I know that E85 needs roughly 130% the volume of gasoline to get the same afr. I know that the stock injectors are roughly 270cc and the stock fuel pressure is about 40psi. I have already installed an adjustable fuel pressure regulator, DW255 pump and -6AN ptfe fuel lines in a return setup. Would raising the fuel pressure to, say 52 psi, provide enough extra fuel for the ecu to adjust injector pulse to keep everything happy naturally aspirated? What injector duty cycle are the stockies at? Is there an extra 20% in 'em?

 

For b series no, you’ll definitely need larger injectors.

 

^ I feel like that needs a little more explanation.

If you increase the fuel pressure to 4bar (58 psi) you can technically pull it off. They don't even have enough flow at base pressure to support much more than a stock engine. Case in point - B18C5s running increased pressure from the factory to make ~200 at the flywheel. The bad news - those old injectors don't spray great at really high pressures, and you'll need to remap your battery offsets to get them to idle and run consistently at low pulsewidths. Good news: modern injectors (EV14 style) have good spray patterns at elevated pressures.

Personal experience -

I'm running Injector Nation 365cc injectors at 58psi on a flex-fuel NA setup. It's not making huge power on E85 or gas. I just did it as an experiment. Duty cycle at 43.5psi was edgy and at or above 95% in some spots at high rpm. The pressure bump along with redoing the fuel lines from the filter to the rail got me back down into the low to mid 80s of duty % while on E85. I tuned the injector offsets but the changes were minimal with my injectors. Car runs great, switching fuels is totally seamless with the S300. I run closed loop and the fuel trims are low and calm at at all blends, so I'm a happy camper.

Last points - If you're trying to pull this off on a stock ecu without flex-fuel capability (minimum S300, in my opinion), it's probably not worth the effort unless you're like, getting ethanol for free or something. If you're trying to pull it off on a stock-ish engine, also still not worth the effort. Good luck!

 

Stock b series injectors are 240cc. They can run out of juice on pump around 180-190whp. H22 obd2 injectors are 280’s, obd1’s are 345. The 240’s wouldn’t be sufficient for e85 even on a mostly stock motor. I’ve had customers with 1650’s and a 450lph pump run out of fuel just over 400whp. That being said I don’t think you’ll gain much if anything from a fuel change unless the motor is knock limited and in that case you’d be better off getting a camshaft that will get your dynamic compression ratio into a safe range for pump fuel before worrying about e85.

 

OK, thanks guys. So the consensus is, no probably not worth all the effort just to avoid buying 850's and tuning to save a couple bucks.

On a similar tangent, in a completely stock motor, if you need 30% more for e85, would simply installing 330's be close enough to stoich for the stock ecu to not even notice the difference? In other words, does 240's + gas = 330's + e85? In theory.

 

You need to tune. Give up on the stock ecu nonsense.

 

Oh I know, kpro is on its way. I just get curious about crazy stupid theoretical stuff.

 

Right on. Then wire in a flex fuel sensor and a wideband, pull some logs and do yourself some learnin’! It’s clear you have a stock-ish NA engine. You’re probably not going to blow it up experimenting as long as you’re relatively smart about it. Give it a whirl and see what you can figure out. 👍🏻