AreThere Ways To Determine How Much More Cam Duration To Use By Using Old Cam?

[bigpoppapreston]

AreThere Ways To Determine How Much More Cam Duration To Use By Using Old Cam?
Forgive me of my ignorance. I'm trying to learn more about engine building. Are there ways one can their current camshaft to determine how much more duration one can safely use by measuring piston to valve clearance and degreeing the cam? Or are formulas or math equations to help assist without spending $400+ for a cam that may not fit and may not be able to sell? For example if im using a cam with intake duration of 234 @.050 and i have ..080" ptv clearance using a checking spring, and .100 ptv on the exhaust with 242 duration @.050, how much more duration i can get away with without flycutting the pistons? I hope im make sense trying to explain myself.

[Erland Cox]

I do not know if this free program has what you need?

http://www.compcams.com/catalog/COMP201 ... 96-399.pdf

Erland

[CGT]

AreThere Ways To Determine How Much More Cam Duration To Use By Using Old Cam?
Forgive me of my ignorance. I'm trying to learn more about engine building. Are there ways one can their current camshaft to determine how much more duration one can safely use by measuring piston to valve clearance and degreeing the cam? Or are formulas or math equations to help assist without spending $400+ for a cam that may not fit and may not be able to sell? For example if im using a cam with intake duration of 234 @.050 and i have ..080" ptv clearance using a checking spring, and .100 ptv on the exhaust with 242 duration @.050, how much more duration i can get away with without flycutting the pistons? I hope im make sense trying to explain myself.

What brand cam is your current cam?

[bigpoppapreston]

I have a Comp cam that I had ground for me. Just received it about a week ago.

[bigpoppapreston]

I do not know if this free program has what you need?

http://www.compcams.com/catalog/COMP201 ... 96-399.pdf

Erland

Thank you Erland. I will certainly check it out!

[CGT]

I do not know if this free program has what you need?

http://www.compcams.com/catalog/COMP201 ... 96-399.pdf

Erland

Thank you Erland. I will certainly check it out!

And your previous cam was comp?

[CGT]

List the lobe numbers of each cam and the intended intake centerline.

[bigpoppapreston]

List the lobe numbers of each cam and the intended intake centerline.

My previous cam was a factory piece. However here are my current cam lobes:

112-000-11 hydraulic roller
3016
13141
113+3

The factory 5.7 hemi cam specs are:

196 duration @.050 and .477" intake
196 duration @.050 and .462" exhaust
LSA 113

[andyf]

The cam companies often publish the lift at TDC number for each lobe. If you know that number for your current lobe and you know your piston to valve clearance then you should be able to figure out what the clearance will be for a different lobe. The math is simple but you do have to take your time to make sure you keep it apples to apples. (lash, rocker ratio, installed centerline, etc.)

[Rick360]

There is more to it than duration but there is a way to do it.

Comp Cams Lobe catalog shows the tappet lift at TDC for 106 CL and 110 CL (Good detailed lobe info ... One of the reasons I use Comp for custom cams). If you know the tappet lift at TDC with your current cam and V-P clearance to compare with whatever lobe you want to go to you can calculate pretty close. Multiply the difference in tappet lift by rocker ratio and that is how much more or less V-P clearance you will have.

Depending on the desired CL of the new lobe you may need to extrapolate the tappet lift at a different CL than 106 or 110.

I normally measure valve drop at TDC before I order a cam to calculate V-P clearance so I know if pistons need cut or if I can find lobes that I like AND will fit.

Rick

[bigpoppapreston]

Excellent Andyf and Rick360. Thanks for helping me.

[MadBill]

You can check the approximate piston/valve clearance by setting a piston at TDC compression, using an air hold to anchor the valves, removing the springs and measuring the valve drops at ~5°after and before TDC for IN and EX respectively. The closest approaches may be a few degrees different but if the measurement is more than say 0.100"/0.125" in excess of Comp's TDC lift x rocker ratio, you should be good.

Always best to re-check with the cam indexed and rockers, pushrods and soft springs in place. Many builders rum tighter P/Vs than this, but best not push it in this case. Google "Checking PTV Clearance" for more info.

[Geoff2]

If you widen the LSA, you can increase duration, keeping the same PTV clearance, all else being equal. However, this combination may not be what the engine WANTS, & it might give the opposite result of what you want to achieve.

[bigpoppapreston]

If you widen the LSA, you can increase duration, keeping the same PTV clearance, all else being equal. However, this combination may not be what the engine WANTS, & it might give the opposite result of what you want to achieve.

Interesting Geoff2, I've read that also. I've read that for every 1° change in ICL corresponds to 2° change in duration where p-t-v clearance is concerned. So 224° duration at .050 on a 110 ICL would have the same ptv clearance as a 220° duration cam on a 108 ICL or a 230° duration cam on a 113 ICL.

[In-Tech]

If you widen the LSA, you can increase duration, keeping the same PTV clearance, all else being equal. However, this combination may not be what the engine WANTS, & it might give the opposite result of what you want to achieve.

Interesting Geoff2, I've read that also. I've read that for every 1° change in ICL corresponds to 2° change in duration where p-t-v clearance is concerned. So 224° duration at .050 on a 110 ICL would have the same ptv clearance as a 220° duration cam on a 108 ICL or a 230° duration cam on a 113 ICL.

bigpoppa,
Do the math yourself so you can play with numbers.

Duration divided by 2 and subtract intake centerline = intake opening event. Add 180 and subtract duration = intake closing event.
Duration divided by 2 and subtract exhaust centerline = exhaust closing event. Add 180 and subtract duration = exhaust opening event.

Example camshaft:
240 duration on 108 LC

240 / 2 = 120
subtract 108 = intake opening event of 12
add 180 and subtract 240 = 48 intake closing event

Since the example is a single pattern camshaft of 240 duration at 108 LC or LSA(lobe separation angle) with no advance/retard the "cam card" is as below:
IO 12 EC 12
IC 48 EO 48

12 + 48 + 180 = 240 duration

If the cam is advanced 4 degrees, in our example the intake centerline is now 104 and exhaust is 112.

240 / 2 = 120
subtract 104 = intake opening event of 16
add 180 and subtract 240 = 44 intake closing event

240 / 2 = 120
subtract 112 = exhaust closing event of 8
add 180 and subtract 240 = 52 exhaust opening event

Now our "cam card" looks like this:
IO 16 EC 8
IC 44 EO 52

16 + 44 + 180 = 240
8 + 52 = 180 = 240

I hope this helps to understand so you can move numbers around and verify your work.