Nom nom nom.

 

I'd rather turn up the boost vs turning up the timing.

 

Yes. We all know you can increase the timing with e85 to make more power but what about an apples to apples. leave the timing alone. let the fuel make the power. 93 and meth vs e85.

 

I do not have access to e85 where I live so I'm stuck with 93/meth. I run 18psi with 93 and meth(70/30 mix) with 18-19 degrees of timing. So far its working well and I only have one meth nozzle.

At lsfest all of the e85 cars/trucks were having problems with high iat's pulling timing. I don't understand why you wouldn't use a water/meth mix even with e85 for the lowered iat's alone. Sure you can add a lot of timing with e85 but it doesn't do you any good if your tune is pulling it all back out when its hot at the track. I also keep my meth/water mix in a cooler at the track and fill it before my pass. I normally see iat's close or lower than ambient temp even in the summer.

 

Do you really care about fuel consumption under boost?
Timing has no impact on fuel consumption, what it would control is exhaust temps and cylinder pressure, basically how well the engine uses the energy contained in the fuel. The fuel flow is based on the air flow, period.


Fun question, heres an extremely simplified explanation...

Gasoline contains 46.4 MJ/kg of energy, methanol is 19.7 MJ/kg, ethanol is 30MJ/kg. Lets remember e85 is 85% ethanol and 15% gasoline, so e85 would be (.85*30+.15*46.4)=32.46 MJ/kg. Lets also assume 20% of your fueling with the 93/meth combo comes from the meth, so on an energy basis, 93/meth energy content is (.2*19.7+.8*46.4)= 41.06 MJ/kg.

Already something should be obvious....you can make the most power, energy wise, on pump 93! e85 only has 84% of the energy content of straight 93 and 93/meth is only slightly better at 88%. This is of course ignoring the effect of detonation. Also dont forget this is based purely on just burning the fuel, not necessarily how much the engine can utilize of that (which is where timing comes into play).

Now, lets say you want to run your engine at 0.73 lambda for e85 and 0.78 for 93/meth. Stoich afr for e85 is 9.0:1, 93 is 14.7:1, and meth is 6.47:1. Dont forget our fuels are mixed! E85 is going to be (.85*9+.15*14.7)= 9.855 and 93/meth is (.2*6.47+.8*14.7)= 13.05.
So 0.73 lambda for e85 is going to be (.73*9.855)= 7.19:1
0.78 for 93/meth is (.78*13.05)=10.18.
0.78 for straight 93 is (.78*14.7)=11.45

AFR is air to fuel ratio, ie, the amount of air needed to completely burn 1 unit mass of fuel. So if we keep our airflow constant (just playing with fuel, remember?) then we are going to use [1- (7.19/10.18)]= 29.4% more fuel with e85 than 93/meth...but is that more energy available?

Just for comparisons sake our turbo moves 40kg of air (about 800hp worth).
Straight 93@0.78 lambda (40/11.45) = 3.493kg of fuel for the air given.
93/meth@0.78 lambda (40/10.18) = 3.929kg
e85@0.73 lambda (40/7.19) = 5.563kg

Using our energy content from earlier:
Straight 93 (3.493*46.4) = 162.08 MJ
93/meth (3.929*41.06) = 161.32 MJ
e85 (5.563*32.46) = 180.57 MJ
Keep in mind we are richer with the e85, at 0.78 (truly apples to apples), it would be 168.82 MJ.

So using straight 93 as the baseline
Straight 93 = 100%
93/meth = 99.5%
e85@0.78 = 104.2%
e85@0.73 = 111.4%

SSSSOOOO.....*based purely on the fuel consumption*, running e85 slightly richer in place of 93/meth will give you 12% more power everything else being equal.

The HUGE caveat to this is all things are NOT equal. Remember how we are injecting a lot more mass of e85? Well that fuel displaces air, so all the sudden you cant push in as much air because some of the volume is fuel, so you volumetric efficiency goes down. By volume e85 is displaces roughly 6% more volume than gasoline, so your gap just shortened by that much. E85 burns cooler than 93, so from a thermodynamic standpoint your engine is now a less efficient heat pump. Also e85 is harder to ignite, ie, you need a stronger ignition system, this is a parasitic loss on the engine, unless you dont run an alternator. The flame front speed of e85 is slower, so using the same timing map of 93 will not allow the engine to fully utilize the power stroke. There are many more things to consider, but this hits the high points.

My opinion is if you run them back to back with no other changes, you will see less power with e85, but what do I know...

 

Tip of the iceberg!

 

problem is you cant run apples to apples on something like this. they are two very different things that require two completely different tunes. plus why would you want to even compare something if you have to handicap one of them to make it fair ... lol.

 

Yea that is how I see it too. Apples to apples for me would be a fully optimized and properly set up tune for 93/meth and a fully tuned E85 set up. That way you can see exactly what you would get with both types of fuels. No one running E85 is going to tune for 93/meth

 

Thank you for taking the time to write that out Atomic. I like the discussion here much better than, get the corn, its great. My closest station for corn is 31 miles away and I would spend over a grand to get corn capable.i want to make darn sure it's worth it.

 

Very nice Richard!