Monthly Archives: February 2011

Gas prices going up, why should you pay even more for higher octane?

Let’s start by understanding what octane means, and what it doesn’t mean. It is not a rating of fuel system cleaning ability. Gasoline has detergents. This renders fuel injector “flushing” as a maintenance item almost always pointless, but that will be another topic. Octane ratings do not define the quality or amount of detergent additives. Most everyone has heard of the practice of occasionally running a tank of premium in a car to “clean it out.” This serves no purpose. Octane ratings do not define the energy load in a gallon of gasoline. There is no automatic correlation between increased octane and increased power. So what does octane mean? It has been taught that the gasoline engine produces power by gasoline/air mixture explosions. This is not strictly correct. The burning should not be a violent explosion, but instead a very rapid flame front should travel across the combustion chamber. But under certain conditions, before the flame front has completed, all of the remaining fuel/air mixture will spontaneously explode. This hammers the piston top and the phenomenon is known as “pinging” due to the noise it makes. Pinging reduces efficiency, and, in excess, is damaging to a gasoline engine. This is more or less how a diesel engine always burns, and why diesel engines are so noisy. It is also why they are built with much more massive and rugged pistons, rods, crankshaft, block etc. than used in gasoline engines.

Whether or not an engine pings depends on:

A: Combustion chamber temperature. Higher temperature means more tendency to ping.

B: Incoming air temperature. Higher temperature means more tendency to ping. Hence pinging is more prevalent in hot weather.

C: Ignition timing. The earlier in the cycle the fuel is ignited, the greater the peak pressure developed and the more tendency to ping.

D: Density of the air/fuel mixture. The greater the throttle application, the more tendency to ping. You might hear your engine rattle and ping going up a hill, but not idling or coasting downhill.

E: Compression ratio. The higher the compression ratio, the greater the mixture density and hence tendency for the engine to ping.

F: And…OCTANE RATING OF THE FUEL. The higher the octane, the more the molecular structure of the fuel is RESISTANT to pinging. That is what octane means and all that it means — the fuel’s resistance to burning in a violently explosive mode.

So, traditional informed wisdom has been that one should use the lowest octane where little or no pinging is heard. Possibly lower in the winter than in the summer, possibly lower for getting groceries than for towing your boat. Modern computerized engine controls make this not so simple. For the sake of maximum efficiency — that is to say maximum fuel mileage and horsepower, minimum emissions — the compression ratio and ignition timing of a modern engine are pushed close to the point of producing ping. The modern engine has a “knock sensor.” This is a microphone on the engine tuned to “hear” pinging. If pinging occurs, it sends a signal to the engine computer that says “Whoa Nellie….back of the ignition timing!” Pinging is controlled, but fuel mileage and power suffer with the less efficient timing setting.

So my advice is consult the owner’s manual. You rarely need more than the recommended minimum octane rating. If the owner’s manual for your car calls for higher than 87 octane, but the weather is cool or you drive gently, try using a fuel with less than the recommended octane. If fuel mileage doesn’t suffer and it doesn’t rattle and ping going up a hill, save yourself some money. Buy the octane rating you need and no more. Gasoline is expensive enough without spending extra to no purpose.

Rollerderby one week from today

We have the Holy Rollers (sponsored by Don’s Automotive) vs. the Rhinestone Cowgirls. These are teams in TXRD, which is the banked track league in Austin. We also have a fine flat track league — Texas Rollergirls. As their sponsor, I wish the Holy Rollers the best, but don’t have high hopes for them at this bout. A lot of their players retired recently. They placed well enough last season that they didn’t get first choice drafting new girls. The word is Kategory 5, captain and easily one of the league’s top 5 jammers, has been seriously cracking the whip training the Rhinestone Cowgirls and they will be very hard to beat this year. Sunday, Feb 20th @ Palmer Auditorium. Parking is easy, show starts at 7:00, out by about 10:00. Be advised many TXRD bouts sell out these days, so you had best buy tickets ahead! Come say hello to me, Tony, Brandon, Torf and whoever at VIP seating. Tony and Brandon from Don’s Automotive are valuable track setup and maintenance workers, as is our family friend Julio. Hard core brutal competition with a healthy dose of Austin weirdness.

Ha!! I thought so — NASA and NHTSA find NO evidence of electronically induced runaway acceleration in any Toyota

See this article. Yes, Toyota had a problem with floor mats that were too thick and a dubious gas pedal in certain cars. But what happened after that was media-induced hysteria with help from some obvious publicity hounds and people looking for a scapegoat for their own driving errors. It became the Audi 5000 phenomenon all over again — but even more out of control due to the power of the internet. Brakes are stronger than engines and a car won’t runaway if you take it out of gear or turn off the engine — end of story.

Our cars and trucks are fixing to lose a little more gas mileage thanks to ethanol

Corn-based ethanol is a huge boondoggle. It is hard to transport, needs lots of petrochemicals to make and is a net environmental loss. Unfortunately, all of Washington is terrified of offending mid-west corn farmers who are accustomed to huge subsidies. There was a recent announcement that ethanol polluting your gasoline is going from 10% up to 15%. A gallon of ethanol contains substantially less energy than a gallon of gasoline. Expect slightly decreased mileage, possible increased hot weather vapor lock problems, more “check engine” lights, and absolutely NO benefit except for some a misguided perception that ethanol in your tank serves a “save the planet” purpose.

Come on, warm up out there! (9:18 AM)

Despite still being in final recovery from a cursed winter cold and sore throat, I am anxiously waiting for warm weather later today to ride the new custom bicycle I just finished. It has a Shimano Alfine 11 speed hub which is difficult to obtain in the US — marketed primarily in Europe and Great Britain. Shifts like a dream, and can be shifted while motionless! Joe Riley did some KICK ASS pin-striping work on it.

Get with it, Click & Clack!

I am not a great fan of these guys because I find it annoying how much they laugh at their own “jokes.” But, apart from that, as much as they are rolling in the $$$, why can’t they hire someone to check their facts? In a recent column they discussed a car with a broken timing belt. On many engines, if a timing belt breaks the pistons and valves crash because they are trying to occupy common space with things out of sync. This bends valves at great expense.

Click & Clack stated that bent valves can only be verified by teardown or by replacing the belt and seeing what happens. By merely removing the valve cover, we at Don’s Automotive have many, many times verified bent valves. It is easy to see if any valves are stuck down. This requires minimal time and NO purchase of parts. If this is what they mean by “taking it apart” they should have discussed this option.

Click & Clack stated that if valves are bent a new engine is required!! That’s news to us here at Don’s Automotive — and many other shops I am sure — who have removed the cylinder head from many a “crashed” engine, sent it to a good machine job to be repaired as needed, and reinstalled it with absolutely NO repercussions down the road.

Click & Clack alluded to a slim chance of extreme good fortune where the belt breaks with the camshaft in a position such that all the valves are half-way open. No such position exists! At any position of the camshaft(s) some valves are closed, some are open and some are in between.

If you enjoy hearing people laugh at their own jokes, listen to Car-Talk. If you want accurate information about matters automotive, look elsewhere.

Journal Launched

Everybody has a “blog.” The sound of that word is unpleasant to me, so I call this a “journal.” Check it out for totally random opinions on automotive and other matters. I seem to be unofficially retired or semi-retired from stock car racing, so there won’t be much about that in here. I have lots of passion for the sport of rollerderby and bicycling, so expect entries related to both of those.