1970s 1978 Seville V8 Gas - What Octane Should I use?

[surfexplorer]

Hi All,

Manual only says to use unleased gasoline.  Any idea what octane I should be using? 

Appreciate any input.

Thanks
SurfExplorer

[bcroe]

That is a low compression engine, same as my 79 Eldo
was.  Lowest grade unleaded ought to work.  However if
the original (time bomb) timing chain set has not been
replaced, you could have some issues with the cam and
ignition timing bouncing back and forth.  That is what
happened to my 79 Toro.  However the Toro 350 had higher
compression.  Bruce Roe

[TJ Hopland]

Yep.  In theory from the factory anything from GM from 71 to the mid 80's should run on 'regular' unleaded.  These days there are several variables especially with a non regular use rig that may make a non ethanol premium a good choice if its available to you.

Also Bruce that posted above is the 70's Cadillac EFI system guru.  Him and a few other members here have figured out how to keep these things running including making some parts so if yours still has the EFI this is about the only place you are going to find people that know that system.     

[surfexplorer]

Thanks- always used premium for past few years but have not put on any significant miles.  Last fill up I tried regular for first time and have not notices any difference so far.  Still has the original EFI. 

Thanks