I think that I finally have a handle on the lash adjustments that can be juggled with the solid cams.

They are advertised and sold at a set lash check point, advertised and duration at .050" numbers and a recommended running lash that is generally different then the advertised check point lash.

I'm using CompCams figures here for their 282S solid cam I have in my 496 BB as an example.

If you tighten the lash up from say the factory recommended running lash number of say .022" to the advertised check point lash number of .015". you have effectively increased the advertised duration figure to what they say the cam is and created a bigger cam! BUT, the duration at .050" stays the same!!

Now if you go the other way to say loosening it up from .022" lash to .030" lash, then you effectively shorten the advertised duration number and created a smaller cam. And again, the duration at .050" doesn't change from advertised!!

This is why a "lash circle" works to see if you are over-cammed or under-cammed.
If you are over-cammed, then run the cam loose to gain more torque!! BECAUSE IT WILL APPEAR TO BE SMALLER!! If you are under-cammed, then tighten it up to gain high rpm horsepower! AGAIN, BECAUSE IT WILL APPEAR BIGGER!!

It took me quite a while to figure this stuff out and I hope it's right and helps others.

And I asked CC about what the effective changes in advertised duration numbers would be at .022" and .030" lash (b/c a 282S is 282 at .015" lash) and didn't get an answer!!

He, He!!! I've got tooo much time on my hands thinking about stuff!!

Hey, Have a happy Turkey Day. I gotta go cook the BIRD. pdq67

Hey pdq67, you seem to be the "Man" when it comes to solid lifter cams and theory, so I will ask you these questions: How tight can you lash a solid before it hurts the valves/and or the engines performance? I have a solid in my 383, it's not as big as I wished, so I decided to tighten up the lash to make it "bigger". The factory calls for a hot lash of .018", so I went to .015". You could hear the engine just "lay down" when I was adjusting it at idle. It sounded absolutely sick. I drove it for 5 or 6 miles to try it out, it felt like I only had half power, if that. The warmer the engine got, the worse it ran. I adjusted it back to .018", it came back to life. I have left it there since. What do you think?

Slow down pdq67! http://www.camaros.net/forum/wink.gif

Look at your cam card again.

Mine says (it's laying on my keyboard as I type):

DURATION AT
.015 TAPPET LIFT 282 282

Since valve lash is checked at the rocker tip - not between the tappet and lobe - the ratio of the rocker must be taken into acount.

0.015" * 1.5 = 0.0225"

So, if you run 0.0225" valve lash you will have an actual duration of 282 degrees.

Your valve lash must also be subtracted from the gross lift on the cam card to obtain actual valve lift.

In my case:

0.495" - 0.022" = 0.473" http://www.camaros.net/forum/smile.gif

Just thought I'd add my two cents on the valve lash theory.
It might be a good idea to be aware of the velocity and acceleration of the lobe before the lash is adjusted too much. Coming off the base circle with a tighter lash could slow the valve down considerably at initial lift. The flip side, opening the lash, could cause the the valve to be hit harder. Either adjustment obviously will change the dynamics of the valve train which in turn affects the fuel/air flow to the cylinder in addition to changing the "appearance" of the cam profile.
I'm not saying that changing the valve lash is not a good idea. Sometimes it is, depending on the application. What I am saying is you could dramatically change other related events inside the motor, depending on the profile of the lobe.
Circle track folks often adjust the lash from track to track, for wider or tighter corners but usually only 2 or 3 thousanths.
One other caveat: opening the lash too much can mushroom the top of the valve stem and pretzel the stem over time.

Crane states that you can go +/- .008/.005 to play around with the cam characteristics. Their website has some good information, too.

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Rick Dorion
69 RS Conv,355,M20,4.10's and I don't worry about stone chips.

Interesting thread PDQ. My 282s cam card recommends .022 lash for both intake and exhaust, but it may be a tad different since I have a small block. CC told me I could tighten up my lash to .016 - .018.

Tightening the lash from .022 to .018 [where I run it] effectively makes my 236* duration at .050" lift, 236* duration at .046" lift. I always wanted to recalculate what duration at .050 was to account for changes in valve lash and rocker arm ratio, but to do that accurately is nearly impossible because of the curve of the cam lobe ramp. (If it was a simple flat ramp it would be easy to figure).

My total lift increases too - from .506" up to .510". (advertised lift is .495 but I'm running 1.6 rockers which makes lift .528" minus .018 lash).

I always wondered if cam manufacturers really even bothered to take valve lash into consideration at all when listing duration at .050" numbers. Don't mechanical cams "act" 6 - 10* smaller in duration than hydraulics anyway?

Eric

Sometimes things aren`t as they appear to be.
Comparing cam`s from one company to another can be very misleading.
As they can and do have different standards to measure by.
It would not be unreasonable to conclude that maybe some cam outfits purposely wiggle the numbers somewhat so as to make their cams look more desirable.

