Turbo FE?

[DRW]

Oh hello, I didn't see this thread earlier. Nice to see another turbo 4 banger on the forums.

Ica13 wrote: "10 lbs of boost does not mean double the air displacement. In fact, the throttle pretty much guarantees you will never fill the cylinders,"

Boost is read from the intake manifold, after the throttle plate, not before the throttle.

Since all cars are different, I can only speak for my car here. When I accellerate I like to use enough throttle to keep in vacuum, about 5in/hg, while shifting around 1500 to 1800rpm. My car still accellerates at a decent rate this way because I've lightened it by about 100 pounds and installed a light flywheel. Here's part of the reason why shifting early and using more throttle improves FE http://www.gassavers.org/showthread.php?t=3140&page=2 scroll down to post #23 and begin reading there. It's interesting, if I do say so myself.

I'm lucky enough to have nearly a full code disassembly from my cars ECU. In it I've found the threshold between open and closed loop based on throttle position (around 35% to 55% depending on rpm) so I can use that info to stay in closed loop and avoid the extra rich fuel tables that are used in open loop. The fuel map shows a 12.4:1 A/F ratio where it just goes into open loop, and it gets richer as the throttle is opened more.

On my car the turbo reaches full boost (20psi) at 3500rpm. At that point the A/F ratio is 10.2:1 It gets richer as the rpms go up, peaking at 9.2:1 at 4500rpm. The A/F ratio is this rich not for power, but to help cool the compressed intake charge which reduces knock. It's sort of like having water injection, or methanol injection, except it's gas. Which means the extra fuel is not used to propel the car, it's used for knock suppresion. It's just one of the strategies used to make max power on a small displacement engine.