Fuel flow rate through an injector is affected by a number of different things. This page focuses on the effects of fuel type, primarily fluid properties (viscosity, specific gravity, etc.).

Viscosity is a term you hear all the time, but probably haven't given it much thought in terms of injector flow rate. But imagine the difference in pouring water through a funnel compared to honey. The flow rate will obviously be different even through the same opening. And the flow rate will increase as the honey is heated or decrease as it gets cooler.

That's an extreme example, of course, but the same principles apply to fuel (with the injector being your funnel). Ethanol can be very different from gasoline and even gasoline from one station can be different from another station.

To illustrate this difference, we ran a number of tests with different injectors flowing gasoline and then again with E85. The same set of injectors was used in both cases. The gasoline measured out to be roughly E6 (6% ethanol) and the E85 measured out to be exactly E85 (85% ethanol). Both cans were filled from the same station at the same time on the same day as the tests were run.

• First, we gathered data using stock DSM injectors. We noted a drop of 13% in flow rate when flowing E85 vs. gasoline.
• Then we ran a set of FIC BlueMax 1450s. We noted a drop of 11% in flow rate.
• Then we ran a set of FIC BlueMax 2150s. We noted a drop of 6% in flow rate.

The results are summarized below. Keep in mind that this is a change in volumetric flowrate. On top of this, you still have to adjust for the difference in fuel type. So not only are injectors “smaller” when running on E85 due to E85's lower stoichiometric ratio, but injectors are even smaller than that due to the difference in volumetric flowrate!

STOCK 450s (click to enlarge)	FIC BM1450s (click to enlarge)	FIC BM2150s (click to enlarge)

So clearly fluid properties need to be taken into account when calculating volumetric flow figures. This effect also appears to depend on the injector type/size too! Like everything else injector related, this just isn't as easy as it seems like it should be at first.