E85 Tuning

The other day i had a friend of mine tell me that he wanted to use E85 in his Mitsubishi Evo, after all the bullshit he has had with that car i was certainly a little hesitant when he told me that and i argued with him that E85 by its very nature is less efficient in the BTU's of energy it releases in combustion only now to have eaten my own words about the whole idea of E85.

I decided to do a little research about E85 in comparison to standard pump gas and found that his plan to use E85 was in fact brilliant. Race gas (C16 and others) at this point has climbed its way up to about $5 - $8 a gallon... thats an expensive way to go about getting high boost and high horsepower without detonation. E85 of course like race gas is very high octane, at 105 octane it is less prone to detonate and allows for predictable tuning. Unlike race gas E85 comes in at about $2 a gallon... big difference, I would say so, now for the problem since like i had said to my friend earlier E85 isnt nearly as powerful in combustion so what does that mean to reach better horsepower numbers... well it means you have to beef up your fuel injection system including but probably not limited to upgrading to a 2nd fuel line, high flow fuel pump, larger cc injectors, and a pretty serious tune from what i can guess. As this graph from Cobb Tuning shows there is a vast difference in the load ethanol requires, almost 25% greater.

So based off all this information i thought i might share what Cobb has done with their GT-R platform and quantify some of their results.

Taken from Cobb Tuning Blog:

The graph below shows the stochiometry of E85 (lamda) is similar for pump and E85 but the volume of fuel required for E85 is much higher by proportion (Air to fuel ratio). Despite these limitation of E85 we wanted to tune our GTR to utilize this fuel. Together, the lower cost, higher octane, and higher overall power potential are simply too much to resist. Furthermore, because E85 has not been used in the new GTR platform I simply couldn’t resist the technical challenge.

Because a stock GTR can use nearly 100% of its available injector capacity on pump fuel the first step in using E85 is to replace the stock injectors with larger units. We chose to use Deatschwerks 800cc injectors. These are ~30% larger than stock and should be able to provide the additional fuel volume needed for E85. The injectors were installed and the car tuned on pump fuel:

Stock - completely stock calibration with 92 octane pump fuel - BLUE

Stage 2 800cc - COBB catless midpipe, COBB prototype cat back exhaust, stock intake, stock fuel pump. - RED

We then drained the tank and refilled with E85 full. I adjusted the calibration with COBB AccessTUNER Pro software and prepared to run the car. The first few runs were done at low boost and all was well. The calibration was then adjusted for higher boost and we attempted a full run. I aborted the run because the motor went progressively leaner at RPMs and fuel demand increased.This increasing lean condition clearly points out a lack of fuel delivery. Because our injectors are mathematically ideal for ~30% higher flow it’s clear that the stock fuel pumps simply cannot keep up with higher duty cycle with 800cc injectors.To combat the lack of fuel we installed two walbro 255s in the place of the stock fuel pumps. The installation took about 4 hours total as the stock in tank fuel surge tank needed heavy but straightforward modification. With new fuel pumps installed we went back to the dyno with high hopes of sufficient fuel delivery. The results are presented in the graph below:

Stock 2009 GTR - 92 octane - BLUE

Stage 2 800cc - COBB catless midpipe, COBB prototype cat back exhaust, stock intake, stock fuel pump, 800cc Deatschwerks injectors - RED

Stage 2 800cc + E85 - COBB catless midpipe, COBB prototype cat back exhaust, stock intake, Twin walbro 255 fuel pumps, 800cc Deatschwerks injectors - GREEN

This E85 Stage 2 configuration is now the highest HP and torque stock turbo car tuned on our Mustang dyno. When the weather clears here in the pacific northwest we’ll find some dry test roads and report V-box data. We’re also planning to rent a local drag strip for development and testing so ETs and trap speeds are coming. As a next step we plan to install some custom intakes. If our early observations are correct this car will make more than 600 whp on stock turbo’s with E85…. all while retaining the factory downpipes.