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Subject: One more question:
45-Shooter    5/13/2013 8:58:31 PM
Does anyone here know why smaller recip engines make more power per cubic inch displacement than larger recip engines? Or why larger engines get better fuel economy than smaller engines of the same power?
 
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WarNerd       5/14/2013 3:32:05 AM
Does anyone here know why smaller recip engines make more power per cubic inch displacement than larger recip engines? Or why larger engines get better fuel economy than smaller engines of the same power?
You need to give examples of the engines you are comparing to fully answer.
 
But as a rule of thumb, small engines are designed for short duration usage, in terms of the period between rests, overhauls, and overall life. So you can shave off more material, or operate it in a marginally save way, and still have an acceptable design life. You can also increase power to weight by increasing the RPM or using less efficient operating cycles, like 2-stroke engines.
 
Large engines are usually designed for continuous duty, for weeks or even years between maintenance cycles. You need more material for durability, better cooling systems, and systems to improve efficiency in the particular operating environment they are designed for because the weight budget is less critical.
 
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oldbutnotwise       5/14/2013 2:51:15 PM
technically they don't, a large capacity engine with the same size piston area and valve area ie one that has more capacity by having more cylinders will produce similar hp/cc (not quite due to mechanical losses but close)
 
where the main difference is the reciprocating mass, the less mass being accelerated and decelerated the more power can be produced
 
the bottom line for an engine is that there is a fixed amount of power can be produced from an amount of fuel/mixture
to gain more power you can either force more fuel/air into the engine or increase the amount it can take, it is usually easier to increase the amount than force more in.
 
oh and by the way HP is not always the important bit, torque is often more important
 
different requirements are often the deciding factor, in the US big slow rev'ing fuel inefficient that will cruise at constant speed for days but will be unsuitable for European roads, different requirement different solutions
 
 
 
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WarNerd       5/15/2013 1:50:52 AM
different requirements are often the deciding factor, in the US big slow rev'ing fuel inefficient that will cruise at constant speed for days but will be unsuitable for European roads, different requirement different solutions
The big engines are often more efficient than the small ones because they can be more optimized and include equipment to harvest ‘waste energy’. They are also often designed for a narrow range of operating conditions to allow further optimization than small engines like in automobiles.
 
The only roads you will find big engines on are railroads. Large IC engines are also used on cargo ships and for backup power.
 
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45-Shooter    ???   6/25/2013 1:34:58 AM

 You need more material for durability, better cooling systems, and systems to improve efficiency in the particular operating environment they are designed for because the weight budget is less critical.
I state that the $8,000 in 1974 dollars was the much poorer investment than the $8,000 spent in 1986 when those 1974 bucks would have been worth about $20,000 in 1986. See "Measuring worth"

 
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45-Shooter    ???   6/25/2013 1:58:56 AM

piston area Only possible if the "Large" engine had a longer stroke.  and valve area ie one that has more capacity by having more cylinders More cylinders imply more valve area and thus will make more power per unit of displacement under the same operating conditions! That is why the build V-12s instead of V-8s with larger pistons. will produce similar hp/cc (not quite due to mechanical losses but close) The engine with the most pistons/valves will make the most power out of any pair that have the same displacement.

 

where the main difference is the reciprocating mass, the less mass being accelerated and decelerated the more power can be produced
Just flat wrong.
 
 

the bottom line for an engine is that there is a fixed amount of power can be produced from an amount of fuel/mixture
This only applies if the piston crown area is identical in the two engines.
 
to gain more power you can either force more fuel/air into the engineTrue! or increase the amount it can take As in higher BMEP?, it is usually easier to increase the amount? Of what? than force more Of what? in.

 

oh and by the way HP is not always the important bit, torque is often more important
Torque with out power is worthless! But power can be converted/multiplied in to more torque!
 
 

different requirements are often the deciding factor, in the US big slow rev'ing fuel inefficient Bet none of your high revving small engines can make the power my big block makes just off idle while burning twice the gas per hour! Fuel efficiency is improved dramatically by lower engine RPMs! Friction goes up as the square of RPMs, but only proportionately to displacement! So when you spin the Honda S-2000's small engine to 8,000 RPMs to make almost as much power and a tiny fraction of the torque of my mountain motor at 2000 RPMs, it will not get anything close to 25 MPG and it will be very much slower than my Camaro! that will cruise at constant speed for days but will be unsuitable for European roads, different requirement different solutions
On my second tour to Germany in the late 70s, I took my '72 Mach-I Mustang with it's Twin four barrel 427 Holman and Moody side oiler along for the ride. You know, it was faster in every way on every road than my 1968 911R! While I freely admit that part of that superiority on some roads was due to the Polly-glass wide ovals and huge four wheel disk breaks, but out on the Autobahn than big Ford would cruise for hours at speeds that would have blown that Porsche up in minutes.
 
