Posted by Sherman in Idaho [72.47.153.163] on Monday, November 09, 2015 at 21:40:42 :
In Reply to: M37CDN, 251s, and Unleaded Gas posted by Greg Coffin [67.176.56.44] on Monday, November 09, 2015 at 21:26:10 :
I'll be curious to hear the better answers to this long-standing question, but I think the realistic answer is we have no choice. Since we can't get leaded gas, we have to run what's available. We're not going to scrap a good motor just because pump gas might wear it out quicker -- better to wait until it does wear out and then scrap it or overhaul it.
But my more optimistic view is that when the flat-head 6s were designed (early '30s?) leaded gas was uncommon, or at least was limited to "high-test", so ordinary engines had to run on anything from "natural gasoline" ("condensate") to the most primitive of refinery products. I believe something like 65 octane was common back then, and 87 octane was aviation gas. That being the case, they couldn't have relied on lead for lubricity or cushioning of the valves. On the other hand, they also expected to overhaul an engine every 40,000 miles.