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The (R+M)/2 blending octane of methanol is 119. Assuming you will be blending with 93 octane pump gas, at 25% methanol concentration, the octane will be 93*0.75 + 119*0.25 = 99.5.
Although methanol can be blended with gasoline successfully, it has two main drawbacks: (i) of all the alcohols, it is the one which is most corrosive to metal components in the fuel system, and (ii) the resulting gasoline / methanol blend is highly susceptible to phase separation upon moisture absorption. (Phase separation refers to separation of the gasoline into a water-rich alcohol layer and a water-poor hydrocarbon layer.) Another potential problen with methanol is that it is often contaminated with turpentine, which forms a residue during combustion that may cause excessive piston ring wear.
In countries which allow the use of methanol in gasoline, it is usually limited to 5%, and a phase-stabilizing co-solvent is usually employed (e.g. isopropyl alcohol or butyl alcohol).
If you use methanol, make sure it is a grade which does not contain turpentine and also has a very low water content. Also, don't let it sit in the gas tank too long or corrosion problems may result.
I personally use 10% toluene and 10% isopropanol, because I am somewhat afraid of the the issues that can be encountered with methanol. My blend avoids the problems associated with alcohols and the final octane when blended with 93 octane pump gas is in the upper 90's.
I mix 5% gas with the Methanol. I would use Top Lube, but I read in the past that it wasn't compatible with the EFI injectors. The 5% gas doesn't completely eliminate Methanols affects on unprotected surfaces, but it goes a long way in reducing the detrimental effects on Aluminum and the drying out of rubber components. I'm still using an aluminum fuel cell and see very little evidence of corrosion as long as I have the race fuel mix. When running straight methanol the results are very obvious, you spill a little Methanol on the side of the Al tank and you have instant oxidation.
As a side note, I had roughly a gallon of Methanol/gas mix sitting in a closed 5 gallon aluminum fuel cell for 6 months. Upon emptying the fuel cell there was little to no evidence of corrosion. I'm sure having a closed fuel system, with the gas additive, and being in dryer than hell AZ only helped things. On the other hand, I have seen corroded AN fittings and harder then concrete rubber lines used on Methanol powered vehicles.
__________________ TT632's Vehicles:
4th gen SOM Formula, 700 HP 427 or 1350 HP TT 421
05 Avalanche. 97 S10. 95 Firebird. 87 Olds 442 60k all orig. 05 POS Rav4. 87 Samurai. C4 Corvette
Can you mix methanol with pump gas 25% meth to 75% gas.
E85 @ 105 Octane (25% @ $2.85) + 'Premium' 93 Octane gas (which at most pumps is actually E10) (75% @ $3.85)
It works out to an effective Octane rating of 96.
I've done this twice now, when in the area to get E85 - both times, post fill up, for about 5 minutes / miles, my 96 LT1 drove poorly, idled rough, and actually stalled once! But, after the PCM compensated, it was fine.
Took about a 1.4 MPG 'hit' too.
(I've decided that the best place for E85 is in my Meth tank!)