Dave:
The symptoms you are describing are all consistent with a lumpy
camshaft. I looked up the specs for the GP2 camshaft, and IMHO it is too
much if you want a decent idle. When you added the 1.65 roller rockers
to it, you made it even worse. The soggy bottom end, the refusal to idle
decently, sluggishness up to 2k RPM are all part and parcel of a large a
cam. If you autocross, then this may be what you wanted, but the fact
that you complain about it in your note says that you got more than you
bargained for.
If you find this unacceptable, then I suggest you go back to
stock rocker arms. You will find this will go a long ways towards
correcting your problems. It will cost you some top end (probably less
than you think) but it will run dramatically smoother. If you find the
power loss is unacceptable, install a nice low restriction muffler like
the Cyclone Sonic Turbo or a Dynomax Super Turbo. You will get back you
top end without the need for the high ratio rockers. If it is still too
lumpy, then you are looking at a different cam.
The GP2 cam is a 278 advertised/227@0.050 duration cam, and this
is over the limit if you want a decent idle. Unfortunately, Good parts
does not state what the lobe center angle (LCA) is on this cam. If it is
tighter than the stock 110 degree LCA, then the fact that it is
227@0.050 is even more over the top for a daily driver street cam. 270
advertised/215@0.050 is about the max if you want a steady idle speed
(it will be a deeper, slightly rougher idle than stock to be sure, but
an inexperienced ear will not be able to tell there is a performance cam
in the engine)
I am sure that there will be those on the list that say "I run
the GP2 cam, it idles like glass, so you are full of hooey Vance".
Without looking at the exact engine setup including porting, carbs,
header, exhaust, rocker ratios, etc, it is very difficult to make
comparisons. In addition, you run into the problem of what the
definition of "smooth" is. Smooth for one person is another person's
"bad boy" gnarly idle.
Let us know what you do...
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Dave Murray
Sent: Wednesday, June 28, 2006 6:29 AM
To: 'Sally or Dick Taylor'
Cc: 6pack@autox.team.net
Subject: RE: Ignition timing at high RPM
Dick,
<snip>
Found a combination that allows the car to pull strongly from 2k up to
5k
rpm: points, alternate distributor (not original), Magnecor plug wires,
new
cap, shaved rotor, bypass coolant through intake manifold, however the
timing instability is still present (at idle also), the car does not
want to
idle smoothly and will stall on occasion, and is extremely sluggish up
to 2k
rpm even with no load.
Dave
|