I love my new XF. I've put almost 2000 miles on it in a little over 2 weeks. I'm curious about fuel. There's a service station a couple of miles from me which sells 100 octane gasoline. My XF is a 2011, normally aspirated. Will it perform better with higher octane fuel? Or would it just be a waste of money? What's the optimal mixture, or is more better? Meaning, if I run at 100 octane with a full tank, will I burn out my drivetrain quickly?

Thanks for any advice.

Mark

 

Waste of money. The engine output is already optimized for the recommended fuel. Direct injection engines already take advantage of the charge cooling provided by injection of fuel directly into the combustion chamber. To work, the ECU would have to have a signal from an engine knock sensor and a timing map to take advantage of that. I don't think any engine manufacturer maps for 100 octane fuel in NA. In Europe 98 RON is the super premium fuel. Their regular is our premium, 95 RON which is 91 PON.

 

Absolutely! N. America and Europe have different rating systems for octane. Our 93 is roughly equivalent to their 98. The cars are 'tuned' to run at full potential accordingly.

100 octane gas might be required for some ultra high compression racing vehicles but no street vehicle has any need for it or will show any benefits. Save your money.

 

You also run the risk of burning the valves...BTDT....loooong ago...

 

Sorry, but that's an old myth. There's nothing in high octane gas that would cause valves to burn or bring any sort of premature engine deterioration.

 

Aboslutly needed.....just as son as you get that much bigger crank pulley made to up the boost alot in the supercharged engine. And advanced timing can(depending on engine) go only so far, more is not better. It is optomized for best performance, economy, and emmissions. That only gains youll see from 100 ostane (better be unleaded) is a service station owners pocket book thickness

 

Thank you all for the replies. So, jagular, the ECU won't adapt to the higher octane? I was hoping for it to do so. It looks like I'll save my money (unless somebody tells me the ECU is smart enough to use the better gas). Thanks.

 

Also, I am in California. Premium here is 91 octane. I know it's higher in other places. If the XF's 5L is optimized for the rest of the US, then that would be either 92 or 93 octane. Would I benefit from mixing a couple of gallons of 100 octane with the rest 91? That should balance out to 93 octane or so.

I like the feel of getting in the fast lane and flooring it for a few seconds, so I'm wondering if a little bit of 100 octane in the tank would make that experience a little more robust.

Thanks

 

The engine will be a 50 state version designed to run on 91.

Highest octane I have seen at the pumps is 94, which is stuffed full of ethanol and gives you poor fuel economy as a result.

I live at 3,000 ft so higher octane fuel is pointless.

Some turbo engines are knock limited and will produce more power if higher octane fuel is available (my SAAB and my Audi turbos both do this). Supercharged engines with knock limited software are not usual. Audi uses a pressure limiting waste gate on their supercharger. I do not know if Jaguar does. Either way, the ECU must be able to adapt the timing to a higher state of tune before adding octane rating will work.

It would be interesting to know from our European friends as their standard fuel equates to our top fuel (91 which is their 95) and they can get 98 (our 94 roughly) which is not stuffed full of ethanol. Even higher octane pump fuel is sold in Europe.

 

I'm not sure if the engine is optimized for 91 or 93. It can tolerate both, but it's possible it simply remaps to the lesser octane fuel when that is used. If that's the case, you might see small gains with higher octane fuel. If it's optimized to the lower octane, you will see no benefit. Other than cost, it probably won't hurt to give it a try. Woodside Road 76 station?

 

if an ecu was able to adapt to a HIGHER octane, no one would need a performance TUNE. now if the ecu senses engine knock for low octane/poor fuel, it will pull timing. The factory tune does NOT change for higher octane, but will adapt for poor quality or lower octane. I hate driving through the mountains in my supercharged Nissan truck to 4 wheel because the octane is always lower since you cant get as much air and fuel in the engine if the air is thinner. Forced induction is differant though since is still forces more air in. although less than sea level. And without the adaptation to pull timing and remap timing and fuel curves you would damage the engine. I always run methanol and water injection to cool the intake charge and combat the mountain octane blend. Last yr on my way to Utah I was filling up with 87 super unleaded at service stations in the mountains and 83 was "regular"

 

I think there's a 76 station in Saratoga which carries 100 octane. That's close to me. But thanks for the tip about Woodside in case my information about Saratoga is wrong.

Ok, I guess this leads into another question. Can somebody recommend a good tuner? If you don't want to reply to this message, you can send me email at: m t r a v i s 9 at y a h o o dot com

To summarize what I've read so far, with a factory tune, I might be able to get some gains if I can get the octane to 93 from 91, maybe, but that's somewhat doubtful. However, in order to actually benefit from full 100 octane, or close to it, I'd need the ECU tuned.

Thanks for all of the advice, guys!

