Expert: Dan Liddy - 7/25/2008

Question
Last time I checked my plugs they were kinda powdery brown.  Should I be replacing the plugs again in combination with a mixture leaning oxygen sensor?  SR20DE with ~120k miles...bought from previous owner with ~70k.  Will this O2 sensor improve performance in your opinion?
Just for fun, if this is addressed how much HP would you guess the motor is making?  HKS exhaust, K & N filter, supposedly 17 degree timing, new ignition everything from Nissan (plugs, wires, rotor and cap).  What's the next logical step here for more power w/o exorbitant price?  BTW I'm located in Sarasota too!

Answer
The light brown color indicates the ideal fuel/air mixture, but is not used to determine their age and efficacy.  It may be that a trip to the scanner will tell you if they are in good condition or not.  With 50,000 miles behind them it would be a bit of cheap insurance to change them.  I hear the new irridium plated plugs are good, and in our Jap stuff I prefer NGK over most other brands, though I never discount the quality of Bosch products.

I've heard a lot about the SR20 motors but haven't worked with them.  You didn't mention which O2 sensor you had in mind, but if it causes a leaner mixture , it will improve performance so long at it's not TOO lean.  Check the plugs again after a hard run.  That means run it hard sor several minutes (on a race track !) and shut it off at speed, coast to a stop and remove the plugs without letting the motor idle.  That is when you get your most accurate readings. They should still be a very light brown for a combination of high performance and better fuel economy.  The next step in this department would be an exhaust gas temperature guage .  They start at about $160 and go from there.

Modern Jap engines last forever, or so it seems. However , with 120K on it you might have someone do a leak-down test on it to evaluate the condition of the engine internally.  Most shops aren't equipped to do this unless they do high performance work.  Twin Cam Motorsports here in town will be able to help you .  Steve Smith, the owner, has the fastest Lotus Elan in the Central Florida Region of SCCA and is pleasant to deal with.  His prices are reasonable , but don't expect any bargains.

Finally, the K&N filter arangement and free exhaust systems do help, mostly you can expect an improvement of between 5% and 15% in horsepower output.   Since I don't know what horsepower you started with I'll let you do the math.  These days, most modifications beyond those are expensive and involve engine dis-assembly and some expensive new internal parts. You can also add a turbo-charger but in doing so you'd be very wise to have an overhaul at the same time. If you'd like to know more about those modifications, write again.

Good luck

Dan Liddy
Sarasota