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Old 03-27-2008, 05:55 PM
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cam question, any truth to this?

i was reading another forum the other night when i came across this.

Here are the numbers for the cam you inquired about. 60113: 294/302 advertised, 243/251 at .050, .560"/.565" 110LSA 106ICL. It looks about right for an honest 500 horsepower 383....then again, may be a slight bit bigger than necessary but what do I know about these durned hydro roller thingys hehe. I know if I were trying to make that kinda power with a mechanical cam, Id shoot for around a 247 or 248 at .050 mechanical cam....but once you figure in valve lash with a mechanical setup, the lobe looks more like a lower 240 degree zero lash cam(like a hydraulic). In other words....generally speaking a 248 degree mechanical cam will "generally" act more like a hydraulic(zero lash) setup with around 242 at .050.
is there some truth to this?

if lift is based on zero lash, wouldn't the duration @ .050" be lower?

wouldn't true lift be what ever was advertised & subtract lash?

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Old 03-27-2008, 06:40 PM
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The "duration@.050" cam spec is measured at the cam, not at the valve. It is the amount of crankshaft rotation duration that the lifter is lifted above .050".
The .050" lifter rise duration spec is a universal established standard camshaft duration spec that allows you to compare 1 cam's general usable rpm range, to another cam.

It is not the only camshaft spec that determines and qualifies the relative performance characteristics of a camshaft, but is the most critical basic, spec to compare the relative engine rpm range of one cam to another.
When picking a cam for a motor, or comparing one cam to another, this is where you start.

The .050" spec does not change. But the effective valve open duration at the the valve is effected by the rocker arm ratio and the valve lash.

So to compare the relative valve open duration of a hyd cam VS a solid lifter cam with valve lash, you have to take in account the effect that the valve lash has on the effective net valve duration @ the valve.

The equivalent effective valve duration (SBC) would be based on a 1.5:1 rocker arm, would be the valve open duration when the valve is .075" off seat.
The valve lash will reduce the valve lift resulting on comparative loss of valve open duration.
Therefore a solid lifter cam (that runs with valve lash) needs a bit more .050" duration to have the same valve open duration as a hyd cam does without valve lash. The comparative difference is about 8 degrees @.050"
So a 248 @.050" solid cam acts like a 240 hyd cam in the motor.
(assuming the lobe shape of the two types of cam lobes are otherwise identical)
The exact comparative valve action difference between a hyd cam and a solid cam depends on the amount of valve lash.
8 @.050" lifter rise is a good comparative "rule of thumb."
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Old 03-27-2008, 08:16 PM
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I asked my "old" engine builder about this, because I some idea's the a solid lift cams lift & duration was effected by valve lash. He said I was wrong. he said the cam duration @.050" & valve lift was not affected by the valve lash, & that advertised valve lift & duration was figured with the lash set at the valve.

so the cam you think has .525 valve lift that has .024" lash, in reality only has .489" lift at the valve.

sense lash affectively makes the cam "smaller", wouldn't you need to take this into account when picking a solid lift cam? in other words a 244 duration @.050" lift is good for about 6-6500 rpm, but if the lash effectively takes 8 out of it, that would turn that 244 @.050 into a 236 @.050 reducing the rpm range of the cam. to get the same rpm out of the solid lift wouldn't you have to go with a 250 @.050?

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Old 03-27-2008, 08:55 PM
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ok, a general explanation as it was tought to me many years ago in college. a solid lifter cam and a hydraulic cam of the same profile will have the same lift duration figures.

a hydraulic cam runs the lifters at 0 lash, all play is taken up by the lifter so as soon as the lifter starts up the ramp the valve opens and duration starts.

now on a solid lifter cam, the cam will have "clearance ramps" to take up the lash before the valve starts to open. these "clearance ramps" are designed into each cam by the origonal designer. this is why a certian cam wiil have specs that say "valve lash .014" while another will say "valve lash .021" while yet another will say "valve lash .030" (the 30-30 duntov) it's the clearance ramps that are designed into the cams that account for the differences.

