My dad had one of these when I was a kid and now my older brother is thinking of buying one again. What gasoline octane rating would be required to safely run this car?

F

Depends on the cam, if it has twin plugs or not, what kind of hot-spots (if any) are in the combustion chamber, and on and on and on...

Dunno what kind of fuel you'd need.

--DD

my 3.6 has 11.3:1 compression ratio.......I normally run Premium, but I've cheated and thrown regular in it once or twice

Your 3.6 has knock sensors, right?

F

run premium, and add a lead substitute...
We can get 94 octane here in NY for about 1.80/gal..

Leaded racing fuels are available in at some filling stations, 104 octane about 4.35/gal....110 octane 4.85/gal... 118....well..

Why not ask the owner what he runs it on?

Mueller's six might get by with 11.3:1 compression and pump gas, but it has nice hemispherical combustion chambers, EFI, and it was made by Germans.

Pop had a Custom 500 w/ 427 police intercepter (bought at state patrol auction), which is about the same motor as this 390 we're talking about. Anyway, it only ran well on "Ethel" (94 octane leaded). Running on anything else it would knock like mad.

-Ben M.

I built my old 1970 F250 with a 390ci up to about 330hp. 10 to 1 comp, cam, rollerrockers,and a big 4 barrel carb. Shoot you could watch the gas gauge go to empty if you stomped on it. Had to have a local racer rebuild the auto tranny to handle the power. Lots of fun, but jeez these days gas is $2 a gallon.

Geoff

not a lot of twin-plug Merc's, i bet :-) ...

This one's got two plugs. Not what you meant? (sorry. bad joke)

this: < http://www.rmauctions.com/events/catalogca...B03&sNumber=054 > the car referred to in the original post, asking what one had to do to run 10.8 compression -- to which DD replied (for some reason) it depended on whether the engine was twin-plugged.

i don't think there were a lot of 1963 Mercury Monterey S55 'Police Special' 390 cid V8's with two plugs per cylinder - 10.8 CR or not ...

Back the timing off a little and run premium and it should be O.K.

If not, a set of Edelbrock Alum heads would certainly take care of it.

The Truck guys do it all the time.

You could also ask Here:

Ford-Trucks FE Engine

or Here:

Cobra Club FE talk

HTH

P.S. the "Police Interceptor" 390 is a solid lifter motor with very agressive cam specs (for a production motor) I think that would put your dynamic compression in a very reasonable range.

Correction--I replied that it depended on a whole lot of things. Twin plugs were one of them. Not that I expect an old Merc to have two plugs per chamber, but other motors do--I was talking generalities.

Mueller's 3.6, for instance.

Rule of thumb is that you can run a full point more compression on the same fuel if you have twin plugs than if you do not.

--DD

lighten up, Dave, you don't have to be so defensive :-) ...

but i don't think your generality is supportable...

i agree it's true for high-compression hemispherical combustion chambers - but AFAIK most American iron - expecially of that vintage - was using good ol' wedge chambers. i don't think 2 plugs buys that design anything. similarly a pent-roof (classic 4-valve design) with the plug located in the center of the 'tent'.

Hmm, good point!! The person I was talking to about the twin-plug setup is a 911 guy, and may very well have only been talking about 911s!!

--DD