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Does a higher octane increase your carís performance?

There are all kinds of octane boosters available for daily drivers and there is plenty of 100+ at the track, but does a higher octane really help any?
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Old 01-16-2005, 05:20 AM
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Only if your car needs it. All depends on your compression ratio. Most cars don't care what gas you use, some high perf ones need 91 octane for full performance, eg Porsche, BMW. Only old pre 1970 cars, the high perf ones or race cars need 100 octane or more.
Old 01-17-2005, 07:41 PM
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Boosting octane is no particular trick. All raising octane does is provide a fuel that needs higher compression ratios in order to ignite. If you are running an engine that has a compression ratio higher than 11.5:1, then you might consider an octane booster should you be unable to attain fuel with the proper octane rating or the engine management computer is not behaving. About the only engines that need a fairly high octane rating these days are light aircraft engines. 101 low lead (LL) gasoline can be found at any airport serving the general aviation community. It is possible to raise the octane rating of a fuel to the point where it will not burn. One thing to consider is that many octane boosters are hard on catalytic converters and are an emissions nightmare.

For automotive engines made in the last 20 years, this is not really necessary. For emission purposes, engine manufacturers determined years ago that lowering the compression ratio was the way to go if the engines were using carburetors and that is due to their imprecise control. In the last few years, computerized engines have gone to higher compression ratios with lean-burn mixtures and provided reduced emissions at the same time.

The good gas treatments are designed to keep the fuel system and combustion chamber clean, period. The principle product used for the increase in octane is toluene. That stuff is frightening. It burns very rapidly and is near death on rubber products.

Personally, I do not like the idea of octane boosters for seal reliability problems, added heat load problems, converter problems and emission problems.
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Old 01-31-2005, 03:17 PM
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I completely disagree with the statement about 11.5:1 compression ratios. Nothing above 10:1 is compatible with pump fuel for many engines of the last 20 years, eg my BMW M635 with a Motronic 2 ignition and fuel system. Some exceptions for the very latest engines newer than 2003 or so and even then they still do not run at optimum perf with fuel less than 94 octane. Air cooled Porsches are even worse. Add almost one full point of compression for fuel requirements, eg 10:1 Porsche is effectively 11:1 water cooled for octane requirements.

As for real engines that run 12:1 and higher compression ratios, tetra ethyl lead added to make 110 octane or higher is what really cooks. Nothing smells better than racing gas, and nothing sounds better than REAL high compression engines, eg 16:1. And nothing RUNS better either.
Old 01-31-2005, 09:09 PM
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I think those kind of rules about compression ratios are bound to be less than completely accurate in very many cases. Lots of different things affect what sort of octane rating a given engine "needs", including the compression ratio, spark timing, shape of the combustion chamber (especially including "hot spots" if any), cam grind, intake and exhaust design, and so on. Even the air/fuel mixture plays a role.

Most of those things are fixed for a given engine, barring an overhaul. Spark timing and mixture, however, are things that can be fiddled with on the fly. Modern engines have knock sensors that signal the engine management system when knocking/pinging/pinking/detonation occurs. The EMS will then retard the timing and/or fatten up the mixture (a little more fuel for the amount of air going in) until it either runs out of adjustment or the knocking stops.

If your car has a knock sensor, and the knock sensor has been retarding the timing or fiddling the mixture, you will obviously be losing some power versus an engine running at its optimum. If changing over to higher-octane fuel is enough to stop the engine from knocking, then you gain back that lost power.

Running an engine that knocks or pings all the time is a good way to destroy it. I've seen a number of interesting "trophies" left over from engines that "knocked a little" (all the time)--holes blown through the tops of pistons, etc.

Race gas is nice stuff. It is only needed if you have built up an engine that specifically requires race gas, or if you have an engine with forced induction that you are cranking up the boost on. Putting it in a regular street car is a waste.

--DD
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Old 02-01-2005, 12:25 PM
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