Useful Cam Data

E

EPA Violator

CR Wrencher
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Mar 8, 2008
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Been doing some measuring on a stock commonrail camshaft, first time I have ever graphed out lobe motion so bear with me but I am pretty close to advertised specs considering the intake lifter kept sticking on me.
Intake (.050 measurements)
Opens 10 deg After TDC on intake stroke
Closes 10 deg before BDC on intake stroke
Max lift .221 in.
Duration 160 deg
Centerline 90 deg After TDC

Exhaust (.050) measurements
Opens 25 deg before BDC on powerstroke
Closes 10 deg before TDC on exhaust stroke
Max lift .294 in.
Duration 195 deg
Centerline 109 deg after TDC

Lobe sep angle 99.5
Overlap was about 80 I thought this was a lot but the damn sticking lifter gave me fits at real low lift areas, does 80 deg of overlap sound right for a stock cam?

First time I ever did this and it's pretty close to what colt cams posts as stock commonrail cam specs. Gonna fix some stuff on my degree wheel and next comes Hamilton's, F1's, and whatever other cam I can get my hands on.
 
That is the info I already give. I think every cam manufacturer should give this kind of info.

You said you were going to give actual valve lift as a function of crankshaft angle which is totally different and I must say a kind of proprietary. I think your numbers might be off bit because a cr cam does not have that much overlap. If you are factoring .001 as the valve opening that might be where your problem lies. On the intake with .010" lash you will not start to open the valve until the cam gets to .006" lift so .000 to .006" is not really overlap. On the exhaust. with .020" lash the exh. valve will not sart to open until after .014" lift. 0-.014" is where ther is still lash. Get rid of these two numbers and your specs will look a bit closer. I think it is cool that you are posting up cam specs, but you are a bit off on a lot of this. Are you measuring the cam in v-blocks or in the engine?

Let me save you the trouble on the Hamilton specs.

Intake 181@.050" .280" lift on a 98 degree centerline
Exhaust 219 @.050" , .307" lift 107LSA
Intake opens at 14 degrees BTDC
Intake closes 22 degrees ABDC
Exhaust opens 55 degrees BBDC
exhaust closes about 2 degrees ATDC
approx. 16 degrees of overlap

The valve events are factoring for lash and rocker ratio on a 24v head. The 12v numbers will vary slightly due to higher rocker ratio.
 
I have the graph rudely sketched on graph paper corresponding to crank ankle I will get it up in a few days. Going on vacation in a couple days.
 
Are you reading off of the pushrod or off of the valve retainer? In my opinion, reading it off of the retainers is the only way to go, because you get to see what the valve is actually doing and you can factor for lash.

Zach
 
I have all the lifts at 20 deg intervals, and thanks for info on the lash, I didn't take that into account.
 
I agree Zach measuring off the retainer is best but I don't have a head on it and I am measuring off the tappet.
 
Hamilton Cams said:
Intake 181@.050" .280" lift on a 98 degree centerline
Exhaust 219 @.050" , .307" lift 107LSA
Intake opens at 14 degrees BTDC
Intake closes 22 degrees ABDC
Exhaust opens 55 degrees BBDC
exhaust closes about 2 degrees ATDC
approx. 16 degrees of overlap
Click to expand...

I take it your opening and closing specs are not at .050?

Paul
 
Correct, they are when the valve opens. .007246" lobe lift on the intake and the intake valve just starts to move and .014925" on the exh. So yes the specs at the valve are when it opens .001" They differ due to different lash settings and rocker ratios. Intake .010" lash 1.38 to 1 rocker ratio.010"/1.38=.007246". .020"/1.34= .014925" this is for 24v ratios. 12v's are intake .010/1.7=.00588" and exh .020/1.7=.011764".

I know that may not jive with how the gasoline guys relate specifications, but it is the exact actual valve events in the engine, which is what you are after. Most of the cam cards I have seen are nowhere close. A lot of cam companies guess at the rocker ratio and don't take into account different size tappets and lash settings. Another issue is that a lot of cam companies use hydraulic tappets which have a small fudge factor as far as exact lash depending on a lot of variables. There is a small window of lash settings you can use with a cummins valvetrain. I modify lash settings slightly to optimize the placement of the valve events.

intakes can run .008 to .020" and exh from .015" to .025"

Zach
 
I'm just used to degreeing cams at .050 off. I like to degree the opening and closing events, not just the center line. Opening and closing is everything.

Thanks for the info on the cam.

Paul
 
Everybody gets all hung up on LSA and lift, but you are right THe valve events dictate a lot of the LSA's depending on the lobe choice and how it will run.

Zach
 
Another thing too, the valve is recessed below the head by .043 in. on the one I measured so it sorta makes sense to use .050 in. cause that is about when the valve is completely clear of the head.
 
The valve depths on most heads range from .025" to .065". Depending on the year and if the head has been decked, of course you are not factoring for the margain(thickness) of the valve and how far the seat is as far as depth. On my heads I have a .020" valve protrusion not a depth. THis aids in low lift flow. I do think it is kind of irrational to look at the .050" number as the closing and opening events. This doesn't fully quantify the amount of overlap or when the exhaust pressure starts exiting the cylinder among other things. Just my opinion. So are you using .050" numbers read off of the pushrod or off of the retainer, and what lash are you factoring in? All that needs to be stated when giving out specs, other wise they are just numbers that are not repeatable. One other thing, the size of the tappet can skew the output a little bit because the larger faces of the CR 1.5" sees lift sooner than would a 1.1" 12v tappet. I use a 24v 1.3"(1998-2002) in all of my measurements because it is a mid point between the large and small tappets

Zach
 
I am using lift as measured from the tappet without lash taken into account, as stated in the original post it is .050 numbers because the dang intake lifter was sticking. Pretty much just times rocker ratio by the tappet lift and that equals valve lift, I will consider lash separately once I get my head on and see what kind of clearance I end up with between the valve and piston. I know there will be variances in valve recess depth i am just using some old scrap stuff I have in the job, don't have my engine parts yet.
 
I cut .070 to .080 off of the heads on engines I run. It provides a nice little bump in low lift flow without hurting anything. Of course I cut the piston to clear the valves.

Zach
 
you cut .070 to .080 off the heads? why? you gain that many cfm at low lift and the machine time is really worth it? not to mention your raising compression from stock slightly and changing your valve speeds off the seat and changing rocker geometry. not saying it wont work but that seems like a waste of time to me. not trying to start an argument....just my thoughts.
 
lenahan05 said:
you cut .070 to .080 off the heads? why? you gain that many cfm at low lift and the machine time is really worth it? not to mention your raising compression from stock slightly and changing your valve speeds off the seat and changing rocker geometry. not saying it wont work but that seems like a waste of time to me. not trying to start an argument....just my thoughts.
Click to expand...

I'm not a valvetrain genius or anything, but how does removing material off the head increase compression? The head smooth already, it's not a gasser that has a dome. The only amount it MIGHT add is from the valve potrusion, but that is so minimal it wouldn't really count. And I see how it MIGHT change rocker geometry since it would be the same as a longer pushrods, but I think there is enough adjustability in the little nut/bolt that you set lash with to make up for it.

Just what I'm picturing in my head...
 
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