Which Fuel?

[Wombat]

Very intersesting topic isn't it. We're going on a decent trip during my holidays towards the middle of this year, driving the VS Berlina with me, the missus, and my two teenage boys up to the Cairns/Innisfail area...we worked out that just the fuel economy difference between the VS and our last car, a 1978 Fairmont GXL 6-cylinder, we will save roughly $50+ in fuel...
However, after reading this thread, we'll be shelling out the few extra cents and using PULP (probably the BP stuff a lot of you seem to like) on the long drive.

As for Octane, spare a thought for people who have high performance vehicles that were designed to run on high octane fuel instead of the goats piss that comes out of our refinerys here...I know a guy with a late 1970's Laverda motorcycle, and it was designed to run on 115 octane fuel, as was standard in Italy at the time it was made...does he have to go through some crap just to take it for a ride or what!

 

[Locksmiff]

QUOTE (jules @ Jan 23 2004, 11:41 AM) maniac,

that's good advice. octane is misunderstood by a lot of people, it has a specific purpose and doesn't always help you go faster. the only thing i'd add is that optimax may give you slightly better fuel consumption, because it's supposed to have more energy density. that has nothing to do with the octane rating and won't cover the extra cost anyway.
I forgot about you for a sec. I was gonna mention a book my cousin has as he has just finished his degree in mechanical engineering. Its on .... um. I dont know without looking. In it it has all the fuelly burny stuff . It opens your eye's a little bit easier over all the fuels out there. I always wondered why drag cars used ethonol or methonol (not sur eon which one) but one of them has a high oxygen content. It made a little bit more sense then.

 

[jules]

fuel is really interesting, it's a complicated topic. i'm not an expert but i have done some research on it for work. oxygenates are i think useful in that they release oxygen in combustion, which is great. they also have emissions benefits, which is why MTBE is used in fuel (ethanol is an alternative), helping cut volatile emissions (from memory).

methanol burns cooler and has a higher octane rating, which is great for drag cars. it's also toxic stuff so you can't use it on the road.

 

[jetspin_vn]

QUOTE (Wombat @ Jan 26 2004, 03:33 PM) I know a guy with a late 1970's Laverda motorcycle, and it was designed to run on 115 octane fuel, as was standard in Italy at the time it was made
Interestingly enough, Avgas grades 100/130 and 115/145 are not in fact octane numbers, but performance numbers. Thus is to say that an engine (specifically aeronautical piston engines) should be able to develop 30% more power at sea level using avgas 100/130, and 45% more using 115/145. This is of course, an absolute load of bollocks and the actual figures amount to more like 5-10%. The variable mixture controls etc ensure that it all really works the same when it comes to planes anyway. They just pack the stuff with lead to get the numbers.

Mike
- Low flying student pilot

 

[Grantis1976]

The hard bit is working out "IS IT WORTH IT?"

I use Optimax, its a personal choice.

The Shell servo "just up the road", normaly sells U.L.P. for 83.9c/L

They always have freash Optimax, selling at 90.9c/L

On an average fill, I pump in, say, 45 L

45L x 83.9 = $37.75

45L x 90.9 = $40.91
So, for an extra $3.16 / tank, I save on fuel filters, fuel economy, and have more fun! When I work out how many K's / tank / $ , I'm much better off! It pays itself off, and get sideways more often !!

Must say, I tried Mobil once, which was twice too many! Go well, go Shell !

Good Luck to All!!!

 

[jafo]

when i had my valiant i used to work for a transport company that sent avgas to moomba on the odd occasion a half a drum would come back on a truck so i used to use it in my tank the power gain wasnt that noticable but the smoothness of the engine was incredible dont know what it was but it ran like a dream.

only thing i found bad about the stuff apparently if you just use straight avgas you burn out engine conponents like rings and valves but cause i used to mix it with leadfree fuel i decreased the risk a bit.

just a funny thing about having the stuff available what i didnt use the boss took home and ran his lawnmower with it imagine the poor little victa screaming its tits off.

 

[jetspin_vn]

QUOTE (jafo @ Jan 28 2004, 09:10 PM) only thing i found bad about the stuff apparently if you just use straight avgas you burn out engine conponents like rings and valves but cause i used to mix it with leadfree fuel i decreased the risk a bit.

Its the truth, and its because the idea of boosting octane is to slow down the combustion of the fuel. The slower the combustion, the longer and smoother the power stroke. If you don't already know, the exhaust valve opens as much as 25 degrees before bottom dead center on the power stroke, to reduce possable back pressure in the combustion chamber. Its fair to assume when your a manufacturer that your customer will run the fuel he is told to, the fuel the engine is set up for. Thus he is presuming fairly that all the fuel will be burnt up before the piston rises in the exhaust stroke.

Heres where the avgas problem arises. If the timing of the engine is left the same, then the spark occurs at the same point with both fuels, but the avgas burns for longer - in some cases well into the exhaust stroke. This means you get hot burning charge escaping past the valves, where it can destroy the valves and seals etc etc. This can easily be avoided, by using a bit of common sense and adjusting your timing if you plan to run high octane fuels alot.

As for the lead itself, the only downside is that it will foul up your plugs a bit. Its entire purpose is to lubricate valve seals in older engines, and to boost octane.

Mike.