At 05:22 PM 5/4/99 -0500, you wrote:
>>351C 4 barrel closed chamber heads from 1970 Torino.
>>Rebuilt with flat top pistons and a 280 Crane Cam
>>9.5 compression, 93 octane gas.(slight ping under load)
>
>Compression with closed chamber heads and flat tops should
>be around 10.5:1. Should not ping with the quench heads and
>a proper curve in the distributor. Open and closed chamber
>heads require different spark curves with the closed chamber,
>heads requiring less total advance (32 to 36 degrees total).
>
>Dan Jones
>
You may be correct about the advance. I have a vacumn
advance that has a mind of it's own. The pinging occurs
when I go from light load to heavy load. The vacumn advance
has the timing advanced just before that point.
I had MAJOR problems 2-3 years ago with
backfiring and missing when going from low load to heavy
load and even on steady driving. After spending over
$1000 in parts, including replacing the heads and ignition
modules several times as well as other items, I found that
the little pot metal stop in the vacumn advance had broken
and therefore the timing was WAY too advanced at times.
This did not show up in the garage with a timing light
or under hard acceleration.
A drill, tap and a 1 cent 6-32 screw ( as a replacement stop)
solved the problem. Mabe it is going bad again.
I seem to recall that I took extra care in computing
the compression ratio. The stock pop up pistons were only
11.5 to 1 and they had a pretty good pop up.
James Barrett Tiger II 351C and others
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