They can hurt cooling and my experience has been they are not needed. I've built motors with and without them over the past 8 years or so and my opinion is they are a waste of time and can create alot more problems than they fix.
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Don't bother giving me "rep", I won't return it and I think it is stupid.
Gracie Barra Clearwater
Gyms in Clearwater, St. Pete and Port Richey
pm me if you are interested in trying a free class at any of the gyms.