Ok so, this is my theoretical question:

On a high-revving, high compression engine, with a huge cam, it is said that some of the fresh intake charge will be lost out of the exhaust valve before it has a chance to burn.

Will this effect A/F readings when tuning?
Will this effect ECU performance when driving?

And....GO!

 

I would purposely tune it to run a bit rich.

 

You will really notice this at idle with engines with very large cams. The air fuel readings will read some impossible value (in practice relative to stock engines) while the car is still idling somewhat steadly. 17:1 or higher is common depending on the cam.

Your theory is correct, although remember the wideband is not the only tool you use, you can tune a car to 90% of its power by using a dyno and doing some math to figure out what the engine should consume at a certain rpm provided all is well mechanically. Along with some judgement on what works and what doesnt based on educated trial and error where math does not fit in. It is not always important to get really bent on reaching exact a/f readings. Most engines will make good power in a large range of a/f ratios.

Just a thought.

 

so my original assumption was that no one really mentions this because it doesnt effect A/F enough to make a dramatic difference in engine performance or safety (running too lean because of false reading)

i guess the only way to tell is if there is a large change in A/F right at the VTEC crossover (assuming one) because the larger lobe would allow more fuel past the exhaust valve during overlap. if there is no shift than it is not being effected.
Am I on the right track?

 

Since the injection event is typically 70 to 90 crank degrees before the intake event, there is always going to be fuel present with the un-burnt oxygen during overlap - which should cancel out a lean indication from the O2 sensor.

Can anyone explain this to me?
Oxygen sensors read/react to unburnt oxygen in the exhaust mixture. So, the more oxygen there is to react with, the leaner it reads. So when you're beyond stoich. on the rich side, and there is no extra oxygen left over in the mixture, how does an O2 sensor know the difference between, lets say 13:1 and 11:1? If there's no extra oxygen left over beyond 14.7:1, what is it reading?

 

I can tell you a little about Bosch wideband o2 sensors. Im sure most of the wideband o2 sensors operate in a similar fashion...
Inside the o2 sensor,there is a "pump cell" that actually pumps a small amout of air inside the sensor housing. This pumped air is matched to the oxygen content of the exhaust to achieve a "specific value". If the exhaust has low oxygen(rich) content,the pump cell has to pump more to achieve this "specific value". The computer then analyzes how much current (milliamps) the pump cell is using to maintain this "specific value".
High oxygen content (lean) and the pump cell doesnt have to pump as much to maintain the specified value..
The computer looks at the pump cell current draw to determine exactly how rich/lean the exhaust really is...

 

And dont forget, the o2 sensor is comparing oxygen content in the exhaust with oxygen in the atmosphere via air reference passage. so even though 14.7:1 is stoich and there is no leftover oxygen present, it still knows where its at compared to free air/atmosphere..

 

If I'm not mistaken, you could still 'read' the plugs for AFR's at idle. They only 'read' with the AFR at time of combustion, so you can check them to see what's going on.