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?

 

Well to begin with, members who are using that cam can give you some advice re springs. The spec card with that cam should provide you with recommended spring pressures at installed heights. You, no doubt will be using a dual spring. The stock seats will accommodate most dual springs with the specs required for that cam, therefore no machining should be necessary.

I would not consider the Crane Kit 99893, "cheapie springs". JMHO

 

springs are descent but the retainers are heavy. I buy the Crne 99893 springs and use lighter Comp retainers with 10 degree locks on my LE1 heads. It is still a chrome moly retainer so it will not be as light as a Ti retainer.

Set the springs up at 1.800 and you will be fine up to 6500 RPM with that cam. If you have the Crane 10308-1 kit and use those retainers, you can get a .060 thick Comp 4771-16 locator and this will get you at the set up ht you want.

I use the PAC 1218 bee hive springs, Comp 795 retainers and Comp 611 locks on my LE2 and LE3 heads.

If you want a dbl spring, make sure and keep it below 155-160 lbs on the seat and below 420 lbs open unless using a billet cam as that much spring pressure can cause the lifter to dig into a cast cam.

Comp 977-16, K-Motion K-800's, Crane 99893, etc will all work for you.

Lloyd

 

I have a GTP cam which is almost identical to the Gm847, I used K-motion k800 dual springs installed at 1.80 and then I used Titanium retainers w/10*locks So far the setup has been great! Normally I am not a K-motion fan! I had too many k750's break but the k800's are a different material than the k750's tool steel that kept breaking, And I gota a heckofa deal on the set with the ti retainers.

 

Thanks for the info everone.

Lloyd, can you clarify why people say to use +.050 locks, I'm just trying to understand the actual workings of that rather than just take everyones word for it. Do you use them on the springs you put into the LE2/3 heads?

Thanks

 

Either use the standard locks or a -.050 lock if you have SA rockers. Justr watch the set up ht and make sure it is not too short and end up having too much pressure. As long as you stick with 145-150 lbs on the seat, you will be fine. This will be at 1.790-1.810.

No need to machine anything or use +.050 locks, even with stock length valves.

Lloyd

 

That is the offset of the lock itself. There is a groove in your valve stem that the lock "grabs" and the retainer "holds" as long as there is spring pressure pushing on the retainer. The different offsets refer to the location of the lip on the lock itself that fits into the groove. People use offset locks when they need more installed height to setup their springs.

If you use a std. lock as say your height is 1.75 with a micrometer and you want 1.80. Well you can either get a longer, heavier valve and shim the hell out of the spring, get a different spring, or use offset locks to get you to the 1.80 height. In this case most just get a +.050 lock that allows the height to be moved up to 1.80. Also one thing to note is that most offset locks aren't exactly what they advertise, so a +.050 is really +.045 or something similar. At least that's my experience.