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Questions and Answers

Carbon Cleaning

Q. Mr. Ciulla, I'm writing to you because I don't want just anybody's opinion. My question concerns keeping carbon deposits in the cylinders under control. I have an 1989 Firebird Trans Am with a 305 V-8, tuned port fuel injection and automatic transmission.

I drive carefully, I don't race or rev the engine or anything like that. I drive only 4-5000 miles a year and it's mostly in town driving - lots of stop and go and low speeds. I seem to get a lot of carbon build up because of this. My plugs are Delco Rapidfire with about 12,000-15,000 miles on them and are the correct heat range. I've wondered if going to a higher heat range might help because of my low speed driving but most people recommend against it.

I don't know as much as I'd like about cars, I'm a chemist so I understand things from that perspective. My question involves nitromethane. I read that adding this to gasoline will give higher combustion temperatures and I began to wonder if adding a tiny percentage, maybe 0.1%, to my gas might help burn out carbon deposits that may be in the cylinders. Like I said, I don't race and I'm not looking for a HP boost and I don't want to blow my head gaskets. I've tried various engine cleaners with no luck. I've heard that a "motorvac" cleaning helps a lot but I'm looking for something less expensive that I can do myself. If not used in the gas, maybe spraying a solution of it into the throttle body might be quick and effective.

My mechanic has suggested changing the plugs and cables but there doesn't appear to be anything wrong with them. The car takes 2 or 3 seconds of cranking before it starts lately and, while this isn't much, it's unusual for this car.

I've never used nitromethane or nitrous oxide before so I don't know what to expect that's why I'd like your professional opinion.

Thank you,
Jim

A. Since both nitromethane and nitrous oxide are not legal for the street in most states, I would rule them out as an option. Besides nitrous oxide is a gas and requires a special injection setup.

For those who don't know, Nitromethane (chemical formula: CH3NO2) is a clear, water-like liquid that can be used as a high energy propellant for a variety of applications, including: high-performance internal combustion engines, satellite thrusters, large-caliber guns, and liquid explosives. In the racing world it is used primarily by drag racers.

Nitrous oxide or nitrogen oxide is a chemical compound, N2O, a colorless gas with a sweetish taste and odor. Also called "Laughing Gas" it is used by dentists as an anesthetic. It is soluble in water, alcohol, ether, and other solvents. Although it does not burn, it supports combustion since it decomposes into oxygen and nitrogen when heated.

The biggest factor in carbon build up is the quality of fuel you use. If you use a good quality fuel such as Shell, Texaco or BP, your build up problem won't be as bad as using a low quality fuel such as Arco.

Since EFI has been used the biggest problem of carbon build up has been with intake valves. Since the fuel injector is aimed at the back side of the intake valve, this is where the most build up occurs. Good quality fuels will inhibit this build up quite a bit.

As for the carbon build up inside the cylinders, the best way to keep that under control is a good long ride, about 20 miles, on the interstate at about 65 to 70 mph. This will heat up the carbon where it will just burn off and keep the insides of the cylinders nice and clean. You can get what's called "top engine cleaners" that claim to clean out these deposits, but I have found a good long drive is safe and effective in doing the same job.

When I get a car that is driven such as you drive yours, low miles and city driving, this is the first thing I do. It will clear up a variety of driveability problems.

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