The engine doesn't seem to notice the difference between the two and feels crispy with both.
Static compression ratio of somewhere between about 9.7 and 10 seem to work fine and therefore pump premium gas is ok. No additives necessary.
Note also that I tried a dual duration pattern on the camshaft with greater duration on the exhaust.
This was recommended by the cam grinder as a way of blowing some of the compression out of the exhausts and fooling the engine into thinking it had a lower compression ratio.
In my case it did not work. Ultimately the compress-ability of the fuel without dieseling, is the determining factor. That is what the octane rating is after all. The higher the number, the higher the cylinder pressure it will take to make it detonate without spark.
I found the closed chamber Cleveland heads very sensitive to this. Seemingly no amount of additive I could put in was adequate to even reduce it.
It got so bad at one point that the engine would just shut itself off completely at about 4,200 rpm.
Currently I am running shaved A3 heads with dished pistons. Actual CR is 9.8:1. Runs great on 93 octane.
Open chamber heads would not be my choice to go with. Simply put, they are just too difficult to make work with this gas and any combination of piston dome configurations.
As AusFord says, it is a different engine with them. They lack the crisp response that the quench heads give.
Again, just my experiences with this engine series. Obviously, I did not try every possible configuration available and frankly, I'm done and this is what I am running and am SATISFIED with it.
As far as cowbells go, I didn't notice any. My engine is too loud.
