Not heard that before, but I do remember from the 80s or so when 'closed
loop' ignition systems started to become common that tromping on the
throttle from idle would cause quite a clatter which you could hear quite
rapidly reduce and cease as the electronics backed off the timing. Now ECUs
generally use 'open loop' systems which use a fixed curve from one of many
according to a whole mass of sensors around the engine. I don't know for
sure, but maybe any audible pinking is bad for these engines, and someone
also mentioned poisoning the CAT or increasing emissions, which could cause
it fail emissions testing. I've also seen performance (not necessarily MGB)
sites say that pinking or knocking can rapidly destroy modern high
performance e.g. turbo engines. Whilst I'm pretty sure the MGB isn't
anywhere near at risk as that, I wouldn't like to drive with audible pinking
as a norm.
The principle of knock retard is that you increase the timing bit by bit
until knocking is detected then rapidly back it off a few steps until it
stops, then gradually increase it again and so on. The theory is that this
keeps the timing in the optimum place whatever the parameters of the engine,
fuel, throttle opening, revs, or load. Ultimately you could do away with
both the vacuum and centrifugal advance gubbins, meaning that one
distributor would fit all MGB engines and give best performance and economy.
Of course, whether it would still pass emissions for those cars required to
do so is another matter, my 73 registered, 72 built doesn't having just
snuck though under the wire.
----- Original Message -----
From: "Simon Matthews" <firstname.lastname@example.org>
To: "Paul Hunt" <email@example.com>
Cc: "Gosling, Richard" <firstname.lastname@example.org>; <email@example.com>
Sent: Friday, August 25, 2006 6:21 PM
Subject: Re: Introducing Shell V-Power
> On 8/25/06, Paul Hunt <firstname.lastname@example.org> wrote:
> > I've recently started
> > experimenting with attaching a knock-sensing retard system in place of
> > vacuum (at least) advance, and that would be the ultimate solution to
> > grade variations and distributor advance curve deterioration with age,
> > that the original curves are ideal for today's fuels.
> That seems interesting, and a little counter-intuitive that one could
> replace an advance system with a retard system. Can you explain more?
> Another interesting question is the amount of knock that you want to
> obtain. It is my understanding (from Ford engine designers many years
> ago), that low speed knock (ie, the type that you can hear) actually
> results in slightly greater power output, so tuning to zero knock may
> be counter productive if your objective is performance.