I am looking for some springs that will fit the stock heads My lift will be .512" so Im guesseing they need to be good for about .530"??
ALso would screw in studs be needed?
thanks I really need these!!!

 

Pinned studs, or screw in studs are a very good idea for any aftermarket springs.

Comps 981's would work for that. Any of your basic 1.25" performance spring will work fine. Comp's 981's are the part # that i've memorized that's all.
You'll probably want to machine down the guide boss, and set it up for positive valve seals.

 

i didnt machine the bosses down and still ran the positive , I actually already have teh comp 981's, i have not found anywere that tell the recomended max lift for them, but I think I read .500" somewere. I am not sure.
Is there anyway to find out?

 

stock heads won't have the retainer to guide clearance for that lift.

 

what is the max lift that will work? I might just have to downgrade to 1.5 rockers

 

.450-.480 depending, you have to check each head individually to find out.

 

.480" is the generally accepted "area" where lift becomes an issue in terms of the bottom of the retainer hitting the top of the guide boss. However, only a physical mock up and measurement can tell for certain.

I've run Isky's 235-D spring at the suggested installed height of 1.750" with no problems before. They're good to .550" lift. (.600" difference between the installed height and coil binding height, subtracting .050" as a 'safety' clearance).

 

If you want to run .512" lift using the comp 981 springs you would want to check and verify the spring installed height.
if it is 1.71" or more you'll be fine. If it is less than 1.71" you won't be fine. Then you need to check the amount of space you have between the top of the valve seal and the bottom of the valve ratainer. Should be a minimum of .512"+.050" or .562". If it is less than this you won't be fine.
You need to remove a valve spring and check these specs by measuring them yourself before running the motor.

Generally, on stock heads; if they were just machined for guide seals without shortening them you will not have enough room for .512" valve lift.

 

well looks like im gonan pass on a cam swap...
I need some heads

 

What cam are you tring to use?

 

http://store.summitracing.com/partde...8&autoview=sku
I was looking at that one, I guess I could use it if I bought 1.5 rockers but I just bought some 1.6 RR's.
Id like a fairly choppy idle thuogh, I really want a Lt4 hotcam but im thinking its to big, but if I have to get heads anyways................ then why not

 

hey dont mean to hijack just wanted to get f-bird's attention

if you have heads with positive seals can the guides be cut down for a cam with lifts over .512 and still retain the positive seal?

 

Yes. Oh, I'm not F-Bird. Oops.

 

yes you can. The gudie boss cutter cuts down the whole step that the seal sits on. just lowers the whole thing.

That comp cam will not have a choppy idle.

 

will the hotcam?

 

Just took a look at the specs on the cam you posted the link to. If you switched back to 1.5 rockers, you'd probably be just fine running it, especially since you already have 981 springs. As for the idle quality, it'll probably be nice and smooth. That cam is nowhere near radical enough to give you a rough or choppy idle. On the other hand, the LT4 hot cam would definitely require some machine work to assure retainer to guide clearance.

 

Ill just have to wait and get some good used heads then. How will I know if aftermarket heads will even work with say .575" lift?

 

If your motor has the GM TPI fuel injection system you need to rethink what you are trying to do. A "rough idle" cam will not work . It will play havic with the EFI ( low manifold vacuum) and will not enhance the tuning effect of the long runner tuned port manifold.

 

i have heard the Lt4 hotcam on some Lt1's and it sounds great. Is that to much cam for the stock ECM? will I still be able to tune it?
I will be running a Lt1 intake or a stealth ram.

 

As far as power is concerned the LT4 hot cam will work very well with the HSR or a LT-1 manifold. You'll have to ask some one that is more into EFI as to how best to tune it. it can be done and will need some dialing in. I'm an old Carb guy so can't really help ya with that.