Even within a particular company the way they present the numbers can be off .

As an example COMP CAMS:
Advertised dur Advertised @ .050
hyd-280 230
solid-282 236

Measured dur @050 minus lash:
Hyd - 231.4
solid- 229.6

Advertised lift:
Hyd- 480
solid- 495
Measured lift with 1.5 rocker:
Hyd- 471
solid- 472.5

Just one example of what can happen when trying to compare quoted specs even within one company ....you might not get what you thought you were getting or worse yet...NEEDED.!!

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68 biscayne 4060lbs
468 iron oval port 10.25-1 TH400 Flowmasters&radials
11.85 ET @ 113.7 MPH

I guess that I don't have a good handle on this yet??? But, I'm trying to get one.

I thought CC listed in their cat. that their Magnum solid cams like the 282S could have the lash varied fom .015" to .030".

And that timing figures were arbitrarily picked to be figured from the .015" lift point on the ramps. And that this figure really has nothing to do with the lash setting.

I don't get why the little Duntov, -097 cam's intake lash is .012" whereas the big Duntov -346 cam's is at .030"? I assume it's in the ramp designs.

As for multiplying or "ratio'ing" lash figures b/c of a change in rocker arm ratio, what do the people that make the non-stock ratio rocker arms say about changing the stock recommended lash setting when a change is made in rocker arm ratio?

I have never heard of the lash being opened up b/c of installing them. But, I never looked for it, either. I do know that CC's cat. lists cams that can be used with large ratio rocker arms and I don't think the lash is any different than the other cams, but I could be mistaken!

This is very interesting to me, so lets continue. pdq67

I'd bet that tight lash cams have a less agressive ramp design than those designed to operate with more lash. I've never seen cam manufacturers publish the exact specs of a cam's ramp - probably kept pretty hush-hush.

So, probably the only way to really compare ramps for sure would be with a good degree wheel, a dial gauge, a couple cams, a pad of graph paper, and a whole lot of time http://www.camaros.net/forum/biggrin.gif

A "Cam Doctor" jig would do it real easy. pdq67

pdq67, good post.

I have always wondered the same thing. My Crane solid calls for .024, but I have found it runs faster in the 1/4 mile when set at .030.

Nevr really knew why, just that I picked up a haor over a tenth when set loose.


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Mark

1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.79 @ 123.95 Slicks / 11.997 @ 114.23 Radials
"Speed KILLS, so drive a FORD and live forever!"
http://personal.lig.bellsouth.net/~racer383/

Member of the "unwanted" 3rd Gen group.

I have a cam lift/crank angle diagram I developed carefully from the factory "30-30" Z/28 cam, and it shows clearly that both the opening and closing ramps are .020" high; the height of these ramps, factored by the (actual) rocker arm ratio, determines the correct lash, which explains why the factory-recommended .030" lash for this cam is incorrect, as we had always suspected.

Stock SB Chevy rockers are NOT 1.5:1, although that's the "design ratio"; at the lash point, they actually measure 1.37:1, and at full open they vary from 1.44 to 1.46:1. If you factor the .020" lobe lift of the ramps through the 1.37:1 rocker arm ratio at the lash point, that tells you that the clearance ramps are all taken up at a lash setting of .0274"; if the lash is set at .030", the lifter is off the clearance ramp and on the acceleration ramp on the lobe before the rocker starts to open the valve, and the same thing happens at valve closing. This causes the valve to be lifted off its seat and returned to its seat at greater than clearance ramp velocity, which contributes to valve seat recession, can cause valve bounce at high rpm, and it's also pretty noisy.

Our conclusion, since proven by many settings of "30-30" cams both in Z/28's and in '64-'65 327/365 Corvettes (which use the same cam), was to set them at .026" COLD. With the "30-30", in order to be sure you're on the base circle, this has to be done by setting the intakes at 90 degrees ATDC and the exhausts at 90 degrees BTDC, as the "30-30" has VERY long clearance ramps, and is the only cam Chevy every made where both the intakes and exhausts are still on the clearance ramps at TDC for each cylinder.

After setting at .026" cold using the 90-degree after/before procedure, if you go back and check clearances at TDC, you'll find they've closed up to about .024", as they're still on the ramps at that point.

Without exception, every "30-30" we've done this way (and those done by others following our procedure who reported back to us) reported more stable idle, improved throttle response, nice mechanical "singing" sound, no "clacking", runs better, sounds better.

If you know the lobe height of the clearance ramp (easy to measure with a degree wheel and a dial indicator on the pushrod) and the ACTUAL rocker arm ratio at the lash position (also easy to measure - one dial indicator on the pushrod, another one on the retainer, and compare the two readings to determine the ratio at each degree point you select), you can determine what the lash should be in order to ensure that the valve is indeed being opened and closed on the clearance ramps, not on the acceleration/deceleration portions of the lobe; this will be a lot easier on both the lifter faces and on the valve stems.

