Thread: Car question
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Old 11-14-2011, 11:44 PM   #12
BigV
Goon Squad Leader
 
Join Date: Nov 2004
Location: Seattle
Posts: 27,063
Quote:
Originally Posted by ZenGum View Post
I love it when you can fix a machine by thumping it. Very primal. RAWR! Og mad! Og Smash! [thwack ... vroom!!] Bwahahaha!
the technical term is "percussive maintenance". It is very satisfying no matter how effective it is.

Quote:
Originally Posted by ZenGum View Post
Oh, and as well as the above ... you are using the recommended grade of gas, aren't you?
gas grade is a measure of the octane in the fuel. Octane's role is to change the point at which the fuel / air mixture spontaneously combusts due to the heat from compression. You experience this as "knocking". It is most common when the engine is under a heavy load such as hard acceleration or towing or driving hard uphill. The mixture detonates before the piston reaches top dead center and/or the spark ignites an already lit combustion chamber and the result is a hard knocking sound. I've never heard of octane having much if anything to do with idle loads.
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