Octane rating is strictly a measure of resistance to detonation. Nothing more, nothing less- one attribute/characteristic only. No connection to Reid Vapour pressure, flame front speed, ethanol content, lower heating value, cleaning additive content or composition, antioxidants, stabilizers, etc, etc. I'm surprised to see statements to the contrary.

I do not totally disagree with your generalizations of detonation and pre-ignition but it must be understood that each normally exists independently of the other and without any inherent connection. One frequently exists without the other, in other words. No one here is advocating operating an engine with any measure of detonation for even a brief period even if they 'could get away with it'.

Yes, varying opinions are what make civil discussions enjoyable.

 

Like JimC64 said on page #1.

We are sitting at $1.68/litre here, and have been for a looooong time.

ALL my/our Jags get our 98 Premium, no exceptions.

A blown piston, overheated engine, whatever, is just not worth the brain cells to consider the lesser fuel.

Then consider the "drinking time" you are going to miss out on whilst you repair that engine, NAH, too stressful.

 

Even children in school here know that they sell lower octane gas beacuse of the elevation, and how it makes normal cars detonate less.

I'm not quite sure why you were trying to make your self feel smarter, but I made no reference that said lower grades of gasoline had different additives or was of a different make up.

What I was referring to was that when modifying a car to run more boost from the turbo or supercharger, 91 octane has a propensity to detonate. Thats exactly what the gasoline rating is, it's ability to resist detonation. In that regard, it makes 91 gas "crappy"

 

No offence intended at all, and there was no way I could have known you and apparently all school children in your area understand why your gas is lower in octane than other areas- and that it makes no real difference.

Perhaps it was this statement with the reference to 'crap' that threw me:

Being that S-types only require 91 octane at sea level, using it at your elevation is actually as waste. I'm fairly sure you could use 89 without encountering detonation as usually there a 2 point decrease calculated for your altitude or greater. Whether a car has FI or not has no bearing.

Seems your statement might have confused George also:

As noted above, 91 is only required at sea level so at 4400 feet there is no possibility of timing being pulled back.

 

I did not mean to be so rude, my apologies for that.

That sentence was supposed to say " so most car owners don't realize that 91 sucks, beacuse ..."

I was typing response quickly on the iPad and it got me.

I was simply pointing out that 91 is not enough when turning the boost up to a huge amount, say 30 psi. Not at the stock level beacuse none of my cars are stock.

 

No harm done, I've got thick skin to match my skull. Your sig '2005 S type R. Stock for now ' might have added to the confusion.

Is it time for the bunny with a pancake? I found him hiding away:

 

LOL Group Hug Time, nice....

PS guys, we are now at the equivalent of $11/gal.

And generally I am at level C!

 

Thanks Mikey! I'm already searching and finding lots of useful posts on here. It really does help to understand what these cars are all about, and what to expect when you can read up on other owners experiences.

Perhaps I should have clarified. The 18.9 cents difference is 94 octane which in my area is only sold at Petro Canada locations which were previously Sunoco, and also at Shell. Yesterday I filled up at Esso, which their premium gas is 91 octane at 15.9 cents more than 87 octane. I paid $1.43 for it when 87 was going for $1.27. Today it dropped again to 125.9! At that difference its close to $1500/year more than using 87. At 94 octane that difference is almost $1800 per year at three fill ups per week.

I'm familiar with the websites you're talking about but they often reference the best pricing scenarios. This is a big city... in the outskirts of it had prices are as much as 3-4 cents per litre less........ but that can be a 1.5 hour drive. Where I am the spread between octane levels are 18.9 cents per litre.

 

Oh by the way.... after filling up with 91 octane fuel I'm experiencing a misfire on cylinder 2 (obd code p0302). Interesting coincidence. Although I know its likely a coil or an injector, do you guys think its because I didn't drive the distance to find 94 octane gas? I was running low and that was an extra 10-15 mins away from my location.

 

@zak...... Please stop stirring up the pot.... LOL

Nothing to do with octane.. Do a search here on miss-fire codes... Lots of reading.. (Hint... Step one, move coils and see if the miss follows)...


Oh... Boy....

Mikey... Sit down bud, drink a cold one, then finish packing....

Oh, and thanks for getting my back over in "X" land....

 

personally at $4.20 a gallon for 93 octane in Michigan, i could care less about the $0.20 difference, as long as my cat drives smoothly

 

Agreed.... but for us here its an extra 76 cents per gallon! Premium is at $5.60 / gal

 

Lol true. Yes I'm having the coils checked in the morning. Injectors too. Just a strange coincidence is all. Day if, you know what I mean??

 

and if you fill up with 15 gals, that is $11.40 more a tank full.

that would be enough for me to change.......


OOOOPPPPS... now I'm stirring up the pot....

 

I guess it's time for a signature update. The s type is the closest to stock of all my cars.

 

Glad we didn't scare you off with our little chest-beating exercise. The moderators usually step in just before we launch into full knuckle dragging poo-flinging mode, or worse.

I guess by now you've realized there's no reason or benefit in using anything higher than 91 octane so that helps with part of your issue. I can only offer you further comfort by stating that your premium at $1.43 is still cheaper than the regular in Montreal...........

One week to go as of this writing.

 

I've been using regular.. 87 octane for sometime now.. However, I do use additives/detergents, every couple of months, just to clean out the fuel injection system, I have not seen any difference in performance. I know in other cars I've had, if it knocks... well go up to a level where you don't get the knocking.

 

Hi Harry-

Thanks for your comments on the octane subject.

There's no need to add anything to the gas, it's already got all the detergents required. High compression engines don't produce any more deposits or clog up fuel injections systems any more than low compression engines.

 

I use 91 if I can find it, otherwise 93 - can't hurt the car. My sympathy to our friends in Canada and the Mother Country; our $4 hi-test looks cheap by their standards.

 

Mikey,
Yes, I understand that, though I've been told that the "regular" gas may not put detergents in the gas, unlike the "premium" ones typically do.

My mechanic said it's a good idea to every once in a while use the additional detergents to clean out the fuel system well and keep things in tip top shape.