Hi,

I just bought a 66 mustang with a 4 valve 302 engine year 1978. The only ethanol free gas near me is 90 octane while the dealer said to use 93. Can I use 90 without damaging the engine?

thank you

 

Ford does not lift a 4 valve 302 in 1978. Compression ratio is only 8.4 to 1. 87 octane gas is good for 8.4 to 1 compression ratio.

 

To further clarify, if the motor is a 302 4V, the V refers to Venturi on throats on the carburetor has. 2V(enturi) and 4V(enturi). 2 barrel/4 barrel.

That being said, with higher octane you will be able to get more timing out of the motor. More timing might be required depending on the type of cam in the heads. High-lift cams require more timing advance, thus higher octane to prevent pinging.

 

All engines were low compression. 87 gas is fine.