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AFR: How rich is too rich?

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Old Aug 4, 2025 | 08:11 PM
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AFR: How rich is too rich?

Question for you Evo guru's regarding AFR, how rich is too rich for stock engne/stock turbo, evo 9 w/ minimal mods? What AFR do you run?


Last edited by JDMFox; Sep 24, 2025 at 09:34 PM.
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Old Aug 5, 2025 | 06:24 AM
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what fuel do you run and are you tuned?

are the quoted ranges at cruise, transient, or full throttle?
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Old Aug 5, 2025 | 07:16 AM
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Couple old but good links to research .

https://www.evolutionm.net/forums/ec...-tune-evo.html

A reputable tuner is always recommeneded. Florida has AG autosports, Slowpoke tuning and Mtuned. You get what you pay for .

Cruise AFR should be around 14-15 AFR if it has small cams.
Getting into boost should be 13.-12.5 until 15psi quickly tapering to 11.2-11.5. I wouldn't suggest 11.8-12.0+ on pump gas or ethanol. Fuel cools the cylinder. Anything in the 10's is a little too rich .
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