Twins....new slant?
07-15-2005, 10:46 PM
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Twins....new slant?
okay, so why does the big charger have to be the secondary? Why couldn't the two be swapped.
I would think the cold side flow characteristics wouldn't change.....you're still either pushing or pulling throught the little one. Does it make a difference which is taking place? And if the little one was spooling earlier than the big one, wouldn't the increased supply and pressure to the big one's intake help to get it spooled just a little quicker?
On the hot side, wouldn't the big charger benefit from the hottest and highest flowing exhaust gasses straight out of the manifold? This could then be dumped into the little one.....ext wg'ed and on out the end.
Just a thought...someone enlighten me as to why we are stuck on the bottom secondary charger theory.....
Thanks
Chris
I would think the cold side flow characteristics wouldn't change.....you're still either pushing or pulling throught the little one. Does it make a difference which is taking place? And if the little one was spooling earlier than the big one, wouldn't the increased supply and pressure to the big one's intake help to get it spooled just a little quicker?
On the hot side, wouldn't the big charger benefit from the hottest and highest flowing exhaust gasses straight out of the manifold? This could then be dumped into the little one.....ext wg'ed and on out the end.
Just a thought...someone enlighten me as to why we are stuck on the bottom secondary charger theory.....
Thanks
Chris
07-15-2005, 11:39 PM
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If you switch the turbos around, wouldn't the big charger be trying to suck more air than the little one can supply?? You simply have to have the chargers arranged the way they are to get any kind of performance.
The proper way of thinking of twins is that you are turbocharging a turbocharger. Remember that the purpose of compounds is to force-feed the small turbo. You can't build up pressure against a large turbo using a smaller one, because it MUST have more airflow to do so. Thus, you have to use the larger turbo to build up pressure against the smaller one.
justin
The proper way of thinking of twins is that you are turbocharging a turbocharger. Remember that the purpose of compounds is to force-feed the small turbo. You can't build up pressure against a large turbo using a smaller one, because it MUST have more airflow to do so. Thus, you have to use the larger turbo to build up pressure against the smaller one.
justin
07-15-2005, 11:42 PM
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You'd have a heck of a time Lighting of
The big charger from idle,once the big charger did light which it won't cause you've restricted the exhaust flow with the smaller housing.Your EGTS would be through the roof.You've also restricted the big chargers air flow by flowing all its air through the small charger.The small charger is primary cause it is the work horse.The small charger spools of idle quickly and brings the big charger up to speed.The big charger only starts to work at the top end.
07-16-2005, 12:08 AM
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First off we need to clarify some things, and I have said this numerous times on here: On a compounded turbo setup (what most people on here call twins, technically its not accurate to call them twins) you have four components: a primary compressor, a secondary compressor, a primary turbine and a secondary turbine.
For AIRFLOW: Normal flow path is out of air filter into primary compressor (large compressor), out of primary compressor into secondary compressor (small compressor) out of secondary compressor and into aftercooler (and yes technically its an aftercooler, not intercooler) , then into intake manifold.
For EXHAUST FLOW: Normal flow path is out of the manifold, into the primary turbine (small turbine), out of the primary turbine and into the secondary turbine (large turbine).
Now here is where the constant confusion on here comes from: THE PRIMARY COMPRESSOR IS DRIVEN BY THE SECONDARY TURBINE.... and the SECONARY COMPRESSOR IS DRIVEN BY THE PRIMARY TURBINE.......
So as for what you are going to call the whole turbo it all depends on whether you call the turbo by its compressor function or its turbine function... Most guys call it by the compressor section, so most of the time on here, the "primary turbo", is the large turbo that gets its air from the air filter. Also allot of times we say 'top turbo' and 'bottom turbo' and that is a result of how they are usually mounted in the truck. The 'Top turbo' is the secondary compressor and the primary turbine; the bottom turbo is the primary compressor and secondary turbine. The top turbo is the small one, like an HX35 and its mounted directly onto the exhaust manifold, the bottom turbo is the big one like an HT3B and gets the exhaust from the top turbo.
