Even though this is not a recent thread it is still from 2012 and there are few good discussions of the Zip Riser on this site. I found more information on the Zip Riser on the Technical section of H.A.M.B. but I would be very interested in a description of your whole cooling setup, fan shroud, percent antifreeze, fan type and size and the engine as well as the radiator specs and the thermostat. I am wringing out a situation where a SBC overheats with a new Walker Cobra radiator and yet there are many examples of setups which do cool well with a SBC 350 in a Model A with a '29 radiator. I am getting close. 34-40 says my flex fan may be a problem, what fan type and size did you use?

Don Shillady
Retired Scientist/teen rodder