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JohnZ
'69 Z28 Fathom Green

JohnZ,
I'm trying to think how to ask what I am wondering about??

Aren't all cam duration numbers arbitrarily picked except for the .050" figures b/c didn't the aftermarket cam manufacturers used to list advertised duration, SAE duration, another duration type with a J in it along the lines of SAE, and duration at .050"?

And that lash didn't figure into any of them.

And they used the .050" figure as an industry standard to get totally off the ramps.

I do know that you can play around w/ lash adjustments to dial in a cam combination if it isn't completely optimized to begin with.

I always wondered about why the little Duntov was a tight lash cam and the big Duntov was a loose lash cam?? I can see that if the .020" and .050" duration figures are right for the engine to run properly, then the cam can have short ramps. And I think One of the cam grinders called it "hydraulic intensity" theory but left off the theory!

IMHO, a solid cam needs just enough lash when hot that the valve is on the seat so that the heat that it has soaked up can be bled off to cool it. Otherwise, the valve will burn! Now if the ramps aren't correct, the cam lifter/combination will experience extreme pounding and wear. Also that modern CAD has allowed cam manufacturers to tighten up on the ramps, thus creating EX type cams!

He, He!! I'm getting a headache from thinking sooo much. pdq67

PS., the old big Duntov is advertised at 345 duration but really a 304 duration cam when you get right down to it and runs good at who knows what duration is at the .024" or .030" lash. I personally would call a solid cams advertised duration figure the running duration number at a lash setting and be done with it!! Isn't this what is being done over on the hydraulic cam side???

I think the Marketing guys at each cam manufacturer are in charge of the numbers! It's the area under the lift curve that counts, and everyone has their own way of expressing it and making it happen. The "30-30" is an unusual example, and I have one, so that's why we went to the trouble of diagramming it one degree at a time. I'm sure the aftermarket cam manufacturers are aware of the disparity between the "design" 1.5:1 Chevy stock rocker arm ratio and the ACTUAL 1.37 at the lash point, but none of them ever mention it.

The procedure I outlined in my post above has the same positive results on the original 097 Duntov when set at .010"/.016" instead of the "spec" .012"/.018", although the 097 Duntov can be set at TDC.

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JohnZ
'69 Z28 Fathom Green

As always John, Thx. for the comeback. pdq67

So based on this discussion I am drawing the following conclusions - pls correct me if I am wrong here:

1. Solid lifter cams specs DO NOT take into consideration valve lash. So lash must be subtracted from published specs to get a cam's "real size".

2. The lift and duration figures published by manufacturers describe the cam lobe profile in conjunction with an assumed true 1.5:1 ratio rocker.

3. Advertised duration figures are nearly worthless since most manufacturers use whatever standard they darn well please.

Eric

Eric68,

1. With regards to lift, that is correct. With the SBC CC282S example the lobe lift is 0.3300" and the advertised lift is 0.495". 0.495/0.3300 = 1.500, so if your rocker ratio is 1.5:1 you must subtract lash from 0.495" to get the actual lift. My cam card lists the 0.495" figure as "GROSS VALVE LIFT", subtracting lash reveals net lift.

2. Again, with regards to lift, that is correct. Actual off the seat duration does not change with changes to rocker ratio provided valve lash is adjusted proportionately. However, the cam seems to have slightly more duration with a greater rocker ratio due to the larger area under the lift curve.

3. While you may not be able to easily establish a perfect correlation between manufacturers or types of cams, you should be able to come very close. Hydraulic cams from Crane list duration at 0.004" tappet lift (Comp uses 0.006" tappet lift). So you do have some duration that is in addition to the advertised number. This would be the 10 degrees or so it takes to open the first 0.003" (assuming 1.5 ratio rockers) and the 10 degrees or so it takes to close the last 0.003". That 10 degree figure comes from a Crane 284 hydraulic I degreed a few years ago, and is not perfectly accurate but it is a ballpark figure.

My opinion is that a solid lifter cam behaves at low speed like a hydraulic that is around 10 degrees smaller. I say 10 and not 20 degrees because those first few thousandths that the valve moves with a hydraulic are at a pretty slow rate. I've not made a lift vs. duration curve for a solid cam so I may be off a little on this.

I conclude that you can compare duration figures between major manufacturers for the same type of cam, and also, with a little correction figure, between types of cams.

[This message has been edited by Ballistic (edited 11-27-2001).]

I agree - nice post/analysis, Ballistic.

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JohnZ
'69 Z28 Fathom Green

One other thing, I think(???), is that duration at .050" won't change due to variations in lash until your lash is over .051"!! Then the lobe gets smaller (and it's duration) with lift! pdq67