JohnA Posted November 9, 2004 Share Posted November 9, 2004 Hi guys, I'm not a regular poster here, mainly a lurker. This is a question aimed at the more technically clued-up. Has anyone tried to run more boost simply by swapping turbo #2? (I know how the sequential system works, that both turbos are the same, blah blah...) I find it surprising that there is no reference anywhere (that I can find) on the above idea. To me it seems logical to keep turbo #1 as is, and only upgrade -and run at higher boost- turbo #2. Wouldn't this keep the transition intact, and stop overspinning of turbo #1? ...or does the lack of wastegate for #1 make this a non-starter? If so, surely a pressure valve could help #1 from overspinning, right? Quote Link to comment Share on other sites More sharing options...
Wez Posted November 9, 2004 Share Posted November 9, 2004 Someone correct me if I am wrong but I am sure the sequential is purely for startup and then its parrallel operation once fully on song. I am not sure how this would work with one turbo bigger than the other for example, you may end up over speeding the first turbo unless you could control it somehow. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted November 9, 2004 Share Posted November 9, 2004 Once operating in parallel mode it is vital both turbo have the same air flow at the same exhaust gas flow, otherwise one will try and vent back through the other. It gives a nosiy shunting effect, and is the way you can tell if a Skyline GTR has a dying, but not yet dead, turbo. So no, you need to run two similar turbos. Quote Link to comment Share on other sites More sharing options...
JohnA Posted November 9, 2004 Author Share Posted November 9, 2004 Thanks Chris. I guess it's the pressure balance for the single wastegate to operate properly, eh? Quote Link to comment Share on other sites More sharing options...
tbourner Posted November 9, 2004 Share Posted November 9, 2004 What do you mean by parallel mode? I thought the first turbo comes on low pressure at low revs, then the second comes on at higher revs, higher pressure, and the first turbo pressure reduces after that leaving the 2nd to do the work? So the TTC causes the first turbo to spool later, adding to the pressure total at high revs but reducing the low down boost? So why would it matter if the turbos were different (I thought the second was bigger anyway!!)? If they start off in sequential and then go to parallel, what's the point in a TTC? Quote Link to comment Share on other sites More sharing options...
JohnA Posted November 9, 2004 Author Share Posted November 9, 2004 looking closely at the diagrams I can see that at high revs, each turbo is fed by three cylinders, yet another blow for the 'bigger 2nd turbo idea' However, it could be a hybrid with the same turbine and a larger compressor, that might work, wouldn't it? Quote Link to comment Share on other sites More sharing options...
tbourner Posted November 9, 2004 Share Posted November 9, 2004 But not strictly 3 cylinders each!! At low revs the intake air valve and exhaust valve are closed so no2 gets no exhaust gas at all!! Quote Link to comment Share on other sites More sharing options...
Ian C Posted November 9, 2004 Share Posted November 9, 2004 The exhaust manifold has a flexible link tube so that all six cylinders feed one turbo when under 4000rpm and both beyond that. Turbo 1 is online all the time, turbo 2 comes into play above 4000rpm. They have to be matched or else the bigger one's output air will stall the smaller one's output air, as Chris describes. Turbo 2 does get exhaust gas under 4000rpm but the control valve *downstream* of the second turbo is closed so no *flow* takes place, so it doesn't spin up. -Ian Quote Link to comment Share on other sites More sharing options...
tbourner Posted November 10, 2004 Share Posted November 10, 2004 Originally posted by Ian C Turbo 2 does get exhaust gas under 4000rpm but the control valve *downstream* of the second turbo is closed so no *flow* takes place, so it doesn't spin up. -Ian Aah, cool. Sorry, wasn't arguing for or against just curious. Quote Link to comment Share on other sites More sharing options...
JohnA Posted November 10, 2004 Author Share Posted November 10, 2004 Thanks Ian. I've been studying the sequential setup from the manuals on mkiv.com Quick question for you then: When people increase boost they typically do it by manipulating the single wastegate at #1, right? That's done either by intervening in the pulsing of the wastegate solenoid, or by lowering the exh backpressure - effectively crippling the flow through the tiny wastegate. (please correct me if I'm wrong!) The question is:D Does this 'upping the boost' affect the pressure balances during the transition period of #2 and back again? I.e., does the typical operation of 'raising da boost' make any of two turbos operate in a way it wasn't meant to? Not just overspinning (that's expected!) but spooling up abruptly, that sort of thing... Quote Link to comment Share on other sites More sharing options...
eyefi Posted November 10, 2004 Share Posted November 10, 2004 there's some interesting ideas being banded around involving compound turbo charging (one turbo feeding another turbo), and there was some aussie guys who built an inbalanced sequential system, but they seem to have vanished these days, never did see the end of the project. compound Quote Link to comment Share on other sites More sharing options...
JohnA Posted November 10, 2004 Author Share Posted November 10, 2004 good one eyefi, that's closer to what I had in mind actually. Interesting read:cool: Quote Link to comment Share on other sites More sharing options...
eyefi Posted November 10, 2004 Share Posted November 10, 2004 yeah, its popular with the diesel guys, i cant find the aussie system that was built, it did look promising at one point. i'll have another look. Quote Link to comment Share on other sites More sharing options...
JohnA Posted November 10, 2004 Author Share Posted November 10, 2004 I think there is a fundamental flaw in his assumptions though. If not, surely the jap designers would have gone for something similar... Quote Link to comment Share on other sites More sharing options...
Soonto_HAS_soop Posted November 10, 2004 Share Posted November 10, 2004 One of the soon to be released BMW engines uses a sequential twin turbo system, with the first turbo being smaller than the second, if I had a scanner I could scan the page I have to show the system that they are using, and looking at the diagrams, it would seem that they allow air to be fed through the smaller turbo when the second one is on line. Ben.. Quote Link to comment Share on other sites More sharing options...
eyefi Posted November 10, 2004 Share Posted November 10, 2004 Originally posted by JohnA I think there is a fundamental flaw in his assumptions though. If not, surely the jap designers would have gone for something similar... it definately works, it has been done, i think there is a link in that thread to a system that borg warner have running. what he is talking about (1500hp - 50psi) is a step further and not really suitable for production cars. Quote Link to comment Share on other sites More sharing options...
JohnA Posted November 10, 2004 Author Share Posted November 10, 2004 Originally posted by eyefi it definately works, it has been done, i think there is a link in that thread to a system that borg warner have running. That's on a boat! This guy thinks that two relatively small turbos chained together can produce airflow that is almost impossible to achieve with massive units connected otherwise. I've got my reservations on this one, although efficiency could go upwards, as more energy will be extracted from the exhaust gases. Quote Link to comment Share on other sites More sharing options...
Ian C Posted November 10, 2004 Share Posted November 10, 2004 Y'know, tractor pullers have reached tri-stage turbocharging now. Madness, and it certainly works, although not really recommended for a street motor 100+psi and a couple of thousand horsepower... Dunno how it would fare clocking it down to a 'mere' 600bhp-ish, I think the complexity and cost would outweight doing things a different way (bigger engine, bigger single turbo). -Ian Quote Link to comment Share on other sites More sharing options...
eyefi Posted November 23, 2004 Share Posted November 23, 2004 hmm, for some reason ive not had any email notifications for this thread?? anyway....... it sounds like the aussie guys r getting the inbalanced sequential system sussed Quote Link to comment Share on other sites More sharing options...
eyefi Posted November 23, 2004 Share Posted November 23, 2004 supraforums thread (if anyone is really interested) Quote Link to comment Share on other sites More sharing options...
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