Quote:
Originally Posted by jwcarguy
X2
GM deleted the rear stem vents for a reason
They only used the 4 port design in early Gen III engines, then deleted/ blocked off rears due to air/ steam pockets going to highest point and purge out front ports
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GM deleted it to lower the production cost and lower the part content, not having the rear stem ports will work fine on a completely stock engine that only sees highway use. Once you start increasing horsepower and using the car hard it becomes necessary to have all four corners vented. I've cut trashed heads apart to look at the water jackets and you would be amazed at how bad they are. Cylinders 2&7 do not have a complete flow path around the combustion chamber so water flow is not very good on those 2 cylinders and makes them prone to developing steam pockets which leads to detonation. Imho this is why you see so many engines that blow up the #7 cylinder.