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Paul Workman · 05-09-2019

I have 11.5:1+ after porting and shaving the heads .020" and I'm not having issues here where we're approx 600± feet above mean sea level (AMSL).

You may not have a problem, or timing could be "tweaked" (or the ECM will do it anyway, if knock is detected).

Marc Haibeck did my dyno tune, and I believe he even bumped the timing calibration a degree or two above "stock". No problems with knock.

If you are living in the mountains, or high planes, for example where AMSL is higher, 92 octane is typical (due to less dense air helps prevent knock) I'm guessing you'll be OK as well (Mine runs fine during the Appalachian and Rocky Mtn runs on 92 and even 91 octane.)

One way to find out would be to put the car on a dyno and see what the knock counts do at WOT. Then you'll know if you need to back timing off a degree or two, OR find an outlet offering 100+ unleaded octane. (The ROUTE 66 DRAGWAY is nearby. So, there are several stations nearby that offer the higher 100+ octane "race gas" (for a price)).

That said, and based on experience with my ~11.5:1 I'm guessing you won't have a problem at 12:1 compression with 92+ octane. YMMV.

05-09-2019	#3
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: Fuel for higher compression I have 11.5:1+ after porting and shaving the heads .020" and I'm not having issues here where we're approx 600± feet above mean sea level (AMSL). You may not have a problem, or timing could be "tweaked" (or the ECM will do it anyway, if knock is detected). Marc Haibeck did my dyno tune, and I believe he even bumped the timing calibration a degree or two above "stock". No problems with knock. If you are living in the mountains, or high planes, for example where AMSL is higher, 92 octane is typical (due to less dense air helps prevent knock) I'm guessing you'll be OK as well (Mine runs fine during the Appalachian and Rocky Mtn runs on 92 and even 91 octane.) One way to find out would be to put the car on a dyno and see what the knock counts do at WOT. Then you'll know if you need to back timing off a degree or two, OR find an outlet offering 100+ unleaded octane. (The ROUTE 66 DRAGWAY is nearby. So, there are several stations nearby that offer the higher 100+ octane "race gas" (for a price)). That said, and based on experience with my ~11.5:1 I'm guessing you won't have a problem at 12:1 compression with 92+ octane. YMMV.