CLASS RACER FORUM - View Single Post - Fuel Injected motor...miss from 1-3K

Ed Wright · 06-11-2012, 09:46 PM

Eric, it is a pain, but you won't get acurate O2 log data at low RPM & lower throttle angles with open headers. Make up a header extention about 3' long, preferably with like a 45 deg bend in the middle, for logging your idle, driving down the return road or pits, and bringing it up against the brake (no 2 step!) to see where you are. A little time spent there wil make it all a lot easier for you or whoever is trying to tune it for you. Big cams pull clean air in open headers (The exhaust actually pulses in & out) during the overlap cycle. That causes bogus lean indications from your wide band. That compunds the issue if your trying to run it in closed loop! A muffler or long enough extention will keep the clean air from reaching the O2 during those pulses.

Good luck.

06-11-2012, 09:46 PM	#10
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: Fuel Injected motor...miss from 1-3K Eric, it is a pain, but you won't get acurate O2 log data at low RPM & lower throttle angles with open headers. Make up a header extention about 3' long, preferably with like a 45 deg bend in the middle, for logging your idle, driving down the return road or pits, and bringing it up against the brake (no 2 step!) to see where you are. A little time spent there wil make it all a lot easier for you or whoever is trying to tune it for you. Big cams pull clean air in open headers (The exhaust actually pulses in & out) during the overlap cycle. That causes bogus lean indications from your wide band. That compunds the issue if your trying to run it in closed loop! A muffler or long enough extention will keep the clean air from reaching the O2 during those pulses. Good luck. __________________ Ed Wright 4156 SS/JA