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Originally Posted by Tripperfx3
Setec and the guy above me both had great posts! Your both actually right, but I must ask you what car actually runs stoich (14.7)? None, because then you leave no lee way for bad gas and the such. Take the new Evo X for example. People have recorded 9.8:1 AFR's on bone stock X's. Hence why the car gets such crappy gas mileage, but at the same time it keeps the engine safe and detonation free. The only time I've seen a car run 14.7 AFR is actually at idle. This is was on my car and a few other while being tuned using a wideband (lamda) 02 sensor. Once you get on the gas your AFR's should drop. Not to mention there are cars now running ethanol and thats a whole other can of worms that I'm gonna leave closed for now lol.
To the OP they have answered your question, but this maybe a simpler one. Like mentioned the car isn't operating efficiently until it's sensors and catalytic converter and at "operating" temps. Also depending on whether your car is in open/closed loop mode, which depends on driving conditions (long trips compared to short trips) will greatly affect your gas mileage. If you can hook up a vacuum gauge and run it into your cabin (simply tee off your intake manifold) the next time you go on a long trip. Try to keep your speeds at around 65-70 MPH and keep your vacuum at 0. This will be hard due to just having bumps in the road slightly knock your foot around, but I guarantee you will get incredible gas mileage. I personally do this with my Evo and did it with my turbocharged 240sx. In my Evo, which has over 400AWHP, rather large 780cc injectors and a 255lph fuel pump I was able to do a 300+ mile trip and still had 1/8th of a tank. With the 240sx which had smaller 380cc injectors and 250 to the wheels I did the same trip and had over a 1/4 left in the tank.
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You said it, the hardest part about answering a post like this is because there are so many variables. I've never tired to use a vacuum gauge during long trips i will be willing to try that, great idea.
But there is one thing bothering me, isn't the evo turbocharged? The AFR recorded by others, were they during acceleration? This could be a greatest of examples as this applies to the very nature of turbo charging. As the engine is accelerated the charged air that comes in, runs through the intercooler right? Wouldn't the air blown in, be denser than the hot intake chamber?? Not to mention, variable valve timing as the actuators retard timing to increase volumetric efficiency as engine speed increases. Wouldn't it require a higher fuel demand? The fuel trim values are most accurate while coasting. Then again I'm beginning to talk about calibrated values under certain driving conditions. Theoretically the mixture should be 1 lambda (14.7:1). Bad gas would create all sorts of problems as you mentioned. Whats worse its only getting crappier and crappier, oh wait i'm sorry its getting "cleaner" or should i say leaner.
The only bad thing about this is that this could go on and on and on....