| 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
Karma: 11
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Senior Member |
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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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| Re: [GMCnet] The heads from Glenn's GMC 455. More issues [message #281859 is a reply to message #281782] |
Sat, 11 July 2015 02:55  |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Senior Member |
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"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. "
I take it that the springs were too large for the seats, and that made them off center?
Agree there is no reason to use stiff or larger springs, and that retaining the rotators is beneficial to our application. Higher RPM will rotate the valves anyway on a high performance application.
BTW, anyone who DOES spend much time at 5K plus in a GMC, I want to see it.
76 Glenbrook
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