CAM
SPECS:
Keep
in mind these profile numbers are just for comparing
the cams to each other; every manufacturer and cam
grinder uses different points in the cycle to take the
measurements and they can be listed at almost whatever
they want them to be with the same cam. Some of this
is advertising nonsense; so when looking at cams for
any car; make sure you are comparing apples to apples.
Even Nissan's published specs are sometimes all over
the place.
Historically
cam specs were advertising figures; like horsepower
that was based on the THEORETICAL amount generated by
the explosion in say 8 cylinders and didn't include
drag from main bearings etc!; or having to move the
crankshaft mass around and around. Engine HP/Torque
means nothing unless it is measured with a chassis
dynamometer with a street exhaust and street air
cleaner system in place.
Such
is the situation with cam measurements. I can look at
you (but not with a straight face) and tell you a
standard grind has 350 degrees of duration. It would
be "true"; but at what point in the cycle is this
measurement being taken? Probably at the point where
the cam has actually been pushed open .001 inch. Not
much gas or exhaust moving by with the valve only open
one thousandths of an inch! Sure would make for
impressive stats specs though.
Some
of the more thoughtful cam grinders and engine
builders use a figure "at .050 lift" to measure
duration; which is what we are doing; and we have
used a cam profiler machine to show this on the
"stock" cams for comparison. Definitely not as flashy
a number bu t more accurate; since adding on the
clearance ramp on to duration is usually thought of as
a joke to engine builders anyway...
Same
with valve lift. Stated figures are THEORETICAL lift;
or GROSS lift; or WHITE CLOUDS on BLUE SKY lift. They
do not account for loss due to valve lash or anything
else.
Better
in comparing camshafts is using LOBE LIFT (CAM LIFT);
that is what the lobe rise is over the base circle
(what is there if all the lobes were
removed).
So
with the above discussion on bogus specs in place; we
have the following information.
130-18,
130-18U. Running a stock new cam on a cam
profiling machine; we find that the duration at .05"
cam lift is 193.5 degrees. Lobe lift is
.237.
130-18R
The cam we use as a "stock" replacement cam is a
little different. They are cut so the duration is
about 214 and the lobe lift is at .255. Still nicely
in the stock range; but with a little bit of a
shove.
Although
there are "metric" and "SAE" cams; it refers only to
the threads in the end of the cam for the bolt that
holds the gear on; so it is important that you return
your bolt WITH your cam core. There is a charge if you
don't or if the bolt you send back has bungled up head
on it; or bad threads. If the threads in the cam are
bad that is not good as a core. Other core info
here.
USED
CAMS
These
are just used cams we have not taken to the cam
grinder. We do not though sell used cams that have
chips out of them or other lobe damage or bearing
journal damage visible to a non-cam machinist; other
than small scratches that many times can be polished
out. Technically speaking you should always use a used
cam with its previously run lifters; in the exact
positions they were in; but it is rarely possible
unless we have recently pulled the engine apart
ourselves and saved it specifically for that purpose.
REGROUND
CAMS
Changing
the cam means changing lifters if you want it to live;
as does proper break in and lube during break-in.
There is little point to using a reground cam with old
lifters. They may "look smooth" but are actually cut
in a very funny way and they will wreck a reground cam
very quickly when they have been run
before.
REGROUND
LIFTERS
We
carry new lifters; and even though they are much more
economical then they used to be; people still balk at
replacing them when theirs "look OK" (but aren't with
a reground cam); so we also carry reground lifters to
make your reground cam happy and go even easier on
your bank account.
