When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
5.0L (1979-1995) MustangTechnical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.
With stock timing (10*) you should be able to use 87. The higher octane gas takes more energy to burn and therefore you can increase your initial timing. Once you go above the factory setting you'll have to use 89 or better.
My car is basically stock - I have headers, o/r H, and flows - and when I put in 93 I can feel a difference. Not much, and its not really worth the extra cash, but the car pulls better.