Best way to reduce compression ratio?

[DusTed74]

Have you done an actual compression test? It would be good to know exactly where you are. I would say that if you're not over 200# then you can possibly tune it out with your current combination.
Have you tried a colder set of plugs? Going down one or two heat ranges could be a step in the right direction.

Ted

 

[2Big]

have you tried octane booster

 

[moper]

I apologize because I know I've told this story a million times. When I built my 408, 93 octane gas was available and I naively thought it would remain available, so I built the engine with 10:5.1 compression. I used forged pistons and had the reciprocating assembly balanced. The pistons are either at zero deck at TDC or maybe a little above, I can't remember. I'm running some ported "J" heads on the engine.

It ran pretty well on the 93 octane, but it detonates like crazy now that I can only get 91 octane, and I am afraid I am going to damage the pistons, so I would like to reduce the compression to 9.5:1 somehow without replacing the pistons.

I'm using a stock Fel-Pro head gasket which is already pretty thick, I believe, so I doubt I'd get much of a C.R. reduction from a thicker gasket, assuming one existed.

Any suggestions for me, or am I "SOL"? Thanks, FABO buddies.

Another vote for tuning it out. Chances are it's close to being fine as was noted. Pre-ignition is a self-fulfilling state. Once it starts - it won't stop until one of the inputs (ignition, fuel, throttle load, or hard parts) is changed to make it stop. I like the idea of a wideband especially if you don't have a good handle on ignition and carb tuning.
I'll add if you now have 10% ethanol - you're already lean all accross the board if you had non-ethanol 93 before. You may also want to make sure you're fueling up at name brand places - Shell or Mobil high test is all I'll use now.