cygnusx1 Posted July 5, 2007 Share Posted July 5, 2007 Good news is that by installing the MS-II and the larger injectors I was able to get my TO4B "Super-V" to spool up quicker. Mainly due to better fuel/timing maps and a nice BIG free flowing intake. Bad news is that if I floor it in fourth at about 2000 RPM's the boost builds to about 10psi by 2500RPM's and I hear the wild goose surge flutter sound from the BOV, and the boost gauge goes bannanas. My first instinct was to add a washer to the BOV spring but then I realized that the increased "flutter pressure" was BAD for the turbo blades and bearing. I use a grainger style {ball-spring} boost controller that is set to 15psi. Is it time to go for an electronic boost controller or is there another relatively simple/budget fix? Please dont suggest not flooring the gas pedal. That aint gonna happen! -Dave "Turkey Call" LISTEN NOW: http://www.wildturkeyzone.com/gobbles.wav Quote Link to comment Share on other sites More sharing options...
CalifaThugz Posted July 5, 2007 Share Posted July 5, 2007 I don't know anything you said about everything, but I hear synchronic blow off valves are good. They don't release pressure until there is a big drop of pressure from the manifold. Quote Link to comment Share on other sites More sharing options...
JustinOlson Posted July 5, 2007 Share Posted July 5, 2007 You could change out the exhaust housing to a larger A/R. Otherwise just get used to downshifting when you are going full throttle. Its not too bad once your used to it. A electronic boost controller could be used to bring in boost slower, but why not just get a larger turbo if you want that. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 5, 2007 Author Share Posted July 5, 2007 You could change out the exhaust housing to a larger A/R. Otherwise just get used to downshifting when you are going full throttle. Its not too bad once your used to it. A electronic boost controller could be used to bring in boost slower, but why not just get a larger turbo if you want that. Yeah once I get up above surge territory it accelerates like a jet fighter. You are right, why spend the $$$ just to bring the boost in slower when I can learn to drive around it. My only fear is that if I surge it enough, I will be needing a new turbo. Looking on ebay though, I see that turbo prices have come way down in the past few years so I am not too worried about shelling out too much. Turbos are even cheaper than the EBC's! In what way would a performance turbo cam make a difference in this situation? Would the engine VE go higher in the low range, high range, or both? Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 5, 2007 Share Posted July 5, 2007 Why not consider a compressor bypass valve? The proper design lets the thing build speed while the compressor is bypassed, closing as pressure in the manifold comes up... This bypass (or blowoff) keeps the minimum flow requirements of the turbine satisfied, while letting it accelerate to full boost building speed. This type of valve doesn't give the cool sound everybody became infatuated with since FnF came out a few years ago, and it's rather boring and quiet...but it lets you build boost quickly and keeps things flowing. I doubt it's anyting to do with the boost controller itself. If indeed you are encountering Minimum-Flow Surge at 10psi, you can play with the controller to see if it doesn't do it at 9, or 8psi, and simply use a two stage that is operaed electronically by an rpm triggered switch. Surge is simply a reaction to the compressors' ability to flow air at a give n pressure. If you exceed it, flow reverses, and you 'surge'. Either lower the pressure at that flow point, or increase the flow through a bypass to stabilize the unit. People may balk at blowing air overboard and 'wasting it' but if the engine can't digest the air, and the turbo needs to move it...you have no other option! The last, most expensive option would be to increase the flow capability through the engine so the flow from the turbo is matched to the flow of the compressor at all points. The last comment is that you are driving your car damn wrong! The engine should not be floored in the wrong gear. This is a typical American Driving Technique. If you want a Small Block Chevy---install one! Get the RPMS up for a proper roll on. You would NOT floor a Normally Aspirated high-performance L6 at 2000 and expect performance, you shouldn't be doing it on a turbo car, either! This is where turbos get the 'lag' misnomer, and all the black stories people tell....If you drove your turbo like you drove a N/A car, the stories of 'turbo lag' and 'non-linear power delivery' would not be an issue. You're lugging the car at tha point, and of course, it's going to protest! Power comes on in L-Engines at 3000 / 3500+ rpms. Remember that, and drive accordingly. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 5, 2007 Author Share Posted July 5, 2007 LOL, yes I know flooring it at 2000 is not good driving (on small liter motors). Sorry I made it sound like I do that for fun...I don't. I am tuning the car and was tuning the high load/low RPM parts of the map for driveability. I just noticed the flutter there where I had never noticed it before the MS-II and the intake reconfiguration. You bring up a great point that actually went right over my head. I used to have my BOV (TurboXS Race Valve) recirculated back to the compressor intake and now it's vented to atmoshpere. I wonder if that's causing the flutter....hmm great point Tony. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted July 6, 2007 Share Posted July 6, 2007 also... every turbo will flutter to a point.. if I "floor" it at 2,500 RPM.. and let the turbo spool a little bit and run 1psi or 2psi and let off. the BOV does not open even really loose.. and causes a small quiet flutter. ever listen to a car with HUGE turbo?! it will naturally flutter slightly. What will damage it is flutter from high boost.. like running 15psi letting off and hearing a LOUD flutter Blow off valves will also flutter when set to a very light setting they will open and close quickly. In addition external wastegates will flutter as well.. same as the BOV with it opening and closing Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 6, 2007 Share Posted July 6, 2007 Oh, for tuning, all is forgiven. I got mine with the proper retard to have 15psi at 1500 rpm... Melted the oil feed line brazed joints... it was not a good day! LOL Quote Link to comment Share on other sites More sharing options...
