Autoworkz and I recently attended an EFI101.com class in Orlando. The class is a basic introduction into how efi works and how to go about tuning standalone ecus. The tuning method they describe requires a good dyno and does not in any way rely on reaching knock/detonation to find optimal timing or afrs. While much of it was review I did learn a bit about tuning AFRs on the dyno. I just want to see what you guys think.
The basic idea behind their afr tuning method is that your engine will make peak power within a certain window of afrs. That is to say you could make peak power anywhere from an afr of 12.5 to 11.5 at 10psi of boost. Any afr richer or leaner than that window will produce a dramatic loss in power. When I say dramatic loss in power I would consider this to be something near 10hp or more but this will vary depending on the engine and the load. So now we know we need to stay within this window of afrs. The next question is where do we want to be within this window. The efi101 class teaches that you should aim for the richest mixture within the window. The reasoning behind this is that while you might gain a very small amount of power (1hp) by running in the leaner area of the afr window, you will lose the advantage of the thermal management the extra fuel provides when running in the richer part of the window. Basically your sacrificing the relatively insignificant gain of 1hp or so for a richer mixture that will keep your engine safer and help it last longer. Makes sense to me.
Now as far as finding this optimal afr you’re going to need a good load holding dyno. The afr tuning process should basically consist of you monitoring power output as you change the afrs. You should be able to see the power fall off as you go past the rich end of the afr window. Bring the afrs back to just before the power fall off and you should be good to go.
This brings up an interesting note. I’m sure most of you have heard someone respond to a dyno graph saying “ lean it out and you should get more power.†Based on what I’ve just gone over I feel a statement like that is very inaccurate. Unless you are very familiar with the specific engine in question there is no way to say exactly what leaning out the afrs could do. A leaner afr could gain 1hp, gain 10hp, lose 20hp, or melt the engine. I looked at some dyno graphs the efi101 instructor had at the class and some of the afrs were as rich as 10.4:1. That means that a mixture of 10.4:1 was still optimal for that particular engine at that particular load. You can’t just assume 12.5:1 is the best afr for power and aim for that.
Now so far this afr tuning method has been aimed at optimizing for power and safety. Of course there are also times when you want to optimize for fuel economy. Fortunately, the fact that ecus have fuel maps and timing maps allows us to tune for both power or economy in the same tune depending on the area of the map we are tuning. When it comes to tuning the afrs for the low load areas of the fuel map we can aim for the leaner side of the afr window. In fact, the instructor said he sometimes leans out the mixture until the engine starts to misfire and then richens it up a bit. The reason we can do this is because the engine is producing a very small amount of power at these low loads (
The basic idea behind their afr tuning method is that your engine will make peak power within a certain window of afrs. That is to say you could make peak power anywhere from an afr of 12.5 to 11.5 at 10psi of boost. Any afr richer or leaner than that window will produce a dramatic loss in power. When I say dramatic loss in power I would consider this to be something near 10hp or more but this will vary depending on the engine and the load. So now we know we need to stay within this window of afrs. The next question is where do we want to be within this window. The efi101 class teaches that you should aim for the richest mixture within the window. The reasoning behind this is that while you might gain a very small amount of power (1hp) by running in the leaner area of the afr window, you will lose the advantage of the thermal management the extra fuel provides when running in the richer part of the window. Basically your sacrificing the relatively insignificant gain of 1hp or so for a richer mixture that will keep your engine safer and help it last longer. Makes sense to me.
Now as far as finding this optimal afr you’re going to need a good load holding dyno. The afr tuning process should basically consist of you monitoring power output as you change the afrs. You should be able to see the power fall off as you go past the rich end of the afr window. Bring the afrs back to just before the power fall off and you should be good to go.
This brings up an interesting note. I’m sure most of you have heard someone respond to a dyno graph saying “ lean it out and you should get more power.†Based on what I’ve just gone over I feel a statement like that is very inaccurate. Unless you are very familiar with the specific engine in question there is no way to say exactly what leaning out the afrs could do. A leaner afr could gain 1hp, gain 10hp, lose 20hp, or melt the engine. I looked at some dyno graphs the efi101 instructor had at the class and some of the afrs were as rich as 10.4:1. That means that a mixture of 10.4:1 was still optimal for that particular engine at that particular load. You can’t just assume 12.5:1 is the best afr for power and aim for that.
Now so far this afr tuning method has been aimed at optimizing for power and safety. Of course there are also times when you want to optimize for fuel economy. Fortunately, the fact that ecus have fuel maps and timing maps allows us to tune for both power or economy in the same tune depending on the area of the map we are tuning. When it comes to tuning the afrs for the low load areas of the fuel map we can aim for the leaner side of the afr window. In fact, the instructor said he sometimes leans out the mixture until the engine starts to misfire and then richens it up a bit. The reason we can do this is because the engine is producing a very small amount of power at these low loads (
Comment