Tuesday, 20 April 2010

Expensive petrol is cheaper for you

Surely if you're in the UAE, you've been following the petrol price hike here, due this Wednesday of 0.15 Dhs/litre. Personally I think the stupid and inefficient Sharjah toll on trucks at 100 Dhs a go is worse and will affect us more, but that is another matter, especially since increasing taxes during a recession is about the dumbest thing that you can do.

Anyway, so here's how you can save money by buying more expensive petrol.

First of all, in the UAE you have two types of petrol: 95 Octane and 98 Octane.. different companies call them different things, e.g. Eppco/Enoc calls 95 = Special, and 98 = Super.

Octane rating is how much heat you'll get when you burn a unit of fuel, so the higher the number the more efficient the fuel is.
Just to get an idea, back in the days, fuel was at 80 octane, and in most countries 90 or 91 octane is normal. However you can get up to 99 or 100 octane apparently.

So, back to the UAE, a full tank of 95 or 98 weighs exactly the same (as far as your car is concerned), however if we go with my car for example, a full tank of 95 costs about 110 Dhs and 98 at 130 Dhs. However, the more expensive petrol can take you about 25% farther on the same tank than the cheaper one.

This is amazing because it means that you waste less time during your short life to stop and fill up for petrol. You also burn fuel more efficiently. You're also saving the environment by making your engine live longer because it's a more efficient fuel and will limit wear more.

The funny thing is that these bastard petrol companies are smart, they do not say that they are increasing the price by a percentage, but instead they increase it by a fixed amount, which is 0.15DHS FOR BOTH GRADES, which means as a percentage the price hike hurts less when you buy the expensive 98. Hence another reason why you should only buy 98.

Here's my tip on how you can save money by spending more money, however the biggest saving for me is time, coz I hate to wait at petrol stations for my tank to fill up.


El Shahlab said...


Here we go again

El Shahlab said...

btw BuJ, even if you want to stick with the 98 Octane, sometimes you just can't because not all gas stations has 'Super'. I face this problem because I used to fill my car's tank with 98 octane only, but sometimes you resort to 'Special' 95 OC because your tank is empty and gas stations around you has only 'Special'.

So I ended up using only 95 because it's more convenient and available at all gas stations. And didn't want to mix Super and Special because I was told it damages the car's engine?

BuJ said...

Yes, I see your point ya Shah!

I did some research and mixing petrols won't ruin your engine at all. It's a bit like this...

you have a masafi bottle from the fridge at 5C and you have a masafi bottle from your kitchen at 25C.
You mix the water together 50/50 in a glass, and the result will be water at 5+10 = 15C

Last time I checked 15C water is ok for you.

Now if you think about it, if you mix water at 95C and 98C at equal proportions you'll get 96.5C which is perfect to brew your tea!

So really, if your car works at 95, then 98 or a mix of anything above 95 is fine.


at the end, you need to check your owners manual.. mine says i need a MINIMUM of 95Oct, so any mix of 95 or 98 is good for me.

the main thing is my cars tend to give much better economy on the 98oct fuel. and cuts fuel stops to a minimum.

so it's safe mixing fuels only if your car works on 95Oct or less.


rosh said...

BuJ, thanks for the post. Honestly I didn't know the higher grade is cost effective. I'm passing your post to all back home. It will be strange seeing litre instead of gallons, especially those numbers. Why'd they change? What are the current average gas prices per litre?

Umm SHJ has a toll of Dhs100 per trip? Well maybe it's a good thing you know. Trucks will be used more efficiently across the Emirate's highways. I mean have you seen the number of empty trucks back and forth at times? It's ridiculous, the amount of traffic clogs, and damage to the roads. So, perhaps they'd use a truck more efficiently, BTW are you sure the toll applies to all SHJ highways / roads?

El, the folks at the dealership told me - "MUST use premium, or risk damaging the engine". I was like, OK.

ultra[blue] said...

Your understanding of what the octane ratings are is a bit off Bujassim.

1st off you have to realize that there are TWO major ways of calculating octane ratings, RON and MON.

So your MINIMUM requirement is sometimes wrong as you need to ask yourself HOW your car's minimum requirement is calculated.

For example, our 95 octane is the same as a 91 octane in the US way of calculation. Our 98 is more of a 95 in the US.

next, the octane rating is basically a numerical number given to a fuel based on it's makeup (By one of the two major ways of calculating) that will tell you how much the fuel can withstand in terms of ignition. NOT how efficient it burns.

