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Old 11-28-2007, 01:38 PM   #7 (permalink)
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Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 55.97 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 72.89 mpg (US)
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One potential effect of raising cylinder pressure too high is pinging/detonation.

RH77 offers some detailed info about the implications:

The more dramatic term for "ping" is "detonation" -- basically the fuel igniting at the wrong time and not having the piston in the right spot to move (some people call it "spark knock". Constant ping will destroy an engine as Ryland put it: extra, undue forces on internals. Rare ping is normal, but I'm like you -- if the car idles funny or pings, I immediately begin the diagnosis and treatment. A common fix for the troubled pinger, is to do a carbon cleanse, adjust that timing, or go up a grade in octane rating. But if you have it happen occasionally, then that's entirely normal. We're talking over 50,000 miles of serious, constant ping to destroy a well-built engine.

Causes range from poorly tuned timing to a abnormal build-up of carbon or even high intake or coolant temps. Ford Crown Vics/Grand Marqs were notorious for building up so much carbon that the engine would ping itself to death. My Father-in-Law's old G-Mq had so much carbon in the intake manifold that it split, spewing raw fuel all over the engine. No fire was started, but at the time, he did trade it on a new 2005 Civic LX Sedan upon the advice of an unnamed son-in-law (and he loves it). Take a ride in a cab and you'll see what I mean. Law enforcement agencies use seafoam or pure water to clean the carbon out of their Crown-Vic units to get them to last forever, so they ping less commonly.

Moral of the story: unless you experience ping every time you drive the car, then I wouldn't worry about it. Otherwise, perform some of the above maintenance.
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