What is everyone doing about the dimpled firewall effect you get when 
you tighten your motor mount bolts up to the hard firewall with 3/8" 
of soft fiberfrax behind it?    I thought about putting phenolic 
spacers behind each bolt but not really interested in the time to do 
it.  I dont care if my firewall is dimpled I just want to make sure 
its safe.  Anyone else have the dimple effect?

Bryan,

 

Don't do it the way you want - over time the frax will compress and the tension of the mount bolts will be wrong.  Get large area washers (probably 2) and cut away the frax around the mount holes so the washers fit.

 

Every one or two years, you should check the motor mount to firewall torque value.  If these loosen up, vibration is rampant.