95 or 93?

[JK8]

So I had this "argument" with this retard excuse for a chemical engineer.
He claims 95 is standard octane for all cars and anything less will damage a car:rolleyes:
He also claims he is getting 800km from his 40 litre tank with 95 octane... Polo 1.6

So I dont mind either of them 93 or 95, I alternate between to 2 every second tank, 2 95 and 1 93....

Anyone want to shed some light on this issue?

[Devill]

http://tsikot.yehey.com/forums/showthread.php?p=1058912


Octane and power

It's a common misconception amongst car enthusiasts that higher octane = more power. This is simply not true. The myth arose because of sportier vehicles requiring higher octane fuels. Without understanding why, a certain section of the car subculture decided that this was because higher octane petrol meant higher power.

The reality of the situation is a little different. Power is limited by the maximum amount of fuel-air mixture that can be jammed into the combustion chamber. Because high performance engines operate with high compression ratios they are more likely to suffer from detonation and so to compensate, they need a higher octane fuel to control the burn. So yes, sports cars do need high octane fuel, but it's not because the octane rating is somehow giving more power. It's because it's required because the engine develops more power because of its design.

There is a direct correlation between the compression ratio of an engine and its fuel octane requirements. The following table is a rough guide to octane values per engine compression ratio for a carburettor engine without engine management. For modern fuel-injected cars with advanced engine management systems, these values are lowered by about 5 to 7 points.

Compression ratio Octane
5:1 . . . . . . . . . . 72
6:1 . . . . . . . . . . 81
7:1 . . . . . . . . . . 87
8:1 . . . . . . . . . . 92
9:1 . . . . . . . . . . 96
10:1 . . . . . . . . . . 100
11:1 . . . . . . . . . . 104
12:1 . . . . . . . . . . 108



Octane and gas mileage

Here's a good question : can octane affect gas mileage. The short answer is absolutely, yes it can, but not for the reasons you might think. The octane value of a fuel itself has nothing to do with how much potential energy the fuel has, or how cleanly or efficiently it burns. All it does is control the burn. However, if you're running with a petrol that isn't the octane rating recommended for your car, you could lose gas mileage. Why? Lets say your manufacturers handbook recommends that you run 87 octane fuel in your car but you fill it with 85 instead, trying to save some money on filling up. Your car will still work just fine because the engine management system will be detecting knock and retarding the ignition timing to compensate. And that's the key. By changing the ignition timing, you could be losing efficiency in the engine, which could translate into worse gas mileage. Again as a practical example, my little tale above about our trip to Vegas on low octane gas. (Whether you want to believe some bloke on the internet or not is up to you). On the low octane gas on the trip down, we could barely get 23.5mpg out of the Subaru. Once I was able to fill it up again with premium at the recommended octane rating, we got 27.9mpg on the way back. A difference of 4.4mpg over 450 miles of driving.

Doing the maths, you can figure out that by skimping on the price during fill-up, you may save a little money right there and then, but it costs in the long term because you're going to be filling up more often to do the same mileage. My advice? Do what the handbook tells you. After all it's in the manufacturers better interests that you get the most performance out of your car as you can - they don't want you badmouthing them, and in this day and age of instant internet gratification, you can bad-mouth a large company very quickly and get a lot of publicity.


Hope this answers atleast some of your questions :)

[Moederloos]

I got 780km on 95 in my 1.6 Hyundai on a long trip. 45l as well.

[Messugga]

Back in the day it might've been an issue but we have lovely things like engine management which monitors air intake and whatnot, so that things don't go wrong end up. That said, certain cars (I think it is the Evo 9) require fuel of a certain quality and octane, which is why they only run on Shell Premium (I stand to be corrected). If you detuned the engine somewhat, it should cope fine with more rubbish fuel, but then you lose some of that lovely power.

As for the 800km on a tank with his Polo 1.6, my dad drives one and the mileage is insane on the open road. It has a 45l tank though, if I'm not mistaken, which equates to a more believable 17km/l. That's open road driving.

[Moederloos]

As for the 800km on a tank with his Polo 1.6, my dad drives one and the mileage is insane on the open road. It has a 45l tank though, if I'm not mistaken, which equates to a more believable 17km/l. That's open road driving.

Sorry - that part is not clear to me. Are you confirming or denying?
I know from my own experience that 17-20k/l is quite possible - but only if one drives sensibly.

[Messugga]

I'm confirming under certain conditions. It's definitely possible on one tank since my dad does it once a year when he drives down to our beach house, without filling up along the way, which is around 840km away. But it's important to take note that he has a 45l tank and NOT a 40l. 17.7km/l as opposed to 20km/l. Tell the guy to read his car's manual and to add the 5l reserve for the fuel tank ;)

Ps. My dad's running on fumes when he arrives there.

[Nerfherder]

As for the 800km on a tank with his Polo 1.6, my dad drives one and the mileage is insane on the open road. It has a 45l tank though, if I'm not mistaken, which equates to a more believable 17km/l. That's open road driving.


I don't think that its that good... I know a deisel that has that kind of economy... but I doubt that a polo would do that.

[JK8]

Thanks Devill!! Nice link.

Do all 2008 cars have min 95 requirements? I thought only Turbo cars and "sports" cars needed 95, not all cars.

So what would a city driven 1.6 Polo use? Im guessing 600 max!
My polo only makes 400km to 450km:( Thats why I tried another fuel.
But its good I dont really mind, its not the car thats heavy on juice its coz the damn tank is so small.:p

[CaTcH21]

Didnt read Devils post, but funny enough with my GTi i get maybe 50 more k's with 93 than 95. also car runs just as smooth.

