An 8 volt battery is a solution to a nonexistent problem. As long as the cables are big enough and the connections are clean and tight, 6 volts is all you need. To charge an 8 volt properly, the voltage regulator must be set to at least 9.5 volts. That is rough on points, light bulbs, and any other 6 volt accessories you might have like heater motors, electric wipers, etc. It also overloads the generator. Most "mechanics" who install an 8 volt battery don't have a clue how to set up the charging system properly, and virtually no hobbyists do.

Bottom line- - - -if you happen to solve a hard starting situation with an 8 volt battery, the improvement will only be temporary, and problems you create will be numerous.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!