Looking for compressor surge solution

[GJarrett]

MAP stage 2 block with NX2 turbo, CVF intercooler and catless downpipe, PD Tuning 93 octane tune dialed in w/25 lbs boost.

Under full throttle load, right after the boost eases off, I hear a single or double "chirp" that sounds like tire chirp but isn't. After feedback from others on this site and further research, I think what I am hearing is compressor surge / "turbo shutter". On the lower boost 87 tune it does not do it. I am seeking advice on a fix while keeping the tuned boost at 25lbs for maximum hp on 93 octane. We went through over a half dozen revisions and datalogs getting the tune dialed in, and I noticed the chirping started about halfway through the process at about 23 lbs boost.

I am not a turbo expert but from what little I know, I believe a BOV could fix it, but at the cost of turbo lag, which I am determined to avoid as much as possible. I've noticed a few discussions regarding the Go Fast Bits DV+ which seems to mitigate lag.

Would a DV+ also prevent the compressor surge? If not, how can I fix the surge?

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[ihasnostang]

i thought something other than using factory recirc was required when using a bigger turbo. Here is a microphone infront of the air box outside the grille with all the factory tubing. you could try the VTA mod temporarily to see if that makes the problem go away.

 

[5550snotamerc]

Do you have the stock, uh BPV (I think that's what it's called, I am new here)? Have you asked PD about it?

 

[Buldawg76]

MAP stage 2 block with NX2 turbo, CVF intercooler and catless downpipe, PD Tuning 93 octane tune dialed in w/25 lbs boost.

Under full throttle load, right after the boost eases off, I hear a single or double "chirp" that sounds like tire chirp but isn't. After feedback from others on this site and further research, I think what I am hearing is compressor surge / "turbo shutter". On the lower boost 87 tune it does not do it. I am seeking advice on a fix while keeping the tuned boost at 25lbs for maximum hp on 93 octane. We went through over a half dozen revisions and datalogs getting the tune dialed in, and I noticed the chirping started about halfway through the process at about 23 lbs boost.

I am not a turbo expert but from what little I know, I believe a BOV could fix it, but at the cost of turbo lag, which I am determined to avoid as much as possible. I've noticed a few discussions regarding the Go Fast Bits DV+ which seems to mitigate lag.

Would a DV+ also prevent the compressor surge? If not, how can I fix the surge?

If you are still using the stock BPV then a GFB DV+ kit will help with controlling the flutter and prevent turbo lag as well. It allows the stock valve to react faster and more precisely to the turbo boost signals. I have the kit on my 2020 and noticed a big improvement right away, the stock BPV is known to leak boost at steady state cruising speeds. Just make sure your BPV o ring is yellow in color not orange, the kit will only work with yellow o ring valve. They changed the BOV in 18+ so your 17 should be good with yellow o ring.

BD

 

[robvas]

How will a different bov cause turbo lag?

 

[GJarrett]

Yes I still have a stock BPV. I plan to contact Ryan at PD Tune after the holidays, but am more inclined to try a mechanical solution rather than a change in tune - because if this is my problem I would think a fix via tune would entail lessening boost (and hp) to under 23 lbs.

Thanks to all for the input and help. I will take a look at mine and make sure it has a yellow O-ring, then give the DV+ a try.

@robvas , we have bypass valves (BPV) which recirculate the excess blowoff back to the intake which keeps more internal pressure available for the turbo to use. A BOV releases it all into the atmosphere (that's the "whoosh" sound some like to hear), so the turbo then has to spool from the starting level of 0 lbs boost again to build back the boost that has been completely released - so there's more lag time while that happens. At least, that's how I understand it. If I'm wrong then someone else here with more knowledge can clarify

 

[5550snotamerc]

Yes I still have a stock BPV. I plan to contact Ryan at PD Tune after the holidays, but am more inclined to try a mechanical solution rather than a change in tune

I just meant to ask them if they knew what was happening. Nobody wants less powah!!!