Basically, in car jargon, how much you can push a motor being it "Pings" or detonation happens.

All fuels are as efficient as the other as long as the motor was made for and tuned with that specific octane level in mind.

If your car's minimum octane rating is 95, that motor was tuned with THAT octane number in mind, and thus is optimized, in terms of timing, and thus of detonation, for THAT octane rating.

Any less and you COULD "ping" meaning you could have detonation inside your cylinder. That happens enough times and you will literally BLOW your motor. I have done this 3 times in the past 10 years. lol.

However, your assertion that using a HIGHER octane rating is more efficient is WRONG. Using a 98 octane fuel in a motor made with 95 in mind will NOT GARNER ANY MORE EFFICIENCY. You are WASTING YOUR MONEY.

My best example is my charger. When it was stock Iused 95 because that is what the factory tuned the car for. When I replaced its motor we tuned it with 98 in the tank and for max. performance based on 98 octane.

If I dare put ONE liter of anything lower than 98 in that gas tank I might as well order a new 60,000 dirham motor. It will blow.

In the US, we tuned my Eclipse Turbo on 101 octane, so that it could achive a higher hp number (for a race) but after the race we had to retune it back for 91 octane.

The same motor will make more hp with more octane simply because the motor can be pushed more and detonation is less likely.


So by just placing 98 into your factory car, you will gain NO EXTRA BENEFIT, not in performance or in efficiency. Octane ratings are a rating of the fuel's ability to burn without detonation, and unless you are retuning your AFR on the dyno (which you arent) it is a waste of money.

And trust me, I dont drive the charger often (once a month) partly because as El Shahlab said, 98 is only available in some places. I wish they sold 101 or even 104, I'd get an extra 20 or so hp out of her!

ultra[blue] said...

the folks at the dealership told me - "MUST use premium, or risk damaging the engine".

Bujassim, the "folks" at our dealers are as clueless as door mats. Your manual will clearly state what octane rating method is used for your car and what the required octane level is for your car.

I will not even get into the stupidity and bufoonery they cause with my modified cars. Its sad that we have stupid people working on our cars. That is exactly why I dont take my cars to the dealers. Even for basic oil changes I take them to Extreme. lol.

ultra[blue] said...

And didn't want to mix Super and Special because I was told it damages the car's engine?

Rubish. We used to mix the 101 with 91 sometimes if a full tank of 101 wasnt available (it was way too expensive)

And this was in a 400 hp 2.0 liter car! So it is very possible and safe. Once again, our dealers are clueless and tools.

BuJ said...

hello Mr Rosh...

i am no motor nutcase (although there is no shortage of those), but i know how to conduct experiments.. and i did a number of them, and it showed for the switch between 95 to 98 octane results in a milage increase for my car which exceeded the cost increase in percentage terms. i don't have the exact numbers, but i remember it made a difference.

for me even if the difference was the SAME, i would still use 98 oct, coz it means i can run an extra 50 or 100 km between fuel stops. and i hate those.

btw ROSH, the road tax for trucks is just at al Dhaid.. and it's to be paid in cash.. how dumb, nothing like salik's radio chip wil be used. this truck road is the main link between the Arabian Sea (i.e. Fujeirah ports) and the rest of the UAE, so loads of trucks use it. Also Fujeirah port is out of the reach of the iranians via hurmouz straight, etc, so it's safer. now 100dhs per truck per journey in a stagnant economy is not smart.

BuJ said...

ABIT, thanks for your time to give me all this feedback.

I see what you say but i don't agree with a lot of it, except the bit about car dealers.. and i think u have a few things confused yourself.. saying that 95Oct in dubai is like 91 in USA doesn't make sense.. it's like saying our 25C is like their 21C!!! no wonder american a/c's are so much better!!

does it apply to speed too? is 100kmh in a car equal to just 90kmh in an american car? that explains all the speeding tickets!

also the guys said :""MUST use premium, or risk damaging the engine"." to El Shah and not me.. i don't interact with them and prefer to read the manual as noted earlier.

finally my observations were not made on the racetrack in the US and didn't cost me $60,000.. in fact i just collected some data from my daily commute using 95 and 98 fuel and taking into account the volume, cost, and milage.

roughly the results were that i get about 25% more milage with about 20% more cost.. that's the rough numbers.. but i don't have specifics, coz i threw away the papers, or filed them in the 2009 diary.

ultra[blue] said...

saying that 95Oct in dubai is like 91 in USA doesn't make sense..