Clifton Posted July 6, 2007 Share Posted July 6, 2007 Still don't know why people want full boost at low rpms. It's not a diesel. The answer you aren't going to want to here is that your turbo is poorly matched. You would be better off with a stock turbo for your driving style. Your compressor is too large compared to the turbine side. Having a compressor that flows 500hp but a hotside that's barely good for 300hp is a poor match. Low rpm surge is the result. You can increase the hotsdie a/r, increase the turbine wheel or both. Yes it will add lag but it will also add HP and get you out of the surge area. Then you can floor it at 2k with out having surge. Another option would be a roots type supercharger. Full boost off idle. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 6, 2007 Author Share Posted July 6, 2007 Low RPM lugging IS NOT my driving style people!!! I have never owned a motor larger than 2.8 liters. All my other motors besides the Z were 2.0 or less. The ONLY reason I brought it up was because I DID NOT get the surge before I switched to MS-II and a Cone air filter right on the compressor. The ONLY reason I drove into "banned driving style" territory is because I was AUTO-TUNING my VE maps and needed to drive in that range. I dont lug my motor!! I love the way this accel curve of this car is exponentially up with speed. You can see it in the datalogs. It accelerates faster, the faster it goes! Back to tech talk. In the three years of driving this same engine and same turbo with factory EFI at 15psi boost, I never got the surge. What changed it? Quote Link to comment Share on other sites More sharing options...
Pyro Posted July 6, 2007 Share Posted July 6, 2007 What turbine are you using? Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 6, 2007 Share Posted July 6, 2007 "Yes it will add lag but it will also add HP and get you out of the surge area. " It doesn't add lag, it changes Boost Threshold. Lag is something different than Boost Threshold (the rpm point at which the engine will give full boost). This term gets so misused it's a 'Freeze Plug' situation with me, like that term is with Braap! Once above Boost Threshold, "Lag" for any modern turbocharger is minimal, usually well less than half a second. Lag is not the difference in time between flooring it, and when it reaches full boost and any point in the rpm range. Like a car with a hot cam, you will not run it below it's camshaft operational limits---same goes for the turbo. You do not operate it below boost threshold. As Clifton correctly stated, if you have set up a mismatched turbine / compressor situation where boost threshold occurs at a point below the rpm point where the engine can ingest the full flow of the compressor at the full pressure capable by the turbo (in essence going to the right on the map, towards the minimum flow surge line) then you have a problem. In this instance, the ONLY option is to either match the parts correctly, OR open a bypass valve and bleed off the excess flow (moving the point of flow in the compressor map again back to the right, away form the surge line). You need a minimum flow number at any given pressure for a compressor cut. If you go below that flow at that pressure, you set up minimum flow surge, and that is all there is to it. In stationary industrial compressors, this point is moved around by altering guide vanes on the inlet, or simply blowing off excess flow to the atmosphere to keep the minimum steady flow through the machine. These are constant speed machines, so the PID control loop for those flows is relatively simple... on a variable speed compressor with non-linear delivery the PID would get pretty complex for throttleing bypass off the engine at minimum flow at low speeds. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 7, 2007 Author Share Posted July 7, 2007 I see, so it probably became apparent to me because I have increased the turbo's ability to spool up and now it blows more air at X rpm-X psi than the motor can ingest at X. Very cool....actually hot, because the turbo moves outside of it's efficient range. It's a T3 Turbine with a TO4B "Super-V" trim (dont really know what a "super-v" trim is other than it's a Garrett spec). I don't feel it's a huge problem because I just have to pedal it until I get to about 2800-2900 rpm's, have it floored by about 3000, and it really puts you in the seat with no surge at all at the current, 15psi. I am not going to further tighten the BOV, in fact, I'll loosen it and just drive it right. Bottom line, a nice free flowing intake WILL change the performance of the turbo noticeably. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 7, 2007 Share Posted July 7, 2007 What you could try to do is have a 'leaky' bov to bleed boost...perhaps a bleeder orifice in the BOV line that closed with an RPM-Activated switch. In other words, the BOV stays open, or partially open while it comes on-boost till about 2500 or 2900 rpms, when the bleed off solenoid closes, and the BOV positively seals, letting ALL boost go to the engine. All you are looking to do is set up stable flow conditions. This may actually help with tuning the way the car comes on-boost. With a programmable output, this would not be so difficult, and with a needle type bleeder on the vent to the BOV, you could tailor the way it bleeds off. Obviously when the switch is activated, it's ON! That may well be a simple solution, and allow you to boot it without issues. I ran a .43 AR on my T3 so I would get 17psi at near 1700rpm. It was GREAT for AutoX, and really suprised people! I am sorry I ever sold that turbine off to put the .63 on the car...it was a different feel altogether. With the new EFI systems available now, the powerband was more like a Supercharged car, the only problem was it was totally out of air by 5500. Short-Shifting all the time. But it scooted like a much larger N/A engine. All depends on what you want. I hit compressor surge on that setup at 21psi. BANG BANG BANG! Not a good sound. Minflow Turkey Gobbling is far more managable than that noise...That noise breaks things. And yes, if you increase the low rpm flow of the engine, you will have the BEST of both worlds: Make power, and stop your surge issue! Quote Link to comment Share on other sites More sharing options...
