The HEMI is more tolerant of high
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ compression due to the more efficient chamber. A poorly tuned 8.2 to 1 440 will knock on 91 if the conditions are right.
There are no over the counter additives that will raise the octane effectively. Forget the claims printed on the can or bottle, they do not work. You can get Sunoco 104 and 110 race gas in 5 gallon pails from a NAPA parts store. I am no chemist, but my basic bonehead math tells me that mixing equal parts of 110 with 91 could average out to 100.5 octane.
In 2013, I started trying to find ways to stop the detonation in my 10.9 to 1 440/493. I tried all sorts of things including spark timing curve modifications, carburetor adjustments, different camshafts and the high octane gas. The 110 octane Sunoco gas has lead in it. MAN that stuff smells fantastic through the mufflers! The 104 octane eliminated most of the knocking but the 110 got rid of it entirely. I ended up putting in thicker head gaskets, dropping the ratio to 10.07 to 1. I can run great on 91 now.
the 'ol 413 screams!....4 gal?$$$$....-=$25.00......
