One thing I like more than developing theory is explaining my theory to others.
The way I see it David being the aggressive type had the cylinder pressure as
high as the fuel could stand, possibly into early stages of autoignition. With
him driving in circles with no time to cool down, cylinder temperatures
were very high to boot. All this adds up to a very sensitive engine.
The not so ideal chamber had a large squish area and a compact combustion
chamber, normally this is considered to contribute to some sort of fast burn.
I'm thinking the well atomized mixture added to this fast burn chamber
consumed much of the charge early in the burning phase. One problem
presents itself. Although the chamber resembles a efficient heart shape
design that's not necessarily so. The chamber is of the bath tub variety with
the valves sunk deep into the head. What this does is create fast initial burn
which is good but contributes to poor burn late in the cycle leading to autoignition.
The way I see it David may have found a fix, that is to use the large droplets
of fuel to slow down the burn and to cool the large quench area to with liquid
keeping this region cool in comparison to the chamber cavity. Basically the
air/fuel mixture in the region was too rich to burn resulting in detention of
flame propagation into the quench zone.
In contrast the ultra fast burn of the atomized fuel resulted in auto-ignition
setting in to the end zone. The fine mist did not prevent flame and heat from
penetrating this area and the resulting tune needed to keep this combination
out of auto-ignition was far from what the engine needed for power.
Quote:
Originally Posted by DavidVizard-GFN
I now had a burning question that defied an immediate answer. Why did
delivering a more finely atomized fuel spray cause the engine to drop so
much power? The Weber carb was, in truth, not so good at atomizing the
fuel - it came out of the auxiliary venturi (booster venturi) in globs rather
than anything that resembled a spray. Yet that ‘A’ Series engine loved it,
and too this day, I have never figured out why globs (yes - globs) work
and even a moderately good spray does not. I put this down to the fact
that there is always more to anything than meets the eye!
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