 

 



 
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45-Shooter    ???   6/25/2013 2:12:13 AM



The big engines are often more efficient than the small ones because they can be more optimized and include equipment to harvest ‘waste energy’. They are also often designed for a narrow range of operating conditions to allow further optimization than small engines like in automobiles.

 

The only roads you will find big engines on are railroads. Large IC engines are also used on cargo ships and for backup power.

The question was a relative one! But the most powerful recip engine on the planet, the Wartsilla 98-14? IIRC, makes 114,000 HP, again IIRC, from ~27,000 liters of displacement, for 4.2 HP/L displacement. It is a two stroke Diesel and only turns about 115 RPM
Talk about BMEP! But a similar two stroke model airplane engine of only 1.6 Ccm makes 110 HP/L @ 50,000 RPMs at a cost of only $20.00 and that WO a supercharger like the big engine above. Pick any technology of engine and the smaller one will make more power per unit of displacement!
 
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oldbutnotwise       6/25/2013 6:14:32 AM
  
where the main difference is the reciprocating mass, the less mass being accelerated and decelerated the more power can be produced
Just flat wrong.
 
show how much you actually know doesnt it

the bottom line for an engine is that there is a fixed amount of power can be produced from an amount of fuel/mixture
This only applies if the piston crown area is identical in the two engines.
Not talking about different engines but a "single" engine (but you are wrong as the  its the displacement that effects power NOT just crown area
 
 
to gain more power you can either force more fuel/air into the engineTrue! or increase the amount it can take As in higher BMEP?, it is usually easier to increase the amount? Of what? than force more Of what? in.

nope you fail again on the the most simplistic ideas, for any given amount of fuel/air mix thier is a fixed amount of power it can produce, to increase the power of an engine you need to provide more fuel/air mix, you can do this my increasing the amount it can take in or by externally forcing more in, but for a fixed amount of fuel air/second two engines will produce the same power (minus losses) given the same conversion efficiency.
 
small engines tend to rev higher because they have less internal momentum but this is only comparatively, an F1 3liter engine will rev to 22000rpm in unlimited configuration
 
the basics are that more cubes = more power easier, however you can get more from a small engine by better engineering  easier than a big engine

oh and by the way HP is not always the important bit, torque is often more important
Torque with out power is worthless! But power can be converted/multiplied in to more torque!

and Power without torque is as useless as you need to apply that multipler which requires additional hardware the less torque the smaller the operating range and the less usefull the engine
 
power and torque are two sides of the same coin and producing the perfect split is the goal of all engine makers
 

different requirements are often the deciding factor, in the US big slow rev'ing fuel inefficient Bet none of your high revving small engines can make the power my big block makes just off idle while burning twice the gas per hour!
Fuel efficiency is improved dramatically by lower engine RPMs! Friction goes up as the square of RPMs, but only proportionately to displacement!
 
which planet did you holiday on as you seem to be still there
 
So when you spin the Honda S-2000's small engine to 8,000 RPMs to make almost as much power and a tiny fraction of the torque of my mountain motor at 2000 RPMs, it will not get anything close to 25 MPG and it will be very much slower than my Camaro! that will cruise at constant speed for days but will be unsuitable for European roads, different requirement different solutions
On my second tour to Germany in the late 70s, I took my '72 Mach-I Mustang with it's Twin four barrel 427 Holman and Moody side oiler along for the ride. You know, it was faster in every way on every road than my 1968 911R! While I freely admit that part of that superiority on some roads was due to the Polly-glass wide ovals and huge four wheel disk breaks, but out on the Autobahn than big Ford would cruise for hours at speeds that would have blown that Porsche up in minutes.
which planet did you holiday on as you seem to be still there
 
 
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45-Shooter       6/27/2013 2:47:42 AM


oh and by the way HP is not always the important bit, torque is often more important

Torque with out power is worthless! But power can be converted/multiplied in to more torque!

and Power without torque is as useless as you need to apply that multipler which requires additional hardware the less torque the smaller the operating range and the less usefull the engine Again you miss the point entirely! Small torque engines and motors typically have very much wider power ranges than bigger engines with more torque! I should know after building 15 mountain motor hot rods so far! None of them had a power band over 5,650 RPM wide and most were under 5000. But the afore mentioned Honda S-2000 has a useful power band that is over 7,200 RPMs wide! But worse than that, smaller two strokes can easily have useful power bands ten to 15,000 RPM wide. But worst of all are electric motors which have very little torque can easily have power bands 250,000 RPMs wide.


