Hello!

Here in VA Ive tested the so-called non ethanol gas in many stations.
Liberty lies.
Pure Gas is perfect.
But Pure is only 87 octane.

Does a USA Xj12 with carbs really need 91 or better?
It has low compression pistons for that era.

Thanks!
John

 

the engine will let you know. Try 87, and then try 91, see how it runs with both fuels.

My 1965 S type runs fine with 87 octane. so does my 1984 XJ-6. But those are not 12's.

 

Jose is right, the engine will talk to you in the form of "pinging".

If you're not getting any pinging the higher octane rating won't do anything for you

Cheers
DD

 

Non ethanol and high octane are totally different things. Pretty much anything running higher compression is going to need higher octane, so yes.

A regular car used fairly frequently won't care whether it has ethanol in it or not. There isn't much reason for concern of 10% causing water build up in the system. Additionally, you would be much better offer buying top tier gas with good detergents in it like from a BP or Shell station than some off-name place that uses non-ethanol. Don't forget ethanol improves octane (E85 is like 108 octane).

The octane requirements are even more important for older cars without knock sensors and the ability to adjust timing. The easiest thing to do is just listen to what the engineers put in the manual, but you can almost certainly assume an engine running 11.5:1 is going to pre-detonate at some point on lower octane (excluding newer VVT systems).

 

But don't forget that the old USA-spec carbureted V12s were low compression engines, something like 7.8:1 compression ratio; maybe some at 9.0:1 depending on year

Cheers
DD

 

[QUOTE=sidescrollin;1873184oDon't forget ethanol improves octane (E85 is like 108 octane).

[/QUOTE]

E85 as sold in North America is about 95AKI octane, not that ethanol has any relevance to the discussion.

 

I use BP or Shell gas only too, though I have had good mileage results with Speedway gasoline.

 

I mentioned ethanol because the OP talks about buying non-ethanol

 

My two cars do just fie on Shell's version. Ethanol included. Choice based on price and convenience.


No reason to dig any deeper....


Carl

 

Many would disagree, buying from top-tier can offer long term benefits of reduced carbon buildup. Not that much deeper, but maybe inconvenient to some that like to buy the cheapest gas and save $0.02/gal rather than finding a nearby shell.

Determining whether you can game the system by getting away with running octane other than spec definitely isn't worth digging deeper. Just put what the engineers say to put in it, they did the digging for us already.

 

Don't forget that US Octane ratings (PON, Pump Octane Number) and European (RON, Research Octane Number) are totally different.
So if the manual states (as mine does) a minimum octane number of 91, most probably it means 91 RON.

That translates to US as follows: RON*(21/22)=PON, ergo: 91*(21/22) = 86.86 PON

That been said, I only use Non-ethanol Shell V-Power Racing, which in Europe is rated at 100RON octane. In the US that would translate to 95.45 PON octane.
I have found out, that my Km/ltr rate goes up accordingly. I get at least 80 Km more with V-Power Racing 100 compared to the lower grade, E5 and E10 fuels.

More on RON/PON/MON can be found here:
Octane rating conversions - PencilGeek's BMW Blog

 

First Ethanol is your friend!! It has 105 octane. And really does a great job of cleaning the carbon deposits that regular gasoline leaves.
The V12 is batch fired. That is a batch of injectors are opened at one time. They let the cam and valves sort out when it goes into the cylinder. ( commonly done on all early EFI’ systems).
There are two common alcohols that are used as motor fuels. Ethanol is the best. Methanol is terrible. It’s what does all the bad things you’ve ever heard of. Ethanol doesn’t do anything bad.
Ethanol is what you drink in BEER, WINE, SCOTCH , BOURBON ETC.
Methanol if you drink it, first you go blind, then you Die!!
INDY 500 cars run 100% ethanol, as does NASCAR ( 15%) It’s really good for our V12’s because it helps dissolve the carbon deposits on the back side of intake valves.
it also helps keep the spark plugs from fouling out. Plus. It increases power output slightly. As well as cause the engine to run slightly cooler. ( the evaporative properties of alcohol).
We racers use E85 ( 85% ethanol) and 15% Gasoline. Our cars are especially modified to use that much alcohol do you can’t put it in your street car.
OK it’s not perfect. Just like gasoline there are some flaws. In gasoline some water is inevitable, in the 40’s it was common to see a glass bowl on the firewall to display how much water was in that particular batch of gasoline. By the early 1950’s research found a trace of water helped.
However water sitting in the bottom will rust the gas tank.
Second, fuel mileage is fractionally worse. Typically less than 1/2 mpg. When I use E85 (85% ethanol) ii lose 2 mpg. In my flex fuel pickup
I really wish the anti Ethanol people would have taken a science class.

 

These are typically not daily drivers & one benefit of higher grade fuels is usually NO ETHANOL, which benefits farmers not engines. Pay the difference for the few thousand miles you drive each year.

