the Arcane Knowledge Thread
07-28-2005, 01:53 AM
#61
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rear diffuser ideal angles, from leading to trailing edge
when designing a rear diffuser system:
a general "rule of thumb" is 7deg, but can run as high as 11deg. typically, a longer, more gradual taper to-end is more effective than a shorter, steeper taper to-end.
too much angle causes seperation and turbulence, which hampers the accelerated air, coming out from under the car, in rejoining the slower-moving air behind the car.
the number of "strakes," ie, lateral fences or vanes running the length of the underside, will make a difference too. these help clean up the turbulent air from the rear tires, as well as "firewall" protect the central "throat" of the venturi. increasing the number of strakes, to a point, enhances downforce.
a general "rule of thumb" is 7deg, but can run as high as 11deg. typically, a longer, more gradual taper to-end is more effective than a shorter, steeper taper to-end.
too much angle causes seperation and turbulence, which hampers the accelerated air, coming out from under the car, in rejoining the slower-moving air behind the car.
the number of "strakes," ie, lateral fences or vanes running the length of the underside, will make a difference too. these help clean up the turbulent air from the rear tires, as well as "firewall" protect the central "throat" of the venturi. increasing the number of strakes, to a point, enhances downforce.
Last edited by bonzelite; 07-28-2005 at 05:44 PM.
07-28-2005, 08:46 PM
#62
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Originally Posted by bonzelite
many thanks, ajrichar, for adding that bit of arcane knowledge. i was heretofore unaware of the prevalent use of the R31 in that year. good job.
it is good to see a fellow enthusiast who enjoys the Australian presence and contributions to Group A racing. i'm an American, but have gotten hooked into the history and stories behind Bathurst, international Group A, and its legends and lore.
it is important for others to understand the major cooperation between Nissan Japan and the Australians insofar as their collaborative development of the GT-R program. in my view, the GT-R, in general, was --and is-- an ongoing result of international cooperation inasmuch as it is a Japanese phenomenon.
feel free to contribute more.
it is good to see a fellow enthusiast who enjoys the Australian presence and contributions to Group A racing. i'm an American, but have gotten hooked into the history and stories behind Bathurst, international Group A, and its legends and lore.
it is important for others to understand the major cooperation between Nissan Japan and the Australians insofar as their collaborative development of the GT-R program. in my view, the GT-R, in general, was --and is-- an ongoing result of international cooperation inasmuch as it is a Japanese phenomenon.
feel free to contribute more.
I take a specific interest in the Australian presence of the GT-R. The car did not have many fans when it ran here, because of two reasons:
1) It wasn't 'Australian.' ie. it wasn't a Ford or a Holden (a local GM division). Despite the fact that Nissan had, as Allan Moffat proclaimed during the 1990 Mallalla round telecast, paid its dues and spent millions of dollars competing in the Australian championship for many years and employed many Australians, fans couldn't get past the fact that it wasn't 'homegrown' (ironically, Ford fans still cheered for the Sierra RS500's despite being turbo 4 cylinders).
2) It was so successful. This is a point that everyone now knows. It happened in Japan. It happened in Australia. The GT-R killed Group A 'Down Under'. It was so devastingly successful that weight penalties and turbo restrictions couldn't stop it winning the championship in 1992. Of course, 1991 was a Touring car holocaust with the GT-R's annihilating the grid and taking a dominant Bathurst win, so something needed to be done. Unfortunately for lovers of motorsport diversity, the GT-R was banned for 1993 onwards, and Australia moved to a two manufacturer V8 category now known as V8 Supercars.
But then, nothing I have said here is new.
The Australian gerbox manufacturer Hollinger produced a local gerabox that Gibson's team ran in their GT-Rs. It proved so good that I believe that the Japanese came and placed their own orders for these gearboxes as well.
