Michael:
"Bowl Work" refers to the valve pocket, i.e. the first 1 inch or
so
of the port that is adjacent to the valve seat. This is where 80% of
the gains to be had from porting are realized, and it should always the
first place to receive attention during porting. The further you move
away from the valve, the smaller the return on your labor.
If a head receives ONLY bowl work, it is called a "pocket port
job"
most commonly. Expect a 10% increase in power for a pocket port. Another
-5% to +5% for enlarging, smoothing, reshaping the rest of the port.
The power can actually go down if you make the rest of the port
too
large, even though the flow goes up. This is because the incoming
air/fuel
charge slows down and you lose the benefits of inertial ramming to fill
the cylinder at typical RPMs. Of course, if you install some gnarly
racing
cam, big carbs, header, etc then within certain limits, a bigger port
will
make even more power.
For street, porting is best confined to the valve pocket. It
sounds
as though your head has had the benefits of a pocket port, which is a
good choice for street.
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of SamuelsMA@aol.com
Sent: October 01, 2005 3:44 PM
To: 6pack@autox.team.net
Subject: Electronic ignition
List members:
One of the reasons I purchased my '76 recently was an extensive list of
engine modifications including a complete engine rebuild, a balanced and
lightened flywheel, cylinder head porting, "bowl work" (whatever that
means), a
high-performance cam, headers, a 9.5 to 1 compression ratio, cold-air
induction,
and a new radiator. The previous owner claims that the car makes about
145 hp
at the flywheel, which seems about right as acceleration is comparable
to the
'70 PI which I used to own.
<snip>
Thanks.
Michael
'76 Tahiti Blue
CF 57044U
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