I belive it has to do with the wagner manifold. The collector are at bad angles and don't permit smooth exit. Which inturns was cuasing it to heat up...On that particular dyno run..dana's #'s were reading 11's. I think that as he got on the boost harder & harder..and started to push upwards of 13psi..the air escaping was bouncing all around and heated the header..glowing red..and the combination of runnin rich cuase the unburnt fuel to ignite.
Sort of how..the ricers are setting up kits to shoot flames out of the exhuast.
Chas