Installed a Typhoon Intake with K&N Filter. It may of been happening before but now with the louder intake I hear what sounds like detonation at about 6500-7000rpms (sounds like muffled volkswagon. I'm using 89 octane gas. Anyone know what might be the problem?

 

Use 91 octane or higher.

 

So that has to be the reason for the sudden change. This is like the third time I've put 89 in it. I was told that 89 was fine but was thinking to myself, with the high compression for top-end performance the RX8 must need at least 91. I guess that just gives me any excuse to drive hard and waste this tank of 89 jo.

L8

 

Yeah the harder you drive the richer the fuel gets, if your running stock, so theoretically the safer you will be.

 

You potentially have increased one of the variables that the ECU changes the mix for. In this case, I'm assuming that you've added more air to the mixture, as well as running fuel with a lower octane rating than what mazda suggests for a stock A/F mixture.

In addition to that, I have no idea where you are geographically, so you potentially are getting the crappy winter gas that people farther north get. I'm going to agree with Velocity 8.

 

That makes perfect sense.

Also a poster on here by the name of roaddemon said he had to change faulty plugs. The sound I'm hearing I heard before when my CRX had one bad plug. The difference is my CRX sounded girgled upon revving anytime. My RX8 girgles only when at about 6500-7000 RPM's.

I'll burn this tank of gas, upgrade to a higher octane and then see if that does the trick, maybe my issue is much bigger.

 

Could be the cat....a couple of people have had to have them replaced....