 

the point I was TRYING to make is that unless you up the boost/compression, you DO NOT need or will benefit from 100 oct fuel. my 580cid with 9.0-1 compression(Ibuilt it specifically to not HAVE TO run race gas) runs on 91-93 octane superunleaded all day long and probobly could get by on 87. the only time I pour race gas in the tank is when Im spraying 400hp of nitrous through the mtor, OR I want to smell the race fuel smell out the exhuast when I cant go to the track and start the car to pissoff my neighbors. Ive even been known to put racegas in the mower for the same reason......ew ew that smell, cantcha ya smell that smell. Think Lynyrd Skynyrd
You cannot just abitrarilly raise timing and think that youll get a performance increase. I t depends on engine loads, throttle opening, temps, baro pressure etc....ignite a mix too soon and instead of igniting the mix as the piston approaches TDC(topdead center) it happens too soon and reduces power because it happens too early when the piston is coming up. you want timing to fire the mix so that by TDC it pushes the piston down with explosive force. This is how the engine runs. too much timing and compression starting creats an engine that wont turnover or turns over very slowly and requires and high torque starter. Factories are much bettre a tuning than you think and more so than many tuners. They have to tune to ALL public drivers and regs. something that a tuner doesnot. They will slight the tune to your want of more performance. But there is just not as much left on the table as there used to be. until you start making other mods and want to tune to squeeze more benefit from these mods. ...intake, exhaust, more boost, gears, cams etc.... you really dont even need to tune for most all boltons since the factory ECU nad tune has a broad range to comphensate from and to. Just ask Andre(AVOS) ge's runnning stock nijectors, pumps and tune. and has bump up hp over 100+ over stock without issue. Something no one else Ive seen here has done. If anyone could go to and use 100 octane it would be someone that has bought his Kenne Bell blower and kit.THEN we could talk about benefits of 100 octane fuel in your car

 

This is absolutely correct and really puts a stick in the spokes of many shade tree mechanics (Bubba) that believe that more is always better. All piston engines have an absolute maximum spark lead or advance setting. Exceeeding this will be counter productive and reduce peak power.

The proper way of tuning is to find out what this maximum 'never exceed' setting is, and run the lowest possible octane that avoids detonation.

Contrary to popular myths, high octane gas does not contain more energy than low octane, nor does it burn faster or slower. Come to think of it, high octane gas doesn't contain octane either.

 

When I lived in the UK and before switching to diesel for economy reasons, I started using 98 Octane over 95. With the lack of ethanol there was an increase in economy that more or less cancelled out the cost increase. I can't say there was a performance difference though. I guess with the higher octane rating the engine could run a little leaner so less fuel was being used. Certainly the ethanol content of US fuel is a problem for economy and engine cleanliness, if not performance too.

 

Sorry to 'pounce', but that's more myth and misunderstanding. Octane ratings do not affect running rich or lean- it does one thing and one thing only. It helps avoid detonation. If the timing is being 'pulled' to stop detonation then the spark is not occurring at it's peak setting which reduces power. If your car was prone to detonation on 95 which was avoided on 98, then that was the source of your poor mileage. Simple as that.

Ethanol as used in E10 is extremely clean burning, much more so than gasoline. I'm not a supporter of any ethanol laced gas, but to put things in perspective the panic over E10 is way out of control. I find it difficult to believe most of the reduced mileage claims. E10 has 96-97% of the energy content of pure gas. This means that a car that normally gets 20 mpg on pure gas would get 19.4 mpg on E10. That's too a narrow margin for most people to reliably measure from tank to tank. I see a bigger swing from tank to tank even when consistanly using the same gas station.

 

This all bring up the subject of why are todays engines so clean, so powerfull and so fuel efficient. Because with injection and computer control you can do things a carb could never do. With a carb, every time you touch the pedal is psrays gas through the accelerator pump nozzles to righen and prevent bogs. Injectors never do this and are seemless.
Back off the gas in a high vacuum situation like decel off the freeway. A carb still is flowing gas even though not needed. Injectors shut off and engine goes full lean. No fuel needed. And i never used to think that any timing could go over 50 degrees of advance. Any carbed engine generally runs 32-38 degrees btdc. Injected computer control cars can and do go over 50 degrees depending on many variables. I meen look at what we have today a v6 pentastar puts out 300 hp. More than a v8 in a z28 or trans am did back in the 90's. And gets better mileage to boot and is way cleaner. My 87 suburban guys at work dont think it would ever pass state emmisisions testing. But i switch to fuel injection and engine management instaed of a carb and it flat blows away the spec for a 87 vehicle and is as clean as newer cars(except nox, i dont run cats or egr).
On ethanol my personal experiance in my nissan truck is it cost me 1mpg over non e fuel. When i go on 4 wheeling trip i generally get 12mpg on the highway and when i can fill up without ethanol far from a major city i get 13. Problem is now places i used to go to and get fuel outside of houston far to the north now carry ethanol too. Ethanol and methanol (alcohol fuels do not have the same btu's, but much higher octane as does propane which is why you have to use more alcohol to maintain similar power output. Methanol race engine run much bigger fuel pumps and lines because they have to run 2 times the same amount of fuel through a engine than gas.. Ok i gotta get back to work. You guys make me loose too much money

 

Brutal-

Carbureted cars typically operate on 50+ degrees of timing too- 36-38* provided by the mechanical advance and an additional 12-15* from the vacuum advance. This would be seen at higher RPM level with small throttle openings (giving high vacuum) typical of highway cruising.

