In cyprus we have 95 octane, 98 octane, 100 octane petrol,is the 100 octane fuel suitable for the rx-8?Will it make much diiference in performance and fuel economy

 

try them all and see what works...

 

lock plz

 

You may want to search in the tech section on this topic. I know there are numerous threads that discuss the effects of octane on the rotary engine.

Off the top of my head, the higher the octane, the worse your gas mileage will be.

 

I always use Shell 91 Octane

 

That's what I would use, but we only have 87, 89 and 93 here in TX.

 

how much does you gas cost?!?! 100 octane is almost racing fuel

 

I filled up for $2.60 last night. (Shell 91 Octane)

Gas prices are REALLY strange out here in California, they vary SO much depending on where you are. Yesterday alone I saw gas stations ranging from $2.57 - $3.05...

 

Their octane rating is probably just RON instead of PON we use in the US which is (RON + MON) /2

 

I have used all 87, 89 and 91 octanes either for a straight month or switch-around every fill-up. Here's what I have noticed:

- 87 octane feel great initially since it leans out the A/F all across the RPM range. Downside to it is that it raises your LTFT all across the RPM range. This means, you wil end up using more fuel than you really need. LTFT got up to 11 at the top end and 8 or 6 at the low end. You get massive ignition retardation up top to prevent knocking.
- 89 octane is about the same way as 87, yet it doesn't raise your LTFT that much. My experience is that prolonged usage of 89 octane got my LTFT up to 8 all across the RPM range.
- 91 octane after using 87 or 89 feels smoother but less kick. The good thing is that it doesn't mess up your LTFT. The highest 91 octane got me was 5 LTFT up top. At the low end, it either goes into 2 - 3 or 0. 91 also gets rid of that popcorn sound when you go beyond 5K RPM.

I like 91 octane the best because the ECU easily corrects the LTFT to the point where it sets it to 0. 87 and 91, I had to use e-manage to recalibrate my MAF signal so that LTFT will go back to 0. It isn't perfect, so I wound up losing MPG.

 

English?

 

So, once you use a lower octane, it retards your ignition timing? I've always wondered about this: if you switch to a higher octane again, then does it advance back to how it was?

 

^ In terms of ignition, yes it advances back to where it should be. Problem is, your LTFT doesn't adjust back down so easily. After running 87 for a long time and switching back to 91. I observed how long it takes to draw down the LTFT after getting back 91 octane. The answer? Never. I found out that +LTFT happens when AFR goes a little lean and -LTFT only happens when AFR is seriously rich (one where your car feels like it's about to die).

So, coming from 87 and going back to 91, you will have proper ignition timing back but you would dump more fuel into every combustion. I reset LTFT by disconnecting the ECU unit and reconnecting it. Apparently the 20 taps to brake pedal doesn't reset LTFT at all. I guess disconnecting the battery works too, but I can't confirm that.

 

Wow, interesting.
How quickly does the LTFT change? ie. how much change would approx. occur in one tank of 87? Ten tanks?

 

What is LTFT?

 

Long-Term Fuel Trim

 

This is one thing I hate about our ECU. After just driving a mile, your ECU will already have added LTFT if it detects lean AFR. As for reducing LTFT, it's very slow to react. You'd have to dump so much fuel in before the ECU starts reducing the LTFT.

These are not exact numbers, but just to give you an idea:

If target AFR is 14.7 and your AFR is at 14.8, it will quickly add LTFT by 1 or 2. When you switch back to 91 octane, chances are your AFR will be slightly richer like say 14.0. ECU will not reduce LTFT yet until your AFR gets to 13.5 or something. That's how messed up this learning mechanism is. It's not as smart as experts say it is. I had to subtract at least 3% of the MAF signal just to get the LTFT to start dropping. Most of the time I just subtract 8% and my car starts shaking. When LTFT is close to 0, I then change the reduction to 3 and finally 2 where LTFT would remain 0 all the time.

 

I use Shell 93 and Chevron 93 exclusivly (Top Teir Baby!) that is all that has ever been in this car. I also add Lucas Complete Fuel System Treatment to every tank (250:1 ratio) and Synthetic 2 cycle engine oil to every tank (250:1 ratio).

I get 20-22MPG city and 24+MPG Hwy. Even last weekend where I was cruising in 5/6 on the highway bettween 95 and 145 I got 18 MPG for that tank.

I would recomend the use of the highest octane/easy to find fuel. By that I mean if most stations have say 98 as their highest, and some have 100, just use the best you can find easily, so I would go with the 98. That way the cars fuel and timing maps dont have to adjust much since your always running the same octane of gas....

thats just my opinion!

Lucky dog, you get the cyprus rally!!!

 

Different octane rating systems in Cyprus perhaps.

 

Not on this side of Texas. We have 91, but no 93.

 

I'm in Lubbock now for school and I don't see 93 octane. The highest I seen is 91.

 

Everything I've seen around here is 93 Octane. 7-Eleven/Citgo has pumps that mix fuels, so I can select 91 if I want to. They mix 1/2 89 & 1/2 93 together and 91 comes out. I'm not sure of the accuracy.

 

Shell Vpower $2.30 a galon excellent fuel

 

that's because west Texas has higher elevation, as elevation increases an engines octane requirement drops due to less intake air filling from the reduced atmospheric pressure

also, the fuel octane rating system is different in Europe. They use RON (Research Octane Number) ratings, the US uses PON (Pump Octane Number) = (RON + MON)/2. MON is Motor Octane Number. RON and MON are determined by different test procedures using the same fuel. RON is always higher than MON.

Here is a chart and info that correlates the different rating systems:

http://www.btinternet.com/~madmole/R...RONMONPON.html

 

In Central (Waco) and East Texas (Tyler) I've seen gas stations that have 87/89/93 or 87/89/91. Every once in a while I pull in to get gas and I find 91 instead of 93 at the same price as 93 at other gas stations.