REFLECTOR: Cooling VG's

[Chuck Harbert]

After reading the recent postings on cooling, I installed larger VG's in 
front of my overhead NACA inlets and my CHT temps were lowered significantly 
(20-30F). Previously, I had used the small VG's (1/4" tall) and my CHT's 
would get up to 425F on climb out on a not-very hot day (75F). I made up a 
set 1/2" tall VG's and my CHT never got up to 400F on an 85F day on climb 
out, plus they cooled to 360-370F in cruise. Next I'm going to see if the 
small VG's will reduce oil temp, although it's not a problem (climb out 
210F, cruise 185F).

At the Arlington Air Show, I talked for awhile with the Gary Garvens, CEO of 
ECI (Engine Components, Inc-Titan cylinders www.eci2fly.com ) who said that 
ideally you'd like your cylinder to run between 350-400F. Above that, you 
start reducing the life because of the unique alloy that all the cylinder 
head mfgs use. In WWII, the brits invented a high copper alloy of aluminum 
which retains it stregth under hi temp, and it's still used today. Under 
higher temps, the copper migrates from the crystalline structure to the 
grain boundary when it causes cracks (technical term is intergranular stress 
corrosion cracking). According to the Lyco manual you can go to 475F, but he 
said they wouldn't likely last to TBO at these temps. Turbocharged cylinders 
are hard on heads. He further recommended that you can rebuild your 
cylinders one time, assuming they've not been run too hard or hot.

Chuck H
Std RG IO-360