i don't usually speak up much on the list,,but u guys seem baldy in need of
some help.
The main way to increase power in engines is to 1:increase the volume of air
intered into the engine, 2: increase the efficiency of the motor, and
3:decrease mechanical friction.
To increase the volume of air you can increase the engines breathing
capibilities, but this is limited by atmoshereic pressure and engine
displacement (i.e. the cyclinder is completely filled and equals the same
pressure as the surrounding atmosphere)
Increasing the volume of the engine(displacement) will also increase the
volume of air that is entered into the engine
Forcing pressurized air allows you increase the volume of air entered into
the engine without increasing the displacement (superchargers ,turbos)
Now comes the efficiency part.
in laymens terms,compressing the air/fuel molecules closer together creates a
"stronger" burn,thus the tighter u compress them the closer they are and the
"stronger" the burn.
And since we want a controlled burn with a gradual pressure rise and not an
"explosion", there are many limiting factors to raising the compression
ratio. here are a few:
1 when you compress a gas you increase it's temperature
2 increased temperatures may lead the mixture to self ignite (preignition)or
explode (detionation)
3 a compressed mixture also burns quicker and the flame front may contact the
piston top (ping)..alot here has to do with combustion chamber shapes and
octane levels (higher number octane actually burns slower)
4 law of dimishing returns, the mechanical energy taken to compress the
mixture will no longer equal the return...i think gains are pretty much non
existiant around a C/R of 20:1
Now we get into staticC/R and linear C/R
static C/R is what the space in the cyclinder is compressed to
(i.e. 10cu inch compressed to a space the size of 1 cu inch=10:1 C/R)
linear C/R is the actual amount of gases being compressed,,due to incomplete
cyclinder fill (at higher rpms) or superfilled (supercharging)...so the
linear C/R varies according to elevation, engine rpms,etc...
one example would be a normally asiprated engine(at sea level 14.7psi) with a
10:1 staticC/R
in effect has the same linearC/R as a supercharged engine running
14.7psi of boost (14.7 atmosphere+14.7boost=29.4psi) at a 5:1 static C/R ratio
OK, since both the liner C/R is the same they will both have the same burn
rates(given all variables are equal),,but the boosted engine is burning twice
as much air/fuel per cycle and should be producing twice as much power
soo increasing boost is definatly more favorable than raising the C/R
sorry for such a long post..hope some of this helps
BTW..this info is not entirely accurate/true but given as just a means for
understanding some basic principles
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