rocks Posted November 19, 2009 Share Posted November 19, 2009 You also have to factor in your in rpm drop after your first gear shift. From 1st to 2nd gear are you going back down to 3500 rpms? If not then you will have some first gear lag but you can live with it. Kind of like my friend with a HX35 on a 2.0 liter subaru. Sure first gear spools at 4500 rpms, but after that when racing it never goes back below 4500 rpms. When I do turbo my 350z, it has a built engine im going to use a master power t70 or a holset HX52 pro. I shift at 8000 rpms and it never drops below 5500 rpms when shifting. I know this is different than the 280zx engine, but the same thoughts apply. I had taken the 350z to a company called HP Performance out here they make thier own turbo kits for mustangs, corvettes, nsx. They suggested a GT42 for the 350z. The same company also told me that due to the dyno results the factory limiter at 6800 rpms was killing the power. I didn't belive them at first. I went home and retuned it to 8000 rpms. I went from a 15.2 1/4 mile to a 14.5 on a low compression cammed engine. Some people think that is crazy but I don't. I am not trying to say make a dyno queen with a bigger turbine housing, but if you are not coming back down below 3500-4000 rpms when shifting do you need a .63 housing? Its all about compromising things at this point. Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted November 19, 2009 Share Posted November 19, 2009 You also have to factor in your in rpm drop after your first gear shift. From 1st to 2nd gear are you going back down to 3500 rpms? If not then you will have some first gear lag but you can live with it. Kind of like my friend with a HX35 on a 2.0 liter subaru. Sure first gear spools at 4500 rpms, but after that when racing it never goes back below 4500 rpms. When I do turbo my 350z, it has a built engine im going to use a master power t70 or a holset HX52 pro. I shift at 8000 rpms and it never drops below 5500 rpms when shifting. I know this is different than the 280zx engine, but the same thoughts apply. I had taken the 350z to a company called HP Performance out here they make thier own turbo kits for mustangs, corvettes, nsx. They suggested a GT42 for the 350z. The same company also told me that due to the dyno results the factory limiter at 6800 rpms was killing the power. I didn't belive them at first. I went home and retuned it to 8000 rpms. I went from a 15.2 1/4 mile to a 14.5 on a low compression cammed engine. Some people think that is crazy but I don't. I am not trying to say make a dyno queen with a bigger turbine housing, but if you are not coming back down below 3500-4000 rpms when shifting do you need a .63 housing? Its all about compromising things at this point. I'm sure Tonyd will say it better, But I think his point was the main reason to go with a larger turbine housing is if you have an exhaust manifold pressure issue. In this case changing the turbine housing will not fix the surging. Why lose any powerband if it gains you nothing? Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 19, 2009 Share Posted November 19, 2009 Goldfish said it fine---why narrow your powerband when you don't have to? The ability to take the car through a corner in the same gear over the most rpm range possible will return the fastes time because the car is known to be 'driveable', gear selection becomes less important, you can run more gear out back for better economy or higher top speed, etc... It's why big V8's are so happy in our little Dattos: they run to 4500 in stock form, but offer scorching performance because of torque. Boost threshold means wider torque plateau. Aside from that... You are making the assumption that the turbine side is his problem---it's not,vit's the compressor side's ability to flow more air! (or less air at a given point.) While a .82 housing might slow down the compressor wheel and 'solve' the surge because it's operating with less flow... you also don't make boost, and STILL run out of compressor wheel at the same point. Quote Link to comment Share on other sites More sharing options...
