Originally Posted By: kschachn
I say apparent as that was the way I was taught in college, and if you Google the term it is in use. Generally the base octane rating is how the fuel under test compares to straight iso-octane (and comparatively against heptane) with no additives, and then when antiknock additives are added it increases the "octane" rating, which isn't due to the base molecules but instead the additive. I've always seen that listed as the apparent octane rating in literature or descriptions. So although the end result is the same (a printed octane rating on the pump label) it distinguishes between the actual octane rating of the hydrocarbon base and the observed performance of the finished fuel in the test engine.
And yeah, there is no need for lead whatsoever in today's automobile engines and no need for additional lubrication. Even if you did have an old engine that had soft seats there's no indication MMO would provide the same benefit as lead to reduce the welding you mention. My point being that lead wasn't there just running around "lubricating" stuff in the engine. If anything it was largely a detriment and caused other issues which were eliminated with unleaded fuel.
Fair enough-admittedly I'm a chemist and not a chemical engineer, but it's always been my understanding that the only way an octane rating can actually be determined is experimentally(using the standardized 1-cylinder engine). Of course, the "calibration points" are iso-octane at 100 and n-heptane at 0, although the now-defunct Kentucky Centralized Fuel Lab I visited/saw in operation used toluene as one of their standards.
I'm also in agreement that MMO doesn't provide any meaningful benefit for reducing valve erosion/recession in fuels designed to run unleaded fuel. I have seen one lead substitute that contains calcium compounds and I suppose MIGHT work, but the vast majority of the ones you see on the shelf are mostly kerosene and often some toluene/xylene tossed in. Presumably the latter increases the octane rating to counteract THAT aspect. The calcium stuff I've seen is expensive enough(and I'm skeptical about having a metal that reactive in the combustion chamber, even if it does have some of the same affects as lead) that rehabbing the head with hardened seats would seem to me to be preferable. Admittedly my MG is a 4 cylinder and not a V8, but I was quoted about $400 for crack checking, surfacing, lapping the intake valves, fitting hardened exhaust seats, and fitting new exhaust valves. Since my head had a visible crack, I spent $700 on a rehabbed head that was ready to drop on the car...
I do see some value in having heavier than normal compounds in gasoline to lubricate the valve stems. As I mentioned too, I seem to have few stuck carburetor needle valves with MMO in my gasoline.
I say apparent as that was the way I was taught in college, and if you Google the term it is in use. Generally the base octane rating is how the fuel under test compares to straight iso-octane (and comparatively against heptane) with no additives, and then when antiknock additives are added it increases the "octane" rating, which isn't due to the base molecules but instead the additive. I've always seen that listed as the apparent octane rating in literature or descriptions. So although the end result is the same (a printed octane rating on the pump label) it distinguishes between the actual octane rating of the hydrocarbon base and the observed performance of the finished fuel in the test engine.
And yeah, there is no need for lead whatsoever in today's automobile engines and no need for additional lubrication. Even if you did have an old engine that had soft seats there's no indication MMO would provide the same benefit as lead to reduce the welding you mention. My point being that lead wasn't there just running around "lubricating" stuff in the engine. If anything it was largely a detriment and caused other issues which were eliminated with unleaded fuel.
Fair enough-admittedly I'm a chemist and not a chemical engineer, but it's always been my understanding that the only way an octane rating can actually be determined is experimentally(using the standardized 1-cylinder engine). Of course, the "calibration points" are iso-octane at 100 and n-heptane at 0, although the now-defunct Kentucky Centralized Fuel Lab I visited/saw in operation used toluene as one of their standards.
I'm also in agreement that MMO doesn't provide any meaningful benefit for reducing valve erosion/recession in fuels designed to run unleaded fuel. I have seen one lead substitute that contains calcium compounds and I suppose MIGHT work, but the vast majority of the ones you see on the shelf are mostly kerosene and often some toluene/xylene tossed in. Presumably the latter increases the octane rating to counteract THAT aspect. The calcium stuff I've seen is expensive enough(and I'm skeptical about having a metal that reactive in the combustion chamber, even if it does have some of the same affects as lead) that rehabbing the head with hardened seats would seem to me to be preferable. Admittedly my MG is a 4 cylinder and not a V8, but I was quoted about $400 for crack checking, surfacing, lapping the intake valves, fitting hardened exhaust seats, and fitting new exhaust valves. Since my head had a visible crack, I spent $700 on a rehabbed head that was ready to drop on the car...
I do see some value in having heavier than normal compounds in gasoline to lubricate the valve stems. As I mentioned too, I seem to have few stuck carburetor needle valves with MMO in my gasoline.
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