Mike:
You have really gone crazy with the cam timing. The 1.65 rockers
means that
you have in effect added even more valve timing and more overlap. This
takes an
autocross cam and moves it up into the bottom of the full race cam
category. You
have a HOT cam, and you are definitely into the regime where other
modifications
are necessary to get things working right.
If what you have is a miss, then opening the gap on the plugs is
the way to
go. The coil will be forced to increase the voltage to fire the plug.
The wider
the gap, the more of the mixture is exposed to the spark kernel, and the
more
likely it is to ignite. Lean mixtures are difficult to ignite, and
because you
have so much overlap, at low RPMS the exhaust charge is mixing with the
intake
charge and leaning it out. This might be why you have been unable to
find anything wrong, because nothing IS wrong. The cam & rockers have
simply
increased the demands on the ignition system.
You can try opening your plug gaps by, say, 0.010" and see if it
helps. At
some point as you widen the gap you will begin to get a misfire under
load, and
that is when the coil no longer has enough grunt to fire the plug when
the
engine is working hard. Then you need to think about a hotter coil - but
be careful
because hot coils increase the current through the points, so you can
burn points.
This is where I think a Pertronix begins to make sense, as they will
handle the
increased current demand should you find a hot coil shortens point life.
You had mentioned the roller rockers before, but I don't recall
you mentioning
the ratio. High ratio rockers are the poor man's cam change, increasing
not only
lift but duration and overlap as well. High ratio rockers add 3-5
degrees of
effective duration to your cam, and in effect move the lobe centers 1
degree closer
together (depending on the size of the ratio change). Since you are
starting with
a marginally streetable cam in the first place, you have made it that
much harder
to tame the beast.
Sounds like a terrific challenge, and it will be that much more
satisfying
when you achieve victory.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of DaCRANEz@aol.com
Sent: May 26, 2005 1:14 PM
To: tr6taylor@webtv.net
Cc: 6pack@autox.team.net
Subject: Cam fixed?
Dick
Since rebuilding the engine about this time last year I have had issues
with
the idle. Recently Vance had a post about how to verify that the cam
timing
was correct. I did the check and found that 11 and 12 rockers were not
even. By
rocking the crank 16 degrees clockwise I could get them even with 1 and
2
closed. Called Vance, he agreed that I was probably off one tooth on the
cam gear.
Corrected that. Reset cam drive gear to Bentley specs. I am running
9.5to 1
CR. Premium gas . 400 ft above sealevel, no anti-run valve, 150 PI cam,
Good's
1.65to 1 rockers. As to the spark exchange I don't hear arcing but the
leading
tip of the rotor is a bit discolored and the posts in the cap are a bit
burnt. I am going to try your suggestion on shortening the spring on
the retard
capsule. I need a small tap as I am going to install a set screw to make
it
adjustable. Sorry about the long tirade last night. I was really
frustrated at not
making any headway. GeeZ-I hope this just isn't due to some bad petrol.
Thanks All
Mike C
|