I dont see where having twins would reduce this tendency. ??? <br><br>And as I said earlier, if its such an issue then why not make a pop off valve instead of a device to slow throttle responce.

 

Well, my theory on why my turbo likes to bark is because of the great differential in pressure on it. You see, I'm still running a K&amp;N drop-in in the stock airbox. I can pull 16&quot; of vacuum on it while putting out 35psi boost (controller set point, it'll go higher). With pressure on one side, vacuum on the other, as soon as the exhaust volume and velocity drop- woof, woof.<br><br>If you were to have pressure on both sides, the difference across the turbo would be considerably less, hence less tendency to bark. Also, the big turbo will have more rotational mass therefore not slowing as quickly as the smaller one. That would give some time (fractions of a second, probably) where even though the exhaust drive is reduced, there is still some pressure being applied to the small turbo. The big turbo is never driven as hard as the small one, so it doesn't have as much tendency to bark.<br><br>Anyway, that's my take on it. I bet you can still bark a compound system if you try hard enough. ;D<br><br>The problem with a blowoff valve would be where do you set it.<br>Don't want to loose normal boost under throttle application, but only when you back off. I don't see more pressure when letting off, or when the rpms drop as the TC engages, just more than the engine can take in relation to the amount of drive available for the turbo. So a regular &quot;pop-off&quot; style valve won't work.<br><br>Now, the BD valve that is linked to the throttle position would probably be the answer. According to their site, they are also working on something to help out under partial load/throttle. It will be interesting to see what they come up with.

 

[quote author=Christian Roth link=board=7;threadid=16360;start=0#154208 date=1056749619]<br>[quote author=LinearX link=board=7;threadid=16360;start=0#154166 date=1056742363]<br>[quote author=Christian Roth link=board=7;threadid=16360;start=0#154117 date=1056734668]<br>Sorry guys, a turbo bark is more commonly known as a turbo surge (off throttle turbo surge). It can destroy a turbo, take a look at all the HX40s that where destroyed becasue of this.<br><br>If you look at all turbo gassers they all have blow off valves or bypass valves to elimanate this surge. <br>[/quote]<br><br>Not all turbo gassers have a BOV. Lots of them don't even come from the factory with one, so it can't be that big of an issue at factory boost settings. I know that they're real popular in the gasser turbo/manual tranny world.<br>[/quote]<br><br>Really, last I checked most of the newer turbocharged cars either have a blow off valve or a bypass valve. I would be intrested in knowing which ones don't. If you understand the theory of operation a gasser would have the off throttle surge almost everytime.<br>[/quote]<br><br>I've owned a turbo gasser before, so I understand how they work. However, it is entirely possible to drive a gasser turbo around and never get into boost, unlike a diesel. I had a Buick Grand National and it didn't come with a blow off valve. There are guys that are running 25-30psi and not using one and they seem to have no longevity concerns with their turbos. I ran 21psi on my factor turbo and never worried about the compressor surge.<br><br>I did some checking, and unless my findings deceive me, I don't think that the Subaru WRX comes with a blow off valve. I could be completely wrong there, but I haven't been able to find mention of one anywhere, and I haven't seen under the hood of a stock one to verify this for sure. I'm not even sure that the 1.8T motors in the Jettas, Audis, etc. come with any type of BOV.<br><br>I'm certainly not nay-saying the benefits of a BOV as I think they can be invaluable for the manually transmission world. They would benefit the most between gear shifts as the BOV keeps the reverse flow of air from slowing down the turbine in the turbo. In turn, that equals more seamless spoolup between gear shifts. The same also holds true for the auto transmission crowd when it comes to racing and they have to throttle for any reason.<br><br>I think the BOV kit is a killer idea, and I intend on checking into one when I put a box on my '03. ;D

 

Monty,<br><br>Compressor surge and bark are not the same thing. You are experiencing surge or a tractive loss of grip on the air.<br>The turbo is not able to grab the air, hence the flutter or surge you hear. Another way to say it would be compressor slip. It is slipping through the air or partially so. Air is a fluid. That being said think of a boat prop that cant grab the water or your hand having a problem grabbing a handful of water. Same thing. This happens on some compressors when the CFM damand is high and the boost pressure is low.<br><br><br> <br><br>Don~

 

Just this have anything to do with disabling or lack of a wastegate?

