91 or 93 octane? for a 4.2 v8. they re both classified as premium so i have no idea which grade to select at the pump...ive always used 93 despite the ridiculous gas prices at the moment. will there even be any difference? i doubt there will be any difference but i wanted to put this out there so u guys can debate...

 

I run 93 but I am super **** about these things and I use my Kroger card and get 20 cent off a gallon which brings 93 down to 89 prices.

 

You live in one of the rare states where you have both available to you.

The west coast, mostly to comply with Kalifonia emissions generally only gets 91 octane. The east coast the standard is 93 octane.

Amocco used to have "Ultmate" which was 94 octane, and sunnoco had "Ultra 94". Since the BP takeover of Amocco, the 94 octane was slowly phased out.

The car is designed and will run perfectly fine on 91, but you may get a slight bit of better performance out of 93.

What ever you do, dont head to the mid grades or regular.

Take care,

George

 

yea i have a kroger card also...20 cents though i only get 10 cents off per gallon if i spend 100 bucks on groceries...

 

That sux here if you spend $50 in groceries you get 20 cents off every gallon.. My primary store is krogers so I always meet the get 20 cents off a gallon special.

Sounds like you need to complain to the main Krogers about your Krogers policies.

 

That may be a state to state difference. They may have the .20 off per $50 in Ohio to match the competition from another chain... Giant Eagle.

I don't know of any Krogers up here in North East Ohio, but I'm sure at some point their markets overlap. We have Giant Eagle Fuel Perks.

 

It might have to do with taxes on fuel also. Your state's fuel taxes may not allow the Krogers in your state to give the higher amount off it may affect their dividens.

 

Man... We don't get crap for shopping at a store here besides what we overpay for. There was one gas station that had one of those drive thru car wash deals attached to it a few years ago, and it had one of those punch card deals where you got a free carwash every 5 or 6 fillups (I think it was over $15 then, tells you how cheap gas was).

Eventually they remodeled the place and turned the carwash into a convenience store.

Take care,

George

 

I've had up to $2.40 off per gallon at giant eagle before. It's great seeing 93 for only 80 cents a gallon! Generally, I'm pretty picky when it comes to fuel and like to stick with Shell 93 whenever possible. I'll go to sunoco, but depending on which station I hit it'll range from either 87-91 or 89-93, with some carrying 94. I believe it was a Sunoco I went to in Toronto (ohio) that had 110 at around $7.50/gal. I don't think I'd want to try running 110.

Sometimes when driving outside of town you don't always have much choice. Couldn't hurt to carry a small bottle of octane booster with you, something that only bumps it up about 4 points.

 

LOL...I believe that there is some law in New Jersey that prevents anyone from having "gas" promotions... I used to remember the major gas stations used to have "give aways" that I would see in Pennsylvania yet they weren't available in New Jersey.... Then there would be the fine print... "..except where prohibited by law".. Like the no self sevice or the Blue Law prohibiting car sales on Sunday (they still have that?).

 

I'm with ya on the Shell thing as well...Just as picky since I did some self testing...Used to not be that way...

Funny thing is I found a few years ago that a local chain, Acme, was actually cheaper for groceries even when you factored in the fuel perks discount... But with everything going up, I may have to re-test that....

 

I do the Kroger thing also. $100 worth of groceries gets me 10cents off. It is a good ploy by Kroger, if I am within $10 of that $100 goal, I go buy more stuff as I always need gas in the STR.

 

I pulled out my owners manual and it says to run 94 octane if avaib. if you run a lower octane you car has to basically be tuned for it.
Anyways I usually run lucas injector cleaner in mine so that boost me up a couple octanes.

 

I have never seen over 91 here in Oregon, but my car does just fine on it.

 

The engine control system does that automatically. It is constantly hunting for the ideal state of tune based on closed loop feedback.

 

6 fillups?

There were stations giving free carwash tickets on *every* fillup. Lots of people had carwash tickets overflowing the glove compartment.

 

Not being rude, but the subject of octane ratings and especially so called octane boosters are one of my 'hot buttons'.

Modern cars like the S-type have knock detectors that will retard the ignition timing to eliminate pre-ignition/knock/pinging if detected. This means that no harm will come if too low an octane fuel is used. On the other hand, the retarded timing means that performance may take a hit during heavy acceleration climbing hills or possibly very high speed driving. No outside adjustment to the engine is required to use lower octane fuel (and fiddling would likely do more harm than good)- it's monitored and adjusted continuously by the engine control system itself.

Using a fuel with a higher octane rating than the engine needs, again to avoid pre-ignition/knock/pinging, will also do no harm but it's simply money wasted with nothing gained in return. The engine will not make 'more power' contrary to myth or offer any of the legendary benefits we all believed during boyhood.

The difficulty comes in not really knowing what octane rating the OEM has designed the car for when a vague specification like 'premium' or 'super' is recommended. An additional point of confusion in the Jaguar manual is the section where they do discuss actual octane ratings. Mine says use 95 RON (research octane number) or better. The problem is that the RON rating system has not been used in North America since the mid 1970s. Our rating system is the average of two numbers, the aforementioned RON and PON (pump octane number), and is referred to as AKI or anti knock index. This is the number we see advertised at the pump. Although not always completely accurate it is possible to presume that a fuel of a known RON number is a certain AKI. 95 RON is equivalent to 90-91 AKI.

The most commonly available high test gas here is 91- so that's what I use. I have had access to 93 and 94 several times, and took advantage, but saw absolutely NO difference. This leads me to believe that the engine's octane appetite is for approx. 91 or 95 RON just like in the owners manual.


The little bottles of octane booster are 99.9% snake oil. If they specify 'boosts octane 1 point'- they mean .1, not 1. Your tank of 91 octane becomes 91.1 not 92. Lucas fuel injector cleaner contains no ingredients that increases octane. Their octane booster product claims a boost of 30 points but at almost ten bucks a bottle, you're better off buying high octane gas (91) to start with.

 

There are or may be times when the knock sensors are NOT monitored, such as high acceleration (WOT etc). I'd be a bit wary of running lower than the recommended octane (or thereabouts).

It's also my understanding that higher octane is a waste. It's been said that's not so during WOT but I have no solid belief either way (nor do I do WOT runs lol).

95 RON is about 91 in USA, I believe.

 

May I ask for your source of this info please? This would be completely contradictory to everything I've read not to mention illogical for Jaguar to design it in or allow this to happen. WOT is one of the few conditions when the sensors MUST be operational!

 

Only one of the 2 CPUs in the PCM is wired to the plugs (well, the COPs) and I understand that CPU is very busy doing time-critical stuff. I understand the other CPU does things which are not so time-critical and is wired to such things as the knock sensors. Jag don't go into much detail, but what I found is in their tech documents on TOPIx. Whether there is time at WOT to hand across from one CPU to the other the knock sensor results is not as far as I can find ever mentioned. Before doing WOT the PCM has had time to figure out lots of things so by then the CPUs may have exchanged as much learned timing data as needed - or they may not.

It is stated somewhere that the O2 sensors are not used at times (such as WOT). They are wired into the same CPU as the knock sensors, I believe, and this leads me to think that it is quite possible that both are not used during WOT. If you're sure the knock sensors must be used, fair enough, but I have seen no evidence to that effect.