I would like to convert numbers on my card to .050" lift, to calculate my DCR. thanx

Intake valve closing at .015" is 71 degrees.
What would this be at .050" lift?

cam is a compcam xe 290s solid flat tappet
252@050. intake .540" lift
260@.050 ex. .560" lift

 

Let me guess you want to figure out what it is at .050", add 15 deg and you have where the valve closes ?

Just add about 4 degrees to the 71 degrees and the valve is closed

 

If u have the cam card info and want help then post it. But what u provided here is only enough to pi&% people off. I can't tell not only what u want but what your cam specs really are. U say u what to convert to .050" lift but then list intk @.050" = .540" and exh =.560".
Y would the card card list only the intake at 71* and no exh numbers. If that is solid cam then what is the lash setting?

Maybe u want to know what lift @.050" after lash is subtracted but i can't read this in your post and it would take a runnout on each lobe with a dial indicator to find it.

Well u can post whatever question u want but if u want a decent answer u need to provide decent info.

cardo0

 

I am not trying to pi&% people off, but your comment there is a start.
I said i wanted the intake valve closing closing point converted from the listed .015" lift TO .050" valve lift. I went on to list the cam duration & lift from the published specs.

Specs:
Valve adjust: .016" lash intake & exh.
Gross valve lift: .540 intake, .558" ex.
Duration at .015" tappet lift: 290 intake, 298 ex.

Valve timing at .015" 252 intake 260 ex.

Cam specs fro cam installed at 106 intake CL
Duration at .050 252 intake 260 ex.
Lobe lift .360" intake .372 ex.

lobe seperation: 110

that is all the cam card information.
Happy Holidays

 

Now the vlv timing spec at .015" = 252intk and 260*exh does not make sense with the later statement that duration at .050" = 252intk and 260exh. Either the lobe is at .015" lift or at .050" lift at 252*/260*.

Another conflict is when u take the .016" lash figure and subtract it from .015" the result is -.001" - i guess meaning the vlv is shut. And .016" is somewhat a "tight lash" cam. Maybe this will help to tell u that actual vlv lift is the result when u subtract the lash value from the Gross Lift value.

So similar to as MotorHead said u can approximate a solid cam actual lift point by subtractrating (not adding) 'bout 4* from the intk 252* (=248*intk @.050") and 260* (=256*exh @.050"). 4* or 5* is a general rule of thumb and can vary due several factors - lash, mfr lobe ramps, etc. Sometimes u can find a hyd cam by the same mfr that has matching lift values (actual not gross lift) for a good comparision - but do not compare cams between different mfrs.

Honestly i don't understand what converting .015" lift closing point to a .050" closing point means or is physicaly possible. The vlv only opens then closes once and it looks like the card says at 290*intk and 298*exh after the .016" (well again .015" max) lash is already subtracted.

I'm not trying to drag u over the coals C3 but i think u have some bad information and its taking u around in circles.

Hope this helps.
cardo0

 

I am not comparing cams. I only want to accurately calculate dynamic compression ratio. The program request the intake valve closing degrees (+15degrees) at .050" to get the results. thanx

 

I needed the same info when planning my build. Called Comp Cams Tech line and asked. He wanted the grind # looked it up and told me over the phone. Give them a call.

 

This has come up before with regards to using the Dynamic Compression Calculator on the Keith black site. This is my take on it, to determine DCR with the calculator you need input how many degrees after bottom dead center the intake is completley closed.

THe people that desingned the calculator know that no one knows when there intake will be competely close so they have to figure a way most people can find this out and the most common spec on a cam card is the .050" measurement. Now once you know where you intake valve is at .050" they have added an estimated 15 degrees to that and that is where your intake is supposed to be closed and that is what you enter into the calculator. Problem is, some cams are going to take much more than 15 degrees to close from the .050" measurement depending on the ramp but I guess they figure it doesn't really matter, the calculator probably gives you a ballpark answer anyway.

Now some cam cards give you a .015" measurement for intake closing instead of .050". In this case I have figured out, for my cam anyway, that my intake valve will be closed with another 4 degrees of duration added, so my 71 Deg ABDC @ .015" becomes 75 deg ABDC @.000 or closed. Am I confusing anyone yet

Anyway I could mathematically figure out what duration my ( and the thread originators ) intake was @ .050" if my ramps were completely linear ( flat ) , even if they aren't I could get within a few degrees but there is no reason to do this as adding 15 degs to my .050" measurement is not going to be as accurate as adding 4 degs to my .015". Do ya follow

 

All that sounds fine but I don't agree with it. Using the point where the intake valve is closed is not how the program works or is intended to work. You made an assumption to fit your need.

I'll give an example as to why using the intake closing point will not work and why they prefer using the .050 point (plus 15). Lets take two cams both at 284* duration with the same intake valve closing point. At .050' one cam has a duration of 234* and the other at 218*. Which one will have a lower dynamic compression ratio. If you base it on when the valve is fully closed, they will be the same. If you base it on the .050" point (plus 15), the 234* cam will have lower DCR. The 218* cam will build higher cylinder pressures than the 234*.

Why KB chooses to add 15 to the .050" is unknown to me. They could have chosen 14 or 16. Evidently 15 is close approximation where their calculator works to give a fair representation of DCR.

 

The point I was trying to make is that their calculator does not ask for the intake closing point. If that is what they wanted, they would state that. They say to use the point where the vavle is at .050" and add 15 to that number.
I believe in my example I already showed why the intake closing point is not a good point to choose. Same advertised duration camshaft but very dissimiliar in how much cylinder pressure will be built. DCR is just another tool that gives an indication of how compression will be built when adding in the cam specs.
When working with mathamatical equations, you have to input the correct data. If the user decides to input incorrect data as he thinks, the results will be misleading.
I have been on KB's website numerous times and used their calculator. The thing I have never seen is what KB feels is good range the DCR should be in. I'm not saying it's not there, I just haven't run into it.

When does the engine make compression? I don't know. I do know that it will make the most compression when the valve is completely closed. One article I read on DCR states compression can not be made until the valve closes, but I can't agree with that statement. That would be like saying you can't inflate a tire if it has a slow leak.

 

Yes I did make an assumption and so did you. You are assuming the DCR that is calculated with their calculator at .050" + 15 degrees is correct and yet you admit this is only an estimate. So with this assumption you have 2 different calculations for 2 cams whose intake valve is completely closed at the same point. Who is correct here, you don't know and neither do I.

I do know that a big cam with big duration can take 25 degs ( 15 + 10 ) or more to completly close after .050" so is their calculator going to give you a much higher DCR if you use the .050" + 15 deg method ? I don't think either one of us knows for sure.

One more thing to think about ; Is the piston making any compression before the valve is completly closed, say at .015", probably.

I think we have to look at the calculator as a good estimate of DCR and that is it, not overanalyze it