N54 High octane E40/50 mix? Potential issues or downsides?

langsbr

Captain
Apr 5, 2017
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07 335i 6MT e90
I know our cars are octane limited from a power perspective, but at what octane are we no longer limited? For instance, E40 has an octane of 98, based on 105 for E85 and 93 with 10% ethanol.

I know some people run full E85 for the convenience and I believe the cooling benefits are met at the E40/50 range, but what of the octane? I would think most evaluations were probably done with race gas, and I don't think that's a direct comparison, especially if using leaded gas.

I am currently fueling limited to E40, but I was hoping to add a few degrees of timing and boost for some extra power and initially thought about adding some Torco or race gas, as 110 leaded is available at the pump here (more 110 leaded pumps than E85!). However, I discovered the metals used in Torco and leaded gas, have the opposite effect on alcohol based fuel, and in turn reduce octane, so that is out.

There are unleaded variants of race gas, MS109 for instance has an octane of 105. Mixing E85 and MS109 to an E40 mix would result in a 105 octane rating, but still have the 40% ethanol for cooling.

Has anyone tried this or have any technical downsides to it?
 

LamboLover

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Apr 6, 2017
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You have identified the octane antagonism issue which has been researched for various combinations - search the academic literature on it.

MON is especially misleading on a modern DI turbo engine. Sometimes the octane index is inversely correlated to sensitivity (RON-MON).
 

langsbr

Captain
Apr 5, 2017
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You have identified the octane antagonism issue which has been researched for various combinations - search the academic literature on it.

MON is especially misleading on a modern DI turbo engine. Sometimes the octane index is inversely correlated to sensitivity (RON-MON).

I guess it comes down to if they are using metals like MMT in the unleaded high octane fuel. If so, then I can see an issue, but I can't find any documentation on what method is used to increase octane in something like MS109, other than it's not TEL.
 

Porgybad

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Nov 30, 2018
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F30 335i N55, E60 535i N54
I guess it comes down to if they are using metals like MMT in the unleaded high octane fuel. If so, then I can see an issue, but I can't find any documentation on what method is used to increase octane in something like MS109, other than it's not TEL.
Call them, there's a vp near my house and the guy is super knowledgeable about the fuels. I have been messing with various mixes but haven't found a proper way to test effectiveness. Their X85 and C85 are also good stuff but can be expensive for anything other than race nights. They also have ms103 at the pump and 96 octane which I've been messing with as well. X85 is prob the best bang for buck i believe it's 109 octane because they use 96 octane as a base instead of 87 which is what's found in pump e85. It's also a little more to it than just octane, the more oxygen in the gas the more powerful it is
 

langsbr

Captain
Apr 5, 2017
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What's funny is the different answers you get from different companies. I called both Torco and Race Gas, they both make race gas concentrate. Both contain MMT, and are pretty equal as far as what they do. Race Gas claims that MMT will help raise octane even in ethanol based fuels, while Torco says it does no good. Most of the research I've seen (granted it's 4 or 5 years old) was regarding TEL and leaded race gas and that it had the effect of reducing octane, or being pro-knock in ethanol. Not much info specifically regarding MMT, but it's still a metal, so I would tend to think it has a similar effect. I guess the only way is to test.