this topic has come up a few times, but i still don't think there is enough solid information to go on when doing a swap. i'm also wondering if there has been any recent progress in this swap that has been documented. i know Mazdatrix had an engine built, but couldn't get it to work that great. i have not heard anything from that since.

this is what i DO know:

- for apex seals either machine the groove to accept earlier 13b seals or use ceramic RX-8 race seals instead of the stock renesis apex seals

- for corner seals use earlier 13b seals instead of the renesis ones

- discard oil scrapper ring


questions in my mind:

- has it been confirmed yet which rotor combination of the renesis rear and front to use? only rears? rear and front in reverse order? etc...

- in terms of porting (non bridge or PP), is there some extra consideration to be given? i believe that the renesis rotors are cut differently to allow the greater intake opening timing, is there any way to take advantage of this?

- are there possible issues with the side seal? it seems that clearance is not as tight as with the 13b, as the side seal is further outboard. i'm not quite sure why this is. if this is a possible issue, is there anyway to get side seal clearance to 13b spec?


i am considering this with a NA 13b streeport rebuild, but i would like to fully know all aspects of the technical differences first. it doesn't seem that there has been much documented progress on this, but hopefully i can get some answers.
i would also appreciate not posting unless it is related to the issues mentioned above (although fell free if you think so). it would be nice to get an informative, archivable thread...

 

Thats what I was lead to believe as to why the renesis rotor would not work. Curious to see what some of the heavy duty engine rebuilders have to say about this. 10:1 compression ratio is attractive!

 

well advantages i see:

- significantly higher compression ratio
- possible porting advantage (as mentioned)
- a better machining process that led to a more balanced rotor
- less mass, so slightly less rotational inertia
- quite a bit cheaper for the rotor new than a FC rotor new

 

Is that becuase they are in production and the 13B ones are not?

 

It's hard to see how a 3% increase in compression compared to S5 NA 9.7:1 rotors can be that attractive, especially since 3% more compression does not ever give you 3% more power (it's physically impossible).

 

I said it was attractive, not that attractive.

every little bit counts.. right?

 

it's actually a 5% increase for me, since i have S4 NA rotors in my S5...
yes, maybe i was wrong in saying this is a SIGNIFICANT increase, but as i mentioned there are other things to consider such as rotor design, weight, balance, etc...

oh, and just wondering why it is physically impossible as you mentioned?

 

In an engieering class quite a few years ago, we were given a mathematical formula (a proven formula, not a theory) that related compression ratio to the amount of extra energy the compression gave you compared to burning uncompressed fuel and air. It was not a linear relationship (i.e. 10% more compresion = 10% more energy), but was IIRC a logarithmic-shaped one. The relationship line was very steeply sloped up to about 5:1 when it started to flatten out, until about 11:1 where it was rising so slowly is was basically flat. This is the clasic law of diminishing returns.

I can't remember or locate that formula now, but I would estimate that around the 10:1 area you might get 1.0-1.5% more power from a 3% increase in compression.

 

So in laymans terms, this is a worthwhile mod only if you are a sanctioned race team striving to get every last scrap of advantage over the competition (i.e 1/10th of a sec. in lap times), right?

 

NZ, nice!! You bring it to the table

 

hmmm...i have not learned this theory specifically, but it makes sense. although it follows the principle of, or rather seems to be, diminishing returns, i think it is a thermodynamics issue specifically. i suspect that you only need so much compression to give you an efficient burn. i'm not quite sure though...

anyways, i don't think i intended this thread to be about the advantages/disadvantages of this. i wanted more information that is current on the technical aspects of this swap. if some the questions in my first post could be addressed, that would be good.

it would be nice if anyone here has actually done the swap...

 

cool!

 

fgjhnxfghjxt

 

ive been told by several guys that run the rx8 rotors that the stationary gears have to be modded, and the side seals didnt seal as well as the s5 rotors, not to mention, you will need the rx8 full rotatine assembly, not just the rotors...
this is all on top of milling the rotors to fit stndard 2mm apex seals...

if your looking for every bit of power n/a then the rx8 rotors are the way to go...

if you want something close, with alot less money spent and no special modifacations needed , then a s5 rotating assembly is the way to go!

 

Racing Beat just released a lightened Renesis rotor:

http://www.racingbeat.com/resultset....rtnumber=10008

 

thanks for the link.
price is a little steep though considering the minimal gain...

 

well these are the emails that mazdatrix sent me months ago about their progress. i have yet to confirm their new progress.

http://www.racingrotary.com/rx8rotors.htm

Justin