By the way, oggers, if you read the paragraph on the page after Figure 8 of NACA-754, it says:
Quote:
The high valve temperatures accompanying operation with fuel-air ratios in the region of 0.065 is one reason why lean-mixture operation is detrimental to valve life. Injection carburetors are frequently adjusted to give a fuel-air ratio of 0.070 for cruising. From the foregoing discussion it is evident that this mixture ratio imposes the most severe temperature on the exhaust valve. The valves would probably give more satisfactory service if operated with a leaner mixture.
[bolding added]
And before you leap at the phrase "reasons why lean-mixture operation is detrimental to valve life", note (with your calibrated eyeball) where the fuel-air ratio of around 0.065 - 0.070 is on the lean curve in the graph: rich of peak EGT.
When the report talks about "lean-mixture", it's not talking about lean of peak mixtures. It's merely talking about a mixture that is lean relative to another mixture that supports combustion. Every mixture that supports combustion is on the lean curve, somewhere. It's just that some are LOP, some are ROP and one is P.
So the report shows that the mixture ratio that imposes the most severe temperature on the exhaust valve is one that results in an EGT that is rich of peak. The report says the valves would probably give more satisfactory service if operated with a leaner mixture than one that results from a fuel air ratio of around 0.065 - 0.070.
...and you think I disagree with that part of the report why exactly?