REFLECTOR: Exhaust/cowling

[Tom]

Had a funky 4 into one exhaust (single crossover), mild steel with no 
slip joints. I knew that this wouldn't work for long and it let go just 
before I needed plane for Christmas travel to be with family (wife is 
pissed). Anyhow I called Velocity and was told the two pipe, 2 into one 
system should be an easy install (IO-360). Bolted up nice and easy but 
the cowling was hitting the pipes at the #1 cyl (left, rear). Cut a slot 
in lower cowl and added a blister with 1/2" clearance, wrapped the 
exhaust and test flew. After landing cowling was bubbling and smoking. 
Tried some insulation on a 2nd test flight but it was touching exhaust 
and had similar issues. 2 questions:
1) how much clearance do you need between exhaust pipe and cowl?--I'm 
working on a larger blister now
2) what's a good insulation material that's not too wide?? thx Tom