AFR vs power - Kawasaki Z125 Forum
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post #1 of 5 (permalink) Old 10-24-2019, 09:13 PM Thread Starter
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AFR vs power

Stumbled onto a video that shows power vs. mixture which is a little different from other things I've read. Makes me want to build a dyno even more than I've wanted in the past. https://youtu.be/JzbLrn-2jyw
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post #2 of 5 (permalink) Old 10-26-2019, 05:11 PM
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Makes me want to build a dyno even more than I've wanted in the past. https://youtu.be/JzbLrn-2jyw
You too huh? Too bad they're so [email protected]#*ing expensive. Even the used ones are $10 000k plus.

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post #3 of 5 (permalink) Old 10-27-2019, 12:39 AM Thread Starter
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Not really, depends how you build it and to what power levels you need to have. A 20 horsepower pump isn't very expensive, then you need a load cell and cheap tachometer to measure the speed of the dyno. I'm thinking of altering the design to bolt up where the wheel goes to get an engine dyno. Large rollers are hard to find and small rollers would spin too fast. I have a pair of 3.5 inch rollers, but after doing some rough calculations, I'd need some pretty extreme gearing to fit the available pumps.

DIY Dynamometer - part 1

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Last edited by Greg_E; 10-27-2019 at 12:45 AM.
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post #4 of 5 (permalink) Old 10-27-2019, 08:21 PM
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"Lean is mean", not so much. They've also show the same on Motor Trend's "Engine Masters". Typically people would say close to 13.0 AFR. The horsepower difference is usually so small it's not actually worth wasting the engine to predetonation chasing it for most people.

Also (not applicable for our bikes, lol) wideband oxygen sensors are usually installed after a header merge collector, and on a V engine, only on one side. This means we're seeing closer to an "average" of all cylinders AFR ratios. If I'm tuning my engine at 13.0, I probably have some cylinders much much leaner than that.

When I was tuning my heads/cam GTO(LS engines are already know to be leaner at cylinder #7), I shot for more the 12.5-12.7 range. I'm sure it thanks me for it.
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post #5 of 5 (permalink) Old 10-28-2019, 11:36 AM Thread Starter
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I've been told and I'm leaning this way more now, put your measuring device in the Lambda mode. We know that Lambda=1 is stoich (enough air to burn all the fuel), but we also know that AFR varies with the fuel mixture (more alcohol= lower AFR). But Lambda remains at a "constant" point of 1 for stoich. What I've read is that you should decided what percentage of Lambda you want for your mixture, and tune to that point. This keeps you from having to fudge AFR curves that vary with the amount of alcohol.

I've seen a lot of high performance builds (mostly with Haltech) running a wideband per cylinder so that they can monitor and tune each cylinder. Nothing wrecks your day faster than a clogged injector and a single sensor, good combination for a meltdown on your $35000 performance build.

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