87 octane and rattling at 6000 RPM!

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Jul 1, 2004 | 07:04 PM

#26

zoom44

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Joined: Jul 2002

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From: portland oregon

Quote:

Originally posted by JimW
Zoom44, That was and interesting read. Thanks for the hook-up, but I'm pretty sure it was pinging that I heard. If that sound was from the resonance intake ports switching, I would notice this no matter what octane I used. I only heard this while using 87 octane and then after I switched back to 93 the sound went away. I have to say it was extremely hot and humid out and I'm at sea level so that might have contributed along with some lousy 87 octane to the situation. Jason is right, if it states it in the manual that 87 octane is acceptable and it nets us better MPG then damit, the car shouldn't do this. After this episode I do not want to use 87 octane again, it is to risky.

you're welcome. my goal is to one day have every rx-8 owner read it

i think your situation is one of the reasons the manual is worded the way it is. since they dont necesarilly test the car at every elevation, under all weather conditions and with every gas they have to hedge a bit. the say the use of X octane is recommended (remember octane is the measure of the fuels resistance to detonation) but that you could get away with a lower octane of X. but of course knock sensors don't somehow react to knock before it happens. they detect knock and then the PCM reacts to that detection with air/fuel and ignition map changes. this is the decrease in performance that is mentioned in the manual. so by using 87 you(not you specifically but all of us who use 87) increase the risk that you will have knock. some will experience it because of prevailing conditions but others in diferent climes and altitudes will not. in your case at your altitude and the type of weather you have at this time of the year it probably is better to move up to 89 or 92. but maybe in the cooler months you could slip back down to 87.

an analogy- smoking increases the risk of heart disease. some who smoke will never have heart disease. but others who are stressed out more in their daily lives and have horrible diets,compounding risk factors, will.

Last edited by zoom44; Jul 1, 2004 at 07:09 PM.

Jul 1, 2004 | 07:28 PM

#27

MEGAREDS

Goh Mifune

Joined: Sep 2003

Posts: 850

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From: Green Oaks, IL

Jul 1, 2004 | 10:11 PM

#28

rx8cited

Senior Member

Joined: Jul 2003

Posts: 1,554

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From: DC Metro Area, USA

Quote:

Originally posted by Mag66
Interesting that the Manual says this.. as both the updated "short guide" and the 'quick tips' booklet that I got which have a print date of April 04 and May 04 respectively.. clearly state to use 91 Octane only... and not to use any lower octane gas.

I agree ...... odd that the three items don't give us the same guidance on fuel.

FWIW, I've been using primarily Shell 87 octane for all of my 9k miles with no issues - I guess I better start saving up for a new engine

.

rx8cited

Jul 2, 2004 | 04:27 PM

#29

JimW

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Joined: Dec 2003

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From: South Florida

MEGAREDS, Yes. That's the exact description that I read. Using the lower octane in winter months does make a lot of sense as well. Thank You all.

Jul 2, 2004 | 05:29 PM

#30

MEGAREDS

Goh Mifune

Joined: Sep 2003

Posts: 850

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From: Green Oaks, IL

The Mazda service department I took the car to said to use the lower octane to help avoid flooding. I don't know if that's good or bad advice - but the 89 octane has been no problem for me since changing over to it... see the log in my signature for details.