Cams, like heads, are a big area, you can really mess up an engine with the wrong cam

Camshafts and the valve train....

"Cams, like heads, are a big area, you can really mess up an
engine with the wrong cam, even more so than with heads.  A 1679
with Weber 34ICTs and standard heads will not run with an Engle
FK98 cam.

Cams have two main measurements, the lift, in either millimeters
or inches, and the duration in degrees of the crank.  The
duration is the time the valve is opened for, the longer this
duration the more fuel gets into the engine and the bigger the
bang when it ignites.  Well, that's the theory, in actual fact
the longer the valve is open for the faster the engine needs to
be running for this to happen, so at idle the engine will not run
all that well.  For street use you should not consider anything
with a duration of greater than 290 degrees.  The most popular
cam I have ever seen used on the street is the Engle W110, it has
286 degrees and 0.431" (10.95mm) valve lift.  Engle also make the
W100 which is often better used on an engine under 1700cc or
heavy weight cars (I use on in my 1776cc crewcab).  The duration
of this cam is only 276 degrees which brings the power band down
where a smaller capacity engine needs it.


Remember this: The longer the duration the higher the power band,
and subsequently the lack of power in the lower rev range.


Cam lift is usually measured in inches ('cos most manufacturers
of VW cams are American, despite being for a German car, don't
ask) and either is at the valve or the cam, so make sure you know
which before deciding on one.  There are different rocker ratios
as well, the standard rockers multiply the lift by 1.1, whereas
others have ratios of 1.4:1 and 1.5:1, this of course means the
cam lift is multiplied by 1.4 or 1.5 to give full valve lift
(less the rocker/valve clearance, usually 0.004"/0.1mm for inlet
and 0.006"/0.15mm for exhaust, keep this to 0.006"/0.15mm for
both on a <100bhp engine).  If you intend using higher ratio
rockers, check the cam card closely and check if you can/should
run a ratio rocker with it.  The more lift you have the more fuel
goes in and the bigger the bang when it ignites, so the higher
the lift the more fuel (well, it almost works like that).  Most
manufacturers have their popular street cams, I've mentioned
Engle's, Bugpack have their 4062-10, which gives a little less
lift and a little less duration, Scat have the C35, Gene Berg has
his GB297, slight differences, but all much the same.  Any of
these cams will work well on the road throughout the rev range,
plus give increased performance over the standard cam.  They all
have around 284-286 degrees and about 0.415 - 0.451".  If you
want a little more lift without the extra duration, my personal
road choice is the Engle VZ25, but these do work better with
modified heads.


If you insist in going over the 290 degree barrier, then it's
your own fault when it's a bit sluggish in town.  Valve lift is
not quite as bad, but please use 1.1:1 rockers as there are very
few road cams that are designed to use a 1.4:1 or 1.5:1 that work
any better than an equivalent one designed to run on 1.1:1
rockers.  Still try to keep your total valve lift to below 0.500"
as this is the limit of a standard head.  Forget the 1.25:1
rockers, they really don't give enough extra for the price you
pay.


There are adjustable cam gears available, don't buy one.  You
cannot set up the cam better that it was manufactured.  If the
cam doesn't match the cam card it came with it is either a faulty
cam or a faulty cam gear, so take it/them back.  There are also
straight cut gears, these prevent cam lash caused by the
synchromesh type gear, but as you won't be running dual valve
springs, you won't need these either, plus they are so noisy.


Dual valve springs are available to fit any head, don't buy them,
you don't need them for street use and they slow your engine
down.  Any extra work you make your engine do, like open valves
with more springs on than they need, will slow it down.  A
new set of single springs is a good idea, as this will keep your
valves closed when they should be closed because twenty five year
old springs don't work as well as they did when they were new.


You can buy chrome-moly pushrods, don't.  You can and should
consider 'cut to length' steel pushrods, these will return your
rocker arm geometry back to the way the factory made it,
efficient."


SOURCE: http://www.cwgsy.net/private/ramva/tech.htm

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