jgkurz Posted November 19, 2009 Share Posted November 19, 2009 I am not trying to say make a dyno queen with a bigger turbine housing, but if you are not coming back down below 3500-4000 rpms when shifting do you need a .63 housing? Its all about compromising things at this point. That might be fine for a drag racing application but an oversized turbine on the street, autocross or even for road racing would make power delivery a PAIN to modulate. Sure, a BIG turbo will usually make more peak power but can also make your engine feel like a 2-stroke. Like you say, it's about compromise. Peak power is only one part of the equation. Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted November 20, 2009 Share Posted November 20, 2009 Tony - Thanks for sharing your knowledge on the subject. People like you make this site a valuable resource. Cheers, Ross Same here. I'm watching this also to determine if I should even bother going thru the swap out from twin GT 25/40's, to a single GT35r with a T4 turbine housing. I'll just start a thread when I'm ready to make up my mind, and hopefully Tony and the other brite minds will help me out with the decision... Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted November 20, 2009 Share Posted November 20, 2009 If the turbo cannot reach the boost pressure that the engine is trying to flow it to, then you are probably pushing the turbo into very high CHRA rpm level, no? That will kill a turbo's bearings. I've put a customer's stock turbo EVO8 into low 11's on one and it only took about 2 months for the turbo to die. It slowly started putting out less and less boost, etc. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted November 20, 2009 Share Posted November 20, 2009 That might be fine for a drag racing application but an oversized turbine on the street, autocross or even for road racing would make power delivery a PAIN to modulate. Sure, a BIG turbo will usually make more peak power but can also make your engine feel like a 2-stroke. Like you say, it's about compromise. Peak power is only one part of the equation. Rocks, a big turbo will take a little more to get it to spool predictably and on cue at low rpm levels. Building a little boost (and only a little) in mid corners for proper weight distribution is tough. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 23, 2009 Share Posted November 23, 2009 Mid corners... don't even get me started on boost threshold coming in halfway through a corner and loosing traction. It was the reason for the whale tail being added to my 240Z... Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted November 24, 2009 Share Posted November 24, 2009 Mid corners... don't even get me started on boost threshold coming in halfway through a corner and loosing traction. It was the reason for the whale tail being added to my 240Z... LOL, I recall an HPDE event with the BMW CCA at MidOhio. The instructor kept telling me to get on the throttle "more... more... more..." in midcorner. I tried to explain the issue of spool and delay of bigger turbos but he didn't seem understand; until I walked past brand new M3's on the straights. Of course they all had to come to me afterwards to tell me I had an oil leak out the exhaust (pump gas endurance tune). Quote Link to comment Share on other sites More sharing options...
jgkurz Posted November 24, 2009 Share Posted November 24, 2009 Mid corners... don't even get me started on boost threshold coming in halfway through a corner and loosing traction. It was the reason for the whale tail being added to my 240Z... Unfortunately the whale tail is only helpful at higher speeds. 2nd and maybe even 3rd gear corners probably wouldn't benefit. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 25, 2009 Share Posted November 25, 2009 Actually, it was a corner that was too fast to take flatfooted on-boost in 2nd because there was no traction from the 265's out back, and if you took it at the same speed in third you were below boost threshold lugging all the way through exiting. (Thanks for that gearspread, Nissan!) With the tail on it you could take it, under boost through the corner solidly planted and on the verge of pushing. Actually if you entered correctly, you could stay on it almost like a chicane, and the front would push to the outside with just enough track to spare. Actually accelerating through in 2nd. If it wasn't a mountianside course, and there was a longer runup to it I would probably stay in third, but...downshifting into second matched entrance and exit speed. You were in secone on boost hard before entering the turn. Before the tail, it was upshift to third to drop out of boost (or at least curtail the power) because you just couldn't keep standing on it or you would loose traction. Modulation in second really kept the engine at peak torque making it a bit slippery. Man, it's been a while thinking about that curve. I hvae to go watch some video to see what I was doing now. It was on boost second gear when I was done. Maybe it was on boost third gear... And second was too low. I know modulating just sucked because you couldn't do anythning after the turn. But with the tail, you could keep your foot in it. It was relatively a slow turn. In the higher gear, your exit speed just dropped so fast it wasn't funny. Speed through the corner before tail was maybe 45. After tail I could accelerate through it passing redline in second and shift into third for the straightaway just after the corner full on boost and pulling hard. It must have been secondand third, because top of third would have been 100, and this corner was half that speed. I suppose I could put 175# of ballast in the back to plant it, but I'm sure it would have affected me elsewhere. The whaletail was rated at 370# at 100 mph. Seemed that if it was linear, I had half that at 50-70 and allowed me to stick through that one. Actually 'higher speeds' and 100mph are not really someting to say these days. In most states you are doing 80% of that speed on the average interstate highway. The little Datsun Kick Tail was not helping it at all, I needed more, and got it with the wing. Quote Link to comment Share on other sites More sharing options...
