TRUE < This results in more expansion =3D lower EGT.> NOT TRUE Imagine the timing advanced to 60 deg before top dead center. This =20 allows more time for fuel and air to burn before tdc resulting in =20 higher cylinder temperature and pressure and a higher rate of heat =20 transfer into the cylinder and head. If the engine is operating at high MP the fuel air mixture may =20 detonate, spiking temperature, pressure and heat transfer rates even =20 higher. After TDC the combustion products expand over the full CR and cool by =20= Boyle=92s law. The fuel releases a fixed amount of energy, and since =20 more of it flows into the cylinder head there is less energy in the =20 exhaust gas. Under normal operating conditions fuel continues to burn after TDC, =20 so pressure and temp do not drop as fast as Boyle's law predicts. =20 More advance means less fuel available to burn after TDC. Yahoo! oneSearch: Finally, mobile search that gives answers, not web =20 links. --Apple-Mail-2-364687252 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=WINDOWS-1252

Bill:

I disagree, based on = watching this many, many times on the fully instrumented test stand.=A0 = The key is where the thetaPP occurs.=A0 As the thetaPP moves toward TDC, = there is more expansion of the burned gases as the piston falls and the = EGT gets lower, even with the same mixture.=A0 That's why during = pre-ignition, EGT falls rapidly.=A0 We have multiple data files which = prove this to be the case.

The latency period of the = fuel is what delays the burning of the fuel prior to TDC in most normal = cases.=A0 It is possible to advance the timing beyond the useful limit = and change all of this.

Walter

On May 29, 2007, at 4:13 PM, Bill Hannahan wrote:

=A0

<RPM:

Higher RPM move the = EFFECTIVE timing closer to TDC.>

=A0

TRUE

=A0

=A0< This = results in more expansion =3D lower EGT.>

=A0

NOT = TRUE

=A0

Imagine the timing = advanced to=A060 deg before top dead center. This allows more time for = fuel and air to burn before tdc resulting in higher cylinder temperature = and pressure and a higher rate of heat transfer into the cylinder and = head.

=A0

If the engine is operating = at high MP the fuel air mixture may detonate, spiking temperature, = pressure and heat transfer rates even higher.

=A0

After TDC the combustion = products expand over the full CR and cool by Boyle=92s law. The fuel = releases a fixed amount of energy, and since more of it flows into the = cylinder head there is less energy in the exhaust = gas.

=A0

Under normal operating = conditions fuel continues to burn after TDC, so pressure and temp do not = drop as fast as Boyle's law predicts. More advance means less fuel = available to burn after TDC.

=A0

Yahoo! oneSearch: = Finally, mobile search that gives answers, not = web links.

= --Apple-Mail-2-364687252--