Octane Rating

[Nium]

I just had an epiphany and wanted to share.

The higher the octane rating of a gasoline the more detonation resistant it is. So 87 octane is more explosive, prone to detonation than 92 octane which would be the more detonation resistant.

See look

http://www.btinternet.com/~madmole/Reference/RONMONPON.html

and

http://wapedia.mobi/en/Octane_rating

Now I understand why timing is set to TDC for 74-76 octane, 3 deg BTDC for 80-85 octane, and 6 deg BTDC for 90-96. Then there's the difference in the rating systems used between the US and the UK. UK use RON and US uses PON so the UK RON rating of 90 would be 87 PON in the US and thus why all Series Landys timing should be set to 6 deg BTDC. I always just did it that way because Ronnie ran better that way now I understand why. kevkon I bet you already knew all this .

Thus when I filled up with 92 thinking I got more bang for the buck I actually got less.

Happy Rovering!

[greenmeanie]

And just to confuse matters more different states in the US use different ratings. AZ, for instance, uses (RON+MON)/2

[Nium]

And just to confuse matters more different states in the US use different ratings. AZ, for instance, uses (RON+MON)/2

RON = Research Octane Number
MON = Motor Octane Number
PON = Pump Octane Number

PON = (RON + MON)/2. It's the same here in PA. The confusing part is when you start comparing to other countries IMO. Because UK only uses RON in so far as I've been able to figure out and we use PON so I always thought it odd to have ignition timing set at TDC for a lower octane fuel (74-76) which I always ASSuMEd was less prone to detonation as compared to higher octane fuel. Which is actually bass akwards. For higher compression engines like say a 9:1 the higher octane is good because it helps cut down on pinging but for Series Rovers with 7:1 or 8:1 it is completely unecassary and just a plain ole waste of money to use higher octane rating fuels.

Cheers!

[kevkon]

And to confuse the issue even more, these ratings are seasonally adjusted!

Walker, I wouldn't say it's a complete waste of money to use a higher octane fuel, though you are correct in saying it's not neccessary in a lower compression engine. Generally, the optimum combustion is one that is controlled and efficient with an even flame spread. That's when the most energy ( ultimately measured in HP) is derived from the fuel. In some cases a higher octane fuel will be the more efficient one in this process, so it's worth the extra cost. Also as we have said, these octane ratings have a ton of variables, so buyer beware. Your not saving money if your fuel is not yielding the most efficient burn and worse, causing pre-detonation.

[Nium]

Wisdom

I must be becoming wiser because when I learn something new it just emphasises the realization I know nothing.

Kevin, in a Series Landie with an 8:1 compression ratio a higher octane fuel could be better or did you mean in a vehicle with a higher compression ratio then that? Curiosity is getting the better of me. Thanks

[kevkon]

It's really not strictly a matter of compression ratios. Other factors to consider are regional fuel supply, climate, type of driving, and timing. The best fuel is the one that works best for you. If say, you can run Shell 82 octane with no problems, then the higher 87 octane will probably not be advantagous. But it dosn't hurt to try the higher octane and compare performance and fuel milage.

[thixon]

Nium,

You have touched upon a source of much pleasure/pain for me. You see, I live in GA. I mean actual GA, not Atlanta, which is not really GA anymore, but a place full of people who are not actually from GA. No offense to anyone on this board from Atlanta.

At any rate, the company I work for is based in a very small town. As such, there are plenty of, well, rednecks. I've had lots of fun in the past crushing their dreams when they pay 5 bucks a gallon for racing fuel in their street cars for use at the local drag strip for "head to head" night.

The exchange usually starts with me commenting that they just wasted money on something that will not add speed. The most popular follow up is something like "oh yeah, then why does NASCAR use it." I love that one.

The pain comes when I actually have to explain octane, compression, head design, etc.

Maybe I should just shut my mouth.....

[NickDawson]

my brain just exploded a little... great thread guys!

[Nium]

Wasting Money

The exchange usually starts with me commenting that they just wasted money on something that will not add speed. The most popular follow up is something like "oh yeah, then why does NASCAR use it." I love that one.

Well once upon a time I lived in North Carolina. Driving from Cullowhee, in the mountains, to Chapel Hill I stopped off in Greensboro to get gas and happened upon a station with 100 octane, near some racetrack I suppose. Well I figured heck this should really make the Honda CRX go like gang busters. Well now I realize I had just wasted my money and probably got worse gas mileage. It was expensive too I seem to recall something like $2.00 a gallon did I mention it was quite awhile ago, I think Regular was something like $1.00 at the time.

How's that for a little bit of funny

[kevkon]

Are you sure that's gasoline you bought?

[Nium]

Pretty sure. It was about 18 years ago so I could be remembering wrong. The Honda CRX did run with it and nothing bad happened to the car. Why?

[kevkon]

Just kidding, you know down South there are other things besides gas that have a high octane rating!

[jgkmmoore]

I LOVE underselling METH..............

Recently, when passing from Washington State into N. Idaho, I noticed the tag on the pump(in Idaho) just as I completed filling both the boat and 42 gals in the Suburban. The tag sez, 'we tetched this gas with a li'l Meth.Ain't go' be no bother,just good deal for U'.
BULLSQUASH !

AIIIIIIIIIIIEEEEEEEEEEEEE !!!!!!!!!! I got a boatload of 10% meth. BAD STUFF for most rubber and many other type fittings/parts in fuel systems. The boat started to crap out after 3 days, but the car took 3 weeks to go bad...started to fail at the beginning of our 365 mile trip back home. Both are in the garage, inop since August.
This would go on for hours if I told the whole story...I shall refrain.
I must warn you though, if you have not been running that junk(Methanol)in your gas, DON"T START. No different than it was in the 70's...but the whole country sold the junk. It's probably the biggest scam foist on the US Public, ever. Maybe worse than Bernie Madoff.
It's made outta corn that you are paying taxes to support growing for fuel instead of food, and then you pay for it again when they mix it with gas. It DECREASES your engine efficiency approx 20%, much more than it is supposed to save you by buying the mix. Total BS, and try to avoid ANY mix of Methanol with petrol. 10% IS NOT ALLRIGHT. Your Landy will run on it tho, but it will also run on whiskey and beer. Go and Google 'Methanol gas mix'....take at least half a case with ya before you sit down.
Above comments about 'Regular' being more volatile than 'Supreme' are right on. The RON/PON numbers relate to Octane value as it applies to Knock resistance, the higher the number, the more knock resistance. Guess how knock resistance is gained??? Riiiight....put the fire out a bit. So, even in the RRC V8s, it's good to run several tanks of regular, then one tank of Supreme to decarbon. 'Techron' mixed gasses in all 3 octanes will keep you clean all the time. If any elected official in your state voted FOR Methanol mix gas, make sure to run 'im outta there next time you vote. Don't believe me...GOOGLE it. Keep all your Rovers happy. grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr....meth makes me soooo mad!!!

[jb_]

What about running a Series on ethanol? I assume that the carb needs to be rejetted.

[jgkmmoore]

jb-You are so kind......

to me, re: my above ravings about 'Methanol'. Of course the 'M' should be removed from each spelling of 'Ethanol' in the rave. One might think I had some personal experience with the poisonous substance.
One may run a Landy on ethanol of course, perhaps without too much resetting of the carby.Understand it's done in India, and as many as 20% of Brasilian cars may run on the stuff. I'm of the thought that it may be better used as a mix for sipping beverages.