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Leaded Fuel Question

Started by december2015, December 05, 2015, 12:57:57 PM

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I have, what I think, is an interesting issue: according to my Chilton's manual, a '74 MGB should use regular leaded fuel of at least 91 octane.  With that as a backdrop, someone suggested that I could possibly use AVGAS 100LL (blue).  This would seemingly provide the lead without having to get it from an additive plus increase the octane.  I have twin carbs and no catalytic converter.  Not that I can go this route in New York but just curious about this as a fuel option in other states.

Many thanks.
Allen Lescak
Albany, NY


Yes, AVGAS 100LL is a leaded gasoline for aviation use only (and you won't find it at an auto gas pump in any State). If you can get it from a general aviation airfield, it will work much better than just unleaded gas. I have a '73, which is virtually identical to your '74, and after trying to retard the timing a bit using premium fuel with some success (reduced pinging; some with run-on when hot and poorer acceleration performance), I ultimately went the route of a "no-lead" head conversion (stainless steel valves and stellite seats, head planed flat, as well as a copper performance head gasket) and continue to use premium unleaded fuel for the best results.  No run-on or pinging and much better performance since. Well worth the cost.

I am also adding an electric fan this winter to keep the engine temp down, which can also help reduce pinging and potential valve damage.

If you use the car on only a limited basis, have problem with pinging and prefer not to spend the time and money on revising the head, premium fuel with the timing retarded 2 degrees or so generally works.  The auxiliary electric cooling fan can help as well.

I hope that helps you.

Best regards,
Art Isaacs
Art Isaacs
AMGBA Tech Staff

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