Understood... I'm positing the difference in octane could contribute to the discrepancy between published numbers and those tested on a dyno here in the U.S.

I'll assume this is rhetorical and a snarky way of pointing out that I used a general description of engine behavior that may not be technically correct.


None of what I posted was meant to be taken as fact, rather a possible explanation for the discrepancy in power figures.

 

No, I've seen this stated here several times. Are people meaning to say 'dial back ignition advance'?

 

This is becoming pedantic and doesn't really address my point, but yes I mean dialing back ignition timing and/or regulating boost pressure via the bypass valve.

 

Just FYI, 95/98 octane (RON) in the EU is equivalent to 91/93 in the US octane rating system.

 

Thanks Foosh, I wasn't aware of that.

So the only difference is the added ethanol in U.S. gas, which wouldn't affect performance in a measurable way. So much for my theory...

 

The ECU pulls back the throttle, this is well known on Jag engines. It's exactly how you can have various power outputs from the same engine. Also the bypass valve on the V6 and the latest V8 is electrically actuated, not vacuum operated meaning it can be precisely controlled.

 

Correct. North America switched to the Anti Knock Index (AKI) rating system in the mid '70s. Europe stayed with the Research Octane Number (RON) system.

Generally speaking there's 4 points difference between the two ratings systems for most commercially available gasolines/petrols.

Jaguar for unknown reasons usually states only the RON requirement which leads to confusion by many owners here.

 

I've been meaning to ask, for those of us in areas where we only have access to 91 octane (AKI) fuel at retail gas pumps, are there easily accessible and recommended additives we can use to get our fuel AKI closer to 93, or is the only option to fuel up at an airport or racetrack? I seem to recall reading something about this being something that can be improved with an additive but I may be mixing that up with something else.

 

As noted earlier, I have never owned a supercharged vehicle, but I do have experience with turbocharged ones of several eras (exhaust pressure wastegate, intake pressure wastegate, intake pressure wastegate with knock detection, and all electronic). My Jaguar is not expected to arrive for another 6-7 weeks, so weigh my comments for speculation and conjecture as you see fit.

Ethanol has 34% lower energy content by volume than gasoline. If the injectors are not sized for it they may be reaching 100% duty cycle. You could get the same power if you could deliver enough fuel, but once the injector is open 100% of the time, that's all you're going to get.

Interesting. It seems somewhat nonsensical but since you say it's well-known, I'll take it as a given.


That would actually allow *better* optimization and control for various grades of fuel. That's one of the ways my current car gets more power and torque from an engine management optimization (fuel, ignition timing, boost pressure, and cam timing) without changing anything else.


I was positing the same thing.


Maybe they neglected to translate from English to American?

 

+1. RON is posted at the pumps in Europe. The US uses (R+M)/2 as the pump octane rating (also known as the AKI). When blending with standard gasoline components the difference between research (RON) and motor octane was about 8 points resulting in a 4 point difference between research octane and pump octane. However, in recent years the heavy use of oxygenated fuel (MTBE, ETBE and ethanol) has messed with the 8 point differential, leaving it unclear whether the RON is 4 points higher than the (R+M)/2. For maximum performance you actually want the smallest spread possible between RON and MON. Research Octane addresses high rpm/power parameters and Motor Octane addresses lo-mid range hi-torque parameters. Ideally the manufacturers would specify both minimum RON as well as MON and the pumps would have both listed. This is based on 20 year old info when I left the gasoline blending business, so things may have changed even more with the newer hydrocarbons that are going into the fuels.

 

If you are simply looking at octane booster additives, in case you were unaware, when they advertise "raises octane 3 points..." That does NOT mean from 91 to 94. What it really means is 91.0 to 91.3 (Thus, three points...)

 

Again, unless I missed something, I don't think there's any evidence of the engines producing more power on 93 AKI than on 91 AKI. If by basic design or through tuning for a given market the engines do not detonate on the recommended fuel (91 AKI) then there is nothing to be gained with higher octane.

I don't know of any additives that are

1) readily available
2) effective
3) affordable
4) acceptable/safe to use on modern cars

Most off the shelf products at the FLAPS will raise the octane by only .1 per bottle. 91 octane becomes 91.1

 

The fast boat crowd recommends Toluene. You can get it in bulk through paint stores. One gallon of toluene per 25 gallons of gas should get you the number you need. Toluene itself is 114 r/m-2 octane.

 

Not necessarily true. If the Octane is less than that recommended, the knock sensors will retard the spark to prevent damage. This will result in reduced power. With the adaptive learning feature of ECUs, some power benefit can be realized with higher octanes, but only to a point.

 

+1.

 

That's the "if" in question. A 91 tune won't gain power on 93, but a 93 tune might lose power on 91.

 

Absolutely. Is there any evidence that the cars here have a 93 tune? If so, being that 91 is the best available in most places here, why would Jag release cars knowing that they would be in an almost constant state of detonation?

 

When the new Ford 5.0L "Coyote" V8 debuted in the 2011 Mustang, Ford claimed 420HP on 93 octane, but they also provided guidance approving the use of 89 as well, with a lower power output of 402HP, if I recall correctly. The guidance stated that the ECU would compensate for the lower octane.

 

Manufacturers make a one size fits all tune for a region. Typically the whole NAFTA region will receive the same tune. This causes some holes where certain weather conditions or fuel grades negatively effect the engine performance.

Simply the manufacturer cannot control where you drive the car, so they make a general tune that balances performance and reliability as best as they can across the board. Sometimes they can't make everything work.

 

Thanks for the info!

Given the F-Type has a 18.5 gallon tank, it looks like the following makes sense...

For Toluene, it looks like you mix 1.5 gals of Toluene to 17 gals of normal 91 octane fuel, you'd end up with a full tank with an effective octane rating of 92.9. Apparently Toluene can be hazardous if inhaled, which makes it a bit risky. Though I guess they used a Toluene mix as racing fuel back in the 80's and 90's.

As an alternative to Toluene, I found a site that sells Sonoco 104 octane racing fuel in 5 gal containers, delivered for $67. If you mix of 3 gallons of 104 octane fuel with 15.5 gal of normal 91 octane, that should result in a full tank with an effective octane rating of 93.1.

Of course, if you go to a track you can get 109 octane there, and then you'd just need 2 gal of that mixed with 16.5 gal of normal fuel to end up at 93 octane.

Not sure if any of these are really cost effective though. Plus this won't really matter unless one has a tune that calls for 93 octane fuel.

Once my powertrain warranty gets to the point where I have 2 years or so left, I plan to go with a new pully and tune to bump up to the claimed 625 ish bhp that is being reported. At that point it may be worth the effort to get that additional octane rating.