My car is approaching 67,000 miles, and the exhaust (Spoon) has been on for about 47,000 miles. A group of friends who had followed my car recently said that there's a lot of black smoke coming out of the exhaust during WOT, and actually lit up a few times when I downshifted (car has factory cat) but only in VTEC/high RPM range. It still gets good highway mileage, about 24-25MPG, still pulls pretty hard (walked a RX-8 2 days ago), oil changed and serviced by Honda regularly, so... is there anything wrong? running rich? or is it time for a new exhaust?

Thanks for your input.

 

Shooting flames? I wouldn't mind that accessory!
Usually flames would point to rich mixture. As a rule of thumb, if the smoke is black, it is fuel. If the smoke is white/gray it is oil.

 

What other mods?

 

Bluish/grey smoke = burning oil ................... NOT good.
White/grey smoke = engine coolant .............. NOT good.
Black smoke at WOT = blowing out the carbon build up in the exhaust system .............. normal for most S2000s.
S2000s run rich as a normal state of tune. This tends to carbon up the exhaust system. Look inside your exhaust tips. What do you see? .................... A lot of black soot. Guess what gets blown out when the flow through the exhaust system get high and hot?
Your engine "might" be running a bit richer than most since your highway mileage is on the lower end of normal. The flames isn't that common and might indicate the cat is going.

 

When is the last time you changed the O2 sensor?

 

I only get up to 21 mpg

 

Hehe! I've seen ya drive.

 

I get 24-25 when I keep out of the vtec.
So, replacement of the exhaust at some point is common for the stook - because of the richness?

CB

 

I don't think so. To date, I have heard of no S2000s that has "had" to replace their exhaust due to the "richness" of the engine. Even some with over 100K miles still have the OEM exhaust in place.
Carbon builds up, carbon gets blown out. It's not a problem in terms of clogging up the exhaust during the as yet normal lifespan of this car. The occasional cat has disintegrated but those had nothing to do with the engine being "rich".

 

The only other time I've heard of exhaust gasses so rich they produced flames was on a local owner's car equiped with a poorly tuned Vortech supercharger. Once heat soak set in, black "smoke" would belch out the exhausts during every redline shift (not to mention that my stock car was able to keep up in the straights.) Anyway, the bumper eventually caught on fire because of the unburnt fuel being deposited on it. No actual flames were seen during the shifts, however.