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Originally Posted by wwb
A couple points....
At normal highway demand (specific RPM and power output), the old pushrod motor actually has a slightly lower BSFC than the overhead cam motor. It also has more torque in the 1500 - 2500 RPM range. Not like it's a big deal, though.... your driving habits will have a MUCH greater influence on fuel mileage than the engine type.
As to the old wives tale about all the benefits of higher octane fuel.... Unless your compression ratio is so high (or your combustion chamber deposits so bad) that you're getting compression ignition, you don't need any higher octane - and backing off the spark timing won't stop the knock - the ECM will realize that it's compression ignition, quit retarding the spark, and light the "check engine" light. In normal operation, the spark will be advanced to the point where the knock detector signals the ECM, and then backed off slightly... this is adjusted constantly - and when incipient knock is determined by spark timing, the fuel grade doesn't matter.
Higher octane fuel does not have any more inherent energy than regular gasoline..... it simply has a higher ignition temperature (and a higher price).
Manifold deposits, combustion chamber deposits, injector fouling, fuel pump wear, etc. are all treated with additives to the fuel, and all grades of a particular brand get the same additives.... and even many different brands use the same stuff.
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Wow!!
Totally respect your opinion but don't agree with it in any way, shape or form.
We live in two very different countries and there's no such thing as universal answers. The lowest octane fuel I can buy here is 91 RON and the highest 100 RON, and we have one of the highest contents of sulphur in our fuels out of the developed world countries. I have tried both of these (and everything in between) in all the cars I've owned and those of the people around me, and the differences in consumption are
very noticeable during steady highway driving (not so much in the city), as is the amount of carbon that accumulates around engine parts.
I've never suggested that high octane fuel has more energy. If that was the case you would feel an engine power increase while driving. All it does is burn slower, and precisely because of that, more completely and efficiently. I don't know what you consider a compression ratio that's "too high" but I know for a fact that all modern cars imported, for example from Europe, suffer from detonation when using our low octane fuel, regardless of miles travelled, so much so that there are specific calibrations that had to be developed by Ford for us to correct this problem. So far, I've never seen an engine light 'on' in one of these cars while pinging, either the ones equipped with EOBD or EOBD II.
Last but not least, it would be a wonderful world if all of those fuel additives worked. The sad fact is that they don't, otherwise I'd never find engines full of crap when you pull them appart, even in those with so very few miles in them that have been looked after and serviced properly.
marc
