A few cam questions?

[Anonymous]

Got these cam specs of "dmgdgoods" on big six section. Whittey replied saying. quote
"That it is a weird cam just because because the seat-to-seat is large but the 050 is modest."

These are the specs on the cam
.05 dur- 204 int/214 exh
cam lift- .280int/.295exh
valve lift- .448int/.472exh
sae dur- 280int/289exh

My new cam from Wade is similar. It is 210.5 / 222 at 50 dur but the advertised is 281 / 287 dur.
Does anyone know why this occurs. Is it inaccurate measuring? I e-mailed Wade all they said was that the Seperation between exhaust and inlet was 11.5 at 50 dur.
Is it possible that it alters from this at the different duration the advertised lift is measured at? Makes it confusing to work out what cam it is?
Kieth at Wade cams told me months ago you must compair the advertised duration with the dur at 50 to determine what type of cam its is.

Cheers Tim

 

[rbohm]

8) cam design can be a strange art. you need to compare cams at .050" as that is the most accurate for comparision. cam grinders grind the opening and closing ramps to avoid opening or closing the valves too quickly, yet still grind a cam that has good lift, and good idle characteristics. the opening ramps are ground with a slow initial opening, that way you can use a lighter spring rate and still not float the valves, and maintain good driving manners.

 

[80broncoman]

I remember " brand C" used a figure in a sales broushure for the 83 or 84 Monte Carlo SS. Get this they said it had a 306 duration cam. I am not kidding, it was very simular to a basic stanard 350 cam somthing like 194or 204 duration at .050

 

[xctasy]

Chevy uses very conservative ramps, and the quoted duration is not at lash.

Be carefull to read what the actual advertised duration is based on .

At lash (like most cam specs),
including ramps (like Chevy),
or 50 thou,
or even 20 thou.

The ramps which are soft are low intensity cams generally, but its possible that you can build duration up to 280 degrees with very little lift if the cam builder has the right lifters.

There is a limit to how much duration can be made on a 80 inch radiius lifter, David Vizard quoted it back in 1988 in his Modifiying the A series engine book.

Note that there is no way on earth Ford would ever make aftermarket cams with savage duration, as load stress on the Ford I6 with hydraulic lifters is imense. The very fact that the chains streatch on our I6's with stock cams is an indication of this. How much more will a savage cam grind load things up?

The cam which has the biggest difference from the 50 thou reading to at lash readings are the ones to consider. A very aggresive 50 thou reading is likely to impart more load stress on the valve train.