Originally Posted by HDDP
No, That's not quite what I meant, but that's probably because of the way I wrote it... What I meant is that the ECU will do everything in it's power to a maintain stoichiometric state... Which is 14.7:1...
As everbody knows, an internal combustion engine should produce its maximum / optimum HP betwween 12.5:1 to 13.2:1 AFR with a lambda of 0.85... But since the OEM ECU will always try to force this engine to maintain 14.7:1, even if you introduce more air, or more gas into the system, your HP gains will probably be much less than if you just adjusted (tuned) the ECU to optimize the air / fuel to the stock set-up...
Please don't get me wrong guys... this engine WILL benfit from various mods, but it won't develop the HP expected unless you tune it to specific changes... And keep the AFR somewhere in the 13 range...
As far as the previous post stating that the AFR was running at 11:1 under full throttle, I can't discount that fact... (running very rich) I've done many dyno's before and they are usually done full RPM for only a few seconds , which means you MASH the pedal for a few seconds to get a reading at redline... This usually produces a "rich" AFR like 11:1 because you've just stuffed a ton of gas into the cylinders without adding the approriate air... My guess is that if you had maintained that RPM for a minute or so, you would have rapidly seen the AFR go back to the mid 14 range as the ECU adjusted the injectors, timing, etc...
I know I have belabored this point to death, but if you really want to see what happens with this OEM engine when fuel or air is added, you have to monitor the AFR and timing simultaneously... You'll be surprised to see how the ECU adjust things...
At high load and 14.7, you will hole a piston, lift a ring land or pop a head gasket! Most ECUs stop takeing input from the O2 sensors at around 75% throttle and stop trying to acheive 14.7 way before that. At WOT on a N/A engine , best (and safe) power is acheived at around 13.5-13.7. On a forced induction engine it is around 12.5-12.7. The reason these things run so darn rich is becuase rich is safe.
As far as showing a rich condition on the dyno because "You just stuffed a ton of gas in the cylinders" is kinda true. The first 1-2 hundred RPM of the pull will show a slightly over-rich condition from the ECU's " accelerator pump" just trying to get the engine going. After that, it is just the fuel map.
I'm not a Bosch engineer, but I am a race engine builder by trade. After 14 years it is the only career I've everknown, so I know it pretty well (but learn new things everyday). An engine is an engine, no matter what manufacturer is on the valve covers. Engine managment systems (ecu) will need to keep the fueling in certain parameters or bad thing will happen.
-Jeremy