07-28-2005, 10:19 PM
#63
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Bathurst lore
lets go back a few years before Group A existed:
on Sunday, May 7, 1815, Governor Lachlan Macquarie proclaimed the site for a town. he called it "Bathurst," in honor of the Secretary of State for the Colonies.
the national significance of this was that it marked the breakthrough from the coast for the young colony, and the beginning of Australia's inland expansion and development.
Bathurst is the oldest inland city in Australia, and, in its 185 years, has accumulated a mass of historical associations; here is one of them:
in 1896, Herbert Thomson of Armadale, Victoria, designed and began to build a steam powered motor phaeton the same year that Henry Ford introduced his "petrol driven quadricycle" in the United States.
whereas Ford made millions of cars, Thomas made 13. the Thomson Motor Car Co, Ltd, selling its vehicles at around 900 pounds each, exhibited a car at the 1900 Royal Easter Show in Sydney. they brought it to Bathurst, and set out on the first overland car journey ever undertaken in Australia:
over the less-than-ideal roads of the times, the 493 mile journey took ten days, at an average speed of 8.72 mph. the car burned 42 gallons of kerosene, at a cost of one penny per mile.
it would be a few years later, in 1938, that motor racing officially came to Bathurst, the Australian Gran Prix, a 150 mile race on Mount Panorama.
on Sunday, May 7, 1815, Governor Lachlan Macquarie proclaimed the site for a town. he called it "Bathurst," in honor of the Secretary of State for the Colonies.
the national significance of this was that it marked the breakthrough from the coast for the young colony, and the beginning of Australia's inland expansion and development.
Bathurst is the oldest inland city in Australia, and, in its 185 years, has accumulated a mass of historical associations; here is one of them:
in 1896, Herbert Thomson of Armadale, Victoria, designed and began to build a steam powered motor phaeton the same year that Henry Ford introduced his "petrol driven quadricycle" in the United States.
whereas Ford made millions of cars, Thomas made 13. the Thomson Motor Car Co, Ltd, selling its vehicles at around 900 pounds each, exhibited a car at the 1900 Royal Easter Show in Sydney. they brought it to Bathurst, and set out on the first overland car journey ever undertaken in Australia:
over the less-than-ideal roads of the times, the 493 mile journey took ten days, at an average speed of 8.72 mph. the car burned 42 gallons of kerosene, at a cost of one penny per mile.
it would be a few years later, in 1938, that motor racing officially came to Bathurst, the Australian Gran Prix, a 150 mile race on Mount Panorama.
07-28-2005, 10:38 PM
#64
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Group B
Group B existed specifically for rally racing, officially created in the same year as Group A:
rally cars before the Group B era were, for the most part, rear-wheel-drive with about 250 horsepower, because any more power merely resulted in wheelspin. the two classes at the time were Group 2 and the more popular Group 4. the rules for Group 4 mandated a minimum production run of 400 copies of a car to meet homologation requirements, in order to encourage the manufacturers to use mass-produced cars. some of the more famous rally cars from this period were the Lancia Stratos, the Fiat 131 Abarth, and the Porsche 911.
however, in 1979, FISA (Fédération Internationale du Sport Automobile, the sanctioning body for rallying) legalized all-wheel-drive for rallying. the manufacturers involved in rallying at the time considered four-wheel-drive too heavy and complex to be successful.
they were all proven wrong when Audi launched its new Quattro in 1980, and announced its intention to use the 1980 and 1981 seasons as development years. the full potential of four-wheel-drive was realized when Audi pilot Hannu Mikkola used a Quattro as a course opening vehicle for one rally. had Mikkola been entered, he would have won by nine minutes!
when the Quattro entered (and won) its first rally, the 1980 Janner rally in Austria, most of the other manufacturers in rallying realized the two-wheel-drive era of rallying had come to an end.
Audi continued its development during the 1981 season, winning several rounds of the WRC, including the San Remo rally, which was an historic event because it was the first ever international rally won by a woman, Michèle Mouton.
