John:
The most critical valve event is the intake closing, which
sounds like ends up exactly where it should. As for the +/- 2 degree
variation on the timing, that is probably pretty typical unless you get
a new cam from someone like Comp Cams or Crane with state of the art
grinding equipment. I certainly would not reject the cam because of that
variation.
Advancing or retarding the cam 6 degrees is a bit much, 3
degrees is more like it. So if you are going to use your stock timing
gears then you are best if you install it straight up.
As for performance differences, there most likely will be no
noticeable difference between a "perfect" cam and your cam. A couple of
degrees gain or loss on duration will not make any difference. The 1
extra degree of overlap will by itself not make much difference. However
the cam figures you quote imply that the lobe centerlines are spread by
1 degree, which depending on the cam may make a noticeable difference.
It will make the idle slightly less lopey and improve fuel economy. The
power band will be wider but peak power will be down slightly.
What is the spec'ed lobe center line angle?
Frankly, you have a very gnarly racing type cam in there, so it
is going to chop and in general be pretty miserable unless you are
building a racer. If you are going to try to run this on the street,
then you need to raise the compression to at least 10:1, have a header
and free flow exhaust, and probably add some low gears as well. Cold
start drivability will be problematic as well.
Vance
-----Original Message-----
From: 6pack-bounces+vance.navarrette=intel.com@autox.team.net
[mailto:6pack-bounces+vance.navarrette=intel.com@autox.team.net] On
Behalf Of John North
Sent: Monday, March 17, 2008 11:37 AM
To: Triumph 6 Pack
Subject: [6pack] More cam timing
The cam I am installing does not measure out to spec. At 50 thou of
cam lift, intake opens at 1.5 BTDC which is 2 degrees late, and
duration is 229, which is +2 degrees from spec. Exhaust opens on
spec, but duration is +2 degrees at 229. Overlap is 8 degrees which
is 1 degree over spec.
My cam sprocket also does not seem to be to spec either because it
advances 6 degrees when I use the offset holes. This is rather more
than I want, at least on the exhaust.
These differences don't seem so great, but my question is what
performance differences might arise from using this cam?
John North
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