S5 NA rotors in an REW
06-30-17, 01:29 AM
#26
That is the idea that people operate under, but that is not reality.
In reality high compression rotors provide more peaky power, not a broader power band.
Go ahead and look at the mazda data above in figure 4.37. 2.3% more power between 2,000 and 6,000rpm going from 9.2CR to 10CR rotors.
So, if you are running 10psi on stock twins and making 250rwhp on 9.0CR and go up to 9.7CR you will get your 2% power increase from 2,000rpm to 6,000rpm for 355rwhp peak.
Notice in Mazda figure 4.37 above the gains from high compression rotors crash at 6,000rpm from the increased pumping losses in moving the air charge past the minor radius in the rotor housing.
Meanwhile, if you had kept 9.0CR rotors and run 14psi you would have the same effective compression ratio
https://www.rbracing-rsr.com/compression.htm
and make much more than 2% power increase (usually 20% increase to 300rwhp) from around 2,000rpm (where stock primary turbo hits 10psi with bolt ons) to 8,000rpm rev limit.
Now, if you are not octane limited (on race gas) the effective compression ratio does not matter and you can run whatever boost you want on either 9.0CR or 9.7CR or 10.0CR rotors.
The 9.7CR rotors change the character of the engine and make it feel snappier but there is not noticeable performance gain.
People have been using higher compression rotors since before Mazda started making production turbo rotaries and you will not find a turbo dyno sheet where you can tell what compression ratio rotors the car is running. The power difference is so small it is lost in the noise unless you have factory dyno cell accuracy.
For Mazda's turbo rotary racing program (not octane limited) they cast a special run of 7.5CR 13G rotors.
Even in their NA racing they used special cast 9.2CR 13G rotors up to the time where they were trying to win Lemans with fuel strategy and low revs and so went to 10CR rotors.
In reality high compression rotors provide more peaky power, not a broader power band.
Go ahead and look at the mazda data above in figure 4.37. 2.3% more power between 2,000 and 6,000rpm going from 9.2CR to 10CR rotors.
So, if you are running 10psi on stock twins and making 250rwhp on 9.0CR and go up to 9.7CR you will get your 2% power increase from 2,000rpm to 6,000rpm for 355rwhp peak.
Notice in Mazda figure 4.37 above the gains from high compression rotors crash at 6,000rpm from the increased pumping losses in moving the air charge past the minor radius in the rotor housing.
Meanwhile, if you had kept 9.0CR rotors and run 14psi you would have the same effective compression ratio
https://www.rbracing-rsr.com/compression.htm
and make much more than 2% power increase (usually 20% increase to 300rwhp) from around 2,000rpm (where stock primary turbo hits 10psi with bolt ons) to 8,000rpm rev limit.
Now, if you are not octane limited (on race gas) the effective compression ratio does not matter and you can run whatever boost you want on either 9.0CR or 9.7CR or 10.0CR rotors.
The 9.7CR rotors change the character of the engine and make it feel snappier but there is not noticeable performance gain.
People have been using higher compression rotors since before Mazda started making production turbo rotaries and you will not find a turbo dyno sheet where you can tell what compression ratio rotors the car is running. The power difference is so small it is lost in the noise unless you have factory dyno cell accuracy.
For Mazda's turbo rotary racing program (not octane limited) they cast a special run of 7.5CR 13G rotors.
Even in their NA racing they used special cast 9.2CR 13G rotors up to the time where they were trying to win Lemans with fuel strategy and low revs and so went to 10CR rotors.