 

NO VACUUM ADVANCE IS FOR HIGH VACUUM CONDITIONS LIKE PART THROTTLE CRUISE . YOU HAVE INITIAL TIMING SET AT THE DIST. THEN VACUUM ADVANCE FOR PART THROTTLE AND CENTRIFUGAL ADVANCE WHEN VACUUM GOES AWAY WITH FULL THROTTLE OPENING AND OR RPM. THEY DO NOT ADD UP AFTER ALL YOU HAVE NO VACUUM AT FULL THROTTLE SO THE VACUUM ADVANCE GOES AWAY. DIFFERANT ENGINES AND CARS REQUIRE OR LIKE DIFFERANT TIMING. I USE TO LIKE TO POWER TIME CARS HIPO FOR STREET OR STRIP. ADVANCE FOR BEST ET THEN WHEN IT SLOWS DOWN PULL THE TIMING BACK A COUPLE DEGREES. FOR INITAL I SET TIMNG WITH A VACUUM GAUGE AS WELL AS THE CARB. I LOOK FOR HIGHEST IDLE VACUUM. AND NO IVE NEVER SEEN A PERFORMANCE OR CARBED ENGINE RUN THAT HIGH ADVANCE UNDER POWER. ON MY OWN RACE ENGINE, WHEN I HAD IT BUILT 15 YRS AGO, I HAD A RACE ENGINE BUILDER MACHINE AND ASSEMBLE I WANTED NO MORE THAN 38* ADVANCE AND RAN 20 INTIAL WITH A CRANK TRIGGER/FLYING MAGNET. THE TIMING COMP I USED PULLED TIMING ON CRANKING TO MAKE EASY TO TURN OVER THAN SWITCH TO FULL INTIAL OF 20. OW THE PROBLEM CAME IN UNDER NITROUS USE WHEN I PULL 10* TIMING DOWN TO A TOTAL OF 28* INSTEAD OF 38*. SO LONGER STORY SHORT I WAS NOT PICKING UP SPEED AND ON THE 3RD PASS SPUN A MAIN BEARING UNDER NITROUS. NOW IM PISSED BECAUSE EVEN THOUGH ITS 850HP OFF THE SPRAY I HAD IT BUILT TO MORE THAN HANDLE 1500+HP SOOOO, I PULLED THE MOTOR, GROUND THE CRANK, NEW BEARING AND RINGS, CHANGED THE CAM TO A LARGER 1 AND REASSEMBLED. NOW THAT I WAS DOING IT I DEGREED IN THE NEW CAM. AND LOW AND BEHOLD THE "RACE ENGINE" BUILDER NEVER CHECKED THE TIMING POINTER HE MADE TO ACTUALL ENGINE TOP DEAD CENTER AND IT WAS 10* RETARDED. SO WHEN I THOUGHT I WAS RUNNING 38* ADVANCE IT WAS REALLY 48*, AND THEN WHEN i SPRAYED THE EGNINE EVEN WITH RACE GAS THAT WAS TOO MUCH TIMING AT 38* ACTUALL INSTEAD OF 28* IN REALLITY. SO A 5 MINUTE ASSUMPTION COST ME 2K IN ENGINE REPAIRS AND CHANGES ALL BECAUSE THE MOTOR DETONATED AND HAMMERED THE BEARING. I DONT LET ANYONE ASSEMBLE ANYTHING OF MINE ANYMORE....
WHEN YOUR RUNNING ON THE HIGHWAY THE ENGINE OVERTAKES VACUUM ADVANCE WITH CENTRIFUGAL FOR TOTAL TIMING. NOW IM SURE THAT SOMEWHERE IN HISTORY SOME MANUFACTURER OR ENGINE IS AN EXCEPTION, BUT AS A RULE OF THUMB FOR MOST IT HOLDS TRUE. THIS IS ONE BENEFIT OF DIRECT INJECTED FUEL, BUT AS MANY ARE NOW SEEING IT HAS CREATED NEW PROBLEMS THAT WERE NOT AND ISSUE BEFORE

 

Brutal- ALL CAPS is very hard to read and is considered shouting, although I know that's not what you trying to do.

The mechanical (centrifugal) and vacuum advance are completely independent from each other, essentially they don't know each other exists. Final timing is the cumulative effect of inital + centrifugal + vacuum. The distributor on my old Corvette is set up to give 50-52ish total, runs great.