what is a/r?
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RE: what is a/r? - 4/9/2007 4:45:38 AM
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5Tizzle
Posts: 1387
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nvm, i found what i needed...
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1973 Datsun 510
quote:
ORIGINAL: Sebba
Thats like trying to stop a train with a BB gun... some things just dont happen...
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RE: what is a/r? - 4/9/2007 4:52:10 AM
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5Tizzle
Posts: 1387
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well its actually more of a laymens terms description that doesnt include the literal 2 word meaning of the acronym....anybody know them?
_____________________________
1973 Datsun 510
quote:
ORIGINAL: Sebba
Thats like trying to stop a train with a BB gun... some things just dont happen...
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RE: what is a/r? - 4/9/2007 8:02:26 AM
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TheEngineer
Posts: 10595
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This is a really quick description of what A/R is which of course means Area/Radius if you found it. Now the a/r is something that describes the size of a housing, whether it be the compressor or the turbine.
The dimension that it defines it the cross-sectional area of the inlet/outlet over the radial distance from the center of the wheel (shaft) to the center of the inlet/outlet.
_____________________________
quote:
ORIGINAL: pilsenblue
Even tho My car looks great It will never be fast. Kinda like a hot girl that dosent give it up
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RE: what is a/r? - 4/9/2007 8:15:07 AM
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Dusty Eclipse
Posts: 4371
Joined: 2/23/2007
From: 11746,21114,34669,34668
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You see? And thats why you are the Engineer, huh?
_____________________________
Current cars: (What I havent wrecked)
1995 Eagle Talon TSi "Jackie" (SOLD) :(
2001 Mitsu. Eclipse GT "Dusty"
2000 Volvo V70R AWD "Mindy"
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RE: what is a/r? - 4/9/2007 8:18:08 AM
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silvercoupe97
Posts: 3265
Joined: 11/10/2006
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quote:
The Turbine Housings
The exhaust and compressor housings on turbo chargers use a "scroll" design. For example, the exhaust housing's scroll is where the exhaust gasses enter the housing and are directed at the turbine. It's basically a smooth, tubular chamber that surrounds the turbine with a slot all the way around that acts as a nozzle to direct the exhaust gasses at the turbine. It's called a scroll because it slowly gets smaller in diameter as a goes around the turbine. This pressurizes the gasses, forcing them out of the slot/nozzle at a fast rate. In turbo-terms, the scroll is measured by the cross-sectional area of the scroll's "tube" (A) and the distance from the center of the "tube" to the turbine shaft (R). The values by themselves are not meaningful to the user and for the most part, R does not change much for different housings, but by dividing R into A, you get the A/R ratio. So, the A/R ratio of the exhaust housing refers to the size and shape of the scroll that is cast into the housing. It basically determines how restrictive the housing will be, versus how quickly the turbine will spin up. A lower A/R ratio (smaller scroll area, A) results in a more restrictive housing. This restriction speeds up the exhaust gasses and increases the amount that the gasses will expand. It's the speed and expansion of the gasses that causes the turbine to spin. So with a low A/R ratio, the turbine will spin up quicker, but as engine output and rpms increase, the restriction of the housing begins to build up too much back pressure on the engine, which reduces performance. A good rule of thumb for when there is too much back pressure is when the pressure in the exhaust manifold is more the half of the pressure in the cylinder. So basically, a larger A/R ratio will improve your engine's top end, while losing some mid range power and increasing turbo lag. A smaller A/R ratio will help the bottom and mid-range, but may effect the top end. On the compressor side, the housing also features a scroll design, but it has the opposite function. The air leaving the compressor turbine has a lot of speed, but not much pressure. The scroll on the compressor housing starts small and gets larger as it approaches the compressor outlet. This collects the air and builds up air pressure. So, the compressor housing is designed to convert the speed-energy of the air coming off of the compressor turbine into pressure-energy, which is much more useful to an engine.
