BB

iTrader: (7)

It seems that some head porters have been using 987 springs where many have been running cams with lift that is greater than .550.

From what I have been reading on the CC site (http://www.compcams.com/Technical/Ca...ML/340-349.asp) the 987 spring has a Max. Rec. Lift of .500. I assume that means a maximum valve lift of .500. Therefore the 987 spring is not good for anything more than a stock cam. Am I understanding this correctly?

Then for a CC XER cam with a .581 lift you need at least a 978 which has a Max. Rec. lift of .600 (see http://www.compcams.com/Technical/Ca...ML/340-349.asp). Right?

And for something crazy like a G5 or TRex you need a 921 that has a Max. Rec. Lift of .650? Right again?

I guess if I am right then I am dissappointed I never did my homework before getting heads with 987 springs and a cam with a lift greater than .500 and wondering why there was valve float and my valves smacked my pistons

I just assumed that I would get a good match when getting a head. Lesson learned - do the math and blue printing yourself or at least know the right questions to ask. Oh well, I am quite accustomed to shelling out money for an education.

99 Black Bird T/A

iTrader: (4)

987's have been used for a long time and have an excellent record with .550 lift cams. Pushing into the .590+ lift watch out with the 987 as it's not up for that. I have .581 lift and 987's and no problems todate. They have been on the car for 15 months. Later this year new springs will go in. Better safe than sorry.

Part of what the max safe lift for a spring is depends on how it's set up. 987's can be set up on the LS1 to live with ~.590 lift, I can't remember the exact number. 987's work very well with .550 lift cams and even .581 lift XE-R's with say 224 duration when properly set up. If one is going for going for a big XE-R cam that's ~230 or so with ~.590+ lift, the 987 isn't best spring to choose and a 978 or other spring is a better choice.

What size cam are you using with the 987's?

How many miles?

How runs at the strip?

What rockers do you have? Some rockers like Yella Terra add mass over the valve and will cause valve float where a stock rocker won't.

BB

iTrader: (7)

.563 lift with a 224 duration. Are you saying you can change the seat or something like that to extend the manufacturer's recommend max lift for the spring. .500 to .581 seems like a huge variance. I would have not expected that much difference unless there is some well know practice of extending that rec. max. lift.

BB

iTrader: (7)

So, with a radical cam like the new TRex would a 978 be OK. Based on the CC charts it wouldn't and you should go with the more expensive 921s. What can a head builder do that extends the max lift a spring can handle?

Mike K.

I am getting some 978 springs and was told that they are good to just over .600 lift. If you are getting the thunder cam I would follow in their footsteps and get the springs they recommend which are the cranes or the 921's.

BB

iTrader: (7)

I agree with you. And if I I was getting a crazy insane cams like the TRex or G5s I would do the 921.

But what I still don't understand is why they are telling you that the 978 is good for just over .600 lift when the manufacturer's recommendation is a max of .600 on the 978. What am I missing?

I guess it may be treated as a guide line or their is some magic I don't understand that enables a head builder to get around this be changing the seat or something.

Another thing I am learning is that you need to know what the distance is between the bottom of the retainer and the top of the seal. This can't be greater than your lift. So, you either have to take the measurement after the head is built or better yet make sure your builder knows the cam you are going to run and have him blue print the head and make sure it is within your cam's specs.

99 Black Bird T/A

iTrader: (4)

Yes, 987's can be used with .563 lift cams without issue and have been. I have a .581 lift cam with 987's that's been issue free. When it's time for springs will probably go with the 978 as thats looking like a better choice. Using 978's on next set of heads. For their time the 987's were great compared to all the single spring junk (ie before the 918) that kept breaking.

I don't set up valvetrains so I can't explain exactly how that is done but the spring install height can be adjusted to a degree. Shims can be used to adjust pressure etc.

Who set up the 987's on your heads?

Mike K.

I suppose they are saying that it is the max recommended lift. They probably have to list a "safe" number so that when people break springs they cannot go back to comp cams and say that they were at fault. Like Blackbird said alot of people have used the 987's with no issues, I have not heard to much about the 978 but from what I have heard they are the stronger spring.

BB

iTrader: (7)

Thanks to both of you for chiming in. I don't want to mention the head porter as I don't want to imply they don't know what they are doing. I am sure they can walk circles around me with valve train math.

In any case, the take away seems to be get the spring that is within the tolerances specified by CC to ensure you get you are insured (so to speak) if a spring malfunctions.

If anyone understands how this value can be manipulated through install height, spring seat, or whatever, I am real interested in learning.

BB

iTrader: (7)

I learned this morning that you can't even trust a vendor's web site or catalog. CC published maximum recommended lift is in error. For example, the maximum recommended lift for the 987 spring is .590 and not the listed .500. That is why they use them in these heads. And the listed maximum recommended lift for the 978 is .600 which is wrong and it correctly .595 - according to the CC tech help line.

Then the head builder says you have to be careful with those numbers as they are still not accurate and the only way to tell is through your own testing of coil bind.

So, you are right that the 987s are cool for most lifts. The 978 isn't going to get you much more but you need the builder to test the springs to see what they really can handle. And the 921 can handle the highest lift. But, these have a short install hieght and may require shims for someone moving from the 987/978 to the 921. And these are new and not yet proven.

So, I guess I am good with the 987s. If nothing else I hope there has been some good information shared here for the community.