Inliners International Forums General Discussion Hi Performance 'safe' compression ratio on pump gas, 292.

You don't need a specific compression ratio for the cam to work, all that does is delay the torque onset and soften low speed response. The larger chamber also reduces TDC engine vacuum.

H-D 45" flathead V twin race engine: 6:1 CR, 270 degree @ .050" cam.

I hate to make recommendations, but yes I think it's either safe or can be tolerated with some minor tweaks.