Some questions about valve springs and valvetrain geometry
03-04-2008, 10:55 AM
#1
Some questions about valve springs and valvetrain geometry My engine is being rebuilt right now and I'm in the process of determining what to do as far as valve springs. Let me say that I am still learning a lot of the complexities of valvetrain geometry so sorry if some of my questions are repetitive.
It seems no matter how much I search the boards and research, there are differing opinions on what kind of springs work with the GM 847 cam (which runs a max lift of .595" on the exhaust side with 1.6 rockers.)
First off, after considering it more, I would like the peace of mind of a dual valve spring so that if there is a spring failure, there is hope that the valve won't be dropped. However, there are a few things about dual valve springs it seems: first, they are heavier than a single beehive style spring (naturally) and thus they don't like to rev as high. They also have larger outer diameters in most cases so the pockets on the heads need to be machined to fit the bigger ones.
Some people have recommended the Crane 99893 springs which are their cheapy dual springs (those are the ones that come in the 10308-1 kit). However, I'm reading that with the heavy weight of the spring, combined with the heavy steel retainers, they are not a great spring for high reving. Also, the kit comes with shims instead of a proper locator which a lot of people don't like. So is there a better double valve spring that will fit in the stock heads? Or am I stuck having to have them machined (not a huge deal unless that turns out to be really expensive).
Secondly, I keep reading about installed height issues with many of the aftermarket springs. For example, with the 847 cam a lot of people say to use +.050" locks. Can someone explain why you need those locks? Does it have to do with coil bind vs. the cam's maximum lift vs. installed height of the springs? For example, if coil bind comes in at 1.1" and a cam has a max lift of .600, then if the installed height of the spring is 1.700" the spring will be hitting coil bind at max lift?
In one thread someone mentioned having the heads machined for larger diameter springs and having the made .050 deeper as well (I assume as an alternative to running +.050" locks?)
Bleh, sorry to ramble on, but it's hard to figure this stuff out when there are so many different opinions out there! I wanted to take my heads in to have them check over the valve guides for wear anyway, should I just have them machine the spring pockets then?
It seems no matter how much I search the boards and research, there are differing opinions on what kind of springs work with the GM 847 cam (which runs a max lift of .595" on the exhaust side with 1.6 rockers.)
First off, after considering it more, I would like the peace of mind of a dual valve spring so that if there is a spring failure, there is hope that the valve won't be dropped. However, there are a few things about dual valve springs it seems: first, they are heavier than a single beehive style spring (naturally) and thus they don't like to rev as high. They also have larger outer diameters in most cases so the pockets on the heads need to be machined to fit the bigger ones.
Some people have recommended the Crane 99893 springs which are their cheapy dual springs (those are the ones that come in the 10308-1 kit). However, I'm reading that with the heavy weight of the spring, combined with the heavy steel retainers, they are not a great spring for high reving. Also, the kit comes with shims instead of a proper locator which a lot of people don't like. So is there a better double valve spring that will fit in the stock heads? Or am I stuck having to have them machined (not a huge deal unless that turns out to be really expensive).
Secondly, I keep reading about installed height issues with many of the aftermarket springs. For example, with the 847 cam a lot of people say to use +.050" locks. Can someone explain why you need those locks? Does it have to do with coil bind vs. the cam's maximum lift vs. installed height of the springs? For example, if coil bind comes in at 1.1" and a cam has a max lift of .600, then if the installed height of the spring is 1.700" the spring will be hitting coil bind at max lift?
In one thread someone mentioned having the heads machined for larger diameter springs and having the made .050 deeper as well (I assume as an alternative to running +.050" locks?)
Bleh, sorry to ramble on, but it's hard to figure this stuff out when there are so many different opinions out there! I wanted to take my heads in to have them check over the valve guides for wear anyway, should I just have them machine the spring pockets then?
