Porting

[Robert Harris]

Vizard goes into it very nicely in the book  - backed up by some basic
research by Heywood.

Quickly - opening the chamber reduces the burn rate of the gasses -
increasing the exposure time of the end gasses leading to their premature
and uncontrolled ignition.

Ideally, the head should be angle milled to reduce the chamber to the
smallest size practical. Any changes to the chamber for flow should preserve
the squish/quench area.  Once you have enhanced the burn rate and swirl, the
swept volume should be increased to the desired compression by a bowl or
dish or reverse dome in the piston. Properly placed, these do not slow the
burn rate and may increase the swirl for better combustion yet. Simply
lowering piston height by shaving the crown will generally be disastrous.
If the squish/quench area opens beyond about .100 in height (in the vicinity
of TDC) it becomes a detonation area.

More will be revealed - if you read the book specifically written just for
the heads you want to do by one of the best builders around.

------------------------------

From: "Andrew F. Gunnesch" <afgun at mongoose.dearborn.sgi.com>
Date: Thu, 12 Mar 1998 11:39:51 -0500
Subject: Re: Porting

How will a larger chamber increase ping knock and detonation?  I'm
curious...

On Mar 12,  8:08am, Robert Harris wrote:
> Subject: RE:   Porting
> Opening up your chamber to lower compression will raise your ping, knock,
> detonation levels to self destruct and in general cost you power and
> economy - but what the heck do I know anyway.
>
> Best Book on Porting Chevy Heads.
>
> "How to Build & Modify Chevrolet Small-Block V-8 Cylinder Heads"
> David Vizard
> ISBN 0-87938-547-2 Motorbooks International
> ------------------------------