[Diy_efi] boosted compression ratio

[Bernd Felsche]

On Sun, Dec 22, 2002 at 07:17:08PM +0000, Mike wrote:
> At 06:59 PM 22/12/2002 +0800, you wrote:
> 
> >Because the detonation occurs in a narrow time window after spark;
> >usually after TDC. So you know which cylinder because it's the one
> >recently fired.
> 
> Yeah just realised - whilst you were no doubt compiling your email ;)
> 
> >"Pings" quite audibly at times from low revs, even with Ultimate 98.
> >But not on humid days. On a cooler day, with say 80% humdity, it
> >feels like the engine is putting out at least 10% more mid-range and
> >even more low-end torque than with 50% or less RH. Of course; as it
> >gets even colder, it doesn't matter that there's 100% RH; it'll
> >still ping.

> Well why the heck dont you add a water injection setup and get the
> humidty artificially - and you could chill it as well :-)

Expense and water is scarce. :-)

Still trying to get a cheap inlet fogger together; that should do
the trick. In winter, I'd have to heat the fog so that the air
temperature rises as well. At 8 degrees C, air is saturated with
only about 8 g of water per kg of air. Heating the air to about 25
degrees increases that to about 20 grams. That's worth 3 Octane
points; but the temperature rise reduces the effect by 1 to 2
points. <sigh>

> >> Does this occur at about say 4000 rpm ?

> >30 milliseconds between sparks; no problem.

> The time is not the issue, its the fact that at higher revs there
> are all sorts of other things that may 'sum' to way too much
> noise floor for effective ping detection...

Unless you know the noise floor and can compensate; which is what
the (defunct) Harris chip did; measure noise floor outside the knock
window and "subtract" that from the knock window levels. Well; it
was rather more complicated but that's the gist. Hopefully, the
valvetrain isn't clattering away just inside the knock window;
though it's conceivable that some valves might be opening or closing
at the same time.

-- 
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