Hi,

Im from the UK (where were not exactly swimming in Rotary experts) and im in the final design stages of building a street legal drag race RWD 98 Mazda 121 with a Rotary engine (It has been done here before in our ThunderSaloon circuit race series, and, in all honesty, is quite simple, well, as simple as converting a FWD shopping trolly into a 500+bhp widearch RWD monster ever is...)

The only 2 real questions i have left is exactly which engine to use, and what gearbox.
So i have a few fairly simple Rotary tuning questions for you...

I need at least 500+bhp (there are too many 700+bhp Skyline GTRs around here to be happy with less!) On 98 Octane fuel and emissions not being a problem at all, what kind of power is achiveable out of the 13B and 20B engines (preferably using a large single turbo) while still being "fairly" reliable, as a street car (it will be used just on weekends, but i dont want to need to rebuild it every 2months)???

Are the cost of tuning 13B+20B engines similar?

How much bigger is a 20B compared to a 13B? (the 13B engine fits quite nicely into the enginebay with plenty of room for huge turbo n intercooler).

Gearbox- What kind of power can a std Rx7 gearbox handle? If its not going to be happy being on the recieving end of 500+bhp, what other gearbox will fit that will be fine (bearing in mind i dont want to spend a fortune on a gearbox). And i presume the 20B engine mates up to the std Rx7 gearbox?

Rear diff wise- how strong is a std Rx7 diff? Are there sensibly priced stronger ones that i could use? Its no real bother if theres no decently priced Rx7 specific diffs available as i can easily use a 9" rear diff off a RS500 Racecar or similar.

Thanks in advance guys,

Steve

 

The 121 is known as the CD Cosmo by the Cosmo crowd, or known as an RX-5 in Australia (it should be called the RX-6 since the REPU came out before it, and the RX-7 came out after it, oh well, bad name marketing I guess). I want to put a 20B in my Cosmo and have already taken some measurements. There are several threaded holes under the tranny tunnel for mounting several different types of tranny and engine combinations. A custom oil pan is needed, as well as custom motor mounts. You're right about there being plenty of space for a turbo. Don't forget about the ample room in front of the radiator for a FMIC. With stock tire circumference and diff gearing of 3.636 in the automatic rotary version, the top speed works out to be 143MPH at 7kRPM. A skyline can probably go faster, so an overdrive tranny and higher geared diff ought to help there. As far as high speed stability, I have no idea. I guess it can do 120MPH stock, but took a long time to get to that speed with stock power. All I'm familier with is the rotary version, so I hope this info was helpful to you.

 

Sorry, i read your questions wrong


The 20B is alot longer then the 13B it is approx 12 inches longer..


-Zach

 

The engine itself is about 6½ inches longer, or about 160mm, but that's just the engine. The pullies of a 20B are quite different (and longer) than my old Cosmo stuff.

 

lol, ive been misunderstood...

Over here the verion of the Mazda 121 im talking about is basicaly a Ford Fiesta Mark4 Built under licence by Mazda. Front wheel drive, 1.4litre 4cyl sheds...

Im pretty certain thas NOT the version you're thinking off...

Cheers any way! were at least trying here!

What about the power question of the 2 engine choices?

Cheers, Steve

 

What im doing is a full transformation of the std car, new floorpan, transmission tunnel, suspension mounts, etc etc etc.

The only reason im using the car at all is that it looks fairly good (with the widearch thundersaloon kit), is light as hell, and is a mazda.

 

just go w/ a 20b, much easier to make the 400+whp you want while still very good on the street. plus if you want more power later on, it'll be a lot easier to get it. before i get flamed, yes a 13b can make that power, but a 20b will be more reliable and have much more low end when you drive on the street. you gotta get a whole new motor anyway and you have to custom build the chassis to accept that motor, might as well drop in the 20b. just use the fd tranny, should be able to handle the power easily.

 

some of the drag racers are getting upwards of 600+hp out of the 13b's. the 20b starts at 300hp, and with a small port at 1 bar it makes 550hp. it is longer than the 13b by about 6-7inches. it is going to take a giant radiator to cool it. any good aftermarket ems will run the engine. it is a little more to do a 20b, there is little off the shelf support for it.

mike

 

What class of racing? because some classes won't let you use a 3 rotor. I don't know how they are set up in the UK but in a lot of events here the put restrictions on rotarys for "unfair advantage"

 

Sounds like a nice combination.. the 20B and the small 121.. *s*
Where in the UK do you live?
Might be worht the trip to see the car..
I know a guy in Norway who can get you a 20B engine.. he has imported a few JC's ...

When will there be any pictures of this monster???

//Magnus