Re: [GMCnet] The heads from Glenn's GMC 455. More issues [message #281782] |
Thu, 09 July 2015 19:20 |
BobDunahugh
Messages: 2465 Registered: October 2010 Location: Cedar Rapids, IA
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I talked about the high performance valve springs that were installed. The springs had too large of a diameter to be used with the stock GM valve rotators. Because of having the spring not centered on the valves. The valves, and valve guides will need to be replaced. The cam that was installed was listed as a towing cam. That cam has a intake lift of.448. Exhaust lift of.472.The GM stock cam has a lift of .440 for both the intake, and exhaust. There was some deration differences also. You need to have the valve spring strong enough to keep the lifter on the cam at all times. The stock spring is 85 lbs at a height of 1.67 inches. That spring will work for both cams. That difference between the 2 cams is less than half the gap of your spark plugs. Remember that the higher the valve spring pressure. ( Of HP valve springs. ) The more load you put on your cam. That you want ZDDP to protect. Use the stock GM springs. Unless you plan on running your engine above 5000 RPM's vary
much. Then I'd install High performance valve springs. Bob Dunahugh
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