Would this sequential twin turbo setup work (theoretically)?
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From: Fort Worth, TX, USA
Re: Would this sequential twin turbo setup work (k24em2)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by k24em2 »</TD></TR><TR><TD CLASS="quote">There was a dodge cummins diesel in an older off road magazine (I think) that had a compounded turbo setup and was running something like 150psi and made 3500ft/lb of torque or some ridiculous number like that.</TD></TR></TABLE>
That is more than my application calls for
That is more than my application calls for
Joined: Oct 2003
Posts: 17
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From: buffalo, ny, usa
ok. I've done the math on this exact concept that seems to be evolving here. And the results all point to the same thing.
The conpound two-stage turbocharging (one feeding the other) is only usable when youre looking for boost beyond that of what a normal single turbo can produce. (Ie: if youre looking for near or over 3.0 pressure ratios of boost or 45psi.....then this is your answer.) you can no longer look for additional boost on top of boost from the first turbo. you have to think in pressure ratios now and then convert it after everythign is all said and done in the end. you have to think about the heat generated from boosting with the first turbo acting on the second turbo. So....
Here is how it works.
you take two turbos. pick the turbo you need that will supply the CFM of the engine you want. then pick the a turbo that flows half the CFM of the large turbo but at the same pressure ratio. this is tricky because you try to match the efficiencey.
so the exhaust flow goes like this:
engine-small turbo-big turbo-out to free air.
the intake goes like this:
big turbo-small turbo-engine.
You see. the exhaust will spin the small turbo first. sucking the air through the large turbo (its big enough to do this) and generating boost fast and early on generating enough exhaust flow to spin up the large turbo. this mostly eliminates low and middle lag while the big turbo comes on line. otherwise big lag you see with a single large turbo only.
you have to take into account of heat as well. the large turbo pressurizes air to 2.1 pressure ratios (30psi) so the charge air passes through an intercooler then into the smaller turbo that only has to pressureize it another 2.1 pressure ratios...so the static atmospheric air that the small turbo is working with and sees is at 30psi. in effect your changing the air for that small turbo so its breathing like its a million feet below sea level. so were also asking that it produces the same pressure ratio as the first, so thats 2x 30psi theoretically right? well the problem is this. the air is so hot now from the first turbo that its less dense. but of high volume and pressure. so in the end....two turbos functioning at 2.1 PR's ech one feeding the other will generate only a 3.0 pressure ratio...because of heat losses and intercooler pressure drops as well.....BUT....it does so at 75% efficiencey....and with reduced or no middle or low end turbo lag.....the charge of the intake air wil lbe about 20 deg. c hotter than a single turbo setup...but...the benefits are astounding. lets do 2.5 pressure ratios each?...youre looking at over 50psi after all the math for the heat is taken care of.
so running this through the math. lets say i want a B18 to run at 8000 rpm with crazy boost with this setup. assume im using two intercoolers each 72% efficient, one after the first turbo and another after the second turbo before the engine intake. lets run them both at a max pressure ratio of 2.25. the result? a setup generating 53psi at 201 deg f. intake temp. and able to do so at OVER 70% EFF!!!. the large turbo i need is one that flows 60lbs/min at 2.25 PR's (possibly a garrett GT4202r, @76%) and the smaller turbo is one that flows30lbs/min at the same 2.25 pr.(mabye a garrett GT3071r @77% eff.), so tell me of a single turbo that can do mostly lag free and deliver a 3.6 pressure ratio at over 75% total efficiencey? and thats the only reason to use that setup really...big huge boost over what any single turbo can make and do it minimizing lag. its up to you to devise a boost controlling method. but the wastegate from the first turbo dumps back into the exhaust after that turbo to power the 2nd turbo. then that wastegate before the 2nd turbo will dump into free air.
(just to let you know of the seriousness of this. over at the supra forum...those guys are talking about 1500 streetable easy lag-free driving HP using setups like this somming soon.)
Modified by robAP at 4:24 AM 7/5/2006
Modified by robAP at 1:07 PM 7/5/2006
Modified by robAP at 1:09 PM 7/5/2006
The conpound two-stage turbocharging (one feeding the other) is only usable when youre looking for boost beyond that of what a normal single turbo can produce. (Ie: if youre looking for near or over 3.0 pressure ratios of boost or 45psi.....then this is your answer.) you can no longer look for additional boost on top of boost from the first turbo. you have to think in pressure ratios now and then convert it after everythign is all said and done in the end. you have to think about the heat generated from boosting with the first turbo acting on the second turbo. So....
Here is how it works.
you take two turbos. pick the turbo you need that will supply the CFM of the engine you want. then pick the a turbo that flows half the CFM of the large turbo but at the same pressure ratio. this is tricky because you try to match the efficiencey.
so the exhaust flow goes like this:
engine-small turbo-big turbo-out to free air.
the intake goes like this:
big turbo-small turbo-engine.
You see. the exhaust will spin the small turbo first. sucking the air through the large turbo (its big enough to do this) and generating boost fast and early on generating enough exhaust flow to spin up the large turbo. this mostly eliminates low and middle lag while the big turbo comes on line. otherwise big lag you see with a single large turbo only.
you have to take into account of heat as well. the large turbo pressurizes air to 2.1 pressure ratios (30psi) so the charge air passes through an intercooler then into the smaller turbo that only has to pressureize it another 2.1 pressure ratios...so the static atmospheric air that the small turbo is working with and sees is at 30psi. in effect your changing the air for that small turbo so its breathing like its a million feet below sea level. so were also asking that it produces the same pressure ratio as the first, so thats 2x 30psi theoretically right? well the problem is this. the air is so hot now from the first turbo that its less dense. but of high volume and pressure. so in the end....two turbos functioning at 2.1 PR's ech one feeding the other will generate only a 3.0 pressure ratio...because of heat losses and intercooler pressure drops as well.....BUT....it does so at 75% efficiencey....and with reduced or no middle or low end turbo lag.....the charge of the intake air wil lbe about 20 deg. c hotter than a single turbo setup...but...the benefits are astounding. lets do 2.5 pressure ratios each?...youre looking at over 50psi after all the math for the heat is taken care of.
so running this through the math. lets say i want a B18 to run at 8000 rpm with crazy boost with this setup. assume im using two intercoolers each 72% efficient, one after the first turbo and another after the second turbo before the engine intake. lets run them both at a max pressure ratio of 2.25. the result? a setup generating 53psi at 201 deg f. intake temp. and able to do so at OVER 70% EFF!!!. the large turbo i need is one that flows 60lbs/min at 2.25 PR's (possibly a garrett GT4202r, @76%) and the smaller turbo is one that flows30lbs/min at the same 2.25 pr.(mabye a garrett GT3071r @77% eff.), so tell me of a single turbo that can do mostly lag free and deliver a 3.6 pressure ratio at over 75% total efficiencey? and thats the only reason to use that setup really...big huge boost over what any single turbo can make and do it minimizing lag. its up to you to devise a boost controlling method. but the wastegate from the first turbo dumps back into the exhaust after that turbo to power the 2nd turbo. then that wastegate before the 2nd turbo will dump into free air.
(just to let you know of the seriousness of this. over at the supra forum...those guys are talking about 1500 streetable easy lag-free driving HP using setups like this somming soon.)
Modified by robAP at 4:24 AM 7/5/2006
Modified by robAP at 1:07 PM 7/5/2006
Modified by robAP at 1:09 PM 7/5/2006
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