A peek into the Heart of Darkness...
01-27-2005, 08:26 AM
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A peek into the Heart of Darkness...
<center><img src="http://www.geocities.com/cburkard2001/TurboClose-up.jpg"></center><p>More pics and discussion on Vortex at the link, below.
Question about turbos that I raised on Vortex (no answers, yet)...
Someone commented that the turbos on the V10 TDI were "small." I'm really clueless about that...so I had a question.
I thought I read somewhere that it was better to have more, smaller turbos because with less mass, they would spin up much faster than a larger turbo, thus providing more boost, sooner (i.e. less "turbo lag").
What is the advantage of a larger turbo? More boost for a given RPM than the smaller turbo?<ul><li><a href="http://forums.vwvortex.com/zerothread?id=1799171">Vortex thread showing V10 TDI engine (new tranny)</a></li></ul>
Question about turbos that I raised on Vortex (no answers, yet)...
Someone commented that the turbos on the V10 TDI were "small." I'm really clueless about that...so I had a question.
I thought I read somewhere that it was better to have more, smaller turbos because with less mass, they would spin up much faster than a larger turbo, thus providing more boost, sooner (i.e. less "turbo lag").
What is the advantage of a larger turbo? More boost for a given RPM than the smaller turbo?<ul><li><a href="http://forums.vwvortex.com/zerothread?id=1799171">Vortex thread showing V10 TDI engine (new tranny)</a></li></ul>
01-27-2005, 11:11 AM
#3
A larger turbo will still produce the same boost pressure, but will have a greater volume of air...
flowing at that time. More O2 means more fuel which means more power for a give combustion cycle. However, that may come with slow moving air. Smaller turbo's get the air moving in and out quicker (torque).
The principle behind the variable intake on TDI turbochargers is the fact that it can adjust Air velocity as well as air volume entering the turbo compressor housing.
Think about when you are filling up your bucket with a hose to wash your car. The water itself is comming out at the same pressure no matter what. Some people like to put their thumb over the end of the hose because it seems like it comes out faster, and will fill the bucket faster. Others just drop the hose in and let it fill up on its own.
Putting your thumb on the hose makes it spray out really fast, but you arent getting as much water through the stream. You will end up with the same amount of water because it sprays faster with less water. However, leaving the hose in the bucket will flow a greater volume in a given amount of time.
The principle behind the variable intake on TDI turbochargers is the fact that it can adjust Air velocity as well as air volume entering the turbo compressor housing.
Think about when you are filling up your bucket with a hose to wash your car. The water itself is comming out at the same pressure no matter what. Some people like to put their thumb over the end of the hose because it seems like it comes out faster, and will fill the bucket faster. Others just drop the hose in and let it fill up on its own.
Putting your thumb on the hose makes it spray out really fast, but you arent getting as much water through the stream. You will end up with the same amount of water because it sprays faster with less water. However, leaving the hose in the bucket will flow a greater volume in a given amount of time.
01-27-2005, 11:48 AM
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That makes sense...
So the larger turbo will have the same pressure as a smaller turbo (say 16-18 psi), but larger turbo will have more air volume. I guess it would also be true that the larger turbo might take a bit longer than the smaller turbo to generate the maximum boost because it's larger. At least for a given exhaust gas pressure.
I guess that would mean that a larger turbo would be preferred for large displacement engines or high-revving engines where the volume of intake air is large.
One of the respondents on Vortex (Drivebiwire - generally quite knowledgable) went into some interesting detail about the "little" turbos on V10 TDI. I'll reproduce it here...
"Those "Little Turbos" will pop the heads off a 1.8T and bend rods. Boost pressure on a these motors is in the area of about 16-18psi of sustained boost.
"Increasing boost pressure on a diesel DOES NOT increase power instead it increases backpressure, lowers air density and reduces power the higher pressures heat soak the intercoolers and cause the compressed air temps to rise thus increasing TIT's and causing the ECU to reduce power further. Boost pressure in a diesel is simply a means of providing more air to bond with the fuel to reduce smoke output. Fuel air ratios are variable 100:1 at idle and as rich as 35:1 under full load ratios can be anywhere within that range at any given time depening on load on the motor. Increasing boost pressure further simply adds air that cannot be utilized.
