I'm rebuilding a Jeep 4.0l engine for a Cherokee. I have put Singh Grooves in the head as there are significant mileage improvement claims made for them. SOMENDER-SINGH.com - Home The grooves reduce exhaust temperature and allow the engine to run leaner, but the ECM of a modern engine compensates by adding more fuel because of the O2 sensor. Hence, the quest to fool the O2 sensor which lead me here. My concern is how do you prevent too lean a mixture which can burn up the exhaust valves. If you've ridden in a small plane, the pilot will lean the engine fuel mixture at cruise and use an exhaust gas temperature gauge to do the adjusting. It seems it may do well to have two O2 sensors, one normal and the other "spaced out" (sorry I grew up in the 60's, couldn't resist). With the two sensors you could choose a proportion of each and adjust the mixture, maybe with a potenteometer like choosing more trebel or bass on a stereo. All the way one way would be full lean, all the way the other would be full normal. It may be good to have an EGT gauge to monitor what is going on. I'd hate to spend $1,000 on an engine kit and machine shop work and then go out and burn up the valves. This site is great!
I'm also curious about the PULSTAR plugs. They may be best utilized if the engine timing were retarded some. Once again, how do you change the ECM? On the Jeep I may be abe to shift the CPS-crankshaft position sensor-some as it is mounted on the bell housing, an adjustment of 5 degrees may be possible. - Scott, Chewy's dad.