The mothball legend as an octane booster has been around for a long time. Prior to the mid 1940’s - WWII changed the demand for chemicals - naphthalene (which is a hydrocarbon, like gasoline) was the active ingredient in mothballs. “Modern mothballs” use para-dichlorobenzene in place of naphthalene – this is nasty stuff and really toxic. Poisoning can occur if you swallow or ingest this chemical in any manner. Due to the toxicity of para-dichlorobenzene, naphthalene based mothballs have again become available.

Early gasoline octane ratings (1920’s) were in the 40-60 range. During the 1930s and 40s, the ratings increased by approximately 20 units as alkyl leads and improved refining processes became widespread (again, thanks to the war machine and the need for higher octane fuels).

Naphthalene has a blending motor octane number of 90, so jamming a significant number of mothballs down the tank could increase the octane. The number of mothballs required to appreciably increase the octane could have some adverse effects. Because naphthalene has a very high melting point (175 F) it will stay as a residue in your gas filter or carburetor long after gasoline evaporates causing a gummy mess!

With modern gasoline (89 – 99 octane), naphthalene is more likely to reduce the octane rating, and the large number required for low octane fuels will probably create operational problems – not to mention emissions..

They do burn, so you will get some power out of them - but higher octane gas or a good additive/octane booster is probably a better and safer way to go. I sure wouldn't put them in anything I own..

My Two Cents,
Glenn