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saw an interview of Lucas english about switching to methanol after 50psi and he mentioned something about octane.
at those boost levels(which many of us likely won’t run), is there such thing as “knock” when running E98 whilst trying to achieve MBT, hence the move to methanol to overcome that?
Hi Danny, At those power levels they switch to Methanol to drastically reduce the charge air temps, some race teams will actually remove their intercooler for weight savings from how much cooler the charge air temps get however some decide to keep it as this aids it even further.
I personally tune the high HP cars we build here at JRP Performance on E90 114 octane from Ignite Racing Fuels. Even though I have had no knock issues running high grade pump E, the reason we do this is the added octane and the fact that it is consistent from one batch to the next unlike your pump E85 fuel, which is usually never 85% anyway.
Most cars can not only achieve MBT on pump E, but the tuner can easily go past MBT if they are not tuning for it and are just throwing numbers in the table, let alone the higher grades and blends of ethanol.
So really the main reason to use Methanol is the cooling properties, also important to note, M1,M5 or really any blend of methanol has a stoich thats very low, such as 6:1-6.5:1, so these cars usually have to run a mechanical fuel pump which makes it that much less street-able, not to mention the cost of the fuel you will be going through.
My Evo 8 made about 980 WHP on my in house MD150 Dynamometer at 50 psi on a 72mm turbo, using E90 fuel, and obviously any knock activity at that power level will be detrimental, however, we never ran into any knocking issues.
Hope this helps!
At very high boost levels E85/E98 can be problematic and you can quite possibly still end up with knock occurring which at high specific power levels can very quickly destroy your engine. Methanol is a much better fuel for high boost application due to the high octane rating coupled with a very high latent heat of evaporation meaning it can absorb large amounts of heat from the combustion chamber as it goes through a phase change from liquid to vapour. The specific boost pressure where E85/E98 reaches a limit becomes a little hard to specify as it will depend on the rest of the engine system and the turbo - Predominantly it's about the heat being produced inside the combustion chamber. Lucas may have chosen 50 psi as a line in the sand but that doesn't necessarily mean that's a golden rule you can apply to every application as witnessed by Roni above.