Quick question...i dont know to much about valves springs but i do know that the 987s should be better that the 612s. Im buying a 306 with 987s springs from flyinz and ive got a set of 612s from my old setup. Flyinz told me he used the stock shims(things that go under the springs) with the springs but he isn't sure it will work with mine. So which should i ues? Oh ya and 987s have 9k miles and the 612s have 1k.

 

I just put on some CM612s on a buddy's Z28 and used all stock stuff except the locks and retainers. Working out very well!

 

yes, they work on stock heads
it will be in your best interest too get a micrometer and check installed height of all the springs before just slapping them on there (there will most likely be discrepencies from valve too valve)

i pulled those 987 springs off Adams car (flyinz) and checked the installed height of all the springs before putting the new 918 beehives on and it was all over the place from 1.75 too 1.90 (could've just been from the jackass that did his heads in the 1st place but could have been something else too)

both are good springs and obviously the lower mileage ones should be better (no miles being best!)
but at the price he wants for all of it, its hard too beat

ps, Adam is a good kid too deal with

 

So were his heads stock or not? Im not to familiar with installed hight and that stuff. Is it very bad to be from 1.75 to 1.90?

 

his heads are GM LT1 castings but ported and polished by some local shop

you want the installed height too be closer from valve too valve then his were. the same across the board

all makes of springs require different installed heights too achieve certain open and seat pressures for best valve control
thats why its best too use a micrometer and shims too set them up correctly when on the car

his, it looks like someone just said "well we'll put a shim here and here but not here or here" .....unchecked

 

You must check the installed height. Its very important on high lift cams with fast ramps like the XE grinds to have the proper installed high or the cam will start to float valves. The cc306 however isnt that extreme so either spring should work fine. I like the cc987s but they are a serious PITA to install w/o a really nice spring compressor.

 

So i should invest in a micrometer to check the installed heigth? How much are they and can you just get them from summit or what?

Thanks guys
James

 

They are 35 bucks from lowes or Hoe depot.