[Diy_efi] RE: Timing and dyno pulls

[Adam Wade]

--- William Shurvinton <shurvinton at orange.net> wrote:

> Re: timing vs detonation on race engines, how come
> so many people get it wrong?

At higher rpms, you need more advance to get the
pressure peak at the right place in the power stroke
(I gather we're all pretty clear on that one).  A lot
of people see advance over a stock setup (which is
going to be geared for emissions as well as power)
getting them additional power, so a lot of people just
pour on the advance, figuring "more = better".

> Can I also infer that OEM apps ( which run close to
> detonation) do this because they are running leaner
> than they should?

Do what?  Retard timing?  In some cases.  That's
usually how a detonation sensor setup works; after
detecting knock, it retards the timing.

> On the temperature issue that has me confused. I had
> always thought that cooler was more powerful

As someone mentioned a few days ago, you want the
biggest CHANGE in temperatures.  Cool intake, hot
exhaust.

> and race cars (F1 in particular) only ran so hot
> because the aero package demanded a limited rad area
> and air flow. Hotter was more efficient.

With the engine components themselves, you are limited
by how much heat the materials involved can withstand
before weakening.  With highly-stressed engine parts
that are built to JUST withstand the stresses of a
race and be as light as possible, managing temperature
is CRITICAL.  So there are conflicting needs; the need
to keep the engine structurally sound, and the
"desire" to have it as hot as possible in the
combustion chamber.

> Can you also confirm on the cylinder head temp issue
> that you accepting that way too hot will cause pre-
> ignition?

That depends.  Pre-ignition, as opposed to detonation,
needs a "hot spot" to light it off.  A hemi head
combustion chamber, as an example, with no carbon
buildup, would be hard to make "pre-ignite", since
there would be good paths for heat to flow out of the
combustion chamber and into coolant passages.  Once
with a lot of sharp corners would be more likely, and
one with cabron build-up, especially in little chunks
where heat could concentrate and cause it to "glow",
would be the most likely.

> I can understand why heating the heads takes heat
> out the reaction, but after a point aren't you
> starting from a hotter charge and so reducing the
> available heat increase from combustion?

It depends largely on how much charge volume is lost
out the intake valve.  Any heating that happens to the
charge after it enters (and stays in) the combustion
chamber is part of the engine's power development,
although depending on where it happens in a
four-stroke engine, this could work AGAINST power
output from the vehicle.


=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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