Using Engine Analyzer, I was able to find the ACTUAL advertised duration of camshafts. This way, you can accurately figure out your DCR and fairly compare camshafts. For example, my camshaft:
Comp Cams 292H
Advertised: 292* @ .006"
Actual Advertised: 308* @ .001"
Previously thought DCR: 9.44:1 (w/ 292*)
Actual DCR: 8.72:1 (w/ 308*)

The duration AT THE SEAT (.000") is even greater, which is 315*. This method takes into account the intesity of the lobe design for good accuracy. I believe when GM rates their cams, they also use .001", but I could be wrong there.

I was VERY impressed with EA3.0 because it predicted my cylinder pressures EXACTLY from when I did a compression test (230 PSI).

Anyway, I hope people can read this and find it helpful when choosing a camshaft.

When using Pat Kelleys DCR program you do not use advertised duration @ .001" lift . . . you use advertised duration @ .006".

I'm not sure what EA 3.0 uses, but your DCR is 9.44 not 8.72:1.

What's the value of such an arbitrary number? If I have a cam with 280° duration @ .006" lift and 300° duration @ .001" lift and compare the cranking compression to a cam with 280° @ .006" and 310° @ .001", which will have more cranking compression? I think the designers of EA3.0 took this into account when they put in the option of choosing cam intensity.

Engine Analyzer uses seat to seat timing at .000" to get figure their DCR. Anything else will be WAY off. Check it out sometime with the cam timing graphs.

From P. Kelly's site:
"Compression of the air/fuel mixture cannot start while the intake valve is open. It may start slightly before the intake valve is fully seated. However, there is no easy way to determine this point so using the advertised duration number provided by the cam manufacture is the next best thing. Most cam grinders use .006" of tappet lift (hydraulic cam), although some use other values, with .004" being a common one. This duration is often referred to as the "seat timing". We will used advertised duration for calculating the DCR."

It sounds like to me he it saying it is difficult to know the exact seat-to-seat timing, so you will have to "make do" with the manufacturers specs.

To me, it doesn't make sense to use .004" or .006". Mostly because the valve it not on the seat, or even close to it. I believe Erson and GM measure theirs at .001" or .000". Using .004" means the valve has fully closed and compression has started, when that is not true. The compression is still being bled off because that valve is still open by .006". When the valve is open by .006", it has as much surface area for air to leak through as does a 1/8" hole. Compression can only start when the valve lift is at .000".

Silver69, you're theoretically right on having to use the .000" number. Yet you just can't say that "My DCR will be X.XX and not Y.YY because I'm using the correct number", and then compare that number to Pat Kelley's ideal of the low 8-point range. Since his findings of that 8-point range were BASED on the use of advertised numbers at .006"

So to answer your question, Pat Kelley is "theoretically" wrong for calling it a DCR calculator, because it doesnt use the correct input data. However, since Pat Kelley has designed his program to run with the .006" number, he has CORRECTLY determined that his with the use of his program, you should aim for the mid to low 8-point range.

So don't compare your DCR number for the .000" lift number to his DCR number.

Your explaination makes sense. I agree that the low 8.X value is based on using .004-6" duration figures with his calculator.

However, I believe he programed his caluclator to use actual seat-to-seat duration. I say this because when I enter the same data under Engine Analyzer and Pat Kelly's calculator, I come up with the same DCR. And I do know that Engine Analyzer uses .000" for seat duration.

This is interesting stuff.

.006" is used to account for flex in the valve train parts. Most people regard GMs .001 spec to be rediculous and not comparable to every other cam manufacturer on the planet.

Do it ho wyou want, but I think you'll find that with 12.5:1 static compression you will ping on pump gas regardless of what you come up with for a DCR.

Oh, I think it will ping too. Just about sure of it. I'm just trying to the bottom of this "DCR" thing.

Wouldn't this be more accurate: Find the exact intake closing angle by using the cam card or calling the cam company. Plug the ICA into Pat Kelleys or whoevers DCR calculator manually without having the program "estimate it"? The progam should be able to calculate the exact Dynamic Stroke, correct?

Lonnie67, the valve timing you are referring to is at the .004" or .006" lift. Notice if you add the IVO to the IVC, then add 180, you get the advirtised duration according to the manufacurer.

I called several cam companies and asked if they had the duration or cam timing at .000 or .001, and they really didn't understand what I was asking. If I remember right, the Comp Cams guy said "The seat duration is 292", then I asked "Yes, at .006 lift. But, I'd like to know what it is at .000 or .001" and He said "Oh, it's 244", which is the duration at .050". I swear, there are only one or two good tech guys at Comp Cams. The rest can be kinda rude or unknowledgable. Other cam companies just told me they didn't have that info :confused: .

[ 12-09-2003, 03:15 PM: Message edited by: Silver69Camaro ]

Eric is right on the valvetrain compressibility. SAE specs .004" tappet lift but many cam companies use .006". At .004" tappet lift the valve is on the seat. At .001" tappet lift the valve has been on the seat for a while. Since most of us don't have the timing or duration at lifts other than the cam's specs, using the mfg's spec is the best we can do.

If you have the cam in the block and a wheel, you can get very accurate event timings. My Comp cam is speced at 296º but is actually 299º with all of the extra 3º between .050" and .006" on the closing side. So it closes 3º later than the cam card says. Without accurate measurements, any calculation is, at best, an estimate.