I was wondering if anyone knew how and what is needed to build a high compression 12a motor? As much as you know would be helpful!

 

Forced induction.

 

hahaha, exactly.

The 12a is already the highest compression of the rotary engines (except maybe for the Renesis?) as far as I know. And I'm pretty sure theres no simple way to increase the naturally aspirated compression like with piston engines. If you just look at the way it works its clear that you would need some special rotors designed to deliver higher compression.

 

Or dump a couple cans of compression in it........

 

lol.... our motors pretty much are as "high compression" as you get.

9.4:1 rotors, and for a 12a you can't get any higher. You *could* find some way to fill in part of the "tub" of the rotor, but it would be way too hard to fill it in evenly to get the same compression on all three sides *and* keep it balanced.

Only more recently did the 13b motors get the chance to venture into 10:1 territory with the new Rx8 rotors.

however, if you're looking for the stuff that you need to build a reliably high-revving high-power 9.4:1 12a motor, I have a thread around here somewhere called the "ultimate streetable 12a" that gives you the ultimate list of 12a mods.

(https://www.rx7club.com/1st-generation-specific-1979-1985-18/ultimate-streetable-12a-529162/)

So our engines are considered "high comp". There were "low comp" 13b's made for the TII and there were low comp 12a's made in japan for the 12aT. Can't remember compression ratio, but the number 8.7:1 rings a bell (I could definitely be wrong).

So.... trochoid was on to something.. if you want more air/fuel to get into the chamber, forced induction (turbo or super) is the way to go. Because our motors aren't low comp motors, they build their boost pretty quick, but you need a good wastegate / intercooler / bov / fuel setup to make it all work like a charm.

I'm gonna start by building the "ultimate 12a" which will give me a bulletproof base for a high boost motor later on if I decide to go that route, AND it'll be ported

I kinda wish someone had made higher comp rotors for our engines, but the 12a didn't see any life past the FB. Someone would have to custom machine them, and that'd be bloody expensive. It would be cool though to do a 12a with multi-side-port and 10:1 rotors Then slap a super on it and show those 13b guys what a 12a can do.

Jon

 

Here's a chart with all the north-american rotor compression ratios and weights.

12a only gets the 9.4:1

I'll find the 12aT compression somewhere

http://www.mazdatrix.com/faq/rotorwgt.htm

Edit: found it! 8.5:1 for the 12aT as per:
http://cp_www.tripod.com/rotary/pg18.htm

 

Put in extra hamsters.

 

Block the exhaust....

 

Hmm maybe the thing isn't getting higher compression rotors, but lighter rotors!

 

Filling in the tubs on the rotors would increase the compression ratio, but it would also reduce the volume. Probably not the way to go...

 

they should of made square rotors lol more bang for buck

 

Why stop there, imagine the looks on the boingers faces if we had multi sided rotors....they cry now

 

hehe octogon rotors

 

Somehow I don't think he's coming back....

Jon

 

If your not averse to running a 13B,and are deadset on high compression,you could build up a 13B 4 port with some S5 N/A or Renesis rotors.You can still strip it down and run the basics with a flowed out Nikki or some other carb to keep things simple.
Toss in an aluminum flywheel,hot ignition,exhaust system and even some porting and youd have a zingy,responsive N/A engine that would actually make a bit of torque,being a bigger 13B.
The Renesis' high strug,high output type N/A personality, but with 1st gen,80's technology......

 

S% rotors are like 9.5:1 and renisi are 10.1:1 I believe. Dont quote me on that.

 

http://www.nopistons.com/forums/inde...opic=59826&hl=

 

Racing Beat used to sell high compression 12a rotors. I may even still have their old catalog with them listed.

Then they stopped selling them. I asked why? Their answer was simple:

"Didn't work".