E85 conversion of a non turbo engine
 

Hey guys,
I'm considering converting my fuel to e85 with the you know mixing of premium. The reason for this is because gas prices where I live is kind of high and I would love to have a lower fuel expense. What do you guys think are the potential drawbacks/benefits of having an e85 RX8 without a turbo?

Not worth the money, the number of gallons you would need to go through to eventually start saving would be quite high, not to mention there are drawbacks to straight E85 you would need to address including the expenses of an increased oil change interval and needing to premix with a E85 compatible rotary premix. That will add cost on top of going to E85 convert in the first place. If youre facing excessive costs of fuel, dont daily the car and get yourself something else to daily drive.

I commute a lot for work and stuff, and the money I saved in fuel costs buying myself a 2016 Mazda 6 to daily drive was enough in savings to pay for the finance payment. My only extra cost was the extra insurance. So I can say I am speaking from experience. Either suck it up and deal with the poor fuel economy, or get something else to daily.

Hey thanks for the reply Ricky.
Yea, the 8 isn't my only mode, Just curious for the new build, I'm not sure how I would need so many more gallons of e85 to make savings. Its like half the price of premium. How much to kits run? I havnt seen one specific to the RX8.

There isnt a kit. You would need to build your own.

Fuel pump upgrade
Fuel injectors
Hardware for tuning
Software for tuning
Cost for a informed person to tune your car properly (best left to knowledge people since ruining this can ruin your engine)

Even at half the cost of gas, youll consume more ethanol than you would gas, so its savings will be less apparent.

Not to mention the other concerns, those add cost as well.

Youd have to drive a lot of miles before the savings catch up to all the expenses of converting to E85. Plus being stuck going to E85 stations.

Any update, how is everything going?

E85 would need to be 40% less that gasoline per gallon just to break even for mpg, let alone the extra cost of the conversion parts and labor justification.
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There is basically no cost benefit to E85, but there is definitely a power benefit. I created my own FlexFuel software patch for S1 Stock ECMs that is free to use. I picked up 20hp on E60 with some increased timing with the higher octane E85.

More info:
https://gromelectronics.net/2025/05/...uick-overview/

https://www.rx8club.com/rx-8-racing-...9/#post5002606

So, I'm running an e85 NA system with the rebuild I've been working on-
With the help of Kyle Mohan and a few others I've been able to get it running and the power difference is there, now could this be because of my streetport / upgraded fuel system, probably...but e85 still is a massive upgrade, it's a very corrosive material which luckily for you, your system is resistant, BUT this doesn't mean you can slap an Eflex fuel kit and run full e85. When using e85 you need the proper oiling because unlike premium delicious gasoline its very dry, so you are left with 2 options
1. Sohn adapter with regular premix 2. use special premix in the gas tank (such as renewable lubricant's rotary premix) because regular premix does NOT mix in well with e85, so it'll just cause you to shoot straight premix through your fuel system (I promise you it's not fun). NOW you've got oil figured.... now fuel requirements, yes, your yellow and red injectors (taken it's a 6 port) can handle e85 but it will be maximizing every tiny bit of your injector which WILL cause them to fail eventually so if you don't want to get some idx1050s or whatever cheap Denso injectors you get, I'd just lower the ethanol content to get e50-e30 for a safe bet while still getting the benefits. Now why should you do it? No not for the gas price and no not for the power but the cooling properties and the much less carbon buildup (knock resistance helps too). Rob Dahm showed an engine with and without e85 and one looked like it ran diesel while the other looked so clean you could probably eat of it (please don't actually eat off it) So if you are looking for power save your money and contact brettus for his turbo manifold but if you are just in a position to be different and make your life just a tad more annoying then I 100% suggest the e85, or get both

There's this Finnish company that offers a "piggy back" e85 conversion kit for lots of cars, they also support versions of the rx8.
eflexfuel com/us/auto-products

https://cimg8.ibsrv.net/gimg/www.rx8...fcef5b01e3.jpg

This was the EXACT company / kit i used, extremely easy to setup and makes it where you dont even need to tune for the e85

Great synchronicity! So, it was easy to setup and the piggy back takes care of the "tune"? On the eflex plus it offers the ability to write custom maps as it is advertised? On the non plus model, you have 2 maps, ethanol or not I think. Anyway, if you have info to share about this, I would be interested.
Edit: Would this work with a turbo kit? Off topic, sorry!
If you have any info, send pm.

Yeah, it's as awesome as you think it is, and it's not just a "tune"
how it works is that you replace your red fuel line with a custom one you have in the kit you buy which allows you to connect an ethanol sensor which detects what percentage of ethanol is in your fuel so then it uses that information to change the latencies of your injectors (through an adapter between your injector and the connecting wires) to said percentage, so it doesn't just have a full ethanol or no ethanol setting, it adjusts your ecu automatically whether you want e10-e30-e50 etc. just by the sensor so you don't even need to touch anything to change fuels, so for instance you are in a rush for gas you don't need to retune your car just fill your tank, it'll do the work for you. The main difference between the regular and the pro is the variety, so with the base model kit it only has dynamic, sport, and eco modes which doesn't leave much room for improvement especially if you have a bunch of mods. so having the pro allows you to actually custom tune your kits latency values but only useful if you aren't only using basic mods (aka turbo mods) there's not much use out of it otherwise. which overall I find the product somewhat easy to install and use, it even has a cute little phone app that tells you what your duty cycle is (how much ethanol your gas has)

The flexfuel patch I've made above also offers a "tuneless" solution, but with the added benefit of adding in extra timing based on ethanol content.

Just sayin.

I was looking at your patch and it looks promising but the 20hp seems like a stretch, I only got the eflex fuel kit cause it was extremely simple to setup but I guess with the price tag I’d hope it would be

The 20hp is real and measured, but also has a 6-8 degree increase in ignition timing so it should be expected. No idea what the eflex kit is doing as far as that, but doesn't look like much... so I wouldn't expect any power gain with it.

What aftermarket parts are you using? Because I’m mainly using a stock fuel system other than replaced the primary to yellow injectors, because I’ve been meaning to upgrade but didn’t know if it would have a huge effect

Stock everything as far as relevant components

Whaaaaaaaa-
I guess I might have backed the wrong horse when it comes to flex fuel systems :tear:

There are 2 kinds of people.
those that want 20% result with 1% effort
those that want 100% result with 100% effort

The ROM with patch already applied is available for flashing on any USDM 6 port ECU, and likely many others if people were to try it. You don't even need any extra hardware to use the patched ROM on your ECU. If no sensor is detected, it will default to factory logic. ROM defs are also available for the flexfuel patched ROM.

There is not effort involved, and you get 100% of the result.

If for whatever reason (read: hardware changes between ECU versions) the binary doesn't operate on your specific ECU, porting the patch to that ECU is as simple as changing addresses in the source code pointers, compiling the software, and patching your ROM with the patch tool.

I would be more than happy to work with anyone looking to do this if their ECU hardware is not compatible with the available ROM.

nice job, 15 years too late for me though 😭
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Ok for the 6 port, what about 4port eu models.
Edit: I mean what would it take to patch it to an eu ecu.

I have little desire to support a 4 port ROM, but if there is a huge amount of people asking for it, obviously it is possible to create a patch for it. Gains would be very minimal.

If I have Mazda edit would I be able to flash this addon ?

I don't know how Mazdaedit works, but if it deals with raw binary files, then yes.

Though I don't know how definitions for the tables and such work..

It would be easier to just go to the open source tools if you wish to use the E85 patch.