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In Reply to: RE: Engine Math...a little posted by JURB on April 20, 2021 at 06:42:40
Ya' gotta compare like to like.....A 'squre' engine is a good starting point.
You can get lost in the sauce and just get confused.
the rule maintains.....For any given level of development, MORE cylinders should produce more power. Greater surface area of pistons for any fixed displacement is why.
It's all PSI......More pistons per given volume of engine means more work can be done.....even though I'd suspect friction goes UP as a function of cylinder to piston surface area.....But only 'bearing' on the rings....
HardChromes is neat, but Chrysler Hemi engine cranks were NITRIDED. That's gonna be harder than a whore's heart. But CAN'T be ground....so it's one and done....
By definition, highest volumetric efficiency is at an engines TORQUE PEAK. This should also be where the engine gets the BEST fuel economy. Of course? If the car is going very fast at this peak, than wind resistance, (DRAG) cuts into such fuel usage.
My 7000 reference was for the Factory / Stock engine.
Too much is never enough
Follow Ups:
"the rule maintains.....For any given level of development, MORE cylinders should produce more power. Greater surface area of pistons for any fixed displacement is why"
Only to a point. A circle twice the diameter has four times the area.
Like a 12" pizza, pi*R^2, about 113 sq. in.
A 16" pizza about 201 sq. in.
The lowly 8" pizza only about 50 sq. in.
What a difference the lowly 4" makes.
So the only main difference is that the peak PSI hits more in the sweet spot of the various cylinders. If it was only the surface area of the piston, a huge one cylinder would be best.
For a real world example, start with an old train, steam. They only had two huge pistons BUT they had steam on tap to keep feeding it until it is really done, extracting the last bit of power out of it. You would have to go on an antique train to see i t, the modern ones are not like that. Newer trains are actually electric. They have a huge diesel connected to a generator and a motor moves the train. They found this to be the best transmission. Really, you want to design an automatic tranny for those ? Eeesh, no way Jose. A thousand clutch plates and sprags ? At least, and I still doubt it would be as reliable.
Anyway, if you were quoting a real rule there, it is only valid in a certain range.
We are controlling for a cylinders VOLUME.....not surface area of a circle.
We were up against your 'double area + 4X surface area' rule in semiconductor processing.
It is nearly as much work to process a 3" or 4" silicon wafer as a 6" or 8" slice. Of course, you
LOSE the edges but the output still grows Nearly 4X the double diameter calculation.....
In an engine? The big ADDITIONAL loss of that of Friction. Forget main bearings, for now, but
Each additional cylinder has rings and while the surface area is increased, adding diameters also
factors in.
And NO, a single cylinder would NOT be best. Given that engines are basically run by PSI, the
increase in surface area for a given volume makes multi-cylinder solutions best. AT ANY given
pressure, the more cylinders produce more power. The DEVELOPMENT proviso certainly applies.
Original Ford Flat Heads were certainly UNDER 100hp....Early versions were 221 cubes. Todays 6cyl
in a Nissan GTR crank out north of 500hp and are insignificantly larger than the Ford.....
With STEAM? You'll find that in MARINE
applicaitons a Triple Expanding engine.....feeding steam from one cylinder to the next, would extract
the most power possible.
I have NO idea what Pizza has to do with anything, except that as YOU, my eyes may be bigger than
my stomach....!
What IS the 'Sweet Spot' of a piston or cylinder?
Too much is never enough
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