1982 firmly established Audi as the team to beat, although Mouton narrowly lost the driver's crown to Opel rival Walter Röhrl.
the 1983 season saw the creation of Groups A and B, and the first real Group B car arrived on the scene - the Lancia 037 Monte Carlo. Audi's first major rival had arrived.
the Group B rally supercars quickly evolved into 500+ horsepower, four-wheel-drive chest-thumping beasts with space frames, kevlar bodywork, and many other high-tech pieces.
the cars reached a point where many wondered if the drivers could not fully control them: for instance, the Lancia Delta S4 could accelerate from 0 to 100 km/h in 2.3 seconds on a gravel road. Henri Toivonen drove an S4 around Estoril, the Portuguese Grand Prix circuit, so quickly that he would have qualified sixth for the 1986 Portuguese Grand Prix.
Nigel Mansell sampled a Peugeot 205 T16 and said it could out-accelerate his F1 car. and, perhaps most impressive (frightening?), the driver's reaction times were cut in half compared with previous rally cars. the Group B rally cars and their pilots were the stuff of which legends are made.
(excerpt from stormloader.com)
rally cars before the Group B era were, for the most part, rear-wheel-drive with about 250 horsepower, because any more power merely resulted in wheelspin. the two classes at the time were Group 2 and the more popular Group 4. the rules for Group 4 mandated a minimum production run of 400 copies of a car to meet homologation requirements, in order to encourage the manufacturers to use mass-produced cars. some of the more famous rally cars from this period were the Lancia Stratos, the Fiat 131 Abarth, and the Porsche 911.
however, in 1979, FISA (Fédération Internationale du Sport Automobile, the sanctioning body for rallying) legalized all-wheel-drive for rallying. the manufacturers involved in rallying at the time considered four-wheel-drive too heavy and complex to be successful.
they were all proven wrong when Audi launched its new Quattro in 1980, and announced its intention to use the 1980 and 1981 seasons as development years. the full potential of four-wheel-drive was realized when Audi pilot Hannu Mikkola used a Quattro as a course opening vehicle for one rally. had Mikkola been entered, he would have won by nine minutes!
when the Quattro entered (and won) its first rally, the 1980 Janner rally in Austria, most of the other manufacturers in rallying realized the two-wheel-drive era of rallying had come to an end.
Audi continued its development during the 1981 season, winning several rounds of the WRC, including the San Remo rally, which was an historic event because it was the first ever international rally won by a woman, Michèle Mouton.
1982 firmly established Audi as the team to beat, although Mouton narrowly lost the driver's crown to Opel rival Walter Röhrl.
the 1983 season saw the creation of Groups A and B, and the first real Group B car arrived on the scene - the Lancia 037 Monte Carlo. Audi's first major rival had arrived.
the Group B rally supercars quickly evolved into 500+ horsepower, four-wheel-drive chest-thumping beasts with space frames, kevlar bodywork, and many other high-tech pieces.
the cars reached a point where many wondered if the drivers could not fully control them: for instance, the Lancia Delta S4 could accelerate from 0 to 100 km/h in 2.3 seconds on a gravel road. Henri Toivonen drove an S4 around Estoril, the Portuguese Grand Prix circuit, so quickly that he would have qualified sixth for the 1986 Portuguese Grand Prix.
Nigel Mansell sampled a Peugeot 205 T16 and said it could out-accelerate his F1 car. and, perhaps most impressive (frightening?), the driver's reaction times were cut in half compared with previous rally cars. the Group B rally cars and their pilots were the stuff of which legends are made.
(excerpt from stormloader.com)
07-28-2005, 11:28 PM
#65
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S12 Silvia
the oft-overlooked, but important S12:
the Nissan Silvia S12 was launched in Japan in the early 1980's. the car was manufactured from 1983 to 1989. the Silvia, outside of Japan, is called a "200sx" or "Gazelle." however, in the UK it was given the original name of Nissan Silvia.
generally, in the UK, the only version of the Silvia available was the hatchback, while elsewhere, was available in both hatchback and a coupe.
