Valve Spring Pressure

[AMXguy]

OK I'm about to wrap this thing up so I promise I'm about done with the questions.

 As I'm getting ready to put my valve covers on I talk to a guy whos a pretty good mechanic and he tells me my valve springs are too light. I have a 440 with a 496/507 lift cam and new Crane springs that are supposed to be 90 lbs seated.
 the paperwork with the spring kit says they're good for up to a .580 lift  at 6500 RPM, both are well above my needs. do I need different springs or not for a street engine?

[gkring]

Sounds fine. You can always go back and shim them a little on the car to bump the pressure if they give you trouble since you have a litle room before coil bind. I am assuming a flat tappet cam (nonroller).

[AMXguy]

Yes flat tappet. isn't part of the problem burning valves if you're not getting closed fast enough? floating the valves is pretty easy to tell but I'm not sure how you'd know any other issues were there until it was too late.

 I would think Crane would know whats required but if you look in the TSM a 440 magnum came with 110-120 lb springs .

[72cudamaan]

Yea 90 lbs. sounds kinda light. What does the cam manufacturer recommend? If you can find that ,go with it. And by the way,shimming is only to adjust installed height. Increase in pressure is negligable.

[moper]

What cam is it, and did you measure the springs you have or is that the catalog spec? You need to knwo what the installed height is on yours, then stick them in a tester to see if they will do what the cam manufacturer specs for pressures. Seat pressure is not as important as over the nose, but on either I'd rather have too much than not enough. Max lift alone cannot be accurately used to gage whether or not a spring will do the job.

[Strawdawg]

from prior post

Ultradyne 288/296, duration at .05 is 231 IN / 239 EX gross lift is 485 IN / 239 EX.   

[Strawdawg]

If that is still it...I would guess from comparable cams that something with at least 120 closed and 320 open would be more suitable...that is from a very quick glimpse...I would look at a few more before saying that is it

[Strawdawg]

Cam looks similar to the Comp XE274H.....Comp springs 911-16 are suggested for that cam with no machine work.

[moper]

I agree, springs are light for that cam...

[AMXguy]

Ok, well since the engine is all together I might as well break the cam in with them and change them out later if need be. other than floating valves at high speed is there any major draw back to being a little light on springs? these shouldn't be so bad that valves should be damaged just cruising around should they?

 Crane clearly states these are 90lbs and they're good for up to 5.80 lift at 6500 RPM. you wouldn't think they could be that far off the mark but maybe so, every place I look tells me the same thing you guys say.

[moper]

It's not a good idea to run light springs. It all depends, but light springs can cause wiped cams, bent pushrods, piston to valve contact... So I wouldnt run it much unless you find out it's ok.

[Strawdawg]

Exactly

[Changin Gears]

The .580 lift probably only refers to coil bind at max lift.  You can break the cam in with those springs.  In fact, an old trick used to be to break a cam in with the outer springs only then install the inner (with dual springs).  A .060" shim would add about 15lbs  (depending on spring rate) to both closed and open pressure (and everywhere in between).

Valve float is a very bad thing.  It is hard on everything in the valve train.  But you won't float the valves if you keep it on this side of 4500-5000.

By the way, someone (crane, comp) sells 1.2 ratio rockers for chebies to break cams in.  Since the valves don't open as much, there is less load on the lifters/cam.

[AMXguy]

Shims aren't a bad idea, 15 lbs would put me well into the safe zone. I've only used them once and as I recall you want hardened ones. any  recomendations on what ones to use or does it matter?

[Strawdawg]

how do you figure that safe zone?