We have a 74 450 SEL. The manual says to use minimum 91 octane to avoid pinging or predetonation, but that was in 73/74 using the Research method of determining octane. I know that they changed to the average of research and motor octane around that time, so what we see as 91 at the pump today is not the same as 91 Research octane. I have gone down to using 89 octane modern gas with no problems. My question is, will I be ok using 87 octane pump gas, since I've read that modern octane gas is rated about 6 points lower than the research method? Lastly, anyone have a good estimate of the motor octane rating of 87 pump gas? (We live in the Southwestern US). Thanks!
- posted
20 years ago