depending on port of entry, the following engines were available:
1.8 turbo non-intercooled, 8-valve (SOHC) CA18ET (UK)
2.0 non-turbo, 16-Valve (DOHC) FJ20E (UK -very rare)
3.0 V6 non-turbo VG30E (United States)
2.0 turbo-intercooled, 16-valve (DOHC) FJ20ET (Japan)
2.0 non-turbo, 8-valve (SOHC) CA20E
the FJ20ET turbo engine is the early forerunner of the SR20DET, and contains many of the same parts.
the Nissan Silvia S12 was launched in Japan in the early 1980's. the car was manufactured from 1983 to 1989. the Silvia, outside of Japan, is called a "200sx" or "Gazelle." however, in the UK it was given the original name of Nissan Silvia.
generally, in the UK, the only version of the Silvia available was the hatchback, while elsewhere, was available in both hatchback and a coupe.
depending on port of entry, the following engines were available:
1.8 turbo non-intercooled, 8-valve (SOHC) CA18ET (UK)
2.0 non-turbo, 16-Valve (DOHC) FJ20E (UK -very rare)
3.0 V6 non-turbo VG30E (United States)
2.0 turbo-intercooled, 16-valve (DOHC) FJ20ET (Japan)
2.0 non-turbo, 8-valve (SOHC) CA20E
the FJ20ET turbo engine is the early forerunner of the SR20DET, and contains many of the same parts.
Last edited by bonzelite; 07-29-2005 at 04:31 PM.
07-31-2005, 04:01 PM
#67
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ride height and Cd
drag is a function of the Cd (coefficient of drag) times the effective frontal area:
on a typical passenger car shape, with 300mm front body-to-ground clearance, adding a simple flat sheet airdam/spoiler shows that decreasing the body-to-ground gap, to 210mm, changed the front Cl (coefficient of lift) significantly: it also reduces overall Cd up to a point: spoiler depth of 90mm shows a Cd reduction of -.04 while Cl change is much larger at around -0.21.
this trend continues up to a point with Cd decreasing, then gradually flattening out again to "factory spec" (a fatter air dam will eventually grow large enough to create *more* drag, eventhough less drag-creating air passes under the car); with Cl improving more and more (less air under the car will effectively disrupt the body's tendency to lift off the ground). i say "up to a point" with these figures because multi-dimensional calculations begin to wander or "break down" as increasing variables (like weight, additional aero add-ons that may increase surface areas) begin to offset or negate other things:
indeed, many variables influence the overall performance of an automobile that has been lowered insofar as its aerodynamic properties. Cd can actually increase with lower ride heights because most vehicles carry non-optimized (uneven) underbodies: as the air tends to stall and break up under the car as it encounters abrupt hard edges and voids, more drag is created.
however, the *total frontal area* is decreased with the lower ride height (less tire surface area is exposed) --a slightly different condition than in the initial example, which is *frontal body-to-ground clearance only* being reduced by an air dam (seeing a slight increasing of frontal surface area).
so there is a trade-off:
a very "slippery" frontal area, lowered and with an upgraded fascia, can be effectively hindered provided the underside is sufficiently "dirty." in such cases, a lowered car will be a compromise between aesthetic enhancement v functionality, insofar as downforce. as well, a case can arise whereby frontal area is slippery enough, thus is sufficiently reduced, as to negate the dragging effects of underbody vortices.
overall handling, though, is often improved as the cars center of gravity is lowered, resulting in less body-roll through cornering. and less "overall drag" reduction can be attained through proper downforce design.
therefore, the focus is in creating "balance":
as the ride height decreases, there is less air that is being forced into the underside of the car, and/ or "venturi." therefore, when optimizing the underside, ie, "cleaning it up," is it is important for the venturi to have a narrower throat, so that the smaller amount of air is accelerated by a greater amount, which causes higher drag losses.
on a typical passenger car shape, with 300mm front body-to-ground clearance, adding a simple flat sheet airdam/spoiler shows that decreasing the body-to-ground gap, to 210mm, changed the front Cl (coefficient of lift) significantly: it also reduces overall Cd up to a point: spoiler depth of 90mm shows a Cd reduction of -.04 while Cl change is much larger at around -0.21.
