I'm trying trying figure out how much force is produced by a gas explosion
in a piston during a normal firing. The air/fuel is correct and the spark
and everything else is optimum. What is the usual pressure that is being
created to push down the piston? Say on a 350.
I forgot the formula for the calculation of max cyl pressure.
I think you will find it in the 700-750psi area.
This is taken from an old pressure/time graph I made on a 350.
This would be the max pressure and decreases rapidly as the piston goes
guessing i would say 8.5 lbs per square inch, (compresion ratio)
area = pie x radius squared or 3.14 x ( .5x 4 ) squared = about 12.5
x 8.5 psi = about 106.25 lbs.
close enough for goverment work as they said in the GOOD OLD DAYS
Interesting calculations there, old John, but it fails to take into account
the force of the fuel/air explosion.
The formula for max cyl pressure is a thermodynamic formula that I don't
recall. I have long since got rid of all my related text books so I can't
look it up for you.
This question brings up memories of my youth mathematically tearing down and
that calculation is partly correct for doing a cylinder compression test
only. not the explosive burning of fuel air in the cylinder. there's a
bunch of thermodynamics involved with this number, but I think 1000psi is a
good ballpark # assuming a good cylinder, rings, etc.
FWIW: a missing metric for calculating the pressure in the compressed
cylinder (top dead center) is that atmospheric air pressure is approximately
14.7 psi. so 14.7psi * 9:1 compression ratio is approximately 132 psi air
pressure in the cylinder.
Hello Mad Dog,
What they've been trying to figure out is the pressure immediately after
ignition of the fuel/air mixture (which decreases with the volume increase
as the piston moves away from the head). A few guys came up with 800 to
1000 psi using different formulae.
Mad Dog, ever consider a cold air intake for the 79 K10 (may be just a
couple drops in the bucket with your NO2 setup)?
That formula is for the cylinder pressure at TDC before the piston begins to
move down in the bore.
Yes, i do have plans to fabricate a air cleaner bonnet that seals with the
hood for use with a cowl induction scoop.
I'm on the fringe of detonation now and have to replace the head gaskets
with steel shims in a effort to minimize the piston/head clearance "quench
I'm shooting for .030" quench area
(don't try this at home).
Redline is set at 6000 rpm so she will live fine with that clearance.
This will bring the compression up over 10-1 but I'm pretty sure the motor
will appreciate it by being able to crank the initial timing up a few
Hello Mad Dog,
Will the scoop be facing forward or the windshield?
Have you considered a water-injection system (very fine mist) to address
your detonation? They have NA and turbo models.
Oh, yeah, sorry (cowl induction scoop), duh... Am considering cutting a hole
in my hood and installing a scoop but more for ventilation, especially in
summer. I've found two or three models that should keep water out of the
engine compartment even in a torrential downpour.
Been doing some reading on water injection systems -- some folks use and
SWEAR BY injecting H2O2, that is, off the shelf hydrogen peroxide (less than
4% concentration), instead of water or water/alcohol. They also add alcohol
to the H2O2 for subfreezing temperatures (50:50) with mixed results (sorry
for the pun).
Am looking around for a single-stage system, low-pressure (60 psi pump), for
injecting water or H2O2 into the high-pressure side of the turbo on our
6.5TD. Besides being less than 10% the cost of an intercooler, I like the
idea of lower EGTs when it kicks in.
Ahhh, toys for the boys.
Are you referring to H2O2 in concentrations good enough for rocket fuel (60%
Also, I haven't heard of bleach blondes being set on fire (ummm, in a
literal sense, that is).
Interesting application, though. I'll be installing a single-stage water
injection system and will definitely try the off-the-shelf H2O2 but am not
equipped to accurately/objectively measure performance improvements. Boys
will be boys...
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