RaceCal 'Tech Insight' - E85/Flex Fuel! What? Why? How?

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RaceCal 'Tech Insight' - E85/Flex Fuel! What? Why? How?

Good evening everyone,

We realise we've become a little slack with our 'Tech Insights' over the last few months, after lock down was lifted and we returned to the workshop, we a had a rather large workload to get through so the Tech Insights unfortunately took a back seat. They always got good feedback so I thought we best pull our finger out and get another one up for you all!

A question we still receive on a regular basis is how E85 maps/Flex Fuel work, what's needed for it and what are the benefits; naturally this prompted this article.

Taking things back to basics, we should first start with the term 'E85' as this is what s traditionally associated with a Flex Fuel program. In short, 'E85' refers to a fuel which is 85% Ethanol and 15% gasoline. (You may also here the terms 'E70', 'E100' etc..im sure you can guess what these mean!) Whilst there are environmental benefits to using E85, most are now using it as in the majority of cases it allows the engine calibration engineer to extract more torque & power from the engine. “How so?” I hear you ask..:Science, mostly.

E85 has two stand out properties that enable us to produce more torque on the dyno. Firstly its octane rating, secondly its cooling ability. Most of you will be familiar with octane rating; the higher the octane rating, the more resilient the fuel is to withstanding knock (detonation). On a pump fuel (97-99 RON) you may find that as you advance the timing/increase the boost, you will hit knock before you reach MBT. (To get a better understanding of this term please read our previous tech insight here). If we increase the octane rating, you will often find you can run more timing/boost; the by product of this being more torque/power.

The octane rating of E85 is in the region of 105-108 RON, however you will often find E85 is still more knock resistant than non alcohol based fuels in this octane range; this is due to its second stand out property; its cooling ability. E85 has a high latent heat of evaporation, what this means practically is, when the fuel is injected, its state changes from a liquid to gas, during this process it absorbs heat that would be present in the intake, thus lowering the intake charge. Cooler intake charges are denser, so you can further create more torque and increase your margin to knock further once again.

Ok, so now you know why its so good, how do we make it work and what else do you need?

You can in theory buy premixed E85 from your race fuel supplier of choice and run without a Flex Fuel strategy; your map however would need to be tailored specifically to the fuel, you cant just pour E85 into the tank and expect the map for V-power to work. The reason for this is the difference in the stoichiometric ratio of the fuel. V-power stoich value is approx. 14.7:1, E85 is nearer 9.8:1. Because of this the AFR on E85 needs to be considerably richer, every car differs but mostly you'll need an additional 40% of fuel with the same volume of air to make the same power.

This is quite a drastic uplift, which then can highligh shortages in the rest of your fuel system. To deliver the extra fuel (its going to be well over 40% as remember the 40% is just to stay the same as pump fuel), the rest of your fuel system needs to be up to the task; fuel pump(s) sizing, injector sizing, feed line sizing etc. If you're at 90% duty cycle on your injectors for your pump fuel map, you know you're going to have to change them when you switch to E85!

As suggested above, you can buy premixed E85, tailor your engine map to suit and off you go, we however prefer to use a Flex Fuel strategy. Whilst premixed E85 should have a consistent Ethanol %, this isn't always the case, coupled with any residual pump fuel in the tank when you drain and swap, you may find you're in fact running a lower level than you may think, might be ok, but also may be quite dangerous if you've optimised your ignition advance and boost levels for the higher concentration. This is where a flex fuel strategy makes your life so much simpler.

For flex fuel to work, you must first install a Flex Fuel sensor in your fuel system. Traditionally we recommend fitting this on the return side after your FPR as the fuel returns back to the tank. This is so the sensor doesn't cause a restriction in flow to the rail. You do however need to be careful if you are running your fuel system close to the limit, as if so you will have very little fuel returning to the tank meaning the sensor wont read accurately. In these instances you can fit the sensor in the feed, we have found using a Y-piece, with one side to the Flex Fuel sensor, the other side on the feed to the rail doesn't cause a restriction, however gives the sensor ample flow for an accurate reading.

What the Flex Fuel sensor does is monitor the alcohol content in the fuel, and report this back to the ECU. In essence it can measure anywhere between 0% - 100%. If the ECU knows this information, we can ask it to modify the map based on the current alcohol content in the fuel. The more alcohol, the more timing and boost etc we can ask the ECU to deliver.

Below we can see where we setup the Flex Fuel sensor in a Syvecs ECU. The sensor outputs a frequency (Hz) based on the alcohol content.

Once the sensor is setup and assigned, we can then begin to calibrate the engine for the varying fuel levels. With the Flex Fuel strategy this is actually quite simple.

To begin, you will calibrate your base fuelling, ignition, wastegate etc for the lowest alcohol content you run. To keep things simple, lets call this 0%. (Most V-power is around 5%) but as we are not adding any extra lets call these maps our 0% no ethanol.

In the Syvecs system this will be done under the initial '1' maps for the above strategies.