 

[quote author=LinearX link=board=7;threadid=16360;start=15#154673 date=1056904375]<br>[quote author=Christian Roth link=board=7;threadid=16360;start=0#154208 date=1056749619]<br>[quote author=LinearX link=board=7;threadid=16360;start=0#154166 date=1056742363]<br>[quote author=Christian Roth link=board=7;threadid=16360;start=0#154117 date=1056734668]<br>Sorry guys, a turbo bark is more commonly known as a turbo surge (off throttle turbo surge). It can destroy a turbo, take a look at all the HX40s that where destroyed becasue of this.<br><br>If you look at all turbo gassers they all have blow off valves or bypass valves to elimanate this surge. <br>[/quote]<br><br>Not all turbo gassers have a BOV. Lots of them don't even come from the factory with one, so it can't be that big of an issue at factory boost settings. I know that they're real popular in the gasser turbo/manual tranny world.<br>[/quote]<br><br>Really, last I checked most of the newer turbocharged cars either have a blow off valve or a bypass valve. I would be intrested in knowing which ones don't. If you understand the theory of operation a gasser would have the off throttle surge almost everytime.<br>[/quote]<br><br>I've owned a turbo gasser before, so I understand how they work. However, it is entirely possible to drive a gasser turbo around and never get into boost, unlike a diesel. I had a Buick Grand National and it didn't come with a blow off valve. There are guys that are running 25-30psi and not using one and they seem to have no longevity concerns with their turbos. I ran 21psi on my factor turbo and never worried about the compressor surge.<br><br>I did some checking, and unless my findings deceive me, I don't think that the Subaru WRX comes with a blow off valve. I could be completely wrong there, but I haven't been able to find mention of one anywhere, and I haven't seen under the hood of a stock one to verify this for sure. I'm not even sure that the 1.8T motors in the Jettas, Audis, etc. come with any type of BOV.<br><br>I'm certainly not nay-saying the benefits of a BOV as I think they can be invaluable for the manually transmission world. They would benefit the most between gear shifts as the BOV keeps the reverse flow of air from slowing down the turbine in the turbo. In turn, that equals more seamless spoolup between gear shifts. The same also holds true for the auto transmission crowd when it comes to racing and they have to throttle for any reason.<br><br>I think the BOV kit is a killer idea, and I intend on checking into one when I put a box on my '03. ;D<br>[/quote]<br><br>If you take a look at the GN technology it is pretty old. We have a couple of 7 &amp; 8 second GN here that run very large turbonetics chargers and they all have a blow off valve.<br><br>And yes the WRX has one and so do all the 1.8T and even the S4. The 1.8T actaully has a bypass valve which dumps boost back into the intake of the turbo. Primary reason for this is due to the Bosch fuel injection system. If you dumped the boost to atmosphere you would create a severly rich conidtion and bog the motor.<br><br>Keep in mind you must understand a compressor map before you will understand why a blow off valve is needed.<br><br>Don you said <br><br><br>In fact a compressor surge and a bark are the same thing. Although a bark is more often refered to as a off throttle compressor surge. Although on the compressor map they are both defined in the same region.<br><br>According to Garret the a surge can be defined as an area of flow instability typically caused by compressor inducer stall.<br><br>This happens when the engine is not consuming enough air. What you described is defined as choke not a surge.

 

Christian,<br><br>Glad you brought this back up.<br><br>Compressor surge is a tractive loss of grip. That part was correct. I originally stated the condition was from a high CFM demand and low pressure ratio. I meant to say it was from a low CFM flow at high pressure ratios. This is a condition where the air can no longer stick to the blade area or has a tractive loss of the air. I got the CFM and PR words reversed in my statement.<br><br>Stall, as you brought up has nothing to do with tractive loss. Stall or choke, as you put it...is on the &quot;right side&quot; of the map. Not the left, as the surge is.<br><br>Don~<br>

 

This is just a war on words but a surge/stall are often described as one and the same.<br><br>Heck I know all the engineers at Garrett and BorgWarner do anyhow.<br>

 

Yeah.... <br><br>Don~

 

[quote author=Christian Roth link=board=7;threadid=16360;start=15#155585 date=1057106007]<br>This is just a war on words but a surge/stall are often described as one and the same.<br><br>Heck I know all the engineers at Garrett and BorgWarner do anyhow.<br><br>[/quote]<br><br>No war here. I'm not nay-saying a BOV at all. The original question posted is if compressor surge would have ill efects on a turbo, and I've not seen an instance, even in very high boost pressures, that is has cause premature turbo failure.<br><br>I do know that factory GN technology is old, but I also know that guys that are running 10 second 1/4s don't all have a BOV. On the flip side, I have several friends turbo mustangs that run 7.50 1/4s and they all use a BOV.<br><br>I think they're a great idea in helping maintain the spool of the turbo, but I don't think they are necessity for longevity of the turbo. Just my take, however.