Lean vs Rich: How Fuel Mixture Really Affects Power (Dyno Tested)

Today, I want to answer a very simple question . How does air-fuel ratio actually affect power output ? Not what people recommend, not what's generally considered safe , I mean what the engine actually does on the dyno when we change AFR . So, we're going to run a series of controlled tests changing only air-fuel ratio and watch how power moves across the RPM range . Before we start testing, let's get on the same page of our air-fuel ratio . AFR is simply the ratio of air to fuel going into the engine . Lower numbers mean more fuel, or richer . Higher numbers mean less fuel, leaner . For this test, we are only looking at AFR under load on the dyno . Not idle, not cruising, wide-open throttle . We're going to start very, very rich at 11:1 air-fuel ratio . We're going to move up to 12.5, 12, I'm sorry, 11.5, 12, 12.5 . Finally, we're going to go to 12.75 . We're going to end at 13. I . I really wanted to continue into the leaner area a bit more . I really wanted to use 12.25, maybe even 12.5 if I was able to get there without knocking . I learned during this test that GM designed some engine preservation safety features into their engine computer logic . No matter what numbers you provide in your tuning, the system will not go leaner than 13:1 under wide-open throttle . But, that's okay because we still got some excellent data out of it . In this video, we're only changing air-fuel ratio . In an upcoming video, we're going to do the same approach and apply it to ignition timing . One variable at a time, and I will pin that video in the comments once it's live . For now, let's start our AFR testing at the rich end of the scale . Behind me is the result of our 11:1 test . The blue line is horsepower and the red line is torque. Torque is where we're going to be primarily focused in this test . At this point, we don't have anything to compare this to , but it gives us a starting point . You can see where torque begins to rise , where it peaks in the mid range