 
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45-Shooter    Reply, part two!   6/27/2013 2:51:19 AM

 

On my second tour to Germany in the late 70s, I took my '72 Mach-I Mustang with it's Twin four barrel 427 Holman and Moody side oiler along for the ride. You know, it was faster in every way on every road than my 1968 911R! While I freely admit that part of that superiority on some roads was due to the Polly-glass wide ovals and huge four wheel disk breaks, but out on the Autobahn than big Ford would cruise for hours at speeds that would have blown that Porsche up in minutes.
which planet did you holiday on as you seem to be still there
 
 different requirements are often the deciding factor, in the US big slow rev'ing fuel inefficient Bet none of your high revving small engines can make the power my big block makes just off idle while burning twice the gas per hour!
Fuel efficiency is improved dramatically by lower engine RPMs! Friction goes up as the square of RPMs, but only proportionately to displacement!
 
which planet did you holiday on as you seem to be still there
On my first tour in Germany, I noticed that you could buy a full size, four door, five pax, Mercedes Sedan with a four banger in it. If it was driven slow, it got alright mileage, but when driven fast enough to keep up with my Ford, the mileage suffered terribly and it was still slower than the Ford! 

On my second tour to Germany in the late 70s, I took my '72 Mach-I Mustang with it's Twin four barrel 427 Holman and Moody side oiler along for the ride. You know, it was faster in every way on every road than my 1968 911R! While I freely admit that part of that superiority on some roads was due to the Polly-glass wide ovals and huge four wheel disk breaks, but out on the Autobahn than big Ford would cruise for hours at speeds that would have blown that Porsche up in minutes.
which planet did you holiday on as you seem to be still there
Just how long do you think you can run an engine at full throttle, load and RPMs? At 7,200 RPMs that Porsche would go about 163 MPH according to the traps at Hochenhiemring, which was my home track. If you were lucky it might last all week on the Flats running over 150 MPH for three to four miles at a whack for a dozen passes WO blowing up! Note that I said MIGHT! At 5,000 RPMs my Ford would cruise at 170 MPH for over 500 hours, or about 90,000 miles of fast street racing and commuting from Prairie Grove, ILL to Park City Utah in 20 hours flat, OR make over 100 passes on the salt flats and several hundred passes at the drags and still get me home over a four year span. What planet are you from?


 
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45-Shooter       6/27/2013 3:02:42 AM

Fuel efficiency is improved dramatically by lower engine RPMs! Friction goes up as the square of RPMs, but only proportionately to displacement!
 
which planet did you holiday on as you seem to be still there
 
So when you spin the Honda S-2000's small engine to 8,000 RPMs to make almost as much power and a tiny fraction of the torque of my mountain motor at 2000 RPMs, it will not get anything close to 25 MPG and it will be very much slower than my Camaro!

On my second tour to Germany in the late 70s, I took my '72 Mach-I Mustang with it's Twin four barrel 427 Holman and Moody side oiler along for the ride. My first big block car! You know, it was faster in every way on every road than my 1968 911R! While I freely admit that part of that superiority on some roads was due to the Polly-glass wide ovals and huge four wheel disk breaks, but out on the Autobahn than big Ford would cruise for hours at speeds that would have blown that Porsche up in minutes.
which planet did you holiday on as you seem to be still there See the quotes below.
 

In 1965, when the new AutobahnA 6 separated the village from the main part of the track, a new version of Hockenheim circuit was built, with the "Motodrom" stadium section. After Jim Clark was killed on 7 April 1968 in a Formula 2 racing accident, two chicanes were added and the track was lined with crash barriers in 1970. A small memorial was placed near the first chicane, at the site of his accident. In 1982, another chicane was added at the Ostkurve (east curve), after Patrick Depailler was killed there in 1980; and the first chicane was made slower as well.

This version used to be quite large, with a very long, fast section going through forests essentially consisting of four straights of roughly 1.3 km, separated by a chicane sequence, followed by a more tight and twisty "stadium" section (so called because of all the grandstands situated there) named Motodrom. This made the setting-up of racing cars difficult, since a choice had to be made – whether to run low downforce to optimize speed through the straights and compromise grip in the stadium section, or vice-versa. The long track length also meant that a typical Formula One race had only 45 laps, limiting the spectators' experience of the race to only that many passes through the stadium.

These events prompted much protest from the FIA to greatly improve spectator viewing, safety and security at the track, as it had become clear that the track was no longer suited to modern Formula One racing.

During the television coverage of the qualifying session of the 2012 German Grand Prix held on the new circuit, former F1 driver and current lead TV commentator for Sky Sports Formula One coverage Martin Brundle stated that he, along with other drivers of his era (mid-1980s to the mid-1990s), didn't really enjoy racing at the old Hockenheim as the long straights often saw only seven or eight finishers from twenty-six starters, with most dropping out through engine or transmission failure caused by the long periods at high speed on the forest straights.



 
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