Exhaust has been covered many times on Roadfly I know, people seem to think / know that most of the systems loose power or don't add any. Same with K&N filters. I had the Super Sprint on my last 850 and liked it. I've heard that it is the only brand that actually adds power.
What I'm wondering is, if the reason that the other brands and even headers, race cats, straight pipes etc don't add power, is simply because they lean down the engine too much. I havn't seen anything that says that anyone of the people who have dynoed their cars have used an exhaust gass analyzer while doing the dyno pulls.
While it's true that durring closed loop operation (part throttle) the O2 sensor dictates and corrects mixture, at full throttle, (presuming 850's run as do other cars) the system goes into open loop, using preset mixture maps. Richening the mixture should get back the lost HP and realize the hoped for HP gain no? Our fuel pressure regulators are vacuum refrenced it seems. The aftermarket makes adjustable vacuum referenced fuel pressure regulators, any thoughts on this? Just remove the exhaust behind the cats and play with mixture while on the dyno and we could know just how much room for improvement there is in the exhaust.
A simple test before buying and installing regulators would be to run the car stock with an exhaust gas analyzer and compare the readings to those of a follow up run with no air filters. Does the car get leaner? Then unbolt the stock cat back exhaust, and do a third run, does the car get leaner? How far away from ideal? 12.8 to 1 is ideal for power is it not? Car probably set to run leaner than that for emissions though, and that may be why any increase in airflow causes HP loss.
