What is E85?
E85 is a fuel blend that consists of 85 percent ethanol and 15 percent gasoline. Ethanol is nothing more than alcohol, just the same as found in alcoholic drinks. Ethanol has been in use as a gasoline additive for quite a while but it is limited to a maximum of 10 percent. Ethanol ignites and burns just like gasoline but it has some very different properties. E85 is often estimated to have the octane equivalent of 105 when compared to gasoline. That makes E85 as good or better than some of the race fuel offerings at preventing detonation and that is a good thing for a number of reasons. The higher resistance to detonation not only provides the engine with more safety but also allows higher power output on a given setup compared to running regular gasoline. On a turbocharged Subaru, this is generally accomplished by being able to run higher boost levels and optimize ignition timing where doing so on gasoline would be limited by a detonation threshold. Ethanol as a fuel is also better than gasoline at absorbing heat from the air. This equates to a cooler and denser air charge entering the engine. The trifecta of higher boost, optimal timing and a denser air charge can allow a given setup to produce significantly more power. On a stock turbocharger, it is not uncommon to achieve 40 to 50 more peak horsepower over gasoline. On larger turbo setups, it is possible to gain 100 or more horsepower by using E85. With flex fuel options that are available or right around the corner, using E85 is going to become even better than ever. Read up on E85, then click over to the Flex Fuel page to learn more about it.
What are the pros and cons of using E85?
E85 is great for protecting an engine in the form of higher resistance to detonation and is great for making higher power on a given setup. However, there are a few things to consider when looking at using E85. Ethanol requires a higher volume of fuel to achieve the same amount of thermal energy as gasoline, so the fuel demand for E85 can be as much as 30-36% greater than gasoline. Keeping up with fueling demans can be challenging as your power demand increases. Even a stock turbocharger Subaru (EJ2X) requires larger fuel injectors and a higher flowing pump to use E85. Since more fuel is being used to achieve the same effect as gasoline, E85 is said to "burn faster" which in a sense is true. Really, it is just getting used faster. The good news is that at light cruising loads, an engine can often be operating more efficiently when using E85 such that the full 30-36% higher demand is not observed. The high demand typically comes at high loads, such as full throttle. Under light loads, some setups will observe closer to 15 to 17% extra fuel use with E85. This is nice because in many areas, the price difference between premium fuel (91 to 93) and E85 is often fairly substantial. Fuel is used faster with E85 but this is often offset with a lower cost to fill the tank. Most people observe a break-even with average driving, a slight advantage with heavy highway use and a slight disadvantage with more aggressive driving. Generally, the overall benefit of using E85 will outweigh these disadvantages for most people.
What about the bad things you hear about E85?
"E85 is not always 85% ethanol, it can be lower."
This is true and the reason is fairly simple. Ethanol is not as easy to ignite when mixed with cold air and sprayed into a cold cylinder. An engine running E85 relies on the gasoline mixed in to ignite the mixture and get the cylinders up to temp until the ethanol can burn better on its own. It is known that 15% gasoline just isn't enough for regions where Winter temperatures get down near and below freezing, so these regions change blends to be around 70% ethanol in winter months. 70% is the minimum in most places. The changes of blends can have an effect on a Subaru tuned on E85 if the air fuel ratio is tuned with little room to move safely. Ethanol has a broader safe and acceptable air to fuel ratio (AFR) range than gasoline. If the AFR is set appropriately for a known ethanol content, it will typically stay within the safe range. At times, a small tune update can be needed for extreme high or low blends but this is easy to handle. With Flex Fuel, we will not need to worry about this and every modded, turbo Subaru (especially those on E85) should have an AFR gauge to monitor at all times.
"E85 doesn't work well in the Winter, it is hard to start the car and it runs poorly trying to warm up."
With proper tuning and an ethanol blend near 70-75%, a Subaru can start just fine in the winter and drive perfectly normal. E85 gets a bad reputation because a lot of tuners don't understand how to tune for it correctly to start in cold weather. It is possible at times to see colder weather before fuel blends are changed out to winter blends and it is possible to see summer blends at some stations even during winter, but this is not very common. Simply adding a gallon of regular gas to a tank of higher blend E85 normally brings it low enough to start well. With Flex Fuel it will be easy to keep your blend lower on your own if needed.
"E85 ruins fuel lines, injectors, pumps, etc."
Modern fuel lines have been E85 compatible for a long time now so there are no concerns there. Many injectors, such as ID1300's and ID1700's have stainless steel internals and are rated for E85 use. Even injectors not rated for E85 are normally perfectly fine. The only concern is with water getting into the fuel, but with a sealed fuel system like that on any normal car, this does not normally happen either. Many fuel pumps are rated for E85 and like injectors, even those that are not, tend to have no issues. The gasoline added to E85 keeps pumps lubricated and working normally.
"If I can't find a full 85% blend, I won't get all the safe power."
