HB280ZT Posted October 9, 2008 Share Posted October 9, 2008 Hi All, Well after much investigation I come to find out I may have a problem with my intercooler, refer to old thread: http://forums.hybridz.org/showthread.php?t=129000 Let me back track a bit here. The original problem was fluttering at between 3000 and 4000 rpms with partial throttle. I changed many things but could never get it to go away until I swapped out my intercooler for a straight tube and guess what no more flutter. So the next thing I did was to plumb in a second boost gauge and see what is happening. One is directly after the turbo and the other is in the manifold. Well did I get a surprise at the difference I am seeing as I drive around. At one point when it started to surge the turbo gauge was reading 20 psi and the manifold was at about 10 psi. Other times I saw TG 5 psi and MG of -10. So what to do? The intercooler is a R.S. Akimoto, core measurements are 20" X 8" X 3.5" with 2.75 inlets and outlets. It is a bar and plate design. So as soon as I can get someone to ride with me and write down numbers I will post some more information. HB280ZT Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted October 10, 2008 Share Posted October 10, 2008 Wow! I get a flutter as well, that I am pretty sure is due to a restriction in the intake. You sure there isnt a bunch of crap in your I/C? Oil or whatever. Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted October 10, 2008 Author Share Posted October 10, 2008 I had it cleaned out awhile back but not lately. When I inspect it I see nothing that looks like it would cause this problem. Hopefully this morning I will get a chance to take the car for a run and try to log some of the numbers. I wish I had a way to flow test the intercooler here locally!! Will keep you all posted on what I find! HB280ZT Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 10, 2008 Share Posted October 10, 2008 Your throttle plate is in between your two pressure points. unless you are checking under WOT conditions, I would fully expect to see this on todays 'hard blowoff' bypass valves. See if you can get your blowoff to work to lift and relieve pressure under partial throttle, or even lift-throttle. That blowoff should LIFT and sound like a "sigh" at the slightest lift of the throttle. I know it's not in vogue to not have a hard-PSHHHHT!!!!-sounding blowoff, but that is what it should be doing. Partial throttle 'driving around' will cause a minimum-flow surge for sure...and that is really what your bypass (blowoff) valve is there to prevent. It keeps the minimum stable flow through the turbine to keep it out of surge. What you previously characterized as a 'boost leak' was actually what you need due to the flow characteristics of the turbo! If the backside of the BOV is tubed to the manifold, it should never have an issue with sealing under WOT or near WOT conditions. People think the BOV should 'seal tight' under all circumstances and this just is not correct. It's supposed to blow off at anything but WOT or near WOT. "Compressor Bypass" -- it lessens the load and keeps the turbo speed up for instantaneous boost once you go to WOT. It's a very misunderstood dynamic, made worse by the recent ricer movies that characterize the 'hard' blowoff noise as 'the thing to have'. Listen to the original Wangan Midnight movie made in the mid 80's and you will hear a proper 'sigh' of the BOV and release of pressure, as well as it doing the minimum flow function. BOV is a really bad misnomer. It's a 'compressor bypass valve' and should be 'leaking' if it's doing it's job. If you don't have one that is tubed on the backside of the diaphragm to hte manifold, get one...the others are a compromise...as you are finding out firsthand! Because it's not venting, you are seeing the pressure rise on the discharge of the turbo, while the throttle plate is partially closed (throttling...) and you are running into the problem because of it. If you don't have the issue under WOT, and don't have the same readings under WOT conditions, likely the I/C is not your issue... inadequate venting of excess flow during times of partial throttle or low flow is... You may want to move your wastegate reference back on the turbo discharge side of the manifold as well, as your wastegate is not opening under these same conditions preventing the overspeed of the turbo causing the upstream pressure rise. G'Luck! Quote Link to comment Share on other sites More sharing options...
Clifton Posted October 10, 2008 Share Posted October 10, 2008 Look up compressor surge and look at a compressor map. Any thing on the left will be surge/flutter. If it's on shift it won't hurt, if it's constant that's different. It's all in the sizing. Add another 500-1000 rpms to the boost threshold or a smaller compressor and it will stop. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 10, 2008 Share Posted October 10, 2008 I'll also add Clifton is correct in that you can size your compressor for the proper needs of the engine, or move your boost threshold around to get a 'properly sized' turbo dynamic. But if you have a high-flow unit for up high breathing, and a hotside setup for down-low torque---then setting up a bypass valve for partial throttle minimum flow situations keeps the thing working without having the surge issue. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 10, 2008 Share Posted October 10, 2008 It would be better, efficiency-wise, to get a boost controller that will dump exhaust through the wastegate when intake flow has peaked. Dumping compressed air is wasted energy (somewhat). Basically, a less aggressive boost curve via wastegate control at part throttle...if that's possible. I just drive around the issue on my car, but I'll try loosening my BOV spring and just letting it vent. It's cheaper and easier than either replacing the turbo or installing an expensive boost controller. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 10, 2008 Share Posted October 10, 2008 On another note: By replacing your intercooler with a length of pipe you drastically reduced the volume of your intake tract. Air is less likely to setup low frequency vibration (flutter) in a smaller volume. In effect you changed the resonance frequency of the system. So attributing the flutter ONLY to intercooler restriction is wrong. You also have a much quicker dynamic response to pressure changes in the system which will certainly change the way the BOV "dances" with the compressor and the throttle plate. Quote Link to comment Share on other sites More sharing options...
