Which fuel to use?

[SAsonic]

A fortnight ago for the first time I used Unleaded 95 in my sonic hatch 1.6, I've been pumping 93 ever since I got the car because the general impression (well here in South Africa at least) was that the 95 was reserved for the more powerful cars.

And to be honest I've had almost 100 km more on the 95 than the 93 and I'm not sure if it's in my mind but it seems to be driving smoother than when I was on 93, my question is whether using a much higher octate fuel on the car could have a negative effect in the long run as I read somewhere that the Americans built the car with an 87 octate fuel in mind, which is not available here so 93 would be the closer one.

Anyone know the answer to this? Should I just permanently switch to 95, the cost difference is about R11 per fortnight which will be roughly $1.5 per month so it's not that big a difference for me

 

[Breezybro]

Higher octane is only better, no downfalls. I'd use top tier before worrying about octane though

 

[SAsonic]

Thanks man. I had read somewhere that it won't burn properly and you could have carbon deposits accumulating and that could be bad in the long run etc so I was worried.


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[mja]

Thanks man. I had read somewhere that it won't burn properly and you could have carbon deposits accumulating and that could be bad in the long run etc so I was worried.


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Pretty sure GM only includes 87 octane and 93 octane spark maps. It could be 87 and 91, based on if it's a car originally destined for California, I'm really not sure, maybe a tuning expert can chime in.

But as to your question, running a higher octane fuel than the one rated will not hurt your car in the slightest way at all. The car will read from the spark maps made for 91/93 octane and not recognize any other difference in the fuel. As long as it is octane, and not a higher mixture of ethanol, or some race fuel like toluene, you'll be fine. Breezy is right though, quality of the fuel is more important than the octane rating for everyday driving. (A very cheap 93 octane, may not actually be 93 by the time it reaches the pumps)

However, if you plan to get your car tuned, you'll be able to make a little more power with 95 octane gas :banana: Just let your tuner know what gas you're using.

 

[Swordsmith]

I have heard two different stories on this.

One is that, as mja suggests, there are two maps, and the Sonic computer uses the knock sensor to determine which to use.

The other is that the Sonic has one map, and backs off on timing using the knock sensor until it dials in "just right" for whatever octane you are using.

The former makes sense.

BUT I have seen people report better performance with each step of octane from 87, 89, 91, 93... and even better with 106 race gas, or the equivalent, E85 (85% ethanol).

IF you believe those stories, and they do seem credible, it is difficult to reconcile that with a strict "two maps" setup.

Perhaps there's some combination of the two at work?

(edit to add) and none of those stories, on either side, are related to the 1.6. In the US we have only the 1.8 and the 1.4T. Not at all sure what that means for the 1.6.