Which fuel to use?

[No Quarter]

Soon I'll start the engine for the first time in decades, but with which fuel?

I ask here, having read "both opinions" online. Some say 98 octane and lead added every time. Some say they just use unleaded 95, have done so for years, no problems.

I use unleaded 95 in the three XJs I've had so far. And some say that all alu head engines have strengthened valve seats, so no need to add lead. How similar are 3.8s from 63 to 70s XJ 4.2s? Octanewise, materialwise?

[Gfhug]

You don’t need lead, can you get premium 98 octane e5 from Esso, Shell, etc.? If you can you’ll be fine. Don’t worry about all these claims of having to put exotic fuels in your car. If you can only get e10 95 octane you may need to de-tune the engine to avoid pinking, but you’ll know how to do that. And many run on that fuel with no problems at all.

Geoff

[No Quarter]

I can get 100 octane nearby, but not sure about E5 or E10. Is that important with all new rubber parts/hoses?

[Gfhug]

Besides going to an airfield to buy avgas where else can you buy 100 octane fuel? And why do you want that?
E5 and E10 are all the standard fuels in Europe which you surely buy at all the normal petrol stations for your other cars. And which you’ll have to use in your E Type in the future, unless you only drive to the airfield!
As they have ethanol, I can’t see how adding any lead additive can eliminate any possible deterioration of fuel pipes from the ethanol.

Geoff

[No Quarter]

In my country all gas stations have 95. Most have 92 and 95. Shell and two local chains (near me) also have 100. No airfields needed.

So the question is if 95 is enough for our hemispheric 9:1, or I should use more expensive 100? I want full performance...

[mgcjag]

See post 38 here viewtopic.php?f=4&t=19072&p=154614&hilit=Octane#p154614

[No Quarter]

Perfect

[mtnjag]

For those in the US who feel depressed, don't feel quite so bad. PON=RON+MON/2

RON versus MON conversion table

If a fuel is marked 95 RON it will be around 87 MON which would then average out at 91 PON and could also be marked 91 PUMP at the gas station. The table below is an approximate guide.

RON
(UK and EU) MON(US test) PON(US pump)
90 83 86.5
92 85 88.5
95 87 91
96 88 92
98 90 94
100 91.5 95.75
Having researched the fuels and taken the time to understand the differences it is less of a worry as shown in the table above. I now realise the low number I’d always seen marked on the pumps at gas stations in the States was misleading (to me) and the fuel is roughly the same octane as the ‘regular’ and ‘super’ I am used to in the UK.

**(Columns don't post right-cut and paste. Just apply them in order too the headers.)

[malcolm]

I use 98 or 99 where I can but frequently use 95when touring in Europe. Never really noticed any change in power or fuel consumption.