 

You really should do a little research before making that statement.
Let me begin by saying yes farmers benefit, both in profit from selling the corn and the feedstock from the corn once ethanol is extracted.
But Ethanol is great for engines.
It runs cooler than gasoline, carries more free oxygen molecules than gasoline so allows more fuel to burn ( thus increasing power) Finally it helps remove the carbon deposits on the back side of brake valves that is the result of Jaguars batch firing of fuel injectors.
That’s what it does for cars driven on the street.

Us Racers love it!!! It’s like Uncle Sam gave us a cheap racing fuel! I can buy E85. ( 85% ethanol ) for $2.39 a gallon. While race gas starts at $7-8.00 a gallon and stuff as good as E85 is over $15.00 a gallon ( last year).

My Pick-up. ( an F150, V8, 4x4 Flex fuel ⛽️ ) normally gets 22mpg to and from work. But I lose 2 mpg when I use E85. ( if I can keep my foot out of it). Something very hard to do because E85 allows me to smoke the tires. ( Yeh 75 years old and I’m still a kid at heart. ). I lose 2 mpg. But save 90 cents a gallon from regular times the 25 gallon tank so I save over $20 a tank full

 

Ah yes, follow the science.

 

I just rewatched that.
Too bad it was a meaningless test. 20 Hours is about 1200 miles!! Not even break in time!
Manufacturing tolerances would account for much of the variations. Plus the test doesn’t support your position at all!!!
I do agree that methanol is really bad for engines while ethanol isn’t . Methanol is also deadly poison. .
While ethanol is what you drink in BEER, Wine, Scotch, BOURBON, etc. it doesn’t hurt your engine. Cars(Trucks) with Flex fuel option have exactly the same warranty as those without it. Next time you have a BEER, are you going to make it non alcoholic?
The Engineers at GM Ford And Dodge disagree with you. My Flex fuel F150 has over 100,000 miles with absolutely no issues.
The times the pure gasoline was worse and ethanol was better and visa Versa is simply variations in manufacturing tolerance.
A more accurate number would be after 50,000 or 100,000 miles with proper oil changes.

 

Wasn't trying to support my position. I was trying to learn. You are basically right, it is not the Ethanol itself that is bad. My experience has shown that the water, which is misable in Alcohol that can be an issue in older fuel systems not designed for it. I have owned & worked on about 60 different makes from the 60's . My system works for me & will stick with it in my 77 S2 XJ6C.

 

Fair enough. I hope I wasn’t too offensive?
With regard water and gasoline? It’s always been present. Long, long, long, before Ethanol was used.
Gas tanks need vents to allow fuel to be removed. That same vent is always open to the air. In high humidity days water in the form of moisture enters the fuel tank. Either the gas stations tanks or your car’s tanks
Back in the 1950’s-50’s it was common to see a glass bowl on the firewall so the owner could see how much water was in the gas.
Then they discovered that a little bit of water helps clean carbon deposits. And causes the engine to run smoother. Then the glass bowls disappeared.
Yes 10% of ethanol can absorb a lot of water. More than gasoline carries with it and is normally drawn into the tank.
I have a series 1 JAGUAR XJ 12 from 1972* It went off the road into storage by the early 1980’s. Before E10 was common. One tank is so badly rusted that when I tried to remove the drain in it to get the 40 year old gas out the whole bottom of the fuel tank tore off. Yet my other XJ6 which has been of the road since 1996. Has perfect tanks.
* I cheated it’s an XJ 6 with a transplant V12

I’m a racer. ( it’s my passion. ). Since 1962 I’ve done everything I can to enjoy the thrill of racing.
The reason I love Jaguars is they provided me with many decades of affordable fun. Race gas is insanely expensive. The good stuff is $15 a gallon. So $2.39/9 a gallon for the extra power?
I love it.

 

One point if I may, that 4.2 liter 6 cylinder has 9-1 compression ratio. Depending on your timing you might easily get by with mostly 87 octane topped off with a few gallons of 91 octane. So instead of 24 gallons of 10% ethanol. You’d have 22 gallons of ethanol free gasoline and 2 gallons of 10% ethanol or about 2% ethanol. Yes they mix together automatically. Your octane would then be almost 90 octane. More than your engine would need.
Don’t forget America uses a different way to measure octane. In England the only use research method. ( RON
Here in America we use research method ( RON ) plus Motor method ( MON) divided by 2. So our numbers are lower while our fuel is as good or better.

Around here we have 91 octane - non oxygenated fuel ( ethanol free) Typically used for boats. But is legal in older Vintage cars. Do you have any Marina’s around?

 

We're lucky here in Iowa, 91 Ethanol free at pretty much every gas station. It's the only thing Iowa has going for it. LOL.

Jeff H