Petraszewsky

I was wondering if the increased volume of fuel with E85 would displace enough air that it would increase boost pressure? For instance with a PD Blower with the same pulley and rpm would the boost pressure be greater with E85 vs 93? Hopefully that makes sense

Unreal

I doubt the difference would be measurable.

But yes, what you are saying makes sense. More fluid in same set volume, would equal more boost.

CI GS

I can't see how that would cause any measurable increase in boost, especially in light of the fact that ethanol will cool the intake charge better than gasoline, which would make for a denser air/fuel charge, and I would imagine a denser A/F charge would displace less space, which would equate to less pressure/boost. So, even if you could find a pressure sensor that could measure the negligible effects of either the additional displacement of the richer A/F mixture or the effect of the cooler A/F charge, one would probably offset the other to some degree. I'm also sure that if there was a measurable difference, one of the Efuel tuning gurus on here wouldn't noticed by now.
The good thing is that what really matters at the end of the day is that your car will make more power on corn juice, for a number of reasons.

Petraszewsky

Makes sense...I just had the thought and figured the large increase in volume might displace enough to increase pressure. I will be using a flex fuel setup so I'll see if my boost gauge notices any differences when I get the build finished.

NJ_phil

I take it you mean cylinder pressure and not boost pressure, 2 different things.
Would think the increase would be negligible, but my math degree is too outdated to prove that out.

Petraszewsky

Wouldn't in theory make the boost pressure rise since it's a incompressible liquid? And cylinder pressure also even though it's a vapor by that point? I'm asking for discussion as I'm not a engineer or pro.

Chiselchst

IMV, yes, yes & yes. Unless the higher volume of E85 would back out the compressor (increased resistance @ higher discharge pressure required [very minute effect]). And also a cylinder pressure increase - not from induction increase in volume, but from greater pressure from combustion, i.e. power...
ETA; in theory there would also be an extremely slight volumetric decrease in gas IF it is cooled by the E85/fuel, assuming induction air is hotter...

Unreal

Need to quantify the volume of fuel. Compared to the intake manifold volume, what is one squirt of an injector that is only in the intake track for a fraction of a second going to do? If you have a 2.5L intake plenum and go from 3mL to 4mL of fluid, good luck ever detecting that.

Chiselchst

...but in theory...
We wouldn't notice it with our measuring instrumentation, LOL...

Unreal

Yes, just like denser air changes boost, and in theory, higher humidity would have the same effect. More water in the air. Most boost gauges used on cars are pretty damn inaccurate thought. Seen people pick up 2-3psi just swapping brands of gauge.

Petraszewsky

I guess I don't see anyone talking about more boost pressure when injecting meth so makes sense. (Not to be confused with adding more boost because you're now injecting meth) It also makes sense that the cooling effect of E85 makes the air more dense which in turn lowers the boost charge vs hot air. All good thoughts so far.

NJ_phil

I would think the different density of using E85 from a compressability standpoint in relation to 93 for the same given amount of air mixture is minimal at boost pressures (<30psi) because E85 and 93 have pretty close compressability modulus. Not like you're comparing water and air since water would hydrolock the cylinder.

But that same 30psi boost can create cylinder pressures over 2500 psi @10:1 CR so the E85/93 density difference is much more significant and pressures would be higher.

Akin to having air in your brake lines... Lightly press on the pedal and it's not noticeable (low boost)...stomp hard on the pedal and it fades to the floor (cylinder pressure).

Any more thought would require me smoking a fat one and pulling out the Jethro Tull albums

Petraszewsky

So far I've only found one article that mentions it:

Scroll down to the bold EFI Tune section of course this article is about a very high horsepower build running pure methanol as fuel so...

http://www.dragzine.com/tech-stories...blown-alcohol/

"Be prepared for a significant increase in boost pressure. We were told by some experts that we would get another 5-6 pounds of boost from removing the intercooler. Well, it turned out that the boost pressure increase was about 12 psi … almost twice as much. The reason it turned out wasn’t just the boost loss from the intercooler and piping, but it was the fact that the increased amount of alcohol in the cylinder was now displacing the air in the cylinder. Since alcohol can’t be compressed, it increased the net pressure in the system since there was a lesser amount of air being compressed."

romandian

stupid stuff like that made me quit reading the mags many years ago.

Petraszewsky

I'm lost what's stupid about it?

schpenxel

That quote is all kinds of stupid. Alcohol in the cylinder increasing boost by 5-6 psi? Don't think so

Unreal

Makes sense. Removing intercooler, and switching to alcohol as only fuel I could easily see 5-6psi increase in boost.

schpenxel

I read it to mean 5-6 for removing intercooler then another 5-6psi for switching to alcohol but maybe that's not what it meant

CI GS

If you meth guys are picking up anywhere near 5-6 psi of boost just from the "decreased compressibility" of alcohol over gasoline, then that must be the best kept secret in the history of hot rodding...
Just goes to show you can't trust a methhead!
And while we're into the mental masturbation on all of this, I wonder how much of a boost increase you get from increasing your IAT, since, after all, heating air causes it to expand, don't it???
Hmmm, maybe I should toss my heat exchanger and charge air coolers too, and see if I can pick up a few pounds of boost that way?

Petraszewsky

I just found the thought interesting. I wouldn't want to make more boost for the sake of making more, unless of course it meant a considerable gain in power. Obviously E85 and methanol can definitely make more power on the same boost vs 93 but my thought was if the fuel itself increased boost by displacing air. In my head the oxygen in the E85 and/or methanol fuels make up for the air they displace with their extra volume over 93. (And 50/50 meth injection as well). Anywho it's just thoughts...