E85 and the MR16DDT

We get asked a lot about e85 tuning on the Juke/Sentra platform, so we are going to do a little write up of the good and bad of this, how to do it RIGHT and how to do it sketchy and the differences between the two.

A few bits of base information you will need:

E85 refers to a blend of Ethanol and Gasoline that is 85% Ethanol and 15% Gasoline. E85 is extremely knock resistant, meaning you can run heaps more boost and timing without risking pre-ignition (knock). E85 requires ~20% more volume to properly combust over normal gasoline. This is important to remember as we go forward.

The direct injection system on the MR16DDT is not currently upgradeable in any significant fashion, so keep that in mind going forward. Injectors and HPFP are what they are.

Now onto the important stuff.

The big question is: Can you tune the MR16DDT on e85?

Simple answer: yes.

Okay have a great rest of your day!

The real question that should be asked is: How can I SAFELY tune the MR16DDT on e85?

Now, if you plan on carrying around perfectly pre-mixed e85 in spare containers in your car and keep 55-gallon drums of fuel at home, this is pretty simple: Tune the car on that fuel and keep using it. But, if you are a normal human being who commutes and travels, it gets a bit more complex.

See, the Juke/Sentra do not have any means of adding something called a "Flex-Fuel-Sensor." An FFS is a device that determines the ethanol content of the fuel system and tells the ECU that value so that fuel trims/maps can be adjusted properly. Without this system, the ethanol mixture you tune the car for MUST be the same every time you fill up your tank. This is an issue for normal drivers. E85 at a gas station is not normally actually e85. We have seen e60 to e90 come out of the same pump at different times of the year. You can actually test the ethanol content yourself before filling your tank up using a test kit available online.

So, what if the fuel is +/- 10% ethanol, it's still very knock resistant?

Willing to risk a $4000+ engine on that? Willing to risk a $4000+ engine on the ethanol content being within 10%?

Didn't think so.

So how can you SAFELY tune a MR16DDT on pump e85? Well, there are three ways:

1: Get multiple tune files made up for different ranges of ethanol content. E60-E90. Once you need fuel, take out your ethanol testing kit, fill the tank up, take a sample and test the content amount. Load up the tune that is closest to that content amount. Obviously, this method comes with disadvantages. You need to carry your laptop around to swap out tunes (unless you're on uprev, then you can pick from your 5 available), and you have to spend time testing the content percentage every time you need fuel. This is obviously the cheapest way to run ethanol safely on your vehicle, but it is not bulletproof. You are still not going to be able to get the exact tune for the exact ethanol mixture. You can also run an ethanol content gauge and adjust your tune file accordingly that way as well.

2: Run an aux fuel system using 2-4 extra injectors powered by an ecu such as a speeduino that can add more fuel as ethanol content rises. Your tuner will have to sort out fighting the oem fuel systems fuel trim adjustments, but it is do-able. This is obviously quite expensive, and requires a bit of fiddling, but it is much much much safer than swapping out tunes.

3: Do a port injection conversion and run a flex fuel system integrated into the ECU you are using. This is the most expensive option for sure, but it is the BEST way to do it.

Now that you have your tuning system sorted out, you do need to be aware of the mechanical limitations of the MR16DDT if you stay DI.

The OEM injectors start getting pretty maxed out around the 400 whp mark (without loads and load of meth injection to help them), this means that around 320 whp, they will be getting pretty maxed out on e85. Now, for most people on stock sized turbos, even with E85, you are not getting that much power, but this does become an issue on something like a Mamba 21T. On gasoline (no meth), you can make a comfortable 270 whp (with a crap torque curve) with a 21T. E85 would allow you to run more ignition timing, and it is possible to safely break out of that 300 ceiling with the right tuning. Your torque curve will suck, but it is do-able. The rule of thumb on injector sizing is, you should never run near or over 90% duty cycle at full power. So, let's assume 320 is the hard limit where the injectors are at 99% duty cycle on e85. We have not tested this, but based on the numbers we will have to generalize here. You can do it; it just isn't great for the fuel system. So, 10% less than 320 is 288 WHP. You can start to see where this may be an issue. Not saying that this is the case, you could make way more than 320 if your fuel system is in tip top shape and the tuning is done right, and you are okay with maxing out the fuel system, sure. But again, willing to take the risk?

Our recommendation would be, put a safe ~320 whp cap on the e85 power being made with the 21T and e85. At that power, check the duty cycle and see where you stand. If you're not at some crazy level, sweet, if you are, back it off a bit. Better safe than making a number.

As for the in-tank fuel pump: The OEM one should be swapped out to a e85 compatible one from Walbro or AEM or (insert fuel system company here). The OEM fuel lines will handle the ethanol fine, as most gasoline has some amount of ethanol in it as an additive, so fuel lines on these cars are made to handle it.

A few things to keep in mind:

Ethanol is extremely bad for a fuel system when it sits for a long period of time. Not anywhere near as bad as methanol, but it is still rough on fuel systems. IF you run ethanol in your DI system, it cannot sit for prolonged periods of time like that. It will damage the injectors or clog up other parts of the fuel system. If you are leaving on a vacation or a long trip, it is highly recommended that the fuel be swapped out to normal gasoline ahead of time.

E85 is not available everywhere. As an example, the closest e85 station near us is 40 minutes away, and we are located in a very populated area. We send up someone to fill up tanks for us with fuel at that station if we know we have e85 tuning to do.

E85 gives terrible fuel economy. Remember, it needs ~20% more volume than gasoline to function, so you're talking about a ~20% reduction in fuel economy.

E85 is a great option for those who do not want to deal with aftermarket turbos but want to make more power. A stock turbo v1 six speed car can make ~230whp on a stock turbo with a very aggressive tune and proper supporting mods (meh torque curve). Swap over to e85 and you can very easily make ~260-270 whp. If you plan on only running that power for quick rides around town, or for dedicated racing, then all you need to do is take a half hour to swap fuels out of the car (using canned e85 premix), change a tune, and boom instant power boost. When you're done, swap fuels back and drive off into the sunset. If you're interested in how to quickly swap out fuels from the car, we can make a quick how-to on draining the fuel tank without any major work. It just requires a few tools and hoses. Just ask below. A flex fuel GAUGE is recommended for this method.