[DeTomaso] burns

[Larry - Ohio Time Corp]

I have no training or experience in F1 or any Funny car motors. Just 40 some
years of cranking wrenches on the stuff you see on the street and in the
dirt (I stay out of the water and air). Combustion chambers and spark plug
locations are designed very carefully today to make sure a complete burn (as
best as can be had) of all the fuel is made. This helps with the exhaust
pollution and MPG of the motor.
 
 
 

Spark Timing Myths Debunked


A widely-held myth is that maximum advance always means maximum power.
Here's what's wrong with this thinking:

The spark plug ignites the mixture and the fire starts burning. The speed of
this flame front depends on the mixture, this means how many air and fuel
molecules are packed together in the combustion chamber. The closer they are
packed together in the same volume, the easier it is for the fire to jump
from one set of molecules to the other. The burning speed is also dependent
on the air-fuel-ratio. At about 12.5 to 13 air-fuel-ratio the mixture burns
fastest. A leaner mixture than that burns slower. A richer mixture also
burns slower. That's why the maximum power mixture is at the fastest burn
speed. It takes some time for this flame front to consume all the fuel in
the combustion chamber. As it burns, the pressure and temperature in the
cylinder increases. This pressure peaks at some point after TDC. Many
experiments have shown that the optimum position for this pressure peak is
about 15 to 20 degrees after TDC. The exact location of the optimum pressure
peak is actually independent of engine load or RPM, but dependent on engine
geometry. 

Typically all the mixture is burned before about 70 deg ATDC. But because
the mixture density and AFR in the engine change all the time, the fire has
to be ignited just at the right time to get the peak pressure at the optimal
point. As the engine speed increases, you need to ignite the mixture in the
combustion chamber earlier because there is less time between spark and
optimum peak pressure angle. If the mixture density is changed due to for
example boost or higher compression ratio, the spark has to be ignited later
to hit the same optimal point. 

If the mixture is ignited to early, the piston is still moving up towards
TDC as the pressure from the burning mixture builds. This has several
effects:

*	The pressure buildup before TDC tries to turn the engine backward,
costing power. 

*	The point where the pressure in the cylinder peaks is much closer to
TDC, with the result of less mechanical leverage on the crankshaft (less
power) and also causes MUCH higher pressure peaks and temperatures, leading
to knock. 

 
 
on and on..... :)
 
 
Larry (burning man) - Cleveland