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hi guys I have started using a 20/80 meth/99oct mix for my builds upward of 600hp looking at the meth/ethanol content in the fuel seems the 99 Oct has around 6% ethanol giving a total of 26/74 what target lambda would you aim for wot at around the 40psi relative of boost
If you're reading and have always tuned for a given lambda, stick with the same (at least thats what I do). If you're a stupid american (like me) and have tuned for a given AFR and decide to go to a different fuel with a different stoich. then you need to tweak things.
I'm not 100% convinced that the fuel mix you're considering is going to give you sufficient knock resistance for a 40 psi target boost so I'd be mindful of this when you're tuning.
With such a small amount of methanol I don't think I'd be changing my target lambda too much compared to where you'd be on pure pump gas. This really is a case of testing to see how the engine responds. On pure methanol you don't really see the power fall away as you move rich like we do on pump gas and it's common to be targeting lambda in the region of 0.55-0.65. Personally I'd probably start around 0.75 and test to see what the engine responds to. It's likely you'll end up a touch leaner than that - perhaps around 0.78.