[wumpus]

Deep in the "living throttleless" thread was a little gem about using exhaust air in the input to reduce throttle losses. Since the present victim is a lawnmower, most of the issues I have are pretty moot.

1. Routing of poison gas under your car. Sure, your emission control should reduce CO production, but I still don't like the idea of shipping it through a bunch of DIY piping. Note that due to basic thermodynamics, you want this as cool as possible. I would expect to pull the exhaust after the muffler, and let it cool on the way back as well.

2. Reducing the fuel input. There is no point doing this on a modern engine unless the ECU is in stoichiometric loopback mode or using a heavily hacked megasquirt. I suppose that a simple relay on the exhaust-to-input control (call it an anti-throttle) that only opens in loopback mode is possible, and presumably won't be in danger of knocking (it might let out a bit of hydrocarbons every time it had to close unexpectedly).

3. Lean burning potential. Since there will be more air in the cylinder, presumably the temperature will go up less than in a normal car (again, assuming a reasonable input temperature). This removes a few problems in going lean (of course, you still have to play with the ECU). On the other hand, I have no idea if this would be more prone to detonation or not. My (rather poor) chemistry knowledge says that gas reactions are based on partial pressure, my gut tells me that detonation vs. combustion isn't a reaction thing, and that the additional CO2 will act as a buffer to prevent knock.