentric shaft(only two total faces, one face per rotor going through a full power stroke) and 2.6 liters after two revolutions (four total faces, two faces per rotor going through a full power stroke). This is directly comparable to a 2.6 liter piston engine with an even number of cylinders in a conventional firing order which will also displace 1.3 liters through its power stroke after one revolution of the crankshaft, and 2.6 liters through its power strokes after two revolutions of the crankshaft. Measuring a Wankel rotary engine in this way more accurately explains its specific output numbers, as the volume of its air fuel mixture put through a power stroke per revolution is directly responsible for torque and thus horsepower produced."

http://wapedia.mobi/en/Rotor_(engine)

 

It would be unlikely since they probably just look it up in a table, but what would you have to lose? (Other than your freedom, driver's licence, etc.)

Dave

 

Nah, it comes up as a 1.3, however as its not the right description, so I have to manually select the model or phone up.

 

forget those ways of measuring it and what not...
user manual says it is 1.3L... just keep it as that instead of making up or theorizing stupid theories....