Not sure what you mean about "where" the detonation issues most commonly show up but my experience has been that once corrected compresson approaches 9 and cranking compression approaches 190 psi, all you need to induce detonation is a hot Texas afternoon and/or some low qualtiy fuel; get both and it's "ping" city. I have run 204s in the fall and winter and pulled them for a set of TW44s for the summer; I live/ride in south Texas. I really like the lopey idle of the 204, very old school hot rod idle.

At 9.2, corrected CR is about 8.7 and cranking compression about 178psi; at 10, corrected is about 9.6 and crankning about 201; 9.3 corrected is about my limit for a street build and I don't like to see cranking compression above 190psi for my bikes.

I don't have a lot of experience with the SE cams except the 203/204 and have built several 100+TQ/high 90s HP bulds with both cams. The 204, IMHO, is a very underrated cam and will make lots of torque under the curve. I would go with the 204 in a softail and the 203 in a bagger; the tune and pipe are, as always, the most important components in those builds.

 

Very interesting, and thanks for the info. When I asked where the detonation occurred I was wondering if was in the midrange, like hard throttle input at 2500 rpms in a higher gear, or at WOT at high-RPM's. I'm surprised the 204's have detonation problems if CCR is at 178psi with stock TC96 compression (9.2), as I'm running 255's which reportedly produce 185psi and I'm having no issues. In fact, I've added 3° of advance below 20% TP in the cruise range (2-3k rpm), tapering to 0 by 60% TP. The threshold for audible detonation is around 5% on my bike, and I'm running lean AFR's in the cruise range, which should encourage detonation. I'm running 93-octane gas.

There's obviously something I'm not considering here, maybe cam duration for one, as the bike with 255 cams is less-prone to detonation than my stock cams were, and I know CCP was lower with that setup. The stock cams would cause detonation with even 1° of additional advance in the cruise range.