Now, as for your question, if I assume you are asking why can’t the primary compressor (big one) be driven by the primary turbine.... effectively, route the exhaust directly into the big turbo first, then into the little turbo.... The answer to that is simple: it would work terribly, if at all. And here is why.... the turbines are EXPANDING and COOLING the exhaust gasses, that is how they deliver power to the compressor. The exhaust leaves the manifold at high pressure and temperature, you pass the exhaust first through the smaller turbine where it is partially expanded and cooled. So when exiting the turbine housing, the exhaust now occupies a much larger volume for a given mass, so next it enters the large turbine which has a much larger open area (housing size) where the additional volume can continue to expand until it reaches atmospheric pressure and leaves out the downpine as a much larger volume and cooler yet. If you reversed the process like you say, you would have massive expansion occurring in the large turbine first, then no additional expansion, in fact probably re-compression in the small turbine.. Completely opposite what you are trying to accomplish.
Likewise the compressor sections are sized as such because just the opposite is happening to the air..... A large volume is first compressed in the primary compressor, exiting with less volume for a given mass flow, so now this lower volume enters the smaller compressor where it gets compressed once more, entering the aftercooler as a much smaller volume yet for a given mass....
There is tremendous misunderstanding about this matter.. Its not about "one spools first, then the other'' or "one pulls and the other pushes", or "ones for off the line and the other is at high RPM"..... no, no, no, no, no, no (did I say NO??) Its compounded compressors and compounded turbines, that’s it. When their sized right both work ALL the time and TOGETHER and in relatively EQUAL PROPORTIONS when at least moderate boost is being built. At extremely light loads, like while cruising, one turbo may be doing a bit more than the other, but mash the pedal, put the fuel to it and if their sized right, BOTH light, and work in perfect unison to deliver boost at cooler conditions and at much higher pressure ratios than is possible with ANY single and while extracting more energy from the exhaust than ANY single could. And don’t forget that last part, because the entire function of a turbo is as a heat recovery device.
The concept, was not invented by a hot rodder or a sled puller by the way, this stuff has been done in industry for a century. Do a little reading on compounded air or natrual gas compressors to understand the compounded compressor part, and some reading on steam turbines to understand the compounded turbine part.
KP
For AIRFLOW: Normal flow path is out of air filter into primary compressor (large compressor), out of primary compressor into secondary compressor (small compressor) out of secondary compressor and into aftercooler (and yes technically its an aftercooler, not intercooler) , then into intake manifold.
For EXHAUST FLOW: Normal flow path is out of the manifold, into the primary turbine (small turbine), out of the primary turbine and into the secondary turbine (large turbine).
Now here is where the constant confusion on here comes from: THE PRIMARY COMPRESSOR IS DRIVEN BY THE SECONDARY TURBINE.... and the SECONARY COMPRESSOR IS DRIVEN BY THE PRIMARY TURBINE.......
So as for what you are going to call the whole turbo it all depends on whether you call the turbo by its compressor function or its turbine function... Most guys call it by the compressor section, so most of the time on here, the "primary turbo", is the large turbo that gets its air from the air filter. Also allot of times we say 'top turbo' and 'bottom turbo' and that is a result of how they are usually mounted in the truck. The 'Top turbo' is the secondary compressor and the primary turbine; the bottom turbo is the primary compressor and secondary turbine. The top turbo is the small one, like an HX35 and its mounted directly onto the exhaust manifold, the bottom turbo is the big one like an HT3B and gets the exhaust from the top turbo.
Now, as for your question, if I assume you are asking why can’t the primary compressor (big one) be driven by the primary turbine.... effectively, route the exhaust directly into the big turbo first, then into the little turbo.... The answer to that is simple: it would work terribly, if at all. And here is why.... the turbines are EXPANDING and COOLING the exhaust gasses, that is how they deliver power to the compressor. The exhaust leaves the manifold at high pressure and temperature, you pass the exhaust first through the smaller turbine where it is partially expanded and cooled. So when exiting the turbine housing, the exhaust now occupies a much larger volume for a given mass, so next it enters the large turbine which has a much larger open area (housing size) where the additional volume can continue to expand until it reaches atmospheric pressure and leaves out the downpine as a much larger volume and cooler yet. If you reversed the process like you say, you would have massive expansion occurring in the large turbine first, then no additional expansion, in fact probably re-compression in the small turbine.. Completely opposite what you are trying to accomplish.
