I was curious and wanted to see if using 87 octane would net better MPG. I have used 87 in the past a few times, but this was pre "M" flash. After putting 5 gallons of 87 I punched it to 6000 thousand RPM in 2nd gear and heard only what I can best describe as a muted sound of tiny bearings rattling around in the motor. I immediately went back to the gas station and filled up with premium as it sounds like detonation. Can this have something to do with "M" flash even though it is suppsed to run richer in this RPM band? Or is something going bad with the car such as the catylitic converter, plugs, coils, ect. I also hear what seems like a loud vacuum leak underneath the car, when I am idling and the clutch engaged. I'd be greatful for any input. Thanks.

I ran two ranks of 87 without issue. Even a few redlines.

I'm back on 91 for the current tank as I want to make sure the engine remains clean... but I can definitely see my gas gauge go down faster with the higher oct.

I've heard this sound also around 6K - what is it?

It sounds like the car is detonating or pinging. I would sure like to take advantage of the lower octane since the manual states that it could be used, but the pinging could be and underlying problem that something else is wrong. As a matter of fact I'm pretty sure it is detonating because it is the same sound that I heard when tuning my former 20G turbo Eclipse at high boost.

Jason, 2 ranks of 87. That's hillarious, because that's what it is, RANK! Yes, I agree about running cleaner and keeping your engine intact.

To the pinging or detination statement. The owners manual clearly states 91+ octane. The rumor is that if you turn the DSC off-off your power and fuel will go up

No, the owners manual states that 87 octane can be used albeit at reduced power. I tried the DSC off and noticed a slight improvement in MPG although the car pulls stronger with the DSC activated in my opinion.

I had the same problem--the dealership went through hell to determine the issue--the cause is low octane. Eventhough I was putting 93 in--I apparently had gotten a hold of some bad gas. They filled it up with premium and the sound was gone--haven't had a problem since. So if you are running 87 octane and experience no issues-consider yourself lucky--I'll stick with 93.

some of this may indeed be pinging but have you all read this thread (http://www.rx8club.com/showthread.php?s=&threadid=24649&highlight=SDAIS) and eliminated what is described there as the noise you are hearing?

I'll have to check my manual again but I thought I remembered it saying the high octane(91-93) was preferred, you could run 89 with reduced performance and 87 could cause engine knocking/damage. I doubt if it causes damage but I am interested now. I will have to read that section again.

Originally posted by Nemesis8
I've heard this sound also around 6K - what is it?



I hear a rattling noise at exactly 3500 RPM. Has anyone heard this? Is this the same noise?

btw, I buy my gas from brand name gas stations, never the discount quickie marts.

Maybe that is why I'm not having issues with the lower grade.

This car has always had Chevron.

I don't understand what is the fascination of putting in cheaper gas when it clearly state in the manual to put higher octane. Granted that gas prices are high, but it's nothing that we can do about it.

Why sacrifice the ability to save $2-$3 per fill-up just so that you can kill your engine life? I don't get it. :confused:

Originally posted by Blue_Chameleon
I don't understand what is the fascination of putting in cheaper gas when it clearly state in the manual to put higher octane. Granted that gas prices are high, but it's nothing that we can do about it.

Why sacrifice the ability to save $2-$3 per fill-up just so that you can kill your engine life? I don't get it. :confused:

The manual clearly states the 87 octane is acceptable, and will not be a problem for the car.

I happen to like going 350 miles on a tank of gas, thanks.



I've only gone two tanks on 87 so far, right now I have 91 in the tank.

Originally posted by Ashah
I hear a rattling noise at exactly 3500 RPM. Has anyone heard this? Is this the same noise?

read the link in my post above that i am quoting here

Originally posted by zoom44
some of this may indeed be pinging but have you all read this thread (http://www.rx8club.com/showthread.php?s=&threadid=24649&highlight=SDAIS) and eliminated what is described there as the noise you are hearing?

Originally posted by JasonHamilton
The manual clearly states the 87 octane is acceptable, and will not be a problem for the car.

I happen to like going 350 miles on a tank of gas, thanks.



I've only gone two tanks on 87 so far, right now I have 91 in the tank.

Whoops...my error. You're right, but I did remember seeing something that shows that it's recommended to use high octane somewhere.

Yes, they claim you may lose power if you use lower oct because the engine will retard timing and other stuff in order to prevent knocking and other engine issues.

I haven't made up my mind about it yet, but I really do like seeing 350 instead of 290 when my low light comes on.

Originally posted by zoom44
some of this may indeed be pinging but have you all read this thread (http://www.rx8club.com/showthread.php?s=&threadid=24649&highlight=SDAIS) and eliminated what is described there as the noise you are hearing? 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.

JimW, where are you buying your 87 gas from?

I wanted to get Shell but there was a problem with the lower octanes messing up the fuel guage due to and extreme amount of sulfer in the fuel, I ended up using Chevron.

What is the build date on your car?

I do not know. Where do I find this? I am going to go outside and see if I can locate it somewhere. I'll be back in a few.

I found it. Sep 03. It was inside the door frame where the Tire psi info is.

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.

My manual does not state this, nor did I get any updates about it. My car has a 2003 build date though. I can assure you I am going to use 93 from now on. I am keeping my fingers crossed, but I do not think it did any damage to the engine.

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.

.

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

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.

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.

Great info, I tried 89 octane and didn't have the problem. Now I'll see if it helps with the mileage. Thanks.