Wether you in to them or not, I've always had brilliant results over the years with low compression pistons and lots of boost on piston engines, and while its been done a lot, a lot more than many make out it seems, on rotarys, I have no idea how its done or how its calculated if its just machined stock ones.

Ive seen road, track, and drag rotarys around the world (especially Oz it seems) with 8:1 rotors or even 7.5:1, like this Racing Beat engine-
http://www.racingbeat.com/Mazda-Perf...tNumber=Engine but dont actually know how they go about it, as I doubt many of them get custom rotors made, they most likely modified stock ones.

Wether you think its a good idea or not I dont mind, but is it just machined down S4 FC rotors then? How can you accurately measure how much bigger to make the dishes on the rotors and then machine them correctly?
It may be simple, but my rotary knowlege hasnt gone that far, yet!

Any interesting info appreciated

 

im sure i read that the racing beat rotors were made by mazda for them when they were attempting there top speed records at bonnieville.

Ill have a look on here as i do remember someone taking material out of there rotors to drop compression, the alternative is bilet rotors, they are £2k a set but you can choose any comp ratio you want

 

do you really think you need lower than 8.5:1 though?

 

Personally yes. Im too used to being able to run 30psi on pump fuel and no AI for held top speed runs and not worry.

RB used 7.5:1 even though they was running meth and not even 30psi, which to me is quite odd, but im sure they had their reasons.

But yeah, its not for everyone im sure, but personally id at least find out if its feasable to do.

 

E85 and you're good with stock rotors and it will make more power. win win.

Edit: didn't see you were in England. Do they have E85 over there?

 

about 3 gas stations in the entire country have it and they are removing it this year as the government has removed the tax break for it.

We pay $8 a gallon for normal pump gas and around $170 for 5 gallons of 109 race fuel.

If we could all get e85 everyone would run it!!!

 

E&J are going the other way with 10:1 rotors running boost. On the other hand I remember seeing one of the Australian companies touting re-profiled dishes. One would think that would involve removing material and thus lowering the compression.

 

Xtreme Rotaries can machine the rotor for lower compression,after the machining is done you get 7:9:1 comp.

Check it out..

http://xtremerotaries.com/cc-combustion-chambers.php

 

Real question is, will it work same on rotary? You can lower compression and run slightly more boost but there is big difference between rotary and modern piston engine. Squish band. You can run low compression pistons but still maintain very compact space where is all charge compressed and ignited. Not in rotary. From all studies, end gases on the trailing side are the problem and it will be very same be it low or high compression...

 

the 7.5 mazda rotors are most likely to be from the factory turbo engine development program.

from 81- to RB's bonneville run in 86, mazda built a turbo setup for racing, they actually didn't have much luck with the whole thing and went 3 rotor NA.

the basic spec was a bridgeport 13B, the 3mm 7.5:1 rotors (its pre FC), mechanical fuel injection, 2 ht-20 turbos, the mazda (i wanna say 757) had a air to air and water air IC, they quoted 500hp@1bar.

RB used a full water IC, and claimed 530hp

the old KSP FC used 8.5 rotors milled out like the guru parts, again full bridge, dual 3037's, 700+hp

 

all good questions; there are so many combinations of engine ideas.

just last week was at local race shop,(specialize in Toyota Supras, 3L) they are of the group for hi-compression and turbos.

there latest 3L 2JZ, 12 to compression, datalog showed 39psi boost , 1457whp, at 9400rpm.

, for a street-strip car ,low comp. is laggy and nonresonsive on the street, supercharged or turbo, but they do come to life on the top end, but sometimes its to late and the other guy won the race.

just maybe, a 10 to 1 rotary with water injection(along with some GOOD tuning), might get the job done, and port it for torque and not so much extreme RPM.
key would be to keep the seals in place, and not bouncin off the housings

 

that's a good point too.

 

Chuck Norris- Cheers for the link, appreciated

Liborek- you may have a good point, unfortunately I dont know enough about Rotarys yet myself, or seen any testing either way, to know. Have you any links/info regarding that?

Going from personal experience this always feels to me as the bigest myth in tuning. Ive done a few engines where ive dropped a whole compression point with no other changes and response and boost threshold are unchanged if you retune to suit, and the power, and most importantly, torque, when you can safely run another 15psi+ of boost safely is enourmous. Power below the boost threshold is affected, but not drastically, and no turbo car should be expected to be used in 'performance mode' below the boosth threshold regardless.
Turbo, port, and cam changes all have far far bigger changes to low down power, powerband, and response, in my experiences.

My rule is run as much compression as I safely can for the boost and fuel needed, but 30psi+ and purely pump fuel really dont mix on even 8.5:1, never mind higher, regardless of spec.

But either way, this is why I didnt want to discuss the pros and cons of this, as though everyone has their opinions, ive had years of experience with low-comp engines so know how they feel to drive

 

Could a lower compression rotor make more power in certain applications being that there would be a little extra room for more air and fuel to be ignited. Or am I dreaming??

 

The same boost/ same setup, will make more power on higher compression, and with advances in technolodgys such as AI and E85, why would anyone want low compression? Yes you're dreaming.

 

possible. combustion chamber shape is important.