petrol saving chemical

Hello,
I got told by a guy who runs a lots of vehicles how he saves on petrol. And that is to put some napthalene in the petol when you fill up at the petrol pump. About 1/2 teaspoon of crystals to a tankful of say 50 litres. This works with standard unleaded but not with premium unleaded. I do a lot of K's to and from work and it does seem to make a bit of difference in power. It's kind of difficult poking napthalene crystals down the unleaded fuel inlet of the car so next time I'll be mixing it in a can first. I got the napthalene from the local supermarket iin the form of sachets - it is what is used in mothballs.

The guy with the car fleet says it doesn't cause engine trouble and mine seems to be running better so I think it is safe. Please try it if you like.
I'm sure there's more motoring tips to come.