"The way you increase power on these motors is to increase fueling and leave the boost pressures alone. The VNT turbos are already at the limits of what the engine can take in. If you look at the V10 tuning you will find that the tuners leave the boost pressures alone and increase the fueling to the point of smoking. This alone leads to a large increase in power.
"Obviously just increasing the fueling does lead to higher TIT's but the V10 pistons take this into account by adding additional cooling channels for oil cooling within the piston domes..."
I guess that would mean that a larger turbo would be preferred for large displacement engines or high-revving engines where the volume of intake air is large.
One of the respondents on Vortex (Drivebiwire - generally quite knowledgable) went into some interesting detail about the "little" turbos on V10 TDI. I'll reproduce it here...
"Those "Little Turbos" will pop the heads off a 1.8T and bend rods. Boost pressure on a these motors is in the area of about 16-18psi of sustained boost.
"Increasing boost pressure on a diesel DOES NOT increase power instead it increases backpressure, lowers air density and reduces power the higher pressures heat soak the intercoolers and cause the compressed air temps to rise thus increasing TIT's and causing the ECU to reduce power further. Boost pressure in a diesel is simply a means of providing more air to bond with the fuel to reduce smoke output. Fuel air ratios are variable 100:1 at idle and as rich as 35:1 under full load ratios can be anywhere within that range at any given time depening on load on the motor. Increasing boost pressure further simply adds air that cannot be utilized.
"The way you increase power on these motors is to increase fueling and leave the boost pressures alone. The VNT turbos are already at the limits of what the engine can take in. If you look at the V10 tuning you will find that the tuners leave the boost pressures alone and increase the fueling to the point of smoking. This alone leads to a large increase in power.
"Obviously just increasing the fueling does lead to higher TIT's but the V10 pistons take this into account by adding additional cooling channels for oil cooling within the piston domes..."
01-27-2005, 01:12 PM
#5
Yea that is where the variable intake comes into play...
at lower RPM's, it has a smaller diameter intake apeture, increasing velocity thereby increasing torque. At higher RPM's, it opens the apeture up wide, lowering the velocity while increasing the volume, thereby increasing the HP.
This is the same principle that has been used on many Naturally aspirated motors with dual intake runners. Japanese V8 (justin)'s V8 SHO has this same process for it's intake. I'm sure if he reads this, he will add his 7 cents...
This is the same principle that has been used on many Naturally aspirated motors with dual intake runners. Japanese V8 (justin)'s V8 SHO has this same process for it's intake. I'm sure if he reads this, he will add his 7 cents...
01-27-2005, 02:37 PM
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Variable intake?
<center><img src="http://home.cfl.rr.com/leebo0456/27019turbo_jpg.gif"></center><p>
...not sure what that is. But if I understand correctly, this is a way to control the speed/volume of the air flowing past the boost stage of the turbo?
What role for the "variable vanes" on the turbo? I guess this helps to control boost pressures without a "waste gate?"
Clearly I need to do some more reading to understand this. I think I'll stop asking questions (thank goodness - right?). Is there a recommended resource that I could read?
...not sure what that is. But if I understand correctly, this is a way to control the speed/volume of the air flowing past the boost stage of the turbo?
What role for the "variable vanes" on the turbo? I guess this helps to control boost pressures without a "waste gate?"
Clearly I need to do some more reading to understand this. I think I'll stop asking questions (thank goodness - right?). Is there a recommended resource that I could read?
01-27-2005, 03:54 PM
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Variable vane geometry. Similar to pitch control on a propeller driven airplane.
This is why I hate the VW diesels. You guys get the latest technology Garret turbos with manifolds that will accept a variety of top notch turbos and we get the 20 year old, non interchangeable KKK turbos.
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01-27-2005, 06:11 PM
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Don't hate they player....hate the turbo game my VW brutha!!!
;-)
Interesting subsequent post by Drivebiwire about turbos in diesels. Their main purpose is to...gotta love love this...reduce smoke.
Again, quoting...
"Yes the turbos simply reduce smoke.
"Diesel make power by injecting fuel directly into the cylinder. Fuel is not carried into the cylinder by the air as in a gasoline engines.
