Re: Unleaded Gas?

Posted by Bob Johnson on February 24, 1998 at 09:37:28

In Reply to: Unleaded Gas?
posted by Harold on February 23, 1998 at 19:02:50

Harold,

The short answer is a Model A does not need leaded gas or a lead additive.

The long answer is as follows.When the Model As were manufactured lead was not a common additive in gas.The reason for this is that the primary reason for adding lead to gas was to raise the octane number.You need a higher octane number in cars that have high compression ratios.Since the Model A has a very low compression ratio, you can even hand crank the car, it does fine on gas with very low octane numbers.In fact My dad said the he used kerosene in a Model A during WW II because gas was rationed, he had yo start the engine with gas first. After WW II the car companies started an engine war to see who could get the most HP from an engine.To do this they started increasing the compression ratios and leaded gas allowed them to do so.By the late 60's there were cars with compression ratios over 11 to 1. Then it was found that lead in gas could cause health problems for people. We also had the oil embargo.This resulted in the end of the HP wars and unleaded gas was introduced.One of the side effects of leaded gas was that the lead helped soften the valve to valve seat contact by coating the valves andseats.This allowed the car manufacturers to use softer metal for the valves and seats.
How does this relate to the Model A?Well originally the Model A came with valves that were made of a hardened steel.The exhaust valves, since they are subject to more abuse, were harder than the intake valves.So a Model A with original valves would have no problem with unleaded gas.However in the 60's thru 70's replacement valves for Model As were manufactured that were not hardened very well and because all gas had lead theyworked OK.So if your engine has these soft valves then you might consider something that will soften the blow on the valves.Most of the engines rebuilt now use hardened valves and/or seats so unleaded gas is OK.

Bob


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