6 Lbs of boost is not enough
12-27-2007, 10:54 AM
#43
In other words, get you VE locked in without meth as much as you can and then exprolate the table up (I usually scale it by 5-10%), then enable the meth and retune for the meth. Where the meth is on, you will be leaning out the VE table a LOT, but you're still shooting for an AFR that will read on your gauge.
Meth's stoich is 6.40, gas is 14.7. Meth is .93 as dense as gasoline (which is 1.07 more dense than meth).
So let's say you want an real AFR of 11.5:1. What does your WBO2 need to read? (WARNING VERY TECHNICAL **** FOLLOWS -- GET OUT NOW WHILE YOU STILL HAVE A CHANCE)
1. get the meth by volume
2. get the meth by mass
3. get the actual percent meth injected
4. find the mixture's stoich
5. calculate what the gauge should read
1. we need is the amount of meth by volume compared to the gasoline. For this example, lets use my truck -- two 15gph nozzles feeding meth and 139lbs/hr (96@43.5 + a 1:1 boost ref'd FPR at 18psi). To get g/h, divide by 6, so I'm pushing 37 gph. Keep in mind that only 1/2 of the meth is actual fuel (meth = 50% methane 50% oxygen) so of the 30gph we're pushing, 15gph is fuel.
2. Ok... so I am flowing 15/39 = 38% meth (gulp) when the PAC is wide open
3. The mass of methanol is 6.59 lb/gal (these next two steps I could skip since I run 100% meth, but they are here for completeness sake), so I take 6.59 * amount of meth in the mixture (in my case = 100) to get 6.59. If I were running water in the mix, I'd need to get it's mass as well -- water's mass is 8.33lb/gal, so we'd take 8.33 * (the % mixture of water). Then we take the mass of the actual meth * 100 / ( mass of meth + mass of water ) to get the percent of methanol in the mix
(sidetrack: say we are running a 50/50 mix of methanol:
mass meth = 6.59 * .50 = 3.295
mass h2o = 8.33 * .50 = 4.165
percent mass of meth = 3.295 * 100 / (3.295 + 4.165) = 44%)
In my case, this is 100%
3a. Another step really simplified by running 100% meth
. To get the actual percentage of meth injected, we take the percent mass of meth and multiply by the percent volume. In my case, 100 * 38 = 38.(sidetrack: for the 50/50 mix
44 * 38 = 17% )
4. To get the mixture's stoich, we take the
actual percent meth * specific gravity difference meth * stoich meth + actual percent gas * specific gravity difference gas* stoich gas =
.38 * .93 * 6.4 + .62 * 1.07 * 14.7 = 12.05
5. to get what the gauge should read, we take the discrepancy between the mixture stoich and the gauge's stoich reference and calculate from there.
Since my mix stoic is 12.05:1, and the gauge is calibrated to 14.7:1, there is an 82% discrepancy. So if I'm targeting an 11.5 then I calculate 11.5 / .82 = 14.0 on the gauge.
What about if I run 50/50? Well, the mix stoich = 14.07, so the discrepancy is .96, so the afr target = 11.5 then the gauge should read 11.5 * .96 = 11.98
You can reverse this last forumla as well, to figure out what you are really running based on your gauge reading:
In my case, if I was running a 11.2 on the gauge with 100% meth, then I'd be hitting an 11.2 * .82 = 9.184 real afr.
Last edited by TurboBerserker; 12-27-2007 at 02:02 PM. Reason: had the gauge to real calc reversed!
12-27-2007, 01:59 PM
#49
actual percent meth * specific gravity difference meth * stoich meth + actual percent gas * specific gravity difference gas* stoich gas
the .62 is the percent of gasoline in the mix (100 - 38% meth)
--and I just saw I had the direction reversed on the gauge to real calculations! Doh! Fixed above.
the .62 is the percent of gasoline in the mix (100 - 38% meth)
--and I just saw I had the direction reversed on the gauge to real calculations! Doh! Fixed above.
12-27-2007, 02:26 PM
#50
Let me see if I understand you correctly
I'm actually running richer than the gage displays if I'm injecting meth into the intake?
Since my mix stoic is 12.05:1, and the gauge is calibrated to 14.7:1, there is an 82% discrepancy. So if I'm targeting an 11.5 then I calculate 11.5 / .82 = 14.0 on the gauge