< Message edited by silvercoupe97 -- 4/9/2007 8:19:46 AM >
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Thanks,
John
6 bolt/2g head,1G rods/2G pistons,FPBig28,MBC,Forge 1G DV,alky inj,AFPR,255lph,780cc, 3" turboback,Centerforce,4 spider,FMIC, Prosport Boost&EGT gauges,AEM wideband,DSMlink, AGX/Skunk2
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RE: what is a/r? - 4/9/2007 8:22:52 AM
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TheEngineer
Posts: 10595
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^^^or alittle more advanced answer 
I was trying to keep it simple 
_____________________________
quote:
ORIGINAL: pilsenblue
Even tho My car looks great It will never be fast. Kinda like a hot girl that dosent give it up
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RE: what is a/r? - 4/9/2007 8:24:31 AM
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Dusty Eclipse
Posts: 4371
Joined: 2/23/2007
From: 11746,21114,34669,34668
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Yea, thanks Silver... its 8 sumthin am... and now my brain can hurt all day , lol...
_____________________________
Current cars: (What I havent wrecked)
1995 Eagle Talon TSi "Jackie" (SOLD) :(
2001 Mitsu. Eclipse GT "Dusty"
2000 Volvo V70R AWD "Mindy"
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RE: what is a/r? - 4/9/2007 10:22:32 AM
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silvercoupe97
Posts: 3265
Joined: 11/10/2006
Status: online
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Lol, my bad guys. I didn't see your post until after I posted TE, lol.
I'm on "mainland" Eastern times at the moment and my cups of coffee got me to that post, lol.
TE's is in layman's terms and is easier to remember though. Good visual btw. Sorry again guys, but now y'all know how I think 24/7, lol.
It's tough for me to think in laymen's terms at times, just ask my DSM buddies, who, after talking shop with me seem to always tilt their heads to one side like a dog who doesn't understand their owners, lol. I just can't help it sometimes
< Message edited by silvercoupe97 -- 4/9/2007 10:23:38 AM >
_____________________________
Thanks,
John
6 bolt/2g head,1G rods/2G pistons,FPBig28,MBC,Forge 1G DV,alky inj,AFPR,255lph,780cc, 3" turboback,Centerforce,4 spider,FMIC, Prosport Boost&EGT gauges,AEM wideband,DSMlink, AGX/Skunk2
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RE: what is a/r? - 4/9/2007 11:51:52 PM
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5Tizzle
Posts: 1387
Joined: 1/28/2006
Status: offline
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quote:
ORIGINAL: silvercoupe97
quote:
The Turbine Housings
The exhaust and compressor housings on turbo chargers use a "scroll" design. For example, the exhaust housing's scroll is where the exhaust gasses enter the housing and are directed at the turbine. It's basically a smooth, tubular chamber that surrounds the turbine with a slot all the way around that acts as a nozzle to direct the exhaust gasses at the turbine. It's called a scroll because it slowly gets smaller in diameter as a goes around the turbine. This pressurizes the gasses, forcing them out of the slot/nozzle at a fast rate. In turbo-terms, the scroll is measured by the cross-sectional area of the scroll's "tube" (A) and the distance from the center of the "tube" to the turbine shaft (R). The values by themselves are not meaningful to the user and for the most part, R does not change much for different housings, but by dividing R into A, you get the A/R ratio. So, the A/R ratio of the exhaust housing refers to the size and shape of the scroll that is cast into the housing. It basically determines how restrictive the housing will be, versus how quickly the turbine will spin up. A lower A/R ratio (smaller scroll area, A) results in a more restrictive housing. This restriction speeds up the exhaust gasses and increases the amount that the gasses will expand. It's the speed and expansion of the gasses that causes the turbine to spin. So with a low A/R ratio, the turbine will spin up quicker, but as engine output and rpms increase, the restriction of the housing begins to build up too much back pressure on the engine, which reduces performance. A good rule of thumb for when there is too much back pressure is when the pressure in the exhaust manifold is more the half of the pressure in the cylinder. So basically, a larger A/R ratio will improve your engine's top end, while losing some mid range power and increasing turbo lag. A smaller A/R ratio will help the bottom and mid-range, but may effect the top end. On the compressor side, the housing also features a scroll design, but it has the opposite function. The air leaving the compressor turbine has a lot of speed, but not much pressure. The scroll on the compressor housing starts small and gets larger as it approaches the compressor outlet. This collects the air and builds up air pressure. So, the compressor housing is designed to convert the speed-energy of the air coming off of the compressor turbine into pressure-energy, which is much more useful to an engine.
Thats actually the first thing i found
_____________________________
1973 Datsun 510
quote:
ORIGINAL: Sebba
Thats like trying to stop a train with a BB gun... some things just dont happen...
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