this trend continues up to a point with Cd decreasing, then gradually flattening out again to "factory spec" (a fatter air dam will eventually grow large enough to create *more* drag, eventhough less drag-creating air passes under the car); with Cl improving more and more (less air under the car will effectively disrupt the body's tendency to lift off the ground). i say "up to a point" with these figures because multi-dimensional calculations begin to wander or "break down" as increasing variables (like weight, additional aero add-ons that may increase surface areas) begin to offset or negate other things:
indeed, many variables influence the overall performance of an automobile that has been lowered insofar as its aerodynamic properties. Cd can actually increase with lower ride heights because most vehicles carry non-optimized (uneven) underbodies: as the air tends to stall and break up under the car as it encounters abrupt hard edges and voids, more drag is created.
however, the *total frontal area* is decreased with the lower ride height (less tire surface area is exposed) --a slightly different condition than in the initial example, which is *frontal body-to-ground clearance only* being reduced by an air dam (seeing a slight increasing of frontal surface area).
so there is a trade-off:
a very "slippery" frontal area, lowered and with an upgraded fascia, can be effectively hindered provided the underside is sufficiently "dirty." in such cases, a lowered car will be a compromise between aesthetic enhancement v functionality, insofar as downforce. as well, a case can arise whereby frontal area is slippery enough, thus is sufficiently reduced, as to negate the dragging effects of underbody vortices.
overall handling, though, is often improved as the cars center of gravity is lowered, resulting in less body-roll through cornering. and less "overall drag" reduction can be attained through proper downforce design.
therefore, the focus is in creating "balance":
as the ride height decreases, there is less air that is being forced into the underside of the car, and/ or "venturi." therefore, when optimizing the underside, ie, "cleaning it up," is it is important for the venturi to have a narrower throat, so that the smaller amount of air is accelerated by a greater amount, which causes higher drag losses.
Last edited by bonzelite; 07-31-2005 at 04:04 PM.
07-31-2005, 07:16 PM
#68
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piston rings and the Slinky toy
america. the mid 1940's:
there are many legends about the emergence of the Slinky toy. a popular one is as follows:
someone ran a machine shop in Philadelphia making helical piston rings for small gas engines: within each engine cylinder, placed over the piston, are two or three springy helical coils of tape that bear against the cylinder wall. their expansion keeps the cylinder gas-tight, and the flat coil keeps lubricating oil away from the burning fuel.
the story goes that, after slicing off the tops of the steel helixes to make the rings, whoever ran the machine shop noticed the properties that now we all know. the identity of this "whoever" remains shrouded.
anyway, some time later, Richard James (a Penn-State mechanical engineering graduate working for Newport News Shipbuilding) got wind of the doctored piston rings, and marketed the concept.
eventually, the enterprising engineer founded James Industries Inc., Holidaysburg, Pa., now run by James's widow Betty. the company's flagship model is made of "cold-rolled spring steel," as divulged by a tight-lipped Mrs. James, fabricated from round wire rolled out at zero tension, flattened, and twisted into the helix. the company turns out 6000 Slinkys a day.
there are many legends about the emergence of the Slinky toy. a popular one is as follows:
someone ran a machine shop in Philadelphia making helical piston rings for small gas engines: within each engine cylinder, placed over the piston, are two or three springy helical coils of tape that bear against the cylinder wall. their expansion keeps the cylinder gas-tight, and the flat coil keeps lubricating oil away from the burning fuel.
the story goes that, after slicing off the tops of the steel helixes to make the rings, whoever ran the machine shop noticed the properties that now we all know. the identity of this "whoever" remains shrouded.
anyway, some time later, Richard James (a Penn-State mechanical engineering graduate working for Newport News Shipbuilding) got wind of the doctored piston rings, and marketed the concept.
eventually, the enterprising engineer founded James Industries Inc., Holidaysburg, Pa., now run by James's widow Betty. the company's flagship model is made of "cold-rolled spring steel," as divulged by a tight-lipped Mrs. James, fabricated from round wire rolled out at zero tension, flattened, and twisted into the helix. the company turns out 6000 Slinkys a day.