solid lifter cams do NOT include "clearance ramp" specs in their lift/duration figure. if the did nobody would be able to compare anything.

back in the old days when solid cams were popular for the street we used to get them in and guys would say tune it up and set the valves. when asked what the lash specs were on the cam they would say "i don't know". we found we could pretty much figure out the lash specs by SLOWLY thghtening the valves until the clicking just stopped--NOT 0 LASH!! then back off one intake and one exhaust and retighten until the clicking just stopped once again and measure the lash on those 2 valves--these figures would be the hot intake/exhaust lash. this had to be done with the engine at operating tempature...
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Old 03-27-2008, 10:15 PM
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Quote:
Originally Posted by 406 ss monte
I asked my "old" engine builder about this, because I some idea's the a solid lift cams lift & duration was effected by valve lash. He said I was wrong. he said the cam duration @.050" & valve lift was not affected by the valve lash, & that advertised valve lift & duration was figured with the lash set at the valve.

so the cam you think has .525 valve lift that has .024" lash, in reality only has .489" lift at the valve.

sense lash affectively makes the cam "smaller", wouldn't you need to take this into account when picking a solid lift cam? in other words a 244 duration @.050" lift is good for about 6-6500 rpm, but if the lash effectively takes 8 out of it, that would turn that 244 @.050 into a 236 @.050 reducing the rpm range of the cam. to get the same rpm out of the solid lift wouldn't you have to go with a 250 @.050?
You really like to confuse yourself, don't you.
Valve lash is at the valve, not at the cam. valve lash does not change the camshaft profile or the .050" lifter rise duration spec of a camshaft.
Valve lash does effect the net effective valve action.
To see the same effective net valve action of a hyd cam, a solid cam need about 8degrees extra ".050" lifter rise duration"
Why? because the valve lash at the valve must be taken up before any real valve motion starts.
The valve lash effectively reduces the valve action (valve lift and running seat to seat duration)

The running engine only sees what the valves are actually doing.

A camshaft say for a SBC that has a .525" gross valve lift (assuming 1.5:1 stock rocker ratio) that uses .024" valve lash will produce a max .501" net valve lift. The camshaft lobe lift is .350"
camshaft lobe lift X rocker arm ratio = gross valve lift.
Gross valve lift - valve lash = net valve lift.

When a camshaft in a SBC causes the lifter to be @ .050" lift, the valve is @.075" lift thru a 1.5:1 rocker arm.
A
.024" valve lash would reduce the net valve lift to .051", when the lifter is at .050" lifter rise.

Advertized duration is neither lash point duration nor valve seat to seat running duration.
Advertized duration is the duration that the lifter is at some specd height off the cam base circle. Typically .004", .0045" .006" .007" for hyd cams.
.008" .012" .014" .015" or .020" are common lift specs for solid lifter cams.
There is no universal standard. The camshaft maker can call it anything he chooses to. And often does play with this spec for marketing purposes.

The advertized duration rarely is the same a the valve "running duration" or "running seat to seat duration"
The purpose of "advertized duration" is to make you want to buy the camshaft.

There are also different designs of solid lifters cams. "tight lash" cams have different "lash ramps" designs that typically use less valve lash.
A "tight lash" camshaft typically has slightly more intense net valve action at low valve lifts up to about .150" lifter rise.
A tight lash cam, can create faster net valve action, (faster on and off seat net valve action), but the allowable valve lash varience window is narrower, as the cam lobe opening and closing "lash ramps" are quite a bit shorter.

"Normal" .022" to .030" lash solid lifter cams are a little more tolerant of valve lash variences.
Thats why the .050" lifter rise spec is used to compare one cam against another as to its shoe size. its the only duration spec that is apples to apples.

