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Forum » General Tuning Discussion » e85 afrs

e85 afrs

General Tuning Discussion

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Page: 1

iam looking for some help for tuning e 85 n/a and forced
i have been told a lot of different things.
i tuned a h22a4 on e85 max power with afr 12.5 petrol afr or .85lamda
i also did a rb25det on 16 psi and it made max power with .85lamda as well
i have a mate that has been tuning fg falcon f6 with 20psi with the same .85lamda
but people are saying that it is to lean
any help thanks

The first point I need to make is that it is very easy to get confused when discussing AFR on E85. E85 has a stoichiometric AFR of 9.8:1 vs 14.7:1 on petrol. The wideband unit natively measures in units of lambda and then converts the reading to AFR units based on the setting for stoichiometric AFR. Most tuners don't bother switching the stoichiometric setting when they change form pump gas to E85 so 0.85 lambda will read 12.5:1 on pump gas or E85. In this case the real AFR on E85 is 8.33:1 (9.8 x 0.85). This is why I always recommend using units of lambda as there is no possibility of confusion. Anyway now to your actual question.

0.85 lambda is probably on the lean side of where I would tune a turbo engine on E85, although this is dependent on engine load (boost) to a degree. I would be more likely to aim for around 0.82 myself under high load. Having said that, you are probably not going to have trouble at this sort of lambda value at the boost levels you are using on E85. One of the advantages of E85 is that it takes a lot of heat out of the combustion charge and this, along with its higher octane rating helps avoid detonation. On pump gas we generally run a little richer to help avoid the chance of knock as the richer mixture runs cooler - This isn't strictly necessary on E85.

I always like to maintain a little safety margin regardless of the fuel, and you are unlikely to lose any power at 0.82 lambda.