08-01-2005, 10:44 PM
#69
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heterodyning exhaust notes
on the street:
typical in wave physics, heterodyning (to combine [a radio-frequency wave] with a locally generated wave of different frequency, in order to produce a new frequency equal to the sum or difference of the two) occurs, at times, on the street between a close encounter of 2 loud exhaust notes.
speaking for myself (as well as others with modified exhaust systems), i have experienced the high-performance sound of deep exhausts (often my own with another) "fighting" each other when in close proximity. this is due to each exhausts' similar, but different, wave frequency overlapping the other, heterodyning, creating an out-of-phase, new "third" waveform.
often, this is painful to the ear, as the human eardrum is incapable of "finding" the proper resonance with the "new" wave thus created, resulting in painful distortion. the effect is exaggerated if the exhausts are exceptioinally loud.
a good remedy to this is to raise the window (as the phenomenon typically happens when the windows are down), slow down (changes the engine's rpm, thus, frequency; allows the other vehicle to pull away), or change gears (chages rpms and frequency).
sometimes, i have found it a challenge to endure the discomfort of the composite "wall of sound" and attempt to "match," as close as possible, the other exhaust's frequency to that of my car --and have found approximate heterodyned success on occasion.
i say "approximate" because i may not be able to completely match the other, but can get close enough to nearly match the other exhaust's note, thus nearly cancelling out the heterodyne effect.
typical in wave physics, heterodyning (to combine [a radio-frequency wave] with a locally generated wave of different frequency, in order to produce a new frequency equal to the sum or difference of the two) occurs, at times, on the street between a close encounter of 2 loud exhaust notes.
speaking for myself (as well as others with modified exhaust systems), i have experienced the high-performance sound of deep exhausts (often my own with another) "fighting" each other when in close proximity. this is due to each exhausts' similar, but different, wave frequency overlapping the other, heterodyning, creating an out-of-phase, new "third" waveform.
often, this is painful to the ear, as the human eardrum is incapable of "finding" the proper resonance with the "new" wave thus created, resulting in painful distortion. the effect is exaggerated if the exhausts are exceptioinally loud.
a good remedy to this is to raise the window (as the phenomenon typically happens when the windows are down), slow down (changes the engine's rpm, thus, frequency; allows the other vehicle to pull away), or change gears (chages rpms and frequency).
sometimes, i have found it a challenge to endure the discomfort of the composite "wall of sound" and attempt to "match," as close as possible, the other exhaust's frequency to that of my car --and have found approximate heterodyned success on occasion.
i say "approximate" because i may not be able to completely match the other, but can get close enough to nearly match the other exhaust's note, thus nearly cancelling out the heterodyne effect.
08-02-2005, 08:40 PM
#70
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scale models for industry use
the wind tunnel:
it is quite common for industrial wind tunnel models to be made in 1:5 scale, ie, approximately 3m long, for use in full-scale wind tunnels. a 1:2 scale tunnel may be used if the length is proportionately longer.
for stylistic purposes, the 1:5 scale model is also used, but, as well, full 1:1 scale models are used, as 1:1 exterior parts may be utilized from prior year models, ie, actual cars, saving time and expense (for example, a door handle assembly design may be used for six or seven years, allowing the modelers to simply scavenge these pre-existing parts).
it is quite common for industrial wind tunnel models to be made in 1:5 scale, ie, approximately 3m long, for use in full-scale wind tunnels. a 1:2 scale tunnel may be used if the length is proportionately longer.
for stylistic purposes, the 1:5 scale model is also used, but, as well, full 1:1 scale models are used, as 1:1 exterior parts may be utilized from prior year models, ie, actual cars, saving time and expense (for example, a door handle assembly design may be used for six or seven years, allowing the modelers to simply scavenge these pre-existing parts).