Okay... I cant help myself... I have to jump in with myho...
Degreeing a cam is a pain in the *** unless you do it all the time. It
should always be done at 050 as it will give a more accurate position. At 020
there is too much movement in the cam to be real accurate. Manufacturers will
give you the 050 numbers if asked for them. They like to use 020 as it makes
their cam sound a lot bigger than it really is. At 020 there is no airflow in
or out of the cylinder yet.
The duration is the degrees the valve is open and you have airflow, therefor
it is (again imho) from 050 and adding the btdc, abdc, and the 180 degrees in
between. A cam that opens to 050, at 10 btdc, and closes to 050 at 10 abdc is
10 + 10 + 180 or a 200 degree cam.
Setting the #1 int valve opening is the easiest place to start. You can then
check open/close on intake, and exhaust. If the cam is symetrical you should
have exactly opposite sets of numbers on intake and exhaust. If the cam is not
you will have to refer to the manufacturers specs on what should be where.
Depending on the numbers, if they are off a bit, advancing or retarding the
cam slightly should give the matching numbers. If using an adjustable wheel I
start in the middle of the adjustment to give myself some room either way.
Dont think this will happen in half an hour... it will take a while unless
you are lucky.
Kass' book is excelent, so is the Isky book.... cheap... & on their website.
to continue.... if you really want to "tune" the thing, have a dyno handy for
a lot of hours... in general.. if you are running a "torque" engine such as the
TR, you are not looking for rpm... advancing the cam slightly (2-4 degrees)
will move the torque curve down in the rpm range giving you more usable
horsepower. If you are an idiot like me and looking for rpm, retard the cam
slightly and move the torque curve up higher on the rpm curve. If you are a
complete idiot like me... get together with your kids & design your own cam...
then you know you dont have the best running car out there, but you know you
have the cam in the car that your kids designed for you... its fun if you
reallly like the added stress and worry...
Good luck,
WEmery7451@aol.com wrote:
In a message dated 3/2/05 3:50:56 AM Pacific Standard Time,
tony@tonydrews.com writes:
<< That is retarded. Moving toward a higher number btdc or lower number atdc
is advancing the cam.>>
I have been degreeing in cams for years using a degree wheel and a made up
cam follower tool that Kas shows in his books. I have gone through Kas's
original D, F, and G-3 cams plus about three or four G-3 regrinds, which have
all
perished in explosions along the way. I have several other cams on the shelf
with a Jack Wheeler discarded Crane cam presently in the engine (Bill Jenks G-3
regrind, Pacos cam, Tabor Cam, another Crane cam, etc., on the shelf).
During my several past efforts to get all of the lobes to open and close as
nearly as possible where they should, I have finally given up on this effort.
I get the Number 1 valve to open as closely as possible where it should open,
and hope that the rest of the valves open and close approximately where they
should. The engines have always run, but maybe not at their total peak
performance.
QUESTION: How is the duration of the cam determined -- by adding the degrees
BTDC and the degrees ATDC plus twice the checking clearance? It is probably
not quite that simple since the numbers do not work out.
Tom
http://www.fot-racing.com/spit/caption/tom_strange.htm
#4 white spitfire
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