There was only one T4-80, Hobbsy's engine is the Webra "T4", and is .87 cubic inches displacement. Its the precurser to the T4-40/60/80 line.

I had two T4-80's - one was flown in my Astro Hog for a few seasons before I sold it. I had the belt skip one tooth on me and it threw off the timing bad enough to know immediately. Perhaps thats what happened? It will still run, but very poorly. I just put it back to the correct position and it was fine again.

AJC