[T3] Kettering Ignitions (Jim Adney)
topnotch at nycap.rr.com
Sat Feb 13 17:34:37 PST 2021
Remember, CR is also a function of the heads, stock late heads were stepped,
but by now most of that has been fly cut away as machine shops got a hold of
And wanted to "clean them up" and over all these years, perhaps multiple
times. Aftermarket heads are a crap shoot, unless you CC any head your
going to use,
And measure deck height you have no idea what the compression ratio really
topnotch at nycap.rr.com
71 Squareback Hothe
65 Notchback El Baja Rojo
93 RX7 Redstur
13 Subaru Outback "Blendin"
From: type3-vwtype3.org <type3-vwtype3.org-bounces at lists.vwtype3.org> On
Behalf Of William Jahn
Sent: Saturday, February 13, 2021 2:07 PM
To: type3 at vwtype3.org
Subject: Re: [T3] Kettering Ignitions (Jim Adney)
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 . When I set it close to TDC without the vacuum line
connected it felt like it had more pep. This was when I removed the
Pertronix and put back points so I had to reset the timing. I haven't set it
@ TDC and tried the advance. I'd set the timing @ 5 BTDC and drive it no
vacuum advance and it pinged so I backed it off to 3 BTDC and it stopped
then I connected the vacuum line and once it was warmed up it pinged. I just
left it there and plugged the vacuum line. I feel 5 BTDC is correct yet it
does not work out well since it pings. It's either the flat top pistons or
the fuel or a combination.
I've read you lower the RPM to 850 engine warm and set the timing . My
mechanical advance does not kick in until over 1,000 RPM . If I recall I
used to set it at 1,000 RPM with a timing light or just set the pointer on
5 BTDC then used a bulb and set it static rotating the dist till the bulb
just came on.
Point being if your 73 is stock with the dished pistons the results would
be different. I think that's why Russ suggested setting it @TDC , this was
when I rebuilt this engine. Before I rebuilt the engine it had dished
pistons and a good vacuum can and it worked fine. Since then they have
altered the fuel we didn't have ethanol then. I see in the Bentley 7.3 and
7.7 compression. With dished stock it's 7.3 don't know if the 7.7 was flat
top they don't state this just the year. My goal is no pinging with the
best performance not numbers.
Before I installed the pertronix in 97 I always ran points yet got a deep
pit that to remove it the regap worked yet part of the pit still existed , I
would need to file through the pont hard surface.
The vacuum advance didn't make any difference @ idle yet it did offer much
better pep on light throttle. I always set the points so both surfaces were
hitting dead center. Rather than deal with filing I just replaced them and
timed it static and it was always dead on with a timing light check. I
didn't have one. I borrowed one . This was why the one fellow suggested
pertronix because every 3,000 miles it began to miss because of the pits.
Once I replaced them it ran fine.
I wasn't until 72 5 BTDC was introduced and they had the dual can to retard
the spark at idle for emissions then did away with this in 73. If I recall
most earlier years were TDC which were on the higher compression engines and
many other early 70's 1600 FI
On Fri, Feb 12, 2021 at 7:06 AM Jim Adney <jadney at vwtype3.org> wrote:
> On 11 Feb 2021 at 21:44, William Jahn wrote:
> > I've never bothered to file points. Don't they have a hard coating
> > past that and it's pretty thin , you file through that
> There's a layer, you can see it, and it's about 1 mm thick. There's
> plenty of material to file if you care to.
> > The one issue is setting the timing. When I rebuilt this engine I
> > used flat top pistons , Russ said at one point I should set it @ TDC
> > rather than 5 BTDC. I Always did and it was not an issue until I put
> > the vacuum advance line back.
> IIRC, you have a Calif, X-engine, FI/AT '73, same as mine. The vacuum
> advance should not make any difference at idle. It doesn't on mine.
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
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