[T3] Kettering Ignitions (Jim Adney)

Jim Adney jadney at vwtype3.org
Mon Feb 15 05:55:18 PST 2021

On 13 Feb 2021 at 11:06, William Jahn wrote:

> To clarify : With the timing set @ 5 BTDC and the vacuum advance connected
> it will ping which it never used to. The flat top pistons increase the
> compression ratio .

You're probably right, that the flat top pistons, plus whatever flycutting was 
done to the heads, increased the compression ration enough to make the 5 
BTDC too much advance. I suspect higher compression ratio will increase 
the flame front velocity, which would shorten the time to max combustion 
chamber pressure.

This is probably why the later engines, with the 7.3 compression ratio got 
that extra 5 deg of advance.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

More information about the type3-vwtype3.org mailing list