Nigel Posted October 10, 2008 Share Posted October 10, 2008 See if you can get your blowoff to work to lift and relieve pressure under partial throttle, or even lift-throttle. That blowoff should LIFT and sound like a "sigh" at the slightest lift of the throttle. I know it's not in vogue to not have a hard-PSHHHHT!!!!-sounding blowoff, but that is what it should be doing. Partial throttle 'driving around' will cause a minimum-flow surge for sure...and that is really what your bypass (blowoff) valve is there to prevent. This is something that I suggested in the other thread (post #26)... http://forums.hybridz.org/showthread.php?t=129000&page=2 It didn't cure the the problem for me because I have an extreme case, but it certainly helped. The only downside is that with the Greedy Type RS BOV that I have, it makes this gawd awful squealing noise every time the valve cracks open, and with the single spring, this occurs between -13 and -15 inHg, which is right in the cruising range. So as I'm driving along, I keep hearing this high pitched EEEEEEEEEEE!!!! sound. I don't know which is worse, the chirping from the turbo surging or the squealing from the BOV! Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted October 10, 2008 Author Share Posted October 10, 2008 Ok where to start. I am using a Tial 50 mm BOV with the 19-21 inhg of vacuum spring in it. As for when it goes off under boost I have not gotten to that yet, that I know of. But when I pressurized my system listening for leaks it would start leaking at about 24 lbs of pressure. Also when I get off of the throttle I can here it release. So if this is not right what to do about it?? As for boost reference point I was using a point right after the turbo and have changed to the manifold to see what it does. Well it moved the flutter up in rpms to between 4000-5000 now. One item I am not really sure of yet is whether or not it is my waste gate opening early because of boost pressure and just bouncing or is it really surge! I really need to drive my car with someone else to watch the gauges and recording what happens because I only see bits of what really is happening as I drive. Will keep you all posted and keep the good information coming. Hopefully someday I get this fixed as it is driving me nuts! HB280ZT Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 11, 2008 Share Posted October 11, 2008 I just went out for two test drives. One with the BOV REALLY tight and I got all sorts of flutter if I lifted anywhere above 3000rpms in any boost. The higher I took the boost, the worse it got. Then I loosened the BOV all the way so it was almost all the way open at idle. I took it for a spin and had very slightly less low end torque becuase it was venting some of the real early boost. On 30%-100% throttle I had no trouble building and holding full boost(15psi). If I backed off the throttle, I just got a nice, soft, gentle, whoooooooooooshhhh. No flutter no drama. I like it. Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted October 11, 2008 Author Share Posted October 11, 2008 cygnusx1, that is great but my BOV is not adjustable without changing springs. So does anyone have any Tial springs they are interested in parting with? I have the -11 psi spring which one should I try next! Engine Vacuum Reading / Color Use Spring Between: - 22 and -23 in/Hg Pink -12 Psi (-24 in/Hg ) - 18 and -21 in/Hg Un-painted -11 Psi (-22 in/Hg ) - 14 and -17 in/Hg White -9 Psi (-18 in/Hg ) - 10 and -13 in/Hg Black -7 Psi (-14 in/Hg ) HB280ZT Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 11, 2008 Share Posted October 11, 2008 Mine technically is not adjustable either. I had stuffed washers inside to build up the spring pressure. You could cut a little at a time off the spring until it stops fluttering. I assume you can access the spring. I can actually reach my finger up inside and feel if the valve is open or closed at idle. You could also hold your hand at the BOV exit and rev it a tiny bit in neutral, feeling for blow off air. I am guessing you want it to be just cracked open at idle in your case. Then adjust from there. Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted October 11, 2008 Author Share Posted October 11, 2008 Well cygnusx1 I did somewhat the same thing you did and no surge now. However I do get just a bit of movement on the boost gauges but nothing like I uses to get, it would buck like a bronco!! Now what I did was go to the local hardware store and get a spring like the factor tial spring and make it work. I had to do a bit of cutting and fitting but it works using my 8 psi wastegate actuator. The only issue there was that I was hitting 14 psi on my datalog! Not sure about that one. However I will change out the wastegate actuator for the 15 psi unit to see if it still does not surge. On another issue now I see that at idle and at part throttle (in the garage) the BOV is open or opening and closing. Is this normal?? HB280ZT Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 11, 2008 Share Posted October 11, 2008 On another issue now I see that at idle and at part throttle (in the garage) the BOV is open or opening and closing. Is this normal?? HB280ZT Yup, under these circumstances, the BOV will be open or almost open at idle. I like it soooo much better than the "choking goose" sound and feel I used to get. When I was doing a burnout or a hard launch, it was almost impossible to modulate when the BOV was too tight. It would buck and catch if I lifted at all to control the wheel spin. Now, I have total control with no bucking or surging. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted October 12, 2008 Share Posted October 12, 2008 i take it I am the only one who enjoys the sound of flutters?? reminds me so much of WRC cars... since they don't use BOV's or bypass valves all you hear is turkey calls.. mmm yummy Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 12, 2008 Share Posted October 12, 2008 I like the sound and it also reminds me of WRC, it's just not great for the turbo or mid-throttle driveability. The WRC guys drive at WOT or OFF all the time. Quote Link to comment Share on other sites More sharing options...
X64v Posted October 12, 2008 Share Posted October 12, 2008 As a side note, the 1gDSM BOV is set up like this from the factory: partially open at idle, a nice ppsssshhhhh on gear shifts, and the same nice steady release on part throttle lifts. If I'm cruising on the freeway at 85, give it just a tiny bit of gas and come back to cruise, the bov lets out a small sigh even though I was no where close to boost. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted October 12, 2008 Share Posted October 12, 2008 Forge motorsports also makes a unit that functions as a bypass valve. Evan Quote Link to comment Share on other sites More sharing options...
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