Changing the valve lash, changes the "effective net valve open/close running duration" of a cam in a running motor.
Less valve lash makes the camshaft seem "a little bigger" by increasing the effective "seat to seat valve duration" and increases the net valve lift area under the net valve lift curve. More valve lash has the opposite effect on a running engine.

Last edited by F-BIRD'88; 03-27-2008 at 10:53 PM.
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Old 03-28-2008, 01:42 PM
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Quote:
Originally Posted by F-BIRD'88
You really like to confuse yourself, don't you.
Valve lash is at the valve, not at the cam. valve lash does not change the camshaft profile or the .050" lifter rise duration spec of a camshaft.
Valve lash does effect the net effective valve action.
You're both right.. the OP was asking if (since the valve events are affected by lash) if he should take that into account if selecting a solid lifter cam. The answer is yes. Although the cam timing events and lift are ground into the cam and can't be changed, the actual valve events are what determine the operation of the engine. So technically, even though the cam doesn't change, the effective valve events DO, so the answer is; Yes 406 Monte... you should take that into consideration when choosing a solid cam to match the output of a hydraulic cam.
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Old 03-28-2008, 02:50 PM
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All camshaft timing events are figured with 0 lash. Subract the lash from the net valve lift and the timing events will also change.

tom
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Old 03-28-2008, 03:18 PM
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so the cam you think has .525 valve lift that has .024" lash, in reality only has .489" lift at the valve.

i was thinking about this at work today & i realized the the lash wouldn't be multiplied by the rocker ratio sense it's set on the valve side of the rocker. it would be .525-.024=.501

You really like to confuse yourself, don't you. be nice. lol

techron said, solid lifter cams do NOT include "clearance ramp" specs in their lift/duration figure. if the did nobody would be able to compare anything.

tom said, All camshaft timing events are figured with 0 lash. Subtract the lash from the net valve lift and the timing events will also change.

which statement is correct, or do both have a little truth to them?
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Old 03-30-2008, 12:14 AM
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your homework

More Homework

You're not done yet

last one

Last edited by F-BIRD'88; 03-30-2008 at 12:46 AM.
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Old 03-30-2008, 11:28 AM
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this is what i was wondering about. but i did learn "some" about overlap & lsa. they play more into it than i realized.

this is the info i was having trouble with.
SOLIDS VS. HYDRAULICS
Comparing specs of a hydraulic vs. a solid camshaft isn't as simple as it first may appear. While it would seem like solid and hydraulic lifter camshafts with the same lift and duration specifications would behave similarly, there are a few considerations not apparent at first. Beginning with the advertised duration numbers, solids and hydraulics are rated by completely different standards. For instance, in the COMP Cams line, hydraulics are rated for duration at 0.008-inch lifter rise, while solids are typically rated at 0.020 inch. Comparing a solid to a hydraulic by advertised duration is like comparing apples to oranges. In regard to lift, things are a little simpler, but again a direct comparison of specs would be misleading. The lash needs to be subtracted from a solid cam's specs to arrive at the true lift at the valve, which can then be compared to the hydraulic cam's specs.

Finally, we have duration at 0.050 inch. While both types of cams are rated in the same way, at the 0.050-inch tappet rise spec, again the numbers can't be directly compared between a solid and a hydraulic. Duration at 0.050 inch is measured in crank degrees at 0.050-inch lifter rise on the opening and closing side of a lobe. The engine isn't interested in how long the lifter is moved, but rather only sees what is happening at the valves. With a solid, the lash will take up some of the lifter's motion before there is any valve motion. In fact, with a 1.5:1 rocker ratio, the solid's duration at 0.050-inch reads as if the duration was taken 0.033-inch lifter rise in hydraulic terms. That's a significant difference. A solid cam will behave like a hydraulic with duration at 0.050-inch spec. of approximately 10 degrees less duration. All of this makes it very difficult to exactly match a solid and hydraulic lifter cam; it certainly can't be done by matching the numbers in a cam catalog or on a spec card.

thanks f bird.
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