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No, running an engine at high RPM doesn't do anything to remove carbon.
Carbon build up can come from a few things, running the engine with wrong fuel/air mix(most common), dirty fuel, leaky valve guides/rings allowing oil into the cylinder.
Carburetor engines allowed owner to "run rich", so they ended up with lots of carbon issues, lol.
"and blowing out the engine" with high RPM was usually not engine carbon coming out, it was exhaust system carbon build up coming out.
Water injection removes carbon build up but it must be done right.
Fuel injected engines don't have the owner accessible fuel/air adjustments, so tend to run with the correct mixture, sensors do fail, so they can run rich, but just not as likely.
Mom, grew up with carbureted engines and probably got that "blow out the carbon" from her father, which didn't apply then either, but Daddy knows best, lol.
I would just let "sleeping dogs lie" on this one, getting between a mother and daughter for a few bucks in fuel would not be a wise decision IMO, lol.
Running higher octane fuel doesn't remove carbon either.
Octane rating is the compression point at which the fuel will ignite without a spark.
If your engine has the compression to run 87 octane then that's what you should use, 93 octane won't run "cleaner" or give better performance, thats not what the 87 or 93 numbers are about, they are compression ratings not "power" ratings.
There is the same amount of "energy" in a gallon of 87 octane as a gallon of 93 octane.
If you have a high compression engine 87 octane will ping or knock as it ignites on its own before the spark, this would reduce engine power, it is a mechanical reduction in power not related to "fuel power", the 87 fuel ignites on the up-stroke so takes power away from the crankshaft, instead of on the down-stroke adding power.
Higher Octane fuel needs to have more "complete strings" of fuel, so it doesn't pre-ignite.
The higher the Octane the fewer "incomplete strings", so the more expensive it is to produce.
"incomplete strings" give the same power as "complete strings" by volume, "incomplete strings" just ignite easier, which happens under higher compression.
The Octane number is a common myth/misconception, it is not about power...it is about compression.
The more expensive fuel treatments do clean light carbon build up off pistons and valves.
But a light carbon build up is not really an issue.
I just did the head gasket on a '97 2.2L with 180,000k, wiped the carbon off with a damp rag, so hardly any, no fuel treatments ever used, had the car since new.
Last edited by RonR; 08-23-2012 at 12:15 PM.