I was messing around with DT2000 and put my cam in with the @.050 specs and had around 500 lbs of torque and thought, great. Then same cam with the specs from seat-to-seat and lost 100 ft lbs of torque. What gives???

Dean

Use seat to seat.

Why is there such a significant difference? If you put in the specs @.050, I would think it takes into account the lobe ramp, so why would it loose 100 ft lbs.

Dean

SAE is .006, but many cam companies give out there advertised duration specs typically at .015 or .020

Crane: .004
Comp: .006
Isky: ~.008

The SAE standard (J-604 5.1) is .004", however J604d is .006".

and some read their performance cams at .020" and .015" depending.

crower's solids are at .020", and their low performance hydraulics at .006"
they may have other numbers that they use as well, i just did a quick scan.

everyone is different, and he needs to know that their are differences in what some cam companies read their advertised duration at.

I have both seat to seat and @.050 for the same cam. What I am asking, is why there is such a difference in ft lbs of torque when using one set of specs vs the other on the same cam.

Dean

Becaused if the Adv. duration is measured at something other than standard, the cam may look bigger or smaller depending on what it is measured at. DD doesnt take where the cam is measured at into account. I would think that you should use .050, because it is a standard that would give you a good comparison between different cams... just my .02 cents.. feel free to correct me if im wrong.

Hard to say which to use. Some adv durations aren't very big but the .050 is alot bigger than another cam with the same adv. IE my lunati solid is only 272adv, but it's 239 @ .050... while say a comp 262 adv, is only 218.

Lobe ramps have alot to do with power. I'd use the .050 because it's more generic, and it's where the valve will be open most.

Engines do not see the .050" duration numbers.
Engines see the 'seat-to-seat' numbers--actually, engines see the opening and closing points---and of course the OVERALL valve lift curve.
Notice, the OVERALL valve lift curve----
It makes no difference whether or not it's a hydraulic or a solid, 'seat-to-seat' duration is 'seat-to-seat', ie--Where the valve is off the seat, generally by about .001" valve lift.
Programs such as DesktopDyno work according to how THEIR programmer understands engines, and cams. Here is their difficulty:
You want to compare 2 cams in the same engine, say a Crane TR-256/4167-2-6 with a Lunati that is 255/263 at .050, and .4176/.4176 lobe lift. Both cams are on 106 LSA, the Crane is 256/266 compared to the Lunati 255/263. No contest, right?
At .020, the Crane is 296/306, the Lunati 288/296, a big difference. But the the Lunati opens as if it were only a 282 intake, not a 288. Much less reversion, much earlier airflow on the intake stroke.
The real catch is at .200---The Crane measures 173/180, the Lunati 176/183. The Lunati is filling the cylinder at a higher rate, and has more time to fill the cylinder.
In actuality, the Lunati would outpower the Crane. Do you think that if you used ONLY .050 numbers, DD2000 could tell the difference between them?
I don't think so.......
At the same time, I think DD2000 and others are useful tools. They are just not the ultimate word.

UDHarold