Sir, this is a fact, I am not saying because of the location they are different, I am saying because the US uses a DIFFERENT METHOD of calculating octane ratings, the numbers are irrelevant unless you know which method your car manufacturer uses. There are TWO major methods... and I believe a few others a s well though I've never heard of anyone using them.

Here is a basic chart:


As you can see in the US method, 87 octane is equal to 91 in ours. and 98 here is equal to 93 there. The list also gives methods for octane calculation that I truthfully havent ever heard of.

You can claim to have seen better fuel economy, but as I am a "motor nut" as you put it this is what I do and have for ages.

its not a hard concept. Your car's ECU is tuned to act a certain way based on some assumptions. One is the octane rating of fuel you will be using. for example, 95 octane. You feed it 89, and you will possibly ping as nothing has told your car it's not getting 95 and thus your ECU does not retard ignition. Same for higher octane, if you put 98 in your car, nothing has told your car its 98. Your car's computer doesnt magically figure this out. It needs to be told so. And "telling" your motor this is a 5000 dirham process plus 3K for the equipment. So like I said, to 99% of the people out there, putting 98 into their cars is simply a waste of money.

If you feel fine with it, pay more for nothing. But unless you are going to sit there on a dyno and re-tune your car to take advantage of that extra octane rating, you get NOTHING in return. This is a fact of the car world.

BuJ said...

aha, thanks ABIT, i think i'm starting to understand things a bit better now... so what you wrote:

"For example, our 95 octane is the same as a 91 octane in the US way of calculation. Our 98 is more of a 95 in the US."

actually means that 95 RON = 91 MON.

coz the way I read it is that 95 RON in the UAE is like 91 RON in the USA.. hence the confusion.. see, i was always taught that unless noted otherwise you need to assume centris parabis which means that all other things are equal except the single variable that you're changing (the 95 and the 91).

this way scientists avoid the confusions of comparing 45 mph with 96kmh.

i still don't understand what you're saying.. so do you mean that since my car is tuned for 95 RON that 98 RON is a waste of money as the performance will be the same?

to be honest, that's what most websites out there said (i did some research before posting the initial post), but i didn't believe it, coz my experiment told me otherwise.. and i took about 3 weeks of testing to come up with my numbers to prove that 98 RON octane is better fuel efficient on my car than 95 RON octane.

hence, there are three explanations for this:

1- My car manual is wrong, and perhaps they meant 98 RON was needed, and putting 95 RON is damaging the engine and reducing efficiency.

2- The theory than using higher octane is a waste of money is also wrong, as purported by some websites including your kind self.

3- My car is a supercar, that uses a combination of solar and nuclear fuel and pouring a drop of petrol in it won't make any difference to performance! The petrol is used to power the stereo which i keep off most of the time!

hemlock said...

i recognize it's a man's world but may i dare share my two cents?
never mind, im going to do it anyways.

buj, im a freak for numbers and with my old car i used to obsessively note the distance covered/fuel tank. for me it was a measure of my driving.

lesser distance covered than average meant i'd been revving like an asshole.

with this car i realised the fuel efficiency went down from 6.7km/ltr to 5.4km/ltr in just a year.

that either meant i needed to take it in for a tune up. or reflect on the meaning of life, the universe and everything, because my driving couldnt have deteriorated so much.

turns out, i had changed the route i was taking to work. instead of driving on shk zayed road, i was now taking Jumeirah Road - which i counted has 36 signals and a dozen speed breakers. the stop & go traffic translated into higher fuel consumption.

also, the winter average is 5.7km/ltr vs 5.4km/ltr (the difference being use of air-conditioning).
one trip to abu dhabi / RAK on emirates road brings the fuel consumption back up to 6.3km/ltr.

point being, can we safely assume ceteris paribus over the three weeks of your experiment? same weather/driving conditions?

BuJ said...

hemlock, now you're talking my language!!!!!

u mentioned good details which any scientist cannot fail to ignore.

thus they deserve answering.

for my experiment, we can safely say that weather conditions were constant and hot at least.. i did the experiments in may/june

i also took the same exact route always. my route starts with a lot of 120kmh motorways and ends up with a few annoying traffic lights so i drop to around 60kmh average.

i generally leave work and arrive to work at the same time which means the traffic density is consistent, (but not absolute)

so yeah, i think it's fairly accurate.

on top of that, i always zero the trip meter when i fill up petrol, and during the summer or winter.. i know on 95 octane i get about 400-430 km from a tank.. and on 98 octane i get 450-480 km.. and if i drive on a lot of motorways, i can get 500km on 98 with no probs.. obviously this is not as strict an experient coz in those 400 or so km, i am driving in many varied driving conditions, and other family members might use the car (we use cars in a communist way, so we all share, and no one has just one car).. other members means different driving habits.. etc..so different economies.

i find it fascinating, and so do u it seems :)

ciao hemmy

Tainted Female said...

