In order of hottest first...

K&B 4C
OS-F / YS 4C
K&B 1L

"Heat" can be added to a 2C in a number of ways......higher ambient temp, more compression, more nitro, hotter plug, leaner mixture. Many combinations will work. I always preferred to run the hottest plug and a slightly richer mixture...which keeps the engine temps cooler (more fuel moving through the engine) and exhaust temps lower (quieter). Especially important with the Webra 160MC as with the very thin sleeve and case around the sleeve, it has little tolerance for running hot from a lean mixture.

Regards,

Dave