raising compression?
 

Hey i want to get more power out of my na S5, i was thinking about turbo but its alot of work, and money i dont have right now. So i was wondering if we can raise compression and how much?

Compression is a function of the rotor. You already have the highest compression rotors available for the 13B. (9.7:1). Rx8 rotors are 10:1 and can be used but require a good bit of money in modification, and really wont net you any more power. A turbo really is the cheapest/easiest way to more power.

What he said.

The only way compression can be raised is in reducing the size of the dish in the rotor, and doing that hurts in-engine airflow at TDC compression. RX-8 rotors have more low-end and midrange power but they don't make more peak power than 9.7 rotors in the same engine.

I've "heard" in several places that LOW compression rotors are the key to high RPM power in all-out racing engines...

Hmm so swapping out the S5 rotors for the S4 would be somthing along those lines of what youve heard? Also doing that would make it safer for me to turbo since it would be lower compression.

It depends - are you seriously trying to make more than 350 horsepower? By "seriously" I mean you know exactly what that entails...

If not, keep the 9.7, they're better.

the competition engines were all 9.4:1 until the R26B, which is 10:1.

i think in the real world, the power difference between 9.4 and 10:1 is really teeny.

i think you would have better results concentrating on the intake/exhaust, or using more new parts in the core engine itself.

If you want to turbo it but can't afford it now. i would upgrade all the stuff that you need for a turbo engine, but also works with NA.

Such as:

Exhaust
Radiator
Aftermarket engine management, PFC, haltech or something like that.
A new header (couldn't be used with a turbo engine, but it would probably be worth it since it gets you some extra hp while you save up for a turbo conversion/or whatever you decide.)
I would leave the intake system working like stock, and just throw in a performance filter in the stock air box.

Luckly i bought the car with a nice exhaust on it so ill leave that, and get the headers when the time comes. This it would be better to swap a t2 motor or just work with what ive got

Really im just looking for about 250hp when im done

Which parts are those im brand new to rotarys, i get the gist of it but not the individual parts

Flat irons, new rotor housings, correct clearances and dimensions on all seals etc. Engine dynamic compression and good sealing is essential for making power and attaining high volumetric efficiencies needed to produce high power outputs in NA engine.

Turbo can somewhat compensate for poor engine, it will just use more air and fuel for same power level.

As Pettersen said, invest in something what you will always need - quality standalone ECU and maybe headers.

I would guess that only very few people with streetable NA 13b's have over 250HP@crank while most are in the 200-220 HP range.

250hp without turbo is a huge goal, definitely brigeport / peripheral port territory. If you are after the most of bang for the buck I would recommend getting and fitting a TII engine, and doing a few mods on that (or selling the S5 n/a car and getting a TII car, not trying to be harsh or anything, but the cost and work involved really add up when doing an engine swap like that). If your new to rotaries it might be a good idea to read the 'street rotary' book, that should get you up to speed pretty good. Good luck!

Sounds like a plan man thanks for the book idea. And im thinking i will just turbo it or swap in a T2

Mada usually offered a competition engine as well as the stock engine that came in the car.

the early Rx3 was a bridgeport 12A, https://docs.google.com/file/d/0Byot...ZLLU5qdXM/edit

the later Rx3 was a peripheral port https://docs.google.com/file/d/0Byot...NoT0xlaTQ/edit

the Rx7 when it came out got a revised peripheral port 12A, and 13B. then in 1980 they added dry sump and mechanical fuel injection. https://docs.google.com/file/d/0Bzy-.../edit?hl=en_US

after a brief experiment with turbocharging (that resulted in the RB Bonneville FC), they went 3 rotor with an engine called the 13J, and then there was a succession of 4 rotors culminating in the R26B engine that they won lemans with

Mazda 4-Rotor Engine Le-Mans

all these engines leading up to the R26B retain the 9.4:1 compression ratio. the R26B uses 10:1 rotors made from a different material.

the R26B parts were really never available to the public for sale, and the older stuff is basically NLA (no longer available) just because its been 30 years!

Wow love the history and info! Thank you. Im learning alot already

N20

Just a little 30-40 shot on a WOT switch. That will add a little chamber pressure...

Would i be able to put a S5 TII UIM/LIM manifold on my 13b this way ill have it for when I get my turbo?

Turbo II intakes are a serious step DOWN in power. They are shaped absolutely horribly, tight bends and weird angles everywhere.

I gained a lot of power everywhere on the curve by going to an S4 N/A. More power down low, in the middle, and it would pull 1000rpm longer on the top end as well.

O ok sounds good thanks man

Racing Beat says that on N/A engines the power difference between low and high compression rotors was very little and that the higher compression Renesis rotors only gained low/mid range power.

Yea thats what im seeing, i would love more low end ass but o well tubro it goes

The higher the compression, the higher risk you have of gasket blowout.:(

? what gasket?

The downpipe gasket. Straightpipe is the way to go if you can get away with it. I'm from California with strict emission laws. We can only get away with running straight pipe (no cat) on the track.

I was told straight pipe on a N/A will make it to where the 5/6 port wont open. Which makes it seem pointless to straight pipe an N/A motor