Originally posted by rabbidrabbit
Also note that putting a higher octane fuel in your car will do nothing for performance or reliability unless it requires it. Way to many folks put high test in a low compression engine thinking it will do some good.
Actually, most modern cars will benefit in terms of power and mileage from using the higher octane fuels, especially when ambient temperatures are relatively high.
The engine management systems we have now use what manufacturers refer to as "adaptive strategy" to optimize performance in real time. In particular, much of the time ignition timing can be stretched out a tad farther without causing detonation when using higher octane fuel, and this allows the management system to take advantage of that to achieve better efficiency.
Car manufacturers aren't going to publicize that because in addition to certifications for emissions and fuel mileage, they also advertise cost per mile figures. But if you're in the loop, factory service representatives will all tell you that their cars run better on premium fuel, and I observed that to be true based on the preponderance of anecdotal information I saw during my career in vehicle repair. 1 to 2 miles per gallon better during highway cruise on 92 octane compared to 87 octane is pretty common.
Aside from that, the other things being said here regarding additives are correct. I've seen many studies that documented enhanced engine internal cleanliness as a result of additves.
This both increases engine life for the obvious reason, and also ensures optimal performance. Calibrations in the management systems are dependent upon fixed sizes in combustion chambers (which are thrown out of whack by deposit buildup) fixed volume delivery and spray pattern from injection nozzles (which are thrown out of whack by deposit buildup) and consistent control of compression and blow-by (which are thrown out of whack by deposit buildup). Power, mileage, and emissions are all affected by all this significantly.
Deposit buildup on the backs of the intake valves in particular is a huge factor. Fuel additives that minimize this buildup prevent an odd phenomenon - the buildups are porous and actually soak up some of the fuel being delivered from the injection nozzles. This creates artificially lean mixtures in comparison to what the management system expects from the table-based fuel delivery, causing the system to have to make "off-center" compensations and almost always resulting in inconsistent performance (such as throttle lag and reduced power/mileage).
Deposit buildup in injector nozzles is also a frequent cause of hard starting, both because of the obvious (wrong volume delivery and spray pattern) and because deposits can cause nozzle leakage - the system should maintain a minimum "rest pressure" so fuel delivery begins instantly when the engine is cranked, but leakage reduces that to zero which means there's a lag as the fuel pump pressurizes the delivery circuit.
There are really significant differences in the additive packages of the various brands. I can't say which fuel is best now, but while I was in the business and privy to current information, Chevron and Shell were always really good. I particularly like the Chevron Techron over-the-counter additives. Also, major brands tend to have higher standards regarding storage facilities and filtration systems, resulting in better physical cleanliness of their fuel.
Bottom line, you get what you pay for, and smart shoppers do better (as is the case with many things
)
culero (ASE certified Master Technician with 25+ years experience, hung up the wrenches in 2001)
