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Making Your Own Ethanol Blend

by Grassroots Motorsports

Posted on 10/10/2024 at 9:00 AM

Chemical formulas



Let’s say your car isn’t configured to run on E85, but you’d still like to take advantage of the benefits offered by ethanol–like more power and a cooler-running engine. Can you run a smaller concentration to get some of the perks? Quite possibly.

Welcome to modern times when most pump fuels contain some ethanol. It’s a renewable resource that also increases a fuel’s octane rating. Most pump gasolines carry the E10 designation, meaning they contain up to 10% ethanol.

E85, as the name suggests, contains even more ethanol. The standard, however, allows the content to range from 51% to 83%. By the way, ethanol content testers start around $15.

While the extra oxygen found in ethanol allows an engine to make more power, there’s a tradeoff: More ethanol is needed to make that power, hence the need for higher-capacity injectors and fuel pumps. Plus, the fuel system components must be compatible with ethanol. 

So, if E85 is too much for your system and E10 isn’t enough for your wishes, can you make your own blend that’s somewhere in the middle? Yes. 

“In the grand scheme,” notes Zachary J. Santner, senior specialist of quality at Sunoco, “gasolines are blends of hydrocarbons. So you can continue to blend them for your own desired purpose.”

Let’s say, for example, that your fuel system can handle some ethanol but can’t deliver enough to support E85–like, maybe E40 sounds like the right concentration. You can mix in some E85 or E98 and, using a weighted average, compute the final blend. (Sidebar here: While the ethanol content of pump E85 can vary, Santner notes that Sunoco E85-R always contains 85% ethanol; likewise, the brand’s E98 recipe never changes.) 

Here’s that weighted average formula:

((volume pump gas)*(% ethanol in pump gas)+(volume E85)*(% ethanol in E85))
(volume pump gas)+(volume E85)