How do you describe cam lift?

[67 B-body]

I have noticed over lots of reading, that we aren't all on the same page when listing cam lift "specs". I for one, have been replying with .601" lift when asked, because I have a solid "non-hyd" camshaft and take valve lash into account. I'm certain others with solid cams Roller or flat tappet alike, have been giving lift without lash included. Mine for example would infact be .6293" lift without lash being included or "removed" from the calculation.
When listing Hyd cam lifts, there is no lash to deduct from the tottal lift at valve. So I think this is probably the only consistant referance to valve lift when people are asked to describe cam specs.
Any thoughts on the topic???

 

[moparpoor]

As most of us,we discuss cams in advertised specs.Their is a great deal of assumption that everybody understands the effects of valve lash,rocker ratios,and duration.When of course not every one does.So the language has been adapted to advertised specs and not measured specs.

 

[67 B-body]

Yes,, advertised is typicaly referanced in Duration, and lift has been left alone in manufacture specs. I sometimes wonder when folks compare cam specs with one another, if they take into consideration the differance in "actual vlavle lift" between listed lift specs on solid and hyd cams? For example, if I told Joe Schmo that I have adequite valve to piston clearance with my .630" lift cam and realy like the way the car runs. He might think he can run a hyd camshaft using the same pistons as mine and cam lift then wind up smacking valves or catch it during assy but wasting money on a camshaft he can't use.
When topics of cam specs are brought up, it's usualy to obtain some sort of referance to how your build compares, or a potential option for you to try.... This information is quite skewed as to how a person states the "true lift".
I don't have as much faith that the majority of readers do understand that lash needs to be removed from the stated lift. Remember, there are awful lot of newbies looking for advice, and I would go even further to say a majority of the topics of cam specs are done so by people who are unable to make a correct choice on there own, or at least unsure of his or her choice enough to get a second or third opinion.
Thanks for your reply moparpoor!

 

[moparpoor]

I agree with you!You can take the right cam and install it incorrectly and make a mess of things.Much less the wrong cam.

 

[Budnicks]

Here a way to look at the camshaft, I have for 35+ years now... One can be stated as Gross valve lift, when the camshaft lob lift is mutiplied {X} by the rocker ratio; example a camshaft with 0.333" camshaft lob lift X 1.5:1 rocker ratio = 0.4995" gross valve lift, the other can be Net valve lift, which is gross valve lift minus {-} lifter pre-load in a hydraulic camshafts or Net valve lift on a solid mechanical/roller is gross valve lift minus {-} the valve tip to rocker arm valve lash {- deduct valve lash}, which could be many different variables depending on lash used... example 0.500" gross valve lift minus {-} valve lash of 0.020" = 0.480" Net valve lift... The at 0.050" lift number in camshaft duration, is for use in installation {camshaft degreed in} for correct duration #'s, as the cam can be installed in many different ways, ground differently or production variables, degree's retarded or advanced, so they give you a # of duration to base the camshaft at their recommended installed position at 0.050" lift in the duration cycle, it will be a much smaller # than an advertised duration #... Lobe centers are at max camshaft lift at that given #.... All of these measurements & #'s are based on & need to be done with the proper length push-rods to have the correct #'s & rocker geometry...

 

[moparpoor]

:laughing6::laughing6:Now half the people that have read this are now confused!!!:confused5::confused5:

 

[Budnicks]

yep

:laughing6::laughing6:Now half the people that have read this are now confused!!!:confused5::confused5:

Yep probably... If they are, they should probably leave the engine building to someone that knows, what it all means or get that knowledge...

 

[67 B-body]

I agree with you!You can take the right cam and install it incorrectly and make a mess of things.Much less the wrong cam.

Yep,,,, OUCHY!!!

 

[Cranky]

Cams and pistons....you need to know what's going on before you select them. Pistons also have an 'advertised' compression ratio and that is usually a figure that can possibly be met if you do all that you can do to achieve that advertised ratio. The best figure to know is the 'compression height' of the piston and do the math or know what CH you need for a particular compression ration with the head, gasket thickness, valve reliefs etc used.

 

[Meep-Meep]

It is absolutely correct that you want to take lash into account but also flexing of the other components, which may be difficult to measure, needs to be included in that equation. There is also coefficient of thermal expansion, which plays more of a role when using aluminum heads and blocks with push rods. Also any angle of the push rod other than straight out of the lifter can slightly reduce net lift because that motion is a vector component. I think people put too much emphasis on lift when the most important event in cam timing is the point where the intake valve closes and you begin to make cylinder pressure. Are you really going to see a difference in .020" - .040" lift? But I bet you will see a difference of a few degrees of intake valve closing.

 

[67 B-body]

Great replies fellas!!!!
Now I hope others interested in some cam specs read this thread!

 

[383man]

Usually when I talk cams I use the stated specs. If its a solid and it says .508 lift then thats how I talk about it. I just figure everyone knows it will be a little less with lash set. It just makes it easier to use the cam specs for talking about them and if someone is not then they should specify what reading they mean. Most Mopar lift specs are stated with the standard 1.5 rockers. As for duration many years ago all they gave was advertised duration but that can be decieving as there is alot of room for error in just where it starts and finishes its duration readings when measuring it with a dail indicator. So most now go with checking it at .050 valve lift. It just means when the valve opens to .050 lift thats the start of duration measurement. It is more accurate as when you hit .050 you can be right on the money with no movement at that spot that can throw the reading off a few degrees. Its the same when checking the cam centerline at max lift. When you get to max lift you will be there for about 4 or 5 degrees so you cant get an accurate reading. Thats why you check the centerline reading twice at .050 before max lift and at .050 after max lift. Then you add them together and divide by 2. Then you have the dead on reading. Makes sense right ? :icon_mrgreen: Ron

 

[451Mopar]

The cam in my Charger has 0.446" lobe lift, but it just does not sound as cool as 0.714" valve lift (zero-lash) with 1.6:1 rocker ratio.

 

[67 B-body]

Usually when I talk cams I use the stated specs. If its a solid and it says .508 lift then thats how I talk about it. I just figure everyone knows it will be a little less with lash set. It just makes it easier to use the cam specs for talking about them and if someone is not then they should specify what reading they mean. Most Mopar lift specs are stated with the standard 1.5 rockers. As for duration many years ago all they gave was advertised duration but that can be decieving as there is alot of room for error in just where it starts and finishes its duration readings when measuring it with a dail indicator. So most now go with checking it at .050 valve lift. It just means when the valve opens to .050 lift thats the start of duration measurement. It is more accurate as when you hit .050 you can be right on the money with no movement at that spot that can throw the reading off a few degrees. Its the same when checking the cam centerline at max lift. When you get to max lift you will be there for about 4 or 5 degrees so you cant get an accurate reading. Thats why you check the centerline reading twice at .050 before max lift and at .050 after max lift. Then you add them together and divide by 2. Then you have the dead on reading. Makes sense right ? :icon_mrgreen: Ron

One of the reasons I bring this all up, is because I have overheard a conversation where two people were comparing cams. One says, "I have a little more lift than your cam"..... Well, in fact he had less lift! The cam with more manufacture spec lift was a solid cam, the other a hyd.. After the solid cam owner takes out the lash, his camshaft lift is something less than the hyd cam.
Just thought it might be worth bringing up to those "cam comparing people"...LOL