Regular Gas vs High Test
 

My '78 5 speed 928 has a stock motor & from what I understand, has an 8.5 to 1 compression ratio. This is a US car. Regular gas ignites quicker than high test & would not benefit a low compression motor. Low compression motors don't pre ignite as quick as high compression motors that need a gas that ignites slower (high test) I don't believe high test is necessary in this car due to the low compression, provided the timing is kept stock. It's been my experience that using high test in a motor designed for regular offers no benefit. It's not a matter money, it's a matter of what type of gas will work better. I don't want to hurt my car & I'm not looking to start a controversy, just want to know if my reasoning correct? What ever happened to the rumors of a new 928 from Porsche?

I would run the low octane too...should be fine. But the extra cost for higher octane pump gas just isn't that much.

Run the lowest octane that doesn't ping.

Or

Run the best gas you can find and tune until it almost pings.