[Devill]

Thanks Devill!! Nice link.

Do all 2008 cars have min 95 requirements? I thought only Turbo cars and "sports" cars needed 95, not all cars.

So what would a city driven 1.6 Polo use? Im guessing 600 max!
My polo only makes 400km to 450km:( Thats why I tried another fuel.
But its good I dont really mind, its not the car thats heavy on juice its coz the damn tank is so small.:p

Lol, i have no idea about these things but im one hell of a googler :p

[cAv]

There's a definite difference...well, so far as my car goes at least. I have a Renault Clio 1.6 Dynamique, on 93 unleaded I get 450/60 kms per tank as opposed to 520/30 kms per tank, both of these are not pushing the tank to the absolute limit but rather filling up in time with a normal fillup only being 38-42 litres at most. This is with a normal round trip of to work and back (110km) on the highway in normal flowing traffic for 90 odd kms of that.

This could be purely placebo effect though but...the car feels a lot more responsive and willing with the 95 ULP in the tank than with the 93. This has also been tested when visiting various branches of my company with open road driving with overtaking and what not and the the tank does better with both octanes but 95 still being the better.

I miss my old Opel...when Sasol had the Super100 leaded petrol :(

[JK8]

Didnt read Devils post, but funny enough with my GTi i get maybe 50 more k's with 93 than 95. also car runs just as smooth.

Wow!
Atleast we agree on something. I also get more out of 93, (plus is makes the turbos whistle sweeter!). It doesnt have that scooby idle though.
Do you also have that min 95 sticker on your fuel cap?

[Devill]

There's a definite difference...well, so far as my car goes at least. I have a Renault Clio 1.6 Dynamique, on 93 unleaded I get 450/60 kms per tank as opposed to 520/30 kms per tank, both of these are not pushing the tank to the absolute limit but rather filling up in time with a normal fillup only being 38-42 litres at most. This is with a normal round trip of to work and back (110km) on the highway in normal flowing traffic for 90 odd kms of that.

This could be purely placebo effect though but...the car feels a lot more responsive and willing with the 95 ULP in the tank than with the 93. This has also been tested when visiting various branches of my company with open road driving with overtaking and what not and the the tank does better with both octanes but 95 still being the better.

I miss my old Opel...when Sasol had the Super100 leaded petrol :(


Lol, some green peace people will kick your arse for that comment :p

[CaTcH21]

Wow!
Atleast we agree on something. I also get more out of 93, (plus is makes the turbos whistle sweeter!). It doesnt have that scooby idle though.
Do you also have that min 95 sticker on your fuel cap?

hehe,

i actually didnt notice any sticker but will go check ...

[Viper25]

I usually fill up with 95, though on a few occasions i have filled with 93. Have to say i dont feel any difference between the two.

[Claymore]

I miss my old Opel...when Sasol had the Super100 leaded petrol :(

Sasol Super100 was, despite the name, 93 octane.

[cAv]

Sasol Super100 was, despite the name, 93 octane.

No way! Seriously :eek:? Down in CT or in the JHB? cos it made a discernable difference in my car and other friends' cars as well. Amazing, the powers of placebo effect :p

[Claymore]

93 octane is more explosive than 95. In a high compression engine (typically turbo or supercharged), this can cause pre-ignition of the fuel-air mixture, which is obviously not very healthy. Modern engines use knock-sensors to detect this, and automatically retard the timing to compensate, but this can reduce the power of the engine.

So you put a higher octane fuel in, and because the pre-ignition isn't happening, the engine management doesn't have to retard the timing, and the engine can put out the correct power.

When it comes to lower compression engines that don't have pre-ignition issues, there's no difference between high and low octane fuel, because the engine doesn't need timing changes on either.

[Claymore]

No way! Seriously :eek:? Down in CT or in the JHB? cos it made a discernable difference in my car and other friends' cars as well. Amazing, the powers of placebo effect :p

Cape Town and JHB. It was around before 95 was introduced. :)

[adamr]

i put 93 usually only in the fast cars do i put 95 ... more octane means she burn better (i think)

[ToxicBunny]

Up here I put in 93 simply cos its cheaper...

at the coast i put in 95 cos its all u can get... notice no difference tbh.

[JK8]

93 octane is more explosive than 95. In a high compression engine (typically turbo or supercharged), this can cause pre-ignition of the fuel-air mixture, which is obviously not very healthy. Modern engines use knock-sensors to detect this, and automatically retard the timing to compensate, but this can reduce the power of the engine.

So you put a higher octane fuel in, and because the pre-ignition isn't happening, the engine management doesn't have to retard the timing, and the engine can put out the correct power.

When it comes to lower compression engines that don't have pre-ignition issues, there's no difference between high and low octane fuel, because the engine doesn't need timing changes on either.

Cool I also think that.
Theres a little more pull when you have 93... The 95 drive is definatley smoother, but less pull.I think with turbo cars and their volatile turbos, its better to use 95 it just means less work for the turbo...

I think.

So if I use half 93 and half 95 I get 94 right?:p

[Claymore]

i put 93 usually only in the fast cars do i put 95 ... more octane means she burn better (i think)

Mean she burn slower, not better.

[JK8]

I put 95 again, feels way smoother and little more powerful I think.
I hope I get over 400 this time!