Winfree

She likes the high priced stuff especially Shell, Exxon, Texaco, but she likes cheap oil

swoope

iTrader: (5)

what is pre detonation? does it get off before it detonates?

and btw..

i run 87, good 87, still 87...

now if i were going to do a track day the rules change..

beers

Freddie

Long trips, cooler weather, easy cruising (even at 80-90 mph), higher altitudes = I burn 89 and consistently get better mileage.

Stop-and-go city driving, agressive driving, warmer weather, sea level = I burn only 91 octane.

Either way, I buy only 76, Shell, or Chevron. I am in SoCal and also drive in Nevada, Arizona, and Oregon.

Nopstnz

Have you experienced any pinging with any of them? Particularly 76? Also, any performance difference between them? I've consistantly put in Sell 93 for 17000 miles and recently switched to chevron, noticed a little more pefromance/smoothness then switched to 76 and thought I noticed pinging/deeper engine tone/equal performance.

copperred

Partially true. Better combustion resistance when compressed.

No. 93 resists igniting when you compress it better than 87. This is due to the higher octane content. The ability to resist compression detonation does not affect the ability of the fuel to burn once actually ignited.

Freddie

I have never experienced pinging except maybe once when I put in five gallons of cheap 87 because that was the only thing available, and I'm not even sure about that. After that experience I filled up with 91 at the first opportunity and have never used 87 again.

Of the three brands mentioned, I sort of think maybe Chevron runs a little stronger, or maybe I've been influenced by advertising and the opinions of a couple mechanics I've known, attesting to the cleaning properties of their "Techroline" (?) additive.

I also have heard that here in the West, the "76" brand has slipped in quality since it went from Unocal to Conoco/Phillips.

I wish 93 octane would be available in California. But, 91 is as good as it gets.

Can anyone say for sure whether altitude changes the effective compression of an engine? Sure seems like it does. For several years I lived at 5,000 feet above sea level, back when we were able to "tweak" our ignition timing at will. On the same fuel, my cars would not ping until I drove down to lower elevations, but then I would need to retard the timing or they would ping horribly. Now I live near sea level but have recently driven at all altitudes from almost 9,000 feet above sea level down to something like 100 feet below sea level (California desert beyond Palm Springs). And no, no pinging in the RX-8.

DAC17

Why would the manufacturer recommend premium (at higher operating cost) if the car didn't need it?

kartweb

Yes it does.

Relative Air Density (RAD) changes with pressure, tempurature & humidity. Higher altitudes have lower pressure. While that doesn't change the compression ratio, it does reduce the compressed pressure and reduces the chance of detonation.

Higher humidity also reduces RAD but the humidity also tends to lessen detonation at a higher rate then the change of RAD alone.

kartweb

I think they tuned it with just enough timing advance that under worst case conditions 87 octane may not be good enough. Mazda wanted every last drop out of the Renesis to help offset some of the other 6 cylider and turbo rice burners in the same class.

I rarely see RAD at 100% and don't drive WOT for more then 2-4th gear a couple times a day so for me it's probably OK to use 4 parts 87 and one part 93. That results with about a 90 octane anyway.

Freddie

Thanks for the sceintific explanation, Kartweb. This explains why naturally aspirated engines lose power at high alititude. So is the effect less pronounced with FI ?

Razz1

Always use premium.

Raptor75

To cover their *** in the rare occasion that a rotary is pinging, by the way my manual says it is fine to use 87 octane. It is cheaper for them to have you pay more then for them to possibly have to replace a malfunctioning engine.

delhi

silly wabbit. Any self respecting performance car must hav ethe mandatory premium gas requirement.

½mv²

Not sure if this will help anyone with their decision-making at their next fuel up, but I have a story that's relevent...




Yesterday my mom borrowed my car because I needed to use her car (Moving stuff, needed the extra trunk/interior space. Well, she used to own an 89 FC, so she's rotary-smart enough to trust not to flood it or stall it or make any other common rotard mistake. However, the owners manual for an FC says 87 octane is fine... so guess what she filled up with?

17.5 gallons of bottom-dollar 87 octane fuel pumped into the tank of an RX that's been running nothing but top-grade 93 octane for all 68,000 miles on the odometer. When she told me I kinda freaked and had to drive it for myself to get a damage assessment. It was a HARD, HARD, HARD start...
rrrRRRRr.rrr.r.r...rr.rr..rrr....rrrwrwr.r....rrrr ..rrrrrRRRRRr....rrr.r.r.r.rrrrrrRRRRAAAABRABRABRA BRABA<finally starts>

I feared the worst. Drove it like an old lady for a good 10 miles. Didn't notice anything. Got on it alittle. No difference. Redlined. Nothing! Got home, turned it off... OMG the car stunk like burning death! Let it sit for 30 minutes, turned it back on. Perfect start. Drove to nearest gas station and topped off with 93. Got home, turned it off, no smell...

It would seem to me, that aside from the first startup, my 8 could give a damn what I put in it. Lower octane = Greater smell, but that's about it!

04RX8man

I've been running 87 for the last three tanks or so and I never had any problems. However I filled up yesterday with 93 and it just seems to run so much better. Idk if its just me but it revs quicker and more smoothly. i think I'm gonna stick with the 93 since I'm only paying a little over 2 dollars a tank.

CarAndDriver

We drive 8's and not Aveos--shouldn't we treat our car well?

It works out to "what" $3 bucks a fillup? Save money somewhere else!

Smileynh

You bought a sports car. If you enjoy reading the specs, drool at acceleration figures, or jus tlove your car don't get cheap on gas :P

Love your 8, give it the gas it was designed to use for max performance.

NH

Detrich

y hasn't this thread been closed yet?

Raptor75

So over 8 years that works out to about $1,248 or

1 x Race Beat Exhaust system
1 x Race Beat induction system
4 x New performance tires

All for free just because you used 87 rather then 93 while getting the same performance and gas mileage. It's your call, by the way my RB sounds so sweet on 87 octane.