71mach1

I have a 71 Mach 1 with a 351.

Do I use premium gas


DO I NEED A LEAD SUBSTITUTE???

texastboneking

What is your compression ratio? Factory motor? Ever rebuilt?

71mach1

Not sure, factory??

Told it was rebuilt......

texastboneking

If its not a race built engine then 87 octane should be fine. I would be more worried about your oil since it doesn't have the zinc additive.

les

Read the manual to the car. The octane rating it suggests for the 289 is about our premium fuel level. Granted when it was new you could put regular fuel in in but back then the fuel had a much higher octane. I run only premium with lead additive. The surviving number of our cars decline every year I am going to make sure mine continues to be on the road.

SoFlaBoss

I recall most 351C's were 11:1 compression, so likely would require premium fuel.

HOSS429

if you dont have a pinging issue run whatever you wish ..

AlsCobra

+1. Run lower grade if you can get away with it.

les

I think in the end it all comes down to preference. What are you putting in and how does it run. If it pings up the rating.