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Introduction to Engine Tuning: Octane and fuel

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Octane and fuel


00:00 - There are several factors that can influence whether or not an engine will suffer from knock.
00:05 However, the octane rating of the fuel is one of the most significant.
00:09 The octane rating is essentially a measure of the fuel's ability to resist knock.
00:14 And, in this case, bigger is definitely better.
00:18 The reason that knock occurs in the engine has to do with the heat inside the combustion chamber.
00:24 As the heat increases, at some point it may exceed the autoignition point of the fuel, and hence the unburnt fuel and air spontaneously combusts.
00:34 A fuel with a higher octane rating has a higher autoignition point, and is therefore less susceptible to knock.
00:42 With a performance engine, it's always advisable to use the highest octane fuel you have available.
00:49 This will ensure maximum performance and maximum engine safety.
00:54 With the exception of ethanol-blended fuels, even the best grade of pump fuel may limit the amount of power you can safely make, particularly with turbo-charged or super-charged engines.
01:06 If you're developing an engine specifically for race use, and don't mind the significant cost increase, using a specially blended racing fuel, such as VP's Q16, can offer massive increases in power thanks to a specially blended fuel with a very high octane rating.
01:26 Q16, for example, which is blended specifically for high-boost, turbocharged engines and has a research octane rating of 120-plus, can allow engines to run at boost levels of 40-plus PSI with relative immunity from knock.
01:44 When compared back-to-back with pump fuel, it's not uncommon to see engine power increase by 50 to 100 percent.
01:53 The cost, however, is significant, and running these sort of specially blended race fuels is usually only viable for short-duration races such as drag racing.
02:04 Of course, these days, ethanol-blended fuels, such as E-85, are common at the pump in many parts of the world.
02:12 And often, these fuels can offer performance similar to special race fuels at a fraction of the cost.
02:18 Running on an ethanol-based fuel, however, isn't without its own set of downsides that need to be carefully considered.
02:26 For example, to make the same power on E-85 that you can make on pump fuel, you need to supply around 35 to 40 percent more fuel.
02:37 This means that, often, the size of the fuel injectors and the fuel pump will need to be addressed.
02:43 Ethanol also absorbs moisture from the air, and if the car is allowed to sit for long periods, this can result in corrosion in the fuel system components.
02:53 Regardless what fuel you intend to use, it's important to understand the implications of that fuel on the performance of your engine.