Spooler Posted November 26, 2009 Share Posted November 26, 2009 Phil, you got it squared away yet? Waiting to hear it purrrr through the gears. Quote Link to comment Share on other sites More sharing options...
Ben Posted November 29, 2009 Share Posted November 29, 2009 An excellent thread on an excellent topic (although at the OP's cost since we are discussing a real 'problem' causing someone real grief). My only comment at this stage is to those who may be advocating a larger turbine A/R to address the issue and the corresponding power delivery which would occur as a result. For a driveable setup - It's not about peak power, it's about the area under the curve. You've got to be happy that you've achieved your current result with a stock head. Perhaps you could fit your new head, raise your CR a bit (1mm gasket) and lose 5psi of boost? (The most amount of power on the least amount of boost, it's the mechanically friendly way to go!) Quote Link to comment Share on other sites More sharing options...
260DET Posted December 28, 2009 Share Posted December 28, 2009 Educational thread, its good to read stuff by people who are not trying to sell you something too. A couple of amateur comments on the 'stonewalling' thing and the indication that the GT35R here was reaching its maximum air pumping capacity. And I think it was John who mentioned a wastegate fix as the solution to a related problem he had. Wouldn't the problem here be one concerning the inability of the engine to take more air due to induction restrictions? Causing the turbo to reach a point where it could not flow more? If the engine's induction system was improved, wouldn't the turbo then be able to flow more thus eliminating the problem? And could this be related to the wastegate thing? The turbo is working hard to overcome engine flow restrictions resulting in an increase in exhaust manifold pressure as the turbine meets more rotational resistence? Too much pressure and the wastegate is forced open against its spring? A lot of exhaust manifold pressure could also induce power robbing inversion, an observation that unduly complicates things at his stage Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 30, 2009 Share Posted December 30, 2009 A Wouldn't the problem here be one concerning the inability of the engine to take more air due to induction restrictions? Causing the turbo to reach a point where it could not flow more? If the engine's induction system was improved, wouldn't the turbo then be able to flow more thus eliminating the problem? This is why it surges. Minimum stable flow can not be maintained for the pressure present, and the compressor surges. As more flow is induced, the flow stabilizes and the low flow low speed surge disapears allowing a clean pull to redline. And could this be related to the wastegate thing? The turbo is working hard to overcome engine flow restrictions resulting in an increase in exhaust manifold pressure as the turbine meets more rotational resistence? Too much pressure and the wastegate is forced open against its spring? You are getting into slip ratios and other things. I doubt this is the problem, and the mechanics you mention aren't really correct. For this to happen exhaust pressure would have to be stock spring weight (say 10psi) HIGHER than intake pressure at least and then it's iffy. Since he removed the wastegate controller and the stock spring did not experience this issue, it tells me it's not on the exhaust side, it's in the controller and what it's doing to the WG Signal. A .63AR turbine housing is nowhere near that point that early in the rpm range. Matter of fact JeffP tested his exhaust backpressure and noted a maximum of +3psi in the hot manifold under full boost at 7000rpms with his last internally gated tests. They flow a lot better nowadays than they did long ago. Comments within quotation in bold. Quote Link to comment Share on other sites More sharing options...
