How can I figure ICA with changes in valve lash? Can 2 or 3 degrees difference be seen with .010 or so in lash change?

Wait, the opening/closing points might change by a few degrees , but the centerline ( or average ) should stay the same. Right?

If the opening and closing points change, dosent the intake closing angle have to change. The way I understand is, a lash setting can make a slight advance or retard of the cam which would change the ica like moving the cam. But I may be misunderstanding :confused:

Originally posted by Dragn70:
How can I figure ICA with changes in valve lash? Can 2 or 3 degrees difference be seen with .010 or so in lash change? Marty,
If you are referring to intake centerline it won't change.

Originally posted by Dragn70:
If the opening and closing points change, dosent the intake closing angle have to change. The way I understand is, a lash setting can make a slight advance or retard of the cam which would change the ica like moving the cam. But I may be misunderstanding :confused: The opening & closing points will change but the centerline of the lobe will remain as it was installed.
It may appear in a different place if you check centerline from seat timing especially on Harolds cams or any asymetrical cam as the opening & closing sides of the cam are different.
I also believe it is why Harold recommends his cams be installed at 6 degrees advanced.
This is why you don't want to find intake center from seat timing & it is recommended to find center by using the .050 method.
Carefully adjust your dial indicator at zero at max lift, then back the engine past .050", bring it to .050" before max lobe lift, take a reading on your degree wheel, turn foward to .050" past max lobe lift & take a reading. Add them & divide by two. This is the intake centerline.

I standunder now. Thanks for the info.

Marty,
also note, it is asking for trouble to open the valve lash .010 wider than spec. This causes excessive shock loads in the valve train. About .004 wider is the upper limit. Closing the lash .010 is not a problem. As a general rule, it is rare to see any sizable change in performance with lash changes. In theory or on a dyno, maybe a small change, on the track usually not enought to see on a time slip.
Larry Woodfin
Crate Racer

I was going to write a similar post to this concerning valve lash for Harold or anyone else here that had some input. When tuning with lash, how much is the duration affected by say a .005" or .010" change in either direction? For example, I have a cam that is 258/268 @ .050" in a 454. If I were to tighten the lash .010" and the car responded favorably, than a bigger cam may be better, but how much bigger is that making the cam think it is?

With respect to tightening up the valve lash...Yes one can go .010 tigher IF your cam has a suggested lash of say .022 or larger....If your suggested lash is .012 and you set them at .002 ...you will likely run into problems.... If your lash is supose to be say .030 and you set them at .020 thats fine...it will likely run differently .... But if it's tight to begine with you are asking for trouble...

Imho, two things you need to watch..

1. Beating the valve train too much if she is loose, and

2. The exhausts CAN tighten up AND this can lead to them burning b/c they aren't able to stay on the seat long enough to transfer enough heat out of them to keep them cool!!

Otherwise, have at it..

pdq67

I recently talked to Isky about lash and the street roller that I am running. Lash specs for mine is .028". They told me that it was safe to go +/- .006" (.022" to .034").

They recommended that if you run mainly on the street, to lash it about .003"-.004" (.024" to .025") tighter than spec. I think this gives you a little extra safety margin if it loosens up a bit.

Easier on parts, easier idling is why.

wish i would've et'd the difference in that old crane cam. man it felt entirely different loose. quicker valve action.

With my old Crane F218/2933 lobe in my last 327 I chased the lash all over the place just messing with it.Crane wants .022.I ran it up to .026 and down to .016.... at .026 it just was noisier...no other differences.At .016 it lost alittle manifold vac and was abit sluggish and nearly silent tappet noise wise....So I just went back to the factory suggestion of .022 hot ( .024 cold in my engine )..
It seemed to run best there.

In my current BBC I have my Isky .003 tighter than suggested and havent yet changed anything...maybe now that the weather is getting better I'll open it up to what they say it's suspose to be.... just to see if anything changes.

The scarriest one I ever heard was a friend of mine who used to run a C/ED car.He had one of those old Cam Dynamics rollers with a lash .035...he ran it at .040 !! and this in a 9800 RPM SBC !! He claimed it ran the best there...But longevity was not a main consern ...as often as these guys change their combos....