i was wondering what you ran in your mustangs, i just run 93 octane (premium) in mine, but in the owners manual it says to us 99.8 octane or something like that?
Try to run 93 as often as possible. Have a high compression 357, so I back off the timing. Will be lowering the compression from 12.5 to around 11.5 with the new aluminum heads, hoping to run 93 all the time.
i was wondering what you ran in your mustangs, i just run 93 octane (premium) in mine, but in the owners manual it says to us 99.8 octane or something like that?
Back when your car was built the method for determining octane was I believe the 'motor' method and that number was higher than the 'research' method (I may have those backwards, but it will all average-out). Today octane is quoted as R+M/2, which you can tell gives us a number alltogether different than what your book says to use.
Except for my motorcycles which require the highest octane out there (93) I use the lowest I can get by with. The Accord uses 87 and the 65 would probably run on 83 if I could find it. It has a stock single-point, vacumn advance distributor connected to ported vacumn with flat-top pistons, 289-2barrell heads shaved .030 and the Crane Fireball-1 cam that probably does not do very well at filling the cylinders below 2000 rpm. Just to see what would happen I advanced the timing in 2 degree increments to find where it would detonate. It didn't seem to matter WHERE the timing was, it would not pre-ignite where I could hear it. It would run like crap...but no noticable spark knock.
Find the lowest octane your engine will tolerate and use that. And I also only use Chevron or another gas listed on BMW and GM's list of 'ultra-pure' gas. These were tested to not allow a carbon build-up on the valves enough to require an increase in octane for 100,000 miles minmum.
My 68 Merc's 390 before the overhaul wanted only 93 with 10.5 to 1 and the stock cam. After the overhaul, 10.25 to 1 and a Crane 272 degree Energizer cam it was fine with 89 and 12* BTDC timing. My 331 wants only 93 with 10.4 to 1, Ford Z303 cam and Canfield heads. My 89 Ranger's roller 5.0 (ported E7's, Ford F4TE roller cam, 9 to 1 ratio pings ever so lightly on 87 and 12* timing, never a sound with 89. The last 67 Stang I had wanted only 93 with a rebuilt 302, 9.5 to 1 ratio, C6OE heads, RV cam (don't know the specs but going by the sound it made idling), cast flat tops .020 down the bore at TDC. I'm with the others, run as little octane as you can with the timing advanced and keep it from pinging. Retard the timing and you lose power and the mileage suffers too. The economics work out in favor of midgrade sometimes over regular, the extra ten cents per gallon often get you a few more mpg than 87 and the cost per mile is less.