Quote:
Originally Posted by Skull Crusher
Carbon deposits. You can't tell from your exhaust tips if it's to lean. Carbon is the black residue left over from the burnt fuel. With 10-15% ethanol used in most fuel today, it leaves a black carbon residue which is collected at the exhaust tip or exit. Every automobile today will have this residue.
You need to run a spark plug chop test and actually look at the base of the spark plug insulator with a magnifying glass. If it's really dark brown or black you're running rich. If it's really light tan, light gray or chalky white you're lean. What you're looking for is; a medium to dark tan. You can install a A/F Gauge but it's readings are more relative to the climatic conditions.
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Soot can deposit on the tips and bumper even if the engine is running lean. And yes, running rich will make more soot but its not all about the A/F ratio, combustion efficiency is why its still an issue with lean running engines.
The reason there is soot is because of incomplete combustion. Even if run lean, not all of the gasoline is completely reacted with the oxygen. The partially oxidized gasoline creates carbonacious particles or soot.
This is where the stock catalytic converters do their job of cleaning up the exhaust flow stream. The stock cats "catalyses" the remainder of unreacted gasoline and force it to react with any remaining free oxygen to form water vapor and carbon dioxide. Both of which are much better in terms of cleanliness.
In the case of the 370Z engine, it won't allow the A/F to go to any extreme for very long. The objective of the ECU and stock cats is to burn all the fuel. Between the ECU and the stock cats very little soot is emitted.
But once test pipes, ART pipes or HFC's are used, some soot will make it through. The best that can be done is to tune it on the slightly lean side of optimum and go with it.