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New cars versus old... Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 20 Apr 2006 05:31:41
In Reply to: Higher Octane Fuels....Bentley's mentions..., Dave B 89 900s Auto, Wed, 19 Apr 2006 14:36:09 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Turbo Saabs reduce boost if they dectect knock; non-turbos retard the timing. Both result in reduced performance. That is true.
However, higher octane fuel does NOT always result in better performance. Octane is a measure of resistance to knock, it has nothing to do with fuel quality. Yes, the refining process to get higher octane is different, and that results in higher cost.
Every engine is different. They're slightly different when the leave the factory, and the differences get bigger with time. Engines build up some carbon on the piston faces and cylinder heads. Some develop hot spots in the cylinders, or run a bit leaner. All of those promote detonation, so those engine are more prone to knock. Engines also lose compression due to wear and leaking from the rings. They can run richer from minor AMM or FPR adjustments, and injector variation. All of those lead to resistance to knock. Of course, the state of tune, including timing, spark plug type and heat, etc, all lead to it, along with outside air temperature, altitude, even humidity.
All of the performance control system only decrease performance from a standard if knock is detected. They don't increase performance until the detect knock. So running a fuel with an octane rating higher than what the engine needs to run without knock at full power is wasted.
What that says is that each engine is different. Some won't knock at full power on 87 octane, and some will require 93 to keep from pinging. So nobody and no book (even as good as Bentley) that can tell you what octane rating your particular engine needs, for your location, weather, and driving style. This is especially true of cars that are now at least 13 years old, if they're on this BB.
By recommending higher octane, manufacturers and Bentley are assuring you that independent of those variables, you'll get all your performance. But you may be paying for octane that you don't need.
I have turbos that get full power on 87 octane. I've had cars that needed 93. Each is different.
Yes, higher octane fuels tend to also contain more cleaners and additives. But that doesn't mean 87 is used toilet water. I toss a bottle of Techron into the tank every 6 months or so - that does a better job of cleaning stuff up than the few pinches of extra additives they throw in to the 93, and is a lot cheaper, even at Techron prices. Gas companies spend money to let you know that their gasoline poduces more power, runs cleaner, and will keep you teeth whiter and your sex life better, just like everybody else selling you stuff.
Try your car on lower octane fuel and see how it performs. If you notice reduced performance, you now know the threshold. If you don't notice reduced performance, you've saved yourself money. You aren't damaging the engine, not unless you hear knock, meaning that the octane is so low that even the performance control can't adjust for it. Not common, but could happen.
Now, in your case, you found that running the lowest octane (usually 87, sometimes lower depending on location) resulted in lower performance. Fine. Maybe 89 or 91 will do it for you. Check it out.
Please note - the octane ratings I've used are for the US market. Different markets/countries may list different octanes - for example, you'll see 95 and 97 in Europe. That actually isn't higher octane - differnt markets use different ways to measure and display octane. The higher Eurpoean numbers correspond roughly to our lower US numbers.
posted by 192.249....
, Thu, 20 Apr 2006 05:31:41 <-- Viewing This Message
, Thu, 20 Apr 2006 15:58:52, Wed, 19 Apr 2006 21:57:19, Wed, 19 Apr 2006 19:55:07
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