Trust you to teach me something new... Even 5 years or so after I first start reading. I had no clue that the hell the octane levels meant. :)

ultra[blue] said...

actually means that 95 RON = 91 MON.

coz the way I read it is that 95 RON in the UAE is like 91 RON in the USA.. hence the confusion.. see, i was always taught that unless noted otherwise you need to assume centris parabis which means that all other things are equal except the single variable that you're changing (the 95 and the 91).

As you like your experiments to be correct, mainly ALL ELSE REMAINING EQUAL.

Were your "experiments" done on a DYNO with 4 computers reading EVERYTHING on the same days with the same temps and the same everything else?

YOu cant drive for one mile and have the temp the same. And all this affects a car. Trust me. If you are going to experiment, then the car should have NO CHANGES aside from the gasoline. IMPOSSIBLE if not in a controlled environment on a dyno.


Good example of my last dyno tune session. 20K AED and a guy flew out from the US because of our insane fluctuating tempts here. Just to set the damn computer.

I know you are tempted to believe your car, BUT even your speedometer is ALWAYS off abit. Fact of life. Thats why they dont count for speed records, they use a combo of GPS and god knows what.

When a car is chooked up to a 500,000 dirham dyno, 3 to 4 computers are recording (data logging) everything.

This is why most sites, especially performance oriented ones will tell you if you have a 95 RON tuned motor, slapping 98 RON into it doesnt add or decrease anything. Its purely a waste of money.

If you want this tested out, go to a local dyno shop and test it. Driving around tests nothing.

YOu say your results are "fairly" accurate. I have seen a 2 degree difference in temp add 6 hp on a dyno. Not kidding.

point being, can we safely assume ceteris paribus over the three weeks of your experiment? same weather/driving conditions?

No, IMPOSSIBLE. its hard enough doing this over 3 consecutive days in the same standing location on a dyno meant to measure everything, let alone a track thru the desert. IMPOSSIBLE.

Again, you can believe as you wish, but the fact is that when cars are tested on correct equipment there is NO benefit whatsoever in using higher octane fuels unless your car is also tuned to take advantage of that higher octane.

This is why I use 95 in the SS but 98 in the Charger. If we had 100+ I'd retune her and use that. But Im not going to use 98 in the SS when it's stock tuning is for 95. Pointless.

ultra[blue] said...

Im going to put this whole debate to rest:

Ordinarily, your vehicle will not benefit from using a higher octane than is recommended in the owner's manual. But if your engine knocks or pings at the recommended octane level, you may need a higher octane gasoline to prevent the knock.

From where is this line?

From MOBILE's own website. They say EXACTLY what I said in my 1st comment:


If the guys SELLING the gas are telling you there is no benefit... where are your voodoo numbers coming from Bujassim? Hum?

I may not know alot, especially when compared to an Engineer like you, BUT building cars I've been doing since 17. This I know like the back of my hand. Poor firefox dreads the car talks... which is about 6 times a day. lol.

ultra[blue] said...


Just for you Bujassim.

CG said...

So I bought a new car. The manual says 98 octane, no ron or mon here.
By error I filled it up with 95. It is nearly empty and I was trying to run it out before filling with 98, and are you telling me that if I fill it now, it will be fine and dandy and be about 97.3 octane? Please advise before my engine pings.

BuJ said...

boss, my advice is to fill up with 98 octane immediately, and the resultant will be the algebraic sum of the 95 and 98 fuels weighted by their respective proportions in your fuel tank..

thus if your tank is in reserve (i.e. 10%) you're average octane rating will be:

(10/100) x 95 Octane + (90/100) x 98 Octane = 97.7 Octane

For the next filling, assuming you fill up again with 98 Octane you'll get:

10% x 97.7 + 90% x 98 = 97.97 Octane

then.. 97.997 Octane, etc..

you get the picture..

as far as your engine is concerned, it'll see it as 98 Oct

fill up now!

hemlock said...

buj, i laughed out loud at your comment to CG - i was going to mention how insane it was, that you did the math - but then i remembered you are an engineer =)

'splains a lot! :D