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View Full Version : Deep Explanation of Engine Knock and how Turbos work


TurboEclipseGSX
12-06-2002, 10:02 PM
here you go guys, for all you peeps who dont fully understand what causes knock-

Knocking happens because as you compress air, the temperature of the air increases. The temperature may increase enough to ignite the fuel before the spark plug fires. Cars with turbochargers often need to run on higher octane fuel to avoid knock. If the boost pressure is really high, the compression ratio of the engine may have to be reduced to avoid knocking.

basically when gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening.

Explanation of turbos-

Turbochargers are a type of forced induction system. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder, and more air means that more fuel can be added. Therefore, you get more power from each explosion in each cylinder. A turbocharged engine produces more power overall than the same engine without the charging. This can significantly improve the power-to-weight ratio for the engine.

In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) -- that's about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high.

thanks to the www.howstuffworks.com website
for more info visit www.howstuffworks.com ;)

TurboEclipseGSX
12-06-2002, 11:07 PM
opps sorry mods, i meant to put this in the newbie forum, my bad

peace

Blackboost
12-07-2002, 02:38 AM
Originally posted by TurboEclipseGSX
opps sorry mods, i meant to put this in the newbie forum, my bad

peace

No problem...;)
Moved to Newbies Forum...

TurboEclipseGSX
12-07-2002, 02:43 AM
thanks! :D

spinAll4
12-07-2002, 08:36 PM
150,000? that is a little extreme at least for turbos on these cars. 100,000 at WOT is more realistic.

autoxr37
12-07-2002, 11:48 PM
Therefore, you get more power from each explosion in each cylinder.

Not to get picky (just don't wanna confuse newbies) but technically it's explosions that you don't want in your cylinders. You want a spark to cause the fuel/air mixture to burn in the cylinder, but not explode. When knock happens, the mixture combusts and burns faster than the speed of sounds, which really is an "explosion". This, as turboeclipseGSX said is a very bad thing, and a fine reason to not even think about going with a low octane fuel to save a few pennies.

While were on the subject, octane is also directly related to knock. The octane of a fuel is directly related to the temperature at which fuel combusts/ignites. The higher the octane, the higher the combustion temperature. Therefore, if your running too low of an octane, when your engine compresses the air/fuel mixture in the cylinder it will combust due to the compression of the air causing increased temps, and not when the spark happens.

Hope I didn't step on any toes, just tryin' to help out. After all, i'm a newbie myself.

TurboEclipseGSX
12-08-2002, 02:31 AM
its all good, i was just giving a basic explanation that could be understanded by newbs ;)

peace