I have heard that regular gas if understood; is not really a bad choice, given it has fewer carbon buildup producing additives, such as anti- knock, is more volatile etc.

since all here is able or would like to be able to manipulate tune, is it conceivable to tune only for regular low octane gasoline for a highly modified tpi motor and live to tell?

and would the performance difference be large?, I really don't care about every last bit of horsepower, I like responsiveness and lower fuel costs wouldn't be a bad thing for me either.

is it as simple as dialing back the spark advance table? to take car of the knocks?

 

I'd run on a higher octane fuel to be on the safe side. Don't want to blow up your engine!

 

depending on how the motor has been modded, you can tune it to run on regular without a problem. but you very well may see a big drop in both performance and fuel mileage.
much over 9.5 with iron heads, it would need better fuel.
if the quench isn't right, it would need better gas and will never run to its full potential, even with good gas.

 

AFR 195 street heads, 10.7 compression,

I like your term "full potential", I want better gas mileage....

 

with aluminum heads, i don't know what the limit is for regular gas. i would guess if you not over it, your very close to it.
hopefully some of the guys that have ran aluminum heads will jump in.