How a solid roller with a lash spec over .020" would effect the advertised [.020" rise] duration number

[dave brode]

All,

I was looking at some baby solid rollers for big block chev. One grind looked extremely slow, at 244"* at .050", and 304* advertised. Then I noticed that it was designed for a .030" lash. https://www.lunatipower.com/street-stri ... 4-304.html

Since the .020" check height would not get the lifter to the end of the lash ramp, would this not make the advertised number look way long?

Opinion on the grind is not the purpose of my post, but feel free. My purpose is to become more learned on how lash effects the events. I have read many threads on the subject, but none covered this scenario.

I did call, and ask if the advertised was derived at .020', and was told all of their solids would be checked at .020". The fellow said that he did not know if the .030" lash ramp would cause the advertised number to be skewed.

Thanks.
Dave

[BigBro74]

I feel that the running or “at lash” durations are all over the place , and generally don’t feel real good about it until I measure it in a block with my dial indicator. I have found that “if” they advertise at .020” tappet movement then tight lash cams ~.014” are about 14 degrees longer at lash. Cams that are .022 lash are about 10 degrees longer at lash. Cams with about .026-.030” are about as advertised. This can change with lash and rocker ratios. All the ones I have measured are flat tappers though and your roller wheel may change some things-not sure.

[BigBro74]

Also- have seen where the same company has many different checking heights for different series of cams etc. which is why I say the advertised durations are all over the place....

[CamKing]

Yes, the designed Lash height, has an effect on the .020" duration, that's why we don't use .020" duration. We list our cam profiles at the actual designed lash height.

Read this, it'll help you understand what's going on.
viewtopic.php?f=44&t=57714

[dave brode]

Gents,

Understood on advertised checking rise varying.

Mr. Jones, thanks for the link. I remember that thread. I wish that I would have stumbled upon it in my searches of the last few days. , I'll re-study. Your method of deriving a published advertised number make one heck of a lot of sense.

I bought the [new] cam for $125 shipped, to hoard if nothing else. I'll try to get a chance try to put it into something and degree its at various tappet lifts. [and report back]

Dave

[CamKing]

Lash is measured at the valve, and .020" duration is measured at the lifter, so .020"lash is different then the .020" duration.
.030" lash with 1.7 rockers would be .0176" at the lifter, and below the .020" duration checking point.

[dave brode]

Lash is measured at the valve, and .020" duration is measured at the lifter, so .020"lash is different then the .020" duration.
.030" lash with 1.7 rockers would be .0176" at the lifter, and below the .020" duration checking point.

Boy, I feel dumb. Thanks for the jolt. I'm going to edit.

[BradH]

Not sure if I ever posted this here, but I did years ago on another site I used to frequent. One quick Google search and one cut-n-paste, and here it is:
--------------------------------------------------------------------------
FWIW, since I had a bunch of notes on this stuff and figured it might be of interest to some others.

Ever wonder what difference all those different lash settings make when looking at solid-lifter (flat or roller) cams? Here's a list of different lash settings and how they effect the seat timing for any given cam. I'm listing the duration points at both SAE (.006" valve lift) and "actual seat" (at the point where the lash is reduced to zero) since I've seen both used.

Lash --- 1.5 Lobe Lift --- 1.6 Lobe Lift
--------- SAE (Seat) ------ SAE (Seat)
.016" --- .0147" (.0107") - .0137" (.0100")
.018" --- .0160" (.0120") - .0150" (.0112")
.020" --- .0173" (.0133") - .0162" (.0125")
.022" --- .0187" (.0147") - .0175" (.0138")
.024" --- .0200" (.0160") - .0187" (.0150")
.026" --- .0213" (.0173") - .0200" (.0163")
.026" --- .0227" (.0187") - .0212" (.0175")

Does this really make much difference? Well, if two cams both share the same advertised specs at .020" of 290* and one is designed to run at .016" lash and the other is designed for .026", the SAE duration for the tight-lash grind is likely to be 300-302* where as the looser-lash grind is going to come in around 288*. So, yeah, I'd say that 12-14* difference in seat timing is going to be pretty obvious if you compared both cams in the same engine.

How about a cam where the lash ramps have been designed to allow a fair bit of lash adjustment to allow for some tuning? Does changing the lash make much difference to what the engine sees? Here's two examples I picked up from some Cam Doctor data published years ago:

Example 1 is on an intake lobe where the lash was reduced from .018" to .014". How much extra duration resulted?
.006" - 4.6* (SAE)
.020" - 3.4*
.050" - 2.3*
.100" - 1.6*
.200" - 1.2*
.300" - 1.2*
.400" - 1.3*

Example 2 is on an exhaust lobe where the lash was increased from .022" to .028". How much less duration resulted?
.006" - 6.9* (SAE)
.020" - 5.1*
.050" - 3.4*
.100" - 2.5*
.200" - 1.9*
.300" - 1.9*
.400" - 2.2*

In both cases the biggest change in duration was right at the initial opening/closing points, but the amount of effective change tapered off significantly starting above .100" valve lift.

I also wanted to comment on what really happens when cam "designers" start mixing & matching lobe families with dramatically different designed lash specs. I had cam that spec'd out 295/305 @ .020", 265/270 @ .050", 180/178 @ .200" w/ the provided lash settings of .018" intake / .028" exhaust. Anyone want to guess what the actual duration split ended up being at those lash settings? I'll get straight to the point and say that all that additional exhaust duration got "lost" w/ the extra .010" in lash and the split ended up being negative (less exhaust duration than intake) from .020" valve lift on up.

[Nut124]

Good thread, thanks.

I would just make the point, not that anyone has suggested this, that trying to gain "duration" by reducing lash is likely not productive.

In my current build, I found the old cams adjusted to the low end of spec for valve clearance. This resulted in very long durations as measured based on the valve coming off the seat, valve lift >0.002. However, the early lift was slow to build and my gut feeling is that it is not beneficial, may be the opposite.

I am installing much bigger cams now, with more aggressive lobe profile. I am setting them up for high side of spec valve clearance. As degreed, this bigger cam has shorter duration, 294 vs 305, but has twice as much lift at TDC and much more "lift integral".

I do not want the early 0.001 - 0.005 lift from tight lash even if it shows more "duration".

Just my gut feeling.

[dave brode]

Veering off, i wonder how slow the lash ramp is on the old GM cams? [327/365 and such]