I have found multiple "Homebrew Racegas" articles. The majority recommend Toluene as an aromatic. Xylene is also listed and has similar properties. It seems that Toluene has been preferred for cost savings (at the time the arcticle was written). Xylene is now more affordable and would yield the same actane with lower ratios due to higher octane {(R+M)/2}.

Question: Are there any drawbacks to using Xylene over Toluene?

Note: High pressure application (up to 26psi).

This is a review I posted on 11-9-02 on another forum.  I have been using Toluene on and off for a while and it works well and has no lead so it does not lead foul the O2 sensor.

"33% Toluene Logged at 20 PSI on Big16G

Tonight I logged 2 runs at 20 psi with 2 gallons of Toluene added to 4 gallons of 93 octane. 4 gallons is based on being just under 1/4 tank, and knowing from draining tank for fuel pump install that means about 4 gallons. I bought a 5 gallon container of Toluene from Porter Paints in Athens, GA in mid June for just under $30 out the door. I think Toluene maintains its octane rating well over time, so I presume it was still 114 octane. By my calculations this means I was running about 100 octane.

I had uncontrollable wheelspin in 1st and 2nd (despite an ultra stiff suspension setup that minimizes weight transfer), so I will focus on the 3rd gear logs. Pull #1 started at 3031 rpm , 22 degrees timing, IAT 71*. O2 started at .88, then .86 most of the run, then .84 at the end as slight knock occurred as I reached 6468 rpm. Knock started at 7 at 4656 rpm and stayed between 3 and 7 until it jumped to 10 at max rpm. Timing stayed between 16 and 20, mostly 20, until dipping to 16 as I hit 10 counts of knock. IPW stayed between 17 and 20.5 ( I have 450's).

The 3rd run was very similar except that I started 3rd at 4625 rpm, and at the very end of the pull above 6200 rpm I saw 12 counts of knock instead of 10, and timing pulled back to 14 at the very end. I also ran to 5125 in 4th with a max of 9 counts of knock and good timing until the 9 counts of knock pulled it to 14*. IAT for the 2nd run was 79* due to increased underhood temps. The car pulled the strongest it has ever run during these 2 pulls. I have never run this much Toluene before. The engine was very smooth, with none of the knock induced roughness I have experienced in the past.

My 2 previous logs from a week or two ago, on 93 octane, were at 17psi creeping to 21 at the end. IAT for those prior runs was 70* for the first run and 66* for the 2nd (later in the evening). The 1st run I hit 20 counts knock sum by 5700 and backed out of it. The 2nd run was to 6281 rpm with 30 counts of knock (ouch!) and perceptible roughness. In one of the runs I had 15 counts knock by 5200 rpm and in the other I had 18 counts by 5400.

The Toluene seems to be a good, convenient alternative to race fuel. Unlike 100 octane low lead aviation fuel, there are no worries about fouling the O2 sensor with lead deposits. 100 octane av is about $2 per gallon around here, so that is a little cheaper than 33% Toluene. I pay about $1.35 per gallon for 93, and $6 per gallon for Toluene, and with a 2 to 1 ratio that is about $8.70 for 3 gallons of the mix, $2.90 per gallon. It is still a lot cheaper than race gas, which is about $5 a gallon around here, and also has lead.

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