Best/ worst experiences with valve spring swap?

Take them to a shop and get them tested and mark each one with their lbs. Then when placing springs in each position use your install height and spring psi to figure where you want them. So if you have a spring pocket that a little deep (some will be a little deeper despite shimming all to shallowest position) then I like to place the springs that are a little stronger in those spots. Comp springs seem to vary quite a bit vs PAC and PAC's x series springs almost all equal. Granted as they season they will weaken up. IMO the best break in is start the car idle up to full ops temp (oil psi dropped) heat soaked and shut car off and let engine cool all the way to amb temp.
 
Take them to a shop and get them tested and mark each one with their lbs. Then when placing springs in each position use your install height and spring psi to figure where you want them. So if you have a spring pocket that a little deep (some will be a little deeper despite shimming all to shallowest position) then I like to place the springs that are a little stronger in those spots. Comp springs seem to vary quite a bit vs PAC and PAC's x series springs almost all equal. Granted as they season they will weaken up. IMO the best break in is start the car idle up to full ops temp (oil psi dropped) heat soaked and shut car off and let engine cool all the way to amb temp.

Can I assume this would be the same as purchasing a set of measured springs from bison, skipping the process where the machine shop tests them?
 
I agree. But, how do I know what poundage I want on the seat and over the nose?

The cam tells you that. For example I run a 215/220 roller cam with over .500" of lift. That needs a lot more spring than a stock or 206/206 flat tappet cam.

Working from memory, Once I married my valves to each hole, giddidy, I measured each spring install height then wrote down tightest to loosest. Then I put each spring in the tester at 1.800 I believe and put the springs in order of stiffist, giggidy, to loosest, giggidy.

After that I eliminated as many variables as I could. Basically doing that first kept me from unknowingly putting the weakest spring in the tallest opening and having to shim the crap out of it. I evened out some of the variance.

After I had each spring married to the valve, I could measure the poundage at the exact height on the base circle. Depending on if it's an intake or exhaust, I could then pull the handle to the exact lift and see what the poundage is over the nose. Don't forget to pull it all the way collapsed and make sure there's room for the lift, the shims, the seal, and a little extra to keep the spring from beating itself to death. Around .100" is nice and safe. If you have to shim the crap out of a weak spring to get the numbers you want, you might run out of room. Also, putting a huge cam under some unmodified heads is a good way to crash the retainer right into the valve guides. If that's the case the guides need to be cut down to make room.

And Buick specific... the exhaust guides aren't cut for seals. If you get aftermarket valves with no oil step they guides HAVE to have seals installed. If you cut the guides for seals on stock valves, they will get killed by the valves and end up just like they were never installed. Also, if building a set of heads and keeping the stock exhausts, make sure to grind a backcut and get rid of that HUGE flow killing ski jump next to the sealing area.


See, easy as 3.14 :D
 
The cam tells you that. For example I run a 215/220 roller cam with over .500" of lift. That needs a lot more spring than a stock or 206/206 flat tappet cam.

Working from memory, Once I married my valves to each hole, giddidy, I measured each spring install height then wrote down tightest to loosest. Then I put each spring in the tester at 1.800 I believe and put the springs in order of stiffist, giggidy, to loosest, giggidy.

After that I eliminated as many variables as I could. Basically doing that first kept me from unknowingly putting the weakest spring in the tallest opening and having to shim the crap out of it. I evened out some of the variance.

After I had each spring married to the valve, I could measure the poundage at the exact height on the base circle. Depending on if it's an intake or exhaust, I could then pull the handle to the exact lift and see what the poundage is over the nose. Don't forget to pull it all the way collapsed and make sure there's room for the lift, the shims, the seal, and a little extra to keep the spring from beating itself to death. Around .100" is nice and safe. If you have to shim the crap out of a weak spring to get the numbers you want, you might run out of room. Also, putting a huge cam under some unmodified heads is a good way to crash the retainer right into the valve guides. If that's the case the guides need to be cut down to make room.

And Buick specific... the exhaust guides aren't cut for seals. If you get aftermarket valves with no oil step they guides HAVE to have seals installed. If you cut the guides for seals on stock valves, they will get killed by the valves and end up just like they were never installed. Also, if building a set of heads and keeping the stock exhausts, make sure to grind a backcut and get rid of that HUGE flow killing ski jump next to the sealing area.


See, easy as 3.14 :D

Is it safe to say that the differences in height are due in part to casting imperfections with the head? Meaning, I can measure my stock valvesprings and if I were to come up with, say, hypothetically my number 3 intake is the tightest, giggity... and number 5 exhaust is the loosest, giggity.... then those locations are going to be the least and most shimmed, respectively, with the new springs? I do plan on getting a measured spring set from bison, and I get what you're saying, put the tightest spring in the tallest opening to help balance everything and require the least ammount of shimming, correct? Also, the previous owner told me the cam is a Comp flat tappet 212/212, that is all I have to go off of, however, I have no reason to doubt it, just surprised he'd leave stock springs in. It does have just a little bit of a choppy idle, but overall pretty smooth. Not sure how to tell what's in there.
 
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Nope, the difference in height is because of several variables. Casting isn't one of them.

The more you have to grind off the valve face, the more the installed (and tip) height increases. The more you have to cut off the seat will increase the tip height as well. If the seat pad gets machined, that can increase the installed height. And, in the case of used heads and valves, plain ole wear will move it up a little.

The only way for the installed height to get smaller is to install new seats or go with oversized valves so the new seat angle is further out and you get to cut fresh meat. In the instance of factory Buick castings, you can get an intake that's has a larger radius of .035".


Tip height is something that hasn't been addressed yet, but it's not relevant for just a spring swap on the car.


Here's something I wrote a long time ago. I was building my 4.1 and went ahead and done up a spare pair of heads I had since I had already set up the cutters for my Ferrera valves. It doesn't covers springs but it does show some oversized seats and bowl porting.

http://www.turbobuicks.com/forums/buick-v6-turbo-tech/79654-how-put-set-heads-together.html

I never bothered to make a part 2, but I did almost trip over one of those castings yesterday :)
 
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