Pyro Posted July 9, 2007 Share Posted July 9, 2007 So, I guess that is a stock T3 turbine. Send your turbo to a turbo shop and have them open up the turbine a little. This will make more hp due to a better flowing exhaust and slow down the boost a little. I'm running a T04B-H3 with a stage 3 turbine. Makes 5 or 6 psi at 3000rpm and full boost (14psi) at 3500. No surge and the H3 is a bigger compressor than the V. Works well with MSA stage 1 turbo cam which pulls to 6500 rpms. If you want to keep the stock cam then use the stock turbine and change the compressor to a T04E 50 trim. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 9, 2007 Author Share Posted July 9, 2007 That looks like a good way to go when I change the cam this winter. I plan on doing a mild build on the lower and upper ends this winter. A cam change will probably be part of it. Thanks for the turbine and compressor advice. I mean I am definitely happy with the way it runs now, but if I am rebuilding the motor, I might as well better match the turbo to the motor. My current turbo is obviously flowing too much air at low revs. I thought about this over the weekend as a cheap, temporary fix. If I go to a bleed type boost controller I can make the boost curve a little less aggressive and keep it off the surge line at lower revs. The ball-spring type keeps the wastegate shut tight all the time while the bleed-type just changes the rate at which the wastegate opens...I think. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 9, 2007 Share Posted July 9, 2007 Yeah, a simple bleeder will provide for a much more 'mushy' coming on of boost. Wastegates typically open at about half full boost, and are open wide by the time full boost arrives---safety concern in OEM applications. Putting the check-ball in there really helps bring the boost on harder. That may be all you need to do to solve the surging...just let it come on a bit softer. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 10, 2007 Author Share Posted July 10, 2007 Here is a datalog screenshot of a FOURTH gear pull. I held it nearly full throttle for about 6 seconds and just look at how steep the light blue RPM curve climbs up. I floored it at about 2200rpms and held it untill I was going stoopid fast for the road I was on, almost 4000rpm. It looks like I let off the throttle a bit and caused some BOV flutter at the top of the MAP curve (white). I didn't get surge in fourth. I changed my BOV vacuum/boost hose to a larger diameter to help the BOV get boost behind it...hopefully it continues to work. The math works out to about 48mph to 80mph in 5.8 seconds in 4th gear. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted July 15, 2007 Share Posted July 15, 2007 also... every turbo will flutter to a point.. if I "floor" it at 2,500 RPM.. and let the turbo spool a little bit and run 1psi or 2psi and let off. the BOV does not open even really loose.. and causes a small quiet flutter. ever listen to a car with HUGE turbo?! it will naturally flutter slightly. What you are describing there is backspin. This is due to the fact that your BOV is not sensitive enough to open with that amount of pressure differential. You are, in effect, running without a BOV for that SPECIFIC circumstance; thus the flutter. What the OP is describing is SURGE which is an entirely different animal. His turbo is just too big for the application. He is off the left side of the compressor map. You can only eliminate that by putting a smaller hotside on the turbo. The engine is demanding too LITTLE air for that pressure ratio and shaft speed. It will damage a turbo much faster than the "stiff BOV spring" thing. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted July 16, 2007 Share Posted July 16, 2007 What you are describing there is backspin. This is due to the fact that your BOV is not sensitive enough to open with that amount of pressure differential. You are, in effect, running without a BOV for that SPECIFIC circumstance; thus the flutter. What the OP is describing is SURGE which is an entirely different animal. His turbo is just too big for the application. He is off the left side of the compressor map. You can only eliminate that by putting a smaller hotside on the turbo. The engine is demanding too LITTLE air for that pressure ratio and shaft speed. It will damage a turbo much faster than the "stiff BOV spring" thing. wizard.. I am not experiencing a backspin .. the surge is slowing the turbo down... a turbo w backspin would be severely damaged Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.