Which is the safest and best one to use.
I am getting the ECU done by Powerchip and it requires 93 octane fuel.
In my city the highest is 91.

 

Not sure of the cash situation, but you would be better off snagging some race gas (ultimately a 55 gallon drum) and mixing in a little with each tank. Much better than cheapy octane boost.

But if you wanna try it...here is a hotrod article on octane boost.

http://www.hotrod.com/techarticles/72498/

If you do run 91 octane, not gonna kill your motor, it will just adjust the timing to compensate and you will lose a few hp.

Here is paragraph from the article.

The power numbers generated with the boosted 91-octane are lower than those made with non-boosted 91, an indication that the fuel additive may have slowed the burn speed and reduced cylinder pressure. One thing is certain, there was no detonation present or we’d have seen it on the dyno charts and in reduced peak crank speed

 

Thanks for the fast reply.

 

Use Torco. There's a distributor on corvetteforum.com that can hook you up. His member name is JBSBLOWNC5.