 

[robvas]

@robvas , we have bypass valves (BPV) which recirculate the excess blowoff back to the intake which keeps more internal pressure available for the turbo to use. A BOV releases it all into the atmosphere (that's the "whoosh" sound some like to hear), so the turbo then has to spool from the starting level of 0 lbs boost again to build back the boost that has been completely released - so there's more lag time while that happens. At least, that's how I understand it. If I'm wrong then someone else here with more knowledge can clarify

that's definitely not how it works. You'd have an infinite loop of boost if it did

 

[Buldawg76]

If the BPV or BOV is slow to close after venting it reduces the residual pressure in the intake tube that has to be replaced which can take a few tenths of a second more than if the valve closes quicker.

The GFB DV+ uses both a better sealing piston face and boost pressure differential to aid in a better seal and faster reacting BPV that improves turbo spool times.

BD

 

[GJarrett]

BD thank you so much for your replies; I think I see now what you are getting at. So, if I follow the reasoning correctly: by the DV+ reacting more efficiently and quickly, it will lessen the amount/intensity of the manifold pressure dump that is causing the surge, thus helping to prevent it? I think that is what you are trying to tell me (?)

PS: I just emailed my tuner to get his thoughts

 

[robvas]

Dumping to the atmosphere is likely going to solve your problem (and possibly running the valve off vacuum instead of electronic so it reacts faster). You just can't get all the air out dumping back into the intake as it is setup right now.

 

[Buldawg76]

BD thank you so much for your replies; I think I see now what you are getting at. So, if I follow the reasoning correctly: by the DV+ reacting more efficiently and quickly, it will lessen the amount/intensity of the manifold pressure dump that is causing the surge, thus helping to prevent it? I think that is what you are trying to tell me (?)

PS: I just emailed my tuner to get his thoughts

Yes the GFB DV+ improves the efficiency and responsiveness of the stock BPV operation. It can actually be setup two different way by adding or removing a spring, so it reacts faster than the stock BPV or without the spring it is approx the same as the stick BPV.

IMO the stock electronic BPV will react faster than a vacuum operated BOV since electricity travels and the speed of light whereas the vacuum signal travels at the speed of sound.

Here are the instructions for the GFB DV+ kit. For what it's worth my eco with the FP tune makes 24 psi max boost and I have the DV+kit with no turbo surge or stutter issues.

https://gfb.com.au/products/blow-of.../dv-plus/t9358-suits-mercedes-ford-and-volvo/

BD

 

[robvas]

The speed of sound is 1,125 feet per second. Vacuum signal would travel through 5 feet of vacuum line in 1/225th of a second

Keep in mind that basically every Mustang centrifugal supercharger or turbo kit out there uses good old vacuum lines and mechanical style BOVs, and when they are set up with a large enough BOV and venting properly, they don't have compressor surge. Even with 1000+ hp worth of air.

Electricity is faster (not quite the speed of light), but you've also got electronics that are processing the signals, a cpu that has to make a decision, and solenoids that have to fire, but with either style that microsecond of a delay is not going to cause any surge.

 

[5550snotamerc]

You all are forgetting one thing-BOV go "PSSSHHH!!!"

 

[Buldawg76]

The speed of sound is not a constant and varies with air density, humidity and altitudes so can be anywhere from 1000/1130 FPs or so depending on those and other variables. Thats why a firearm projectile or jet plane can break the sound barrier anywhere from 1000/1130 or so FPS.

Electricity is measured as the speed of light which is 186,000 MPS so just a little faster than sound.

So, on the big power turbo cars electric is not the best option. They also rely on high pressure CO2 bottles to control and maintain the extreme boosts they run to make those big numbers. Vacuum and springs are not really good at controlling 60+ psi of boost using a BOV.

Our cars are nowhere near that level so it's just personnel preference IMO.

BD

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