RE: Re: US vs. EURO 1.8 16V (123hp/139hp)?????

[Brad Sheridan <brads@mindspring.com>]

At 09:30 AM 1/12/99 -0500, you wrote:

>the main difference between K-jet and KE-jet is the knock sensor
>ignition and O2 sensor (correct me if i am wrong...,  well, i know you
>will).  so the higher hp came from possibly richer mixture and vacuum
>advance ignition?  what i don't get is why a vacuum advance ignition is
>better than a knock sensing ignition...  doesn't the knock sensor allow
>the distributor to be as advanced as possible without knocking?  isn't
>this better, in that it's ALWAYS fully advanced, and a vacuum advance
>has set curve that it follows...  hmmmm...  confusion growing... 

In theory, if it were an adaptive ignition, it could keep the ignition
curves fine tuned so that they are nearly as fully advance as needed. But
most ignition controllers aren't up to that level. The ones I've read about
seem to follow more along the lines of having a set curve that it follows,
and if it senses knock, take X degrees out of the timing. From what I've
gathered, the VWs with knock sensors do have a bit more advanced curve, but
I haven't verified this.

  One thing to realize is that once you sense knock, you have to retard the
ignition a good bit to get back out of the knock. So for example, you're at
a set RPM/engine load, at a set ignition timing, and have no knock. If you
advance the timing 1 degree, and then you start getting knock, you have to
retard the timing more like 4 or 5 degrees to get the knock completely
stopped. So you want to avoid getting into the zone where you are getting
knock.

HTH,
Brad


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