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180 wanabe

98 Vs 95 Octane With The Factory Ecu

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Hi there

For years I've been filling up with 98 octane and for the most part when it came to my 308rwkw 180sx and my super sport bikes "GSXR1000, ZX6R" it seemed to be the logical thing to do

Until the last 3 tanks I have been doing the same with my V35, however I decided to give the 95 a go and see if I noticed any difference

As far as I can tell the car runs exactly the same which is no surprise I guess given that its running the factory ECU, interestingly enough I seem to be getting slightly better fuel economy as well on the 95 compared to the 98 :/

So my thinking is that the factory ECU will do things such as advance/retard the timing on its own depending on how much knock it is detecting, however there is only so far that it can advance the timing. Perhaps the factory ECU is limited/unable to advance the timing past the point where any benefit would be noticed running the higher 98 octane ?

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Perhaps the factory ECU is limited/unable to advance the timing past the point where any benefit would be noticed running the higher 98 octane ?

from my understanding, the logic for running 98 is that the fuel in Japan is higher octane than 95, dont know what it is, and its confusing on the net as they talk of different scales / measurements. I think most people are actually concerned that the ECU can't stop the pre-detonation. These engines have pretty high compression.
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In USA the g35 coupes run 93 octane and its considered the premium fuel over there... So I see why not you could run 95 octane..

Although I always use shell v power in mine to be safe, might try a tank of 95 next time see how That goes..

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In USA the g35 coupes run 93 octane and its considered the premium fuel over there... So I see why not you could run 95 octane..

Although I always use shell v power in mine to be safe, might try a tank of 95 next time see how That goes..

US octane ratings are different to ours, their 93 is the equivalent of our 98.

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The idea of using 98 comes from the fact that Japanese base fuel is 97 octane. Hence their cars are produced to work on that level of fuel. 98 is the closest thing that we have so, that's why most people use it.

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the difference between 95 and 98 is 4 cents.

Oi! Get back to the wasteland! :domokun:

LOL.

Yeh you raise a fair point.

But I also go through a tank of fuel a week. at $0.04c a litre difference, that equates to $170 p/a - which means i need to earn $300 before tax to pay for it - which means I work half a day a year for free, just to pay for that 4c difference....Ok i'm over thinking this.

But I always run 98.........even on my LS400 which had a 90L tank......$150 fills make you want to cry!!

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IMO the ECU is not smart enough to reduce timing for 95 oct fuel. It has a knock sensor in the middle of the valley, and if that senses too much knock, it will retard. It doesn't sense your fuel and adjust.

The knock sensor doesn't work very well either, as shown by the fact we had a car with a hole through #6 piston to replace the engine on, from too much det.

4 cents a litre, or risk having to change a motor if you get it wrong. I know what I'm doing.

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Anyone who is seriously affected by paying an extra 4c per litre should not have bought the car in the first place. I hear that most of the cars built by Great Wall will run on 93, go and buy one of those.

I would imagine that almost everyone here would have spent at LEAST $1000 in aftermarket parts and mods for their car, somehow the extra few $$$ on each tank of fuel just seems really trivial in the grand scheme of things.

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IMO the ECU is not smart enough to reduce timing for 95 oct fuel.

^^ this. the FSM states the knock sensor is only a last line of defence device, it is not used for tuning.. the ECU ignition maps are preset and don't change unless the knock sensor detects knock, then it switches to a 'knock map'.

The manual for my car says to use 96RON fuel, which I assume is what they have in Japan?.. I have been using 95RON since I have had my V35 without issue.. I ran a test of 98 for 3 consecutive tanks about 6 months ago, I couldn't detect any improvement in performance and it didn't make any changes to fuel economy, so I have gone back to 95.

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^^ this. the FSM states the knock sensor is only a last line of defence device, it is not used for tuning.. the ECU ignition maps are preset and don't change unless the knock sensor detects knock, then it switches to a 'knock map'.

The manual for my car says to use 96RON fuel, which I assume is what they have in Japan?.. I have been using 95RON since I have had my V35 without issue.. I ran a test of 98 for 3 consecutive tanks about 6 months ago, I couldn't detect any improvement in performance and it didn't make any changes to fuel economy, so I have gone back to 95.

This is exactly my point

I have run 98 for years and now that I have started to run 95 I can't detect ANY difference, everything feels and sounds the same and yet I am getting slightly better fuel economy which is one of the main reasons why I have raised this point

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technically, running a fuel with considerably higher octane than the ECU is tuned for, can result in reduced fuel economy.. I found this when I tried my old J30 maxima on 98 for a bit.. but I wouldn't expect to see any change between 95 and 98 on a car that is tuned for 96.

So I can't say why you are acheiving better economy on 95..

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