260DET Posted January 1, 2010 Share Posted January 1, 2010 Thanks Tony, makes sense, my main interest is the GT35R on my VG30DET with MT. Present rear housing is a 1.06, looks like a .82 would be better than the laggy 1.06. So far the internal gate has not been a problem but ATP have an improved setup which I'm considering. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 6, 2010 Share Posted February 6, 2010 (THIS IS CONCURRENTLY-POSTED FROM THE SURGE STICKY AS I THOUGHT IT WAS APPROPRIATE TO HAVE IT ON BOTH THREADS) I have run across a guy in our company's design engineering department that has a Z32 Twin Turbo. Indeed, the control technology DOES now exist out there now to control the BOV as a true 'unloading valve' meaning at low flow/high boost situations (higher boost, lower rpm engine demand) the BOV opens and vents exxtra flow to allow the turbos to spool up in a stable portion of their map and not surge on the way up the rpm band. Big Phil seemed to be having an issue like this, and my recommendation was to try and get a boost control valve set up like this, I just didn't know if one was currently available. It is, and they are electronically adjustable to dump excess flow overboard so you can run hellacious flow turbos at lower speeds without low-flow surge, and take advantage of their better high-flow high boost characteristics 'up top' in the RPM range now. It has a total PID loop control apparently, allowing for variable dumping and staged blowoff. I have this guys e-mail, so I will get some details on the control system he set up on his Z32 to prevent low-flow surge on his car. He said the way the car pulls now dumping extra flow overboard is FAR harder than it did when it was surging and trying to develop more horsepower lower in the RPM Range. It allows you to run a much higher boost much sooner in the RPM range without surging. Cool, huh? This technology appeals to someone like me who will run a turbo at Bonneville, as I can now consider a FAR larger turbo flow than I would have otherwise considered, and simply blow excess boost overboard at lower rpms (say below 6000rpms) to keep the turbo flow stable and allow a higher boost level for more power (traction permitting). It is also applicable to Big Phils situation in that he's marginal low-flow at some points of his turbos flow curve---if he could simply vent some flow at that point in the rpm range, he could keep 22psi on the engine, and pull harder than he otherwise could (the other alternative is to run it at a boost level where it doesn't surge) The hardest part of controling turbocompressors is people equate boost to flow. They are separate entities working against each other. If you can dump flow, you can run a higher boost lower in your engine's rpm range and not get the honking surge like BP did. On conventional controls they only relate to boost pressure, but if you use a controller that references rpms and can control an overboard dump for flow, you begin to have total boost/flow control. It also makes wastegate control much easier to handle---and your turbocharger starts operating in a more limited rpm range near peak efficiency, rather than up down and sideways all over it's curve during engine operation. Get it up and spooled, and keep it there, dumping excess flow when necessary to keep the flow stable at whatever boost you choose. Quote Link to comment Share on other sites More sharing options...
EvilC Posted May 18, 2010 Share Posted May 18, 2010 Bumping a good thread for newbies like me. I am at the point where I am reading/learning about what turbo I may want to run. I am trying to find this old engine calculator I had, to determine my flow and more. I am going to being running a 3 liter block and a Braap head for my setup. Thanks to everyone who put some good info into this thread! Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 25, 2010 Share Posted May 25, 2010 I'll add another 'bump' in the same week, as the guy with the controller is due back from China soon, and has still not responded to me which control system it is. Unbeknownst to him, though, I was in the corporate office and have SAVAGED his cubicle. He will be opening drawers and finding yellow stickies that say 'Contact Tony D on your Z32 Wastegate Controller Setup'... They are all over his cubie now at eye level, under things, in drawers, I even upturned his 'Wheel Man' (a figure made of turbine wheels) and stuck several on his rump... When you go for training, you have 'spare time' for once in your life. I simply chose to use it to bug the hell out of him remotely to buck up details on his controller system. I will probably be in Malaysia or Indonesia when he returns, or gets irritated enough (gets the idea) to give me the information. He doesn't want me to have to come over to his house... Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted June 7, 2010 Share Posted June 7, 2010 on some of the newer cummins diesel engines the turbo has shaft speed sensors.i would assume this is used as an input to the engine ecm.the engine ecm would use this to compute the output for the vgt adjustor servo on the turbo.engine has no waste gate-the vgt just lets some of the exhaust gas by on the turbine side.some of the newer after markit efi systems can use turbine speed and control a vgt Quote Link to comment Share on other sites More sharing options...
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