The gas station down the road from me sells 100 octane gas.  I have a stock 318 2bbl  1973 plymouth satellite....will such gas harm my car in any way??

No!  

no, but i dont think the engine needs gas like that.

Nop it will not but  you might need to tune your carb up once you sart to run 100+ octane.  Make sure your spark is hot you some times run the rick of fouling oiut pulgs now and again in the spark is to cold for the fuel.  I found this out the hard way.

You do not have to tune your carb or anything...

There is no reason for you to buy gas like this for a low-performance engine like you are talking about... 93 octane is more than you'll ever need... Remeber octane does not equal more power. High octane does not equal high power.. Octane raises the flash point of the fuel. It actualy makes the gas less flamable. When gas is compressed in a combustion chamber it gets hot. In a high compression engine ( over 9.5:1 with iron heads and 10.5:1 with  aluminum heads ) the compression can make the fuel flame before the spark lights it. This is called detonation or pre-detonation. It is very harmful to engines for a vasriety of reasons.  Higher octane fuel resists the tendency to flame under high heat without spark allowing a high compression engine to run "properly". The fuel lights when its supposed to, when the spark fires. 

So.. you can see with your 318..it just isnt going to require high octane fuel. You should not be experiencing detonation and hench will gain no benifit whatever from 5.00 a gallon fuel but a hole in your wallet.

I experianced this problem while I was in Reno for Hot August nights last year.  Do you thin k that the altiude had an effect on the carb enough to effect the fuel ratio? (the followinf is an example agreeing with your statement) In our drag car we Run 12 gallons 93 with a bottle of  Lucas oil fuel treatment and it runs just fine and that motor has 12.5 to 1 compression.  We have not run her higher than 3500 feet thus far.  So Nascar really does not need to run 110 then?

Altitude does effect the carb enough to cause a rich/lean condition..

I dont know what Nascar runs in the way of compression. In my street car I run 12:1 with aluminum heads and must use a mix of 100 and 93 50/50. I have found no additive that will stop the det with regular 93 ( I have not tried lucas ). My engine was tuned on a dyno to ensure proper air fuel and distributor curve throughout the power band. I sure wish I could run the car without goog gas.. I'd buy a truck load of that lucas stuff.

This is the mixture that we use in our race car for race day.  5 gallons of 92 w/ one black bottle of 104+ octane boost in that 5 gallons x 2 and one bottle of Lusas oil to the 10 gallons that is wha ti was told makes 109 I think.

How much volume is the lucas additive ?  

It is 12 fluid ounces if that is what you mean. 

See thats the thing I dont get.. Volumetricaly (sp) 12 oz of anything in 10 gallons of fuels isnt going to do squat.. even if that stuff was 300 octane ( which it isnt ) it wouldnt raise the octane in 10 gallons more than a point or so. However I'm not saying your full of crap either.. I just ordered some VP octane boost. I have heard good thing about that and we'll see how it does... Anyway I glad you have a solution that work for you. How I find one as well.  

We are using it mainly for the Lubrication of the valves since the bottle "treats up to 20 gallons" it works quite well.  #'s I am not so sure on for octane rating just a ball park figure.