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Gasoline additives

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Sure, manna from heaven for FI engines. The practice of fortifying fuels with xylene and tolulene was banned in Formula-1 racing in the mid-80's. Xylene and tolulene each have both a lot more chemical energy and octane than today's piss-poor gasoline (toulene = 114 octane, xylene = 120 octane). Xylene and tolulene are the ONLY real octane boosters. At a refinery if a batch of gasoline comes up short on octane they add just enough xylene and/or tolulene to meet the required octane target, and this is very expensive to do. 'Race gas' blends do not do this, the manufacturer will add LEAD to increase the octane rather than xylene or tolulene because it is much cheaper - sure you get the octane, but no more energy in your fuel.


The back-story: gasoline has both xylene and tolulene in it; these chemicals are called 'aromatics' and the federal government has pretty-much concluded that when xylene or tolulene escape into the air it accounts for a major part of the smog problem (benzene is produced from combustion of tolulene/xylene, very very toxic plus a huge carcinogen). It is for this reason that there are those damned little rubber booties on fuel pumps in many states. Laws were also passed decades ago limiting how much xylene/tolulene molecules could be present in gasoline, which is why our gasoline is 'watered down' compared to yesteryear.


Remember potential energy in fuel is not to be confused with octane, these are two separate topics. The density of tolulene is something like 15% more than that of gasoline, that gives you an idea how much more heat/gallon it contains. So, if you put a gallon of yesterday's pump 91-octane gas in a shallow pan and a gallon of today's pump 91-octane gas and light both on fire you will observe that the old fuel is *a lot* hotter (it contains more chemical energy/heat). The flip-side of the coin is that xylene and tolulene need more energy to vaporize, so using too much can cause freezing (poor cold starting) - or on some applications may lower intake charge temps.


From what I have seen, FI engines benefit most and using a 10-12% mix of tolulene or xylene is common in some circles; adding xylene and tolulene up to 20% will not harm your engine (remember it's already in gasoline to begin with) but at $5+/gallon in bulk is very expensive; concentrations above 30% are not recommended. Conventional wisdom is to start at 10% and increase concentration until no more improvement is noticed.


Other limiting factors: you might dilute the lubrication package in your unleaded fuel too much, causing serious valve seat erosion (exceeding 15-20% mix). The max-power stochiometric ratio drops from 12.1:1 (gasoline) to around 9.8:1 (100% tolulene), so tuning may be required to compensate. Xylene and tolulene are about the best possible petroleum solvents you can get, expect fuels with higher concentrations to wash down a lot more oil off cylinder walls and definitely reduce mileage between changes. Lastly, remember that higher octane means that more fuel will burn on the way OUT of the combustion chamber - if the vehicle is still running catalytic convertors plus enough tolulene/xylene to exceed approximately 95-octane then exhaust temps will skyrocket and you will burn-out your cats.


Napthalene (moth balls) is a poor-man's octane boost, but makes the engine run *very* dirty, it will not pass sniffer test and quickly builds carbon all over pistons and valves. Naptha is also now a federally regulated substance, so moth balls today no longer contain naptha, the moth balls you buy in the store now will not raise octane but actually damage your engine. Too much napthalene will damage your engine as well over the long term.


Mr. P. :)

Edited by misterp (see edit history)
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Mr P...


You should change your name to Mr. WIZARD !


You have tons of information. You are a asset to this forum !!



Well according to my kids (with me right now for the summer) my name is Mr. History Channel :D


Mr. P. :)


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Hmmmm. I wonder if anyone has ever slipped-up with the gas funnel and spilled thinner all over their paint. :banghead: I'm thinkin I'll stick with the store bought octane booster. Real interesting info BTW Mr. P.

Edited by NebraSSka truck (see edit history)
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Hmmmm.  I wonder if anyone has ever slipped-up with the gas funnel and spilled thinner all over their paint. :banghead:  I'm thinkin I'll stick with the store bought octane booster.  Real interesting info BTW Mr. P.

Actually thinner will not harm the clearcoat at all, it will just leave an oily residue.

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I'm thinkin I'll stick with the store bought octane booster. 


Store bought stuff is almost worthless...it typically adds octane POINTS...that is, will change the octane from 93.0 to 93.6 AT BEST...waste of money.


It's nothing more than toulene with a couple cleansers added in (same cleansers that are already in any name-brand gasoline). Thing is, b/c you're only adding 12oz of the stuff, it can barely change the octane rating.


So either:


1) Buy good race gas


- OR -


2) Add toulene...


...or leave it be.


- Brian

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I'm sorry maybe it's me this just seems absolutely rediculous. Don't get me wrong I am not a tree hugger, but putting this stuff in to your fuel, for whatever horsepower, and dumping god knows what poisons in to the air (as stated above)seems stupid. Save your money, buy a turbo or supercharger. God, I must be getting old!

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