Once complete, you can then fill the tank to the max alcohol content you are going to run, for this as we've been discussing E85, lets say 85%. Fill the tank, monitor the 'fuelcomp' channel, until you see your desired figure.

We repeat the process of the pump fuel mapping, however we carry this out under the '2' maps. I.e Run-Mode Fuelling > Base Injection Time 2. Repeat this for your ignition, wastegate maps etc etc. As we now have alcohol in the fuel, expect to be able to increase your timing, boost pressure etc to make more torque/power.

Now you have done both ends of the spectrum, the ECU knows what to do at 0% and 85%, we must now tell it what to do between. Below we can see how the ECU will choose to blend between your Base 1 (0%) and Base 2 (85%) maps. The ECU will then blend these two maps together for any alcohol content between these two figures.

Once this is fully calibrated the ECU will take care of the rest for you. You can run to the shops on pure pump fuel, the next day before a drag event pour in any desired amount of ethanol upto 85% and your set. You can run, 20,30,55,58,65,67,71% etc, it doesn't matter, anything between 0 and 85% and you don't need to do anything else.

A question we get asked quite commonly on Syvecs is, what Cal Select can I be in for boost when running Flex Fuel; do I need to be in Cal 1 for pump fuel and a specific Cal for E85? Whats the max boost I can run? Will I run too much boost if I dont change Cal if I swap back to pump fuel?

It can get a bit complex so we will try and make it simpler for you focusing a bit more on the wastegate/boost side.

Just like the fuel and ignition base tables, the same happens for Wastegate Target. You have your 'Max Manifold Pressure Target 1' (Pump Fuel) and 'Max Manifold Pressure Target 2' (E85)


If we now head up to 'Calibration Switches' > 'Wastegate Control' > 'Wastegate Control MAP Target Adjustment' you can request the ECU to modify the target based on the Cal switch position.

Below we can see a table trimming boost in various Cal positions which can also be referenced against gear. You can use this to aid with traction etc.

If we pick a few Cals as an example, you will see how it works.

  • Starting with Cal 1, we are requesting -2500mbar target adjustment in every gear.

  • So in 'Max Manifold Pressure Target 1' (Pump Fuel) the value in this table is upto 2900mbar. So on pump fuel in Cal 1 we are taking 2900mbar max target and subtracting 2500mbar which equals 400mbar. This means the max target in Cal 1 on pump fuel will be 400mbar. In this instance that figure puts us in vacuum so we are essentially requesting minimum boost (wastegate pressure).

  • Now lets repeat that as if we had E85 in the tank, lets look at the 'Max Manifold Pressure Target 2' table in the screenshot above. You'll see this is now up at 3300mbar. So if we do the same calculation, 3300mbar – 2500mbar equals a max target of 800mbar. Again, this still remains in vacuum (wastegate pressure requested) but you can see how the max target has changed automatically based on the fuel composition.

  • We've stayed in Cal 1, swapped fuel and the ECU has took care of everything for us.

Lets look at one more Cal example where its not our spring pressure map. So if we look at Cal 7, you'll see the trims requested aren't quite as extreme.

  • In First gear, we are requesting a target reduction of 1000mbar.

  • On pump fuel, like before we need to reference 'Max Manifold Pressure Target 1' which is 2900mbar. We will now subtract the 1000mbar which leaves us at 1900mbar target.

  • Lets now put some ethanol in the tank, get us up to E85 but remain in Cal 7. So now the ECU will look at 'Max Manifold Pressure Target 2'. So we take 3300mbar – 1000mbar which makes the target 2300mbar.

  • So like before, same Cal but different fuel and the ECU adjusts automatically and raises the boost when there is E85 in the tank.

As long as your tuner has set the strategy up correctly, you can run any cal with whatever Ethanol % you like.

One thing to note is these maps will also look at the 'Wastegate Manifold Pressure Target Transition' table under the Flex Fuel strategy so the above examples would be a blend if you weren't above your chosen fuelcomp value for 100% of target progression, however the ECU still adjusts and raises or lowers the boost automatically.

Are there any downsides to running E85?

As with anything unfortunately there is, however the negatives are mostly outweighed by the positives.

Some things to look out for however:

  • Fuel System, like explained earlier in this article, you need considerably more fuel delivery for E85 so make sure your fuel system is sized accordingly.

  • Fuel consumption, as you can probably work out, as you're burning more, your fuel consumption will go up.

  • Corrosion, E85 is 'hygroscopic', this means it absorbs moisture from the atmosphere. The moisture absorbed can then start to corrode the inner workings of your fuel pump, injectors, fuel lines etc. Further more the alcohol can also damage rubber fuel lines, so we'd always recommend using a PTFE E85 safe fuel line. 

And there we have it, a RaceCal Tech Insight into E85 and Flex Fuel, hopefully this has answered some questions you may have had surrounding the strategy, however if you have any more please don't hesitate to ask via email, on our Facebook page or Instagram!

Thanks for reading!

Thanks, Rob

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