Valve lash kill and thrill

I would like to hear your experience in changing for the better and worse performance,How much change in lash and gain in performance track or street for SFT and Solid rollers. .TYIA

I always tighten mine up .008-.010 just because and never an issue. As far as performance never compared back to back but make things quieter for sure....

Interesting info.That is a lot to tighten up when the spec may only be .020

On my hemi I used to run the lash a little looser than recommended. Felt a little snappier to me w/ it .003" on the loose side. Whether it made any difference on the timeslip or not, I don't know.

.020 is a tight spec for most cams. If I remember right I ended up at .008 COLD on my Keith Black block and 440-1 heads. Lots of growth with that combo but I'm usually at .008-.010 like thumper said with a cast iron block and aluminum heads.

Tight lash cams, .020 or tighter when hot, can not be ran safely with NO more than 25% tighter lash when hot. I use the old rule that if the motor likes less lash at the track on back to back runs then it needs a bigger camshaft
I've seen tighter lash work better as well as not working as good on engines on the dyno and at the track also, it depends on the combination normally

Cams that use tighter design lash, and/or faster ramps have less of a lash tuning window before you start compromising durability.

I have noticed a difference with as little as .002. Not huge, but could feel it. And .004 loose was worth 10 PSI cranking compression and an inch of vacuum on one combination. You're not supposed to go much looser than the spec, I've heard .002 is OK for most, some might tolerate more.

My understanding is tighter is not an issue as long as its closing and there is some lash. Although every .001 tighter you go is going to add more duration than the last .001. The slower the lobe the more the lash is going to effect it (more duration for every .001)

What would make a fast ramp rate? .003 or .006 lift
per cam degree?

More change in lift per degree would be “faster”.

And some lobes just have smoother transitions from one portion of the lobe to another, even if the peak velocities are nearly the same.

This is where it’s best to be able to talk with someone at the cam supplier who understands those minute differences between the lobe families....... and what kind of affect it may have on your combo.

Dug up this, in case it helps: VALVE LASH TECH

I see on google that a .050 lift gain from .006 to .050 lift would be a fast ramp rate. and .030 an avg ramp;slower]

or
An exapme of a fast ramp cam would be an Ultradyne Cam it had a 276int/276ex for advertised duration and the
duration @.050 was 221int/221ex. This is a fairly fast ramp for a
hydraulic lifter cam.

That’s a hyd cam..... and imo, not a very fast one @55* “hydraulic intensity”.

The lower the number/difference between .006 and .050, the higher the intensity.

The Comp XE/HL lobes have 44* hyd intensity(275@.006>231@.050).
The normal XE lobes are usually in the 44* range as well(268@.006>224@.050).

Even most of the old school HE and Magnum cams are 50* or less.
(270@.006>224@.050 = 46*)
(280@.006>230@.050 = 50*)

The Thumper intake lobes are 52* hyd intensity, but the ex lobes are slower with 56* hyd intensity.

Some of the Lunati VooDoo cams are 43* hyd intensity.

Although pretty much every cam lobe design is a compromise of some sort.

Thanks a ton for clearing that up!

Of course, none of that has anything to do with “lash”.

I see a lot of people increasing lash to adjust for having too much duration trying to be street strip,pump gas so is the down side only having more valve noise?A SFT would be more at risk of dammage I would think.

😳

Hey we have all done things to our car that satisfy the butt dyno feeling, but fail to produce on the time slip.

You can believe it or not, but you're moving the valve open and closing points slightly. The engine idled 50-75 RPM higher and was just a little more crisp without touching anything else. It's like moving your cam timing a half or 1 degree.

IIRC, most cam companies suggest making lash changes for testing in .004" steps (assuming the lash ramp allows for that much range of adjustment); .002" makes a difference, but not much of one. That's part of why I posted the link above, in order to quantify some actual at-the-valve duration changes resulting from the different tests referenced.

Tell four different people to set the lash to .018" on the same engine and you could end up w/ actual lash ranging from .016" to .020" simply because of the variations in their technique.

For engine dyno testing, I believe that repeatability within 1% is considered very good. But that's still saying that if pull #1 made 600 HP and pull #2 made 606 HP w/ absolutely no changes between them, they're still considered to have "repeated". I doubt a lash change of .002" can be validated w/in a 1% variance, even if there is some other characteristics that change as a result (e.g., if you can A-B-A test an idle speed increase).

Tighter makes it look like a bigger cam, loser makes it look smaller. correct?

BradH Thank you for your link and other input!I just wanted to be sure to say that.I changed my lash .008 tighter from .020 spec and will go back as a A B A test

Yes.

There are of course limits.
Too loose will destroy the parts, the tappet is not the only location of slack.
Too tight is only dangerous one way: the valve does not close. A valve left open .002" stops working, and says so (DV).

I've own and driven a V.W powered sand rail for a lot of years, I ended up buying motor parts from several different off road racers in SO CA to make it faster. In the process I learned from them that all air cool V.W. motor have solid lifters and the factory spec of setting the lash cold at .0040 was to loose, those racers suggested setting them at .0000 or just tight enough to be able to still
rotate the pushrod by hand , but not easily, just barely able with two fingers to rotate them at outside air temps when cold That worked well on that motor
I did find out on my last pump gas motor with a set of Harland Sharp 1.65 ratio single shaft rocker arms that combination of parts on that motor the lash would only change by .0010 from room temps to 180F

I have read that a .010 tighter lash was equal to 1pt in compression less for someone trying to adjust for lower octane so would a looser lash be a gain in 1pt cr?

That statement makes far too many assumptions for me to put any faith in it, regardless of the source.

Right. And what "compression"? I guess because were adjusting valve timing with lash adjustments, it must mean dynamic "compression". And of course the collective "we" cannot even agree on exactly what valve position we should use to calculate dynamic compression. All that said, I cannot see it changing dynamic compression 1 pt.

I do know that my motor will blow 5 psi more with 0.004-5" lash added.