Manifold height?

I ran my motor for like a year and a half with the crossovers blocked. Then for the next winter--which I only drive it when the roads are clean--I removed the exhaust crossovers shims. Motor ran better all the time, even after driving it for a 1/2 hour. Next spring I left it alone, was running so nice and clean, the plugs were not getting dirty and needed to be clean like before, I left the exhaust heat open when summer came. When its 80+ yeah, maybe then blocking the exhaust heat might be good but where I live even in the summer its not 80+ at night time.

Here in Michigan I leave the exhaust heat open year round, 90% of the time its the best way for my motor.

Blocking exhaust heat is for high compression-12-1 and up and or high heat, 90,100+ degress weather, like Texas, AZ, FL.

IMO