'65 4.2 vs unleaded?

[jagwit]

Would a '65 4.2 be unleaded compatible? My guess is NO?

[Heuer]

All XK engines had alloy heads with hardened valve seats so compatible with unleaded fuel. Try to use the highest octane you can find for best performance. Shell V Power or BP Ultimate.

[jagwit]

All XK engines had alloy heads with hardened valve seats so compatible with unleaded fuel. Try to use the highest octane you can find for best performance. Shell V Power or BP Ultimate.

That's good news!! However, surely the octane to be used depends on the compression ratio of the engine? How would I find out what the CR is on this '65 4.2?

[Heuer]

Cylinder head is stamped with engine number with a suffix determining whether it is 8:1 (-8) or 9:1 (-9). In the day the 9:1 was expecting 5 Star petrol (100 octane) whilst the 8:1 was expecting 4 Star (97 octane). Given most super-unleaded fuels are 97 octane (and ethanol free or less than 5% ethanol) that is the one to use almost exclusively. You can use lower octane but expect problems from ethanol and lowered performance, and increased fuel consumption.

[Vonkie]

And tell him to use Castrol Valvemaster additive.

[jagwit]

All XK engines had alloy heads with hardened valve seats so compatible with unleaded fuel.

Given David's statement, why do your recommend that Frank?

[Vonkie]

Coz it still helps for valves designed for leaded fuel, especially where the best we can get is 95 Octane.

[Heuer]

The additive won't make any difference to the valves ability to run with unleaded but it will increase the octane rating of the fuel which could be a bonus.

[jagwit]

but it will increase the octane rating of the fuel

By how much will it increase the octane rating David? Is the increase really meaningful from say, 95 to 98 or is it more academic from 95 to 95.2?

[Heuer]

Depends on what it is composed of but typically the improvement can be 0.2 RON ranging up to 3 RON: http://www.fuelexpert.co.za/Octane-Booster-Shootout.php

Only time we need it in Europe is when driving into Italy. Once you are off the Autostrada's the fuel is poor quality and don't be conned by the 'Super' label on the pump.