Numbers&Letters?

What were the letter codes next the the racing # that traditional hot rods ran in the 40's
I know it has something to do with class but not sure.
I searched a couple key words and i couldnt find anything.

 

Engine size, then class.

A/R would have an A designating the largest engine (at that time, now they have AA) R would designate roadster.

Later on it went to A/SR with the S designating street.

Take a look at the SCTA site.
They may explain it there, but best bet is to get one of their rulebooks.

Same goes for NHRA far as the numbering goes.
One

 

Awesome, thanks
i knew there was a association but couldnt remember what it was