What the heck
 

I just picked up a 77 with 2.7 this weekend. Here is what I know:
It requires premium gas. It has updated tensioners and fan + 183000miles so we know it's been rebuilt. It has similar power to my sc that ran well. It never got over 210 degrees in some really spirited driving 100mph for 10 mins.
Thats it. Thats all I know as the previous owner had no papers. What gas did the original need? I used regular in the sc but this clearly needs higher octane. Would it be safe to say it's got higher compression pistons? It still has cis so not too high I guess.
Anyone want to venture what I might have?

You have an unknown engine that burns premium gas......enjoy!

-Andy

hrmnn... sounds like you have a running engine ;)

Who told you it needed premium gas? IMO all these cars need premium gas.

If you think you need it due to detonation, that could be a function of the timing? Have you checked the timing? Plug Gap? Altitude where you are driving? Intake system? Was it a recurved Dizzy? Have you had compression test, leak down? Not enough information to get a coherent response.

If you drop the engine and show us what you have, Im sure some experts can chime in...

Ok, it's definatly a 77 2.7 case. I'll check ignition timing and see if that's off. Case #6270937