"If you over fuel a diesel you will make power but the engine begins to smoke and exhaust temperatures rise more than likely beyond the limits of the metals used in the pistons and block. Adding a turbo increases the available air that the high pressure fuel can mix with. This in turn leans out the combustion reducing temperatures and reduces smoke. Since the turbo increases the available air for combustion this to an extent allows for a slight increase in fueling upto the smoke maps limit where smoke occurs.
"The primary reason in a diesel for a turbo is simply smoke control when making higher engine output. Most diesels in a steady condition do not rely on much boost at all because of the unregulated amount of air that can enter the cylinders. Only under high loads or hard acceleration do the turbos supply high boost pressure/volume. Again this reduces the likelyhood of smoking under load.
"If you want to think of it another way, a turbo simply increases the fueling that can be injected to the motor.
"If you want to increase TDI output all you have to do is increase fueling...up to a point that smoke and temperatures approach limits. You can increase boost but this will not change the dynamics of the combustion process due to the design of the piston bowl and dome swirl characteristics. The fuel is still limited in terms of how quickly it can bond with oxygen and spontatiously ignite. Even if you have higher boost pressures this has little effect on the fixed dynamics of combustion in the cylinder. Increasing boost for the most part will lead to increased backpressure or surging due to the engines inability to take in any more air volume. Again diesels are designed to ingest the maximum amount of air under all conditions, increasing boost pressures more than likely will cause the turbo to operate in surge, translated the engine simply can't take in any more air than what is already being rammed in.
"Overfueling for the most part is the easiest and safest way to increase power. Increasing Cetane, reducing sulfur and fuel particulates further reduces soot formation when pushing the limits of smoking and temperatures. Advancing the injection timing also aids in reducing combustion temperatures while giving the fuel more time to completely burn during the combustion event(s).
"Grant it there are more complex issues involved but simply put a turbo on a diesel simply reduces smoke output."
Interesting subsequent post by Drivebiwire about turbos in diesels. Their main purpose is to...gotta love love this...reduce smoke.
Again, quoting...
"Yes the turbos simply reduce smoke.
"Diesel make power by injecting fuel directly into the cylinder. Fuel is not carried into the cylinder by the air as in a gasoline engines.
"If you over fuel a diesel you will make power but the engine begins to smoke and exhaust temperatures rise more than likely beyond the limits of the metals used in the pistons and block. Adding a turbo increases the available air that the high pressure fuel can mix with. This in turn leans out the combustion reducing temperatures and reduces smoke. Since the turbo increases the available air for combustion this to an extent allows for a slight increase in fueling upto the smoke maps limit where smoke occurs.
"The primary reason in a diesel for a turbo is simply smoke control when making higher engine output. Most diesels in a steady condition do not rely on much boost at all because of the unregulated amount of air that can enter the cylinders. Only under high loads or hard acceleration do the turbos supply high boost pressure/volume. Again this reduces the likelyhood of smoking under load.
"If you want to think of it another way, a turbo simply increases the fueling that can be injected to the motor.
"If you want to increase TDI output all you have to do is increase fueling...up to a point that smoke and temperatures approach limits. You can increase boost but this will not change the dynamics of the combustion process due to the design of the piston bowl and dome swirl characteristics. The fuel is still limited in terms of how quickly it can bond with oxygen and spontatiously ignite. Even if you have higher boost pressures this has little effect on the fixed dynamics of combustion in the cylinder. Increasing boost for the most part will lead to increased backpressure or surging due to the engines inability to take in any more air volume. Again diesels are designed to ingest the maximum amount of air under all conditions, increasing boost pressures more than likely will cause the turbo to operate in surge, translated the engine simply can't take in any more air than what is already being rammed in.
"Overfueling for the most part is the easiest and safest way to increase power. Increasing Cetane, reducing sulfur and fuel particulates further reduces soot formation when pushing the limits of smoking and temperatures. Advancing the injection timing also aids in reducing combustion temperatures while giving the fuel more time to completely burn during the combustion event(s).
"Grant it there are more complex issues involved but simply put a turbo on a diesel simply reduces smoke output."
01-27-2005, 06:50 PM
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I thought variable vane turbo configurations...
...were designed to more precisely control the amount of exhaust gas driving the impeller, thus optimizing the amount of boost provided.
Perhaps they also control the aperture size as well?
Perhaps they also control the aperture size as well?