Likewise the compressor sections are sized as such because just the opposite is happening to the air..... A large volume is first compressed in the primary compressor, exiting with less volume for a given mass flow, so now this lower volume enters the smaller compressor where it gets compressed once more, entering the aftercooler as a much smaller volume yet for a given mass....
There is tremendous misunderstanding about this matter.. Its not about "one spools first, then the other'' or "one pulls and the other pushes", or "ones for off the line and the other is at high RPM"..... no, no, no, no, no, no (did I say NO??) Its compounded compressors and compounded turbines, that’s it. When their sized right both work ALL the time and TOGETHER and in relatively EQUAL PROPORTIONS when at least moderate boost is being built. At extremely light loads, like while cruising, one turbo may be doing a bit more than the other, but mash the pedal, put the fuel to it and if their sized right, BOTH light, and work in perfect unison to deliver boost at cooler conditions and at much higher pressure ratios than is possible with ANY single and while extracting more energy from the exhaust than ANY single could. And don’t forget that last part, because the entire function of a turbo is as a heat recovery device.
The concept, was not invented by a hot rodder or a sled puller by the way, this stuff has been done in industry for a century. Do a little reading on compounded air or natrual gas compressors to understand the compounded compressor part, and some reading on steam turbines to understand the compounded turbine part.
KP
07-16-2005, 03:09 AM
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Thanks Kevin......crystal clear now. I knew there was a good reason, just had to understand what it was. When I was playing around with maps from a T46....remember the thread?....all the holset guys said the thing would grenade at 50 psi......I said no worries, I don't need 50 out of it. The top turbo will be making ~ 20-25, therefor for a 50 psi set, I only need an additional 25 of clean, cool air. I always knew they worked together, and unlike on and off "staged" compression, but was unclear on why they were arranged the way they were. Thanks for clearing it up.
Chris
PS Kev.....yes, the '51 will be getting a healthy dose of a much wilder set of compounds
.....hence the reason for this post to begin with.......
Chris
PS Kev.....yes, the '51 will be getting a healthy dose of a much wilder set of compounds
.....hence the reason for this post to begin with.......
07-16-2005, 02:44 PM
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My concept
Simple but im clueless still bout twins.. I STILL DONT GET IT... But the large one has to be on the bottom, simply because if the large one is on top it naturally makes less rpms than the smaller turbo, now if you try and force too much air into the second one, ur impeller wheels will go kapoot..... NOw if the larger one is on the bottom, then just the inverse happens, u can spool the heck outta the small one on the top, feed that compressed air to the bottom one, and have less a chance of not hurting anything, plus u build boost with boost which gives u even more boost!
I think im learnin... bear with me
Tx
Simple but im clueless still bout twins.. I STILL DONT GET IT... But the large one has to be on the bottom, simply because if the large one is on top it naturally makes less rpms than the smaller turbo, now if you try and force too much air into the second one, ur impeller wheels will go kapoot..... NOw if the larger one is on the bottom, then just the inverse happens, u can spool the heck outta the small one on the top, feed that compressed air to the bottom one, and have less a chance of not hurting anything, plus u build boost with boost which gives u even more boost!
I think im learnin... bear with me
Tx
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07-16-2005, 02:52 PM
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close, but you're not feeding the bottom turbo w/ the top, you're feeding the top (smaller) w/ the bottom (larger)
and the smaller turbo takes the pressurized air from the larger turbo and pressurizes it furthur...
Forrest
and the smaller turbo takes the pressurized air from the larger turbo and pressurizes it furthur...
Forrest
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