The reality is that the power difference between a 70% blend and a 90% blend of E85 is very minor at moderate power levels. On some setups it might not even be observable on a dyno. A 70% blend still has a very high effective octane equivalent and strong resistance to detonation. Tuning to the bleeding edge of power on a large turbo, high boost setup might offer up observable gains, but with more moderate tuning on moderate turbo/boost setups, the power that can be made using a high blend will often be the same as what can be made on a lower blend. A tune done correctly for a low blend should run safely on a higher blend and vice versa. As mentioned, all E85 tuned Subarus should have a wideband, so an owner should always know if they are running at a proper air fuel ratio at high loads. Furthermore, with flex fuel, we will have even less to think about with lower or higher blends as they can be accounted for on the fly.
What do you need to run E85 on a Subaru?
You will need a Cobb AccessPort V3 to run flex fuel on the 2004+ STi and 2006+ WRX. For 2002-2005 WRX, it is possible to use an open source tune called CarBerry using a 2002-2003 WRX ecu or a number of JDM 16 bit ecus are also supported .
At the bare minimum, you need to upgrade your fuel injectors and fuel pump so they can supply the extra fuel needed to run E85. The smallest size injector you can run is 750cc but it is never recommended to run "just enough" extra. The most common starting point is a 1000cc injector such as the Injector Dynamics ID1000. These injectors can run perfectly on both gasoline and E85 while supplying enough fuel for the stock turbo charger and even some larger turbo upgrade options.
There are lots of fuel pump options available. It is suggested to look for at least 300 lph of flow and E85 compatibility. For 2005+ LGT and 2008+ WRX/STi, it is best to look for a "compact" pump offering for a drop in replacement in your fuel pump housing. Non-compact pumps require cutting to fit.
How big of injectors are need to support XXX power?
There are many factors that affect just how much power a given injector size can support. Fuel pump selection, available base fuel pressure, intended peak boost, and other factors have to be considered.
A a general estimate of supported wheel horse power (WHP) for the Injector Dynamics line up is below. It is important to note that these estimates assume stock (43.5 psi) base fuel pressure, and that fuel pressure is rising and holding 1:1 with boost.
ID1000 ~ 400 whp
ID1300 ~ 500 whp
ID1700 ~ 660 whp
ID2000 ~ 860 whp
It is important to keep in mind that injectors flow more as the pressure is raised. If your fuel pump supports enough flow to raise the base fuel pressure, you can gain more fuel supply and support more power. As rough estimate, if a base pressure of 50 psi can be used, there can be enough extra flow for about 6% more power. That can stretch ID1000s to 430 whp and ID1700s to 700 whp. 60 psi of base pressure can stretch things even farther if the pump supports it. As much as 14-15% more fuel supply is possible if this base pressure is supported by the pump selection. This is good to keep in mind when choosing an injector.
Fuel pump considerations
Pump selection is just as important to consider as injector selection. You need to choose a pump that can flow enough fuel at the needed pressure to keep up with the fuel demand, which is very high when using E85. In addition to pump selection, how you power the pump is important as well. Hard wiring a pump is a commonly used approach. It ensures larger pumps have enough amperage as they draw a lot of power to supply high volumes of fuel.
As a general guideline of what can be supported by different pump options:
300-340 lph pumps ~ 400-450 whp
This is a common flow rating for "drop in" pump upgrades. These work well for a stock turbo and smaller upgraded turbo cars. By 400-450 whp, these pumps tend be be out of flow. Even with bigger injectors and tuning around dropping fuel pressure, they don't offer much beyond this power level so skip past these if your goals exceed this amount of power. Hard wiring can be needed to reach the higher end of the supported power on pumps this size.
Walbro 485 ~ 500-550 whp
This pump offering is more suited to higher power levels, On a stock fuel pump controller (not recommended due to higher current draw and risk of FPC failure) this pump can support 500 whp or more. When hardwired, it can support closer to 550 whp.
Twin fuel pumps: ~ 650-700 whp
This can be a cheaper way to supply enough flow for higher power levels since you double the flow to keep the pressure maintained. Twin 485 fuel pumps have been found to support as much as 650-700 whp.
Big in-line fuel pumps: ~ 700+
When it is time to get serious with fueling to support higher power or the risk of running twin pumps doesn't sit as well with you and your budget supports a better fuel system, a big single in-line pump is the way to go. At this point you will need to put together a full back-half fuel system that include a surge tank, the pump and generally upgraded fuel lines to and from the engine bay, Fuelab's biggest pump has been found to support up to the 800 whp range. Beyond this, the big offering from Magnafuel or something of similar flow is the next option to consider.
3 port boost controller
A 3 port style (such as GrimmSpeed) allows higher boost levels that the stock boost controller. Generally a must-have with an upgraded turbo but paired with E85, it can support higher boost on a stock turbo.
Upgraded bypass valve
Also a normal upgrade to do on a bigger turbo setup but even on a stock turbo, this can be upgraded for a little more peak boost.