RossD SuperDork
Dec. 7, 2011 10:27 a.m.

I have questions.

I have a stock '91 Miata. I recently purchased a second hand 14b turbo, manifold, downpipe, and a new aluminum radiator.

Most of my questions have to do with Megasquirt and which version is right for me.

I'd like to be able to put any fuel (from 93 oct (E0), 87 oct (E10), E85 and even E100, if I can find it) into my tank at anytime, and have seemless operation. My power goal is 150 hp. If I can maintain 30 mpg that would be a plus. This car is my DD during nice summer days with little to no intentions for AX or HPDE.

I'm expecting the system to be able to change ignition and boost on the fly depending on what the flex fuel sensor says is going into the engine. I also am expecting to have a wideband and flex fuel sensor (holy E36 M3 the GM FF sensors are expensive!)

I'm planning on purchasing more parts with up coming tax return money, so I'll have more than enough time to read and reread to nail my attack pattern for this project.

I enjoy messing with setting and I know the tuning process may be arduous at times, but being an engineer, I kind of get off on that.

So do I need MS2 or MS3 with the expansion board? MSextra...?

Anyone else megasquirt a flex fuel vehicle or at least tune for E85? and with a turbo? Comments, concerns... Which books do I need?

At this point I'm all ears.

Thanks, Ross

alfadriver SuperDork
Dec. 7, 2011 10:45 a.m.

To be truly flex fuel, it will be challenging.

In addition to the fuel sensor, I would suggest a control system that uses a WB sensor to supplament that. It will end up running a lot better, and a lot more robust to fuel.

Couple of things to note- the amount of fuel to get e85 running can be alarmingly a lot. E100- don't run below 70F if you can get it. But so much more than E0 would be that you should make sure that the controller can adjust the amount of open loop fuel needed based on the type of fuel running when it was shut off last.

Dave's Honda is turbo E85, I'm sure he can share some of his findings.

Lastly- for E100- I had found a webpage that showed how to make a still. A legal one, since it's for driving and not drinking (knowing the different kinds of alcohols, I would never drink my own swill....). Had thought it would be super cool to bring my own fuel to a challenge.... Since you are posting this- I hope that you can make DIY E100 part of your project.

Keith SuperDork
Dec. 7, 2011 11:09 a.m.

We're planning on building a flex fuel version of our E85 Miata. But we're using a Hydra, so I can't help with what Megasquirt parts to use.

JohnyHachi6 Reader
Dec. 7, 2011 11:25 a.m.

We ran E85 in our supercharger 1UZ miata at the challenge earlier this year. MS1 will handle that no problem.

As has been stated, switching between fuels is going to be really tricky. You'll probably need some custom code to change the fuel delivery and spark maps based on the FF sensor readings. For this you might need one of the newer MS units.

I would recommend talking to DIYAutoTune. They're very friendly/helpful and may have done something like this before. They're always doing neat projects with the megasquirt systems.

Another thing to keep in mind - if you run a high(ish) powered car on E85 you will need very large injectors and a large fuel pump, since E85 has a much lower AFR at stoich than gasoline. We were getting close to the limits of our 440cc/min injectors on the 1UZ and that's with 8 of them.

RossD SuperDork
Dec. 7, 2011 12:17 p.m.

Re E100: If I have to distill E100, I probably won't use E100. I just wanted to cover my bases in terms of fuels I could encounter during a summer road trip.

I'm already aware that I'll probably need larger injectors, but how big? Especially if I want it flex fuel, is there a lower limit to fuel injectors? Where is the sweet spot in terms of percentage of total capacity? 20-80%?

alfadriver SuperDork
Dec. 7, 2011 12:24 p.m.

In reply to RossD:

awww.. I thought it would be a cool experiment. You wont find anything higher than E85 in the US, unless home made.

for peak, since you are planning on stretching the envelope, so to speak, 90-95% peak flow isn't too unreasonable. 90 would be better.

To really take advantage of the fuel, and since you can't have variable compression, you should also plan for the ECU to control boost. Really crank it up in E85, but variable boost based on fuel type. If you can swing premium, you should be able to run the turbo with modest boost on a stock compression 1.6. And by that I mean that I think 150hp is very, very reasonable.

RossD SuperDork
Dec. 7, 2011 12:41 p.m.

Can you have injectors too big? Or if I'm at, say, 90% of capacity at WOT with E85, will I still be able to idle with 93 oct (E0)?

alfadriver SuperDork
Dec. 7, 2011 12:48 p.m.

In reply to RossD:

Yes. And it's possible to have idle problems on a hot motor on E0 if tuned for peak flow on E85.

If you can swing a variable input pressure, that would be helpful.

Still, your power goals are reasonable enough that you should be able to find an injector that will do your peak flow and still be able to idle well enough. I think the MS sites have some estimators for injector sizing.

Keith SuperDork
Dec. 7, 2011 12:48 p.m.

If you go too big, you'll have trouble dealing with the short injector on times at idle. Depends on the injectors you're using - we have some 1000cc ones that will idle better than 550s.

150 hp is easy to do on a 1.6 Miata turbo motor.

JohnyHachi6 Reader
Dec. 7, 2011 12:51 p.m.

yes, injectors can get too big to control well at idle, which is why some cars, like RXs have staged injection. Take a look at what comes in high-powered forced induction cars and that will tell you about how big you can go (I think ~600cc/min seems to be the limit for a nice low idle). You probably won't need to go that big on a 1.6 though unless you're running massive boosts.

Edit: as Keith said some injectors will work better than others.

MadScientistMatt SuperDork
Dec. 7, 2011 1:26 p.m.

MS2 and MS3 can use a flex fuel sensor to adjust fuel and spark - MS2's strategy is pretty simplistic, but they're working on some more sophisticated strategies for MS3.

Note that MS2 based MSPNPs with flex fuel support built in are right around the corner. Also, it seems some Ford Tauruses used a flex fuel sensor that behaves exactly like GM's.

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