Pressure Pulsing at Part Throttle, Measurements and a Solution

[erikgross]

Originally Posted by RobBeck

Erik,
You pressure tested your stock BOV with the return venting to atmosphere and it didnt leak until 18psi!?

Yup. I put a piece of tape over the hole in the valve and it held pressure just fine. I went to 18psi or so, but it may hold more. I just didn't test above that.

--Erik

[RobBeck]

You were venting it to atmosphere though right, with the return hole plugged? If not it wouldnt leak until 50+psi or at which time the plastic implodes.

I find this very strange, I have tested the stocker and it leaks pretty bad. Even a brand new 1G DSM BOV begins leaking ~14psi.... of course they all just get worse as pressure increases.

I dont know, I am thinking your gauge maybe bad.......

Rob

Originally Posted by erikgross

Yup. I put a piece of tape over the hole in the valve and it held pressure just fine. I went to 18psi or so, but it may hold more. I just didn't test above that.

--Erik

[erikgross]

Originally Posted by RobBeck

You were venting it to atmosphere though right, with the return hole plugged? If not it wouldnt leak until 50+psi or at which time the plastic implodes.

I find this very strange, I have tested the stocker and it leaks pretty bad. Even a brand new 1G DSM BOV begins leaking ~14psi.... of course they all just get worse as pressure increases.

I dont know, I am thinking your gauge maybe bad.......

I'm pretty confident of my results. The pressure gauge I used was a GReddy 52mm mechanical gauge, which I've verified to be consistent with at least 3 other boost gauges (boost controller, turbo timer, and Defi boost gauge).

The only thing plugged was the little 1/8" hole in the center of the actual valve inside the BPV housing. The inlet, vacuum nipple, and outlet of the BPV were unobstructed.

The testing method was the one illustrated on my web page:
http://www.team3s.com/~egross/3S/Mai...est/index.html

As far as the BPV goes, the test leaves the outlet of the BPV open to atmosphere and pressurizes both the inlet side of the BPV and the BPV vacuum line. This is almost exactly the operating conditions of the BPV under WOT. The only exception is that the outlet side of the BPV may see a pound or two of vacuum due to intake restrictions.

With those test conditions in a quiet garage, any leaks are obvious by the dropping needle on the pressure gauge and the hissing sound.

[Paul H.]

This is a great thread; I hope someone figures out the part throttle surging

[RobBeck]

Youve convinced me. I need to get my stocker back and try it out... could do it in like 2 seconds with some stuff I have laying around.

Rob

Originally Posted by erikgross

I'm pretty confident of my results. The pressure gauge I used was a GReddy 52mm mechanical gauge, which I've verified to be consistent with at least 3 other boost gauges (boost controller, turbo timer, and Defi boost gauge).

The only thing plugged was the little 1/8" hole in the center of the actual valve inside the BPV housing. The inlet, vacuum nipple, and outlet of the BPV were unobstructed.

The testing method was the one illustrated on my web page:
http://www.team3s.com/~egross/3S/Mai...est/index.html

As far as the BPV goes, the test leaves the outlet of the BPV open to atmosphere and pressurizes both the inlet side of the BPV and the BPV vacuum line. This is almost exactly the operating conditions of the BPV under WOT. The only exception is that the outlet side of the BPV may see a pound or two of vacuum due to intake restrictions.

With those test conditions in a quiet garage, any leaks are obvious by the dropping needle on the pressure gauge and the hissing sound.

[jeff97vr4]

My factory BPV leaks as soon as pressure is applied, whether or not the hole is covered. It doesn't leak as bad with the hole covered, but there is still a healthy leak.

These are two pictures of the hose layout, it should be obvious without trying to identify what goes where. If it isn't clear, I could go to "Paint" and try to label things. That is something I hate to do. You can see the pressure taps for the front and rear IC pipes. The blue hose teed off of the outlet of the solenoid valve is to monitor the pressure.

Originally Posted by RobBeck

Jeff,

I have noticed that some turbos seem to use the wastegate actuator source at the turbo outlet/pre-intercooler, whereas the 9b/13g/15g/dr's/etc all use the OE style compressor housings with no bung for the pressure source for the actuators... whilst using the Y-Pipe Nipple as the source. The wrx compressor housings do have them, so when I reinstall I plan on using them to source the actuators..... as opposed to the Y pipe. Perhaps this would help abit with your troubles, would also assure both turbos are working equally as hard.

Rob

Rob,

This phenomena occurs when the wastegates are closed. The HKS EVC IV uses the plenum pressure as the control pressure. The pressure tap was at the stock position at the outside bend of the y-pipe. It is now one of the nipples I added by the outlet for the BOV. Since there is one control point, the EBC, the source of the pressure to activate the actuator isn't important. When I had the 3.6 psi gauge connected to the two IC pipes, there was zero difference in pressure between the two turbos under normal operation. The two turbos appear to have very similar flow/pressure behavior.

There are advantages and disadvantages to using the pressure at the outlet of the turbo for the control pressure. With an EBC, there isn't a good reason that I can think of to not use the plenum pressure for the control level.

Jeff

[LeMoN1438]

Very interesting thread...This is making me rethink buying the greddy type s bov to solve my part throttle problems. I am now thinking whether the EVO or the EVO MR bov will help solve this problem, as that is a stock style bov but still an upgrade. Keep up the good work trying to solve this annoying issue.

[RobBeck]

If you use the smaller bung on the Type S it will react alot faster, but leak as well. The 1G DSM is also a great OE style BOV, upgrade from our stocker.

Jeff,

I believe using the comp housing for pressure sources Y'd together will definitely keep the turbos working equally together.... probably more notable at higher boosts tho. Either way, it doesnt sound like its your issue..... did you try the Type S using the smaller bung too (sourced from the plenum side of the throttle body)?

Rob

Originally Posted by LeMoN1438

Very interesting thread...This is making me rethink buying the greddy type s bov to solve my part throttle problems. I am now thinking whether the EVO or the EVO MR bov will help solve this problem, as that is a stock style bov but still an upgrade. Keep up the good work trying to solve this annoying issue.

[jeff97vr4]

Originally Posted by RobBeck

Jeff,

... did you try the Type S using the smaller bung too (sourced from the plenum side of the throttle body)?

Rob

Rob,

This was over a year ago, , and I think I may have tried just capping the nipple for the lower chamber. Both of my Greddy S valves were sold before I confirmed that the problem wan't caused by leaking valves. The problem revolves around being able to lose or bleed off pressure at the right time and still not leak at high boost pressure.

Incidentally, I had thought about various schemes to keep the wastegates open below some rpm and throttle position to control the pressure in the IC pipes. But the potential solutions were too complex so I didn't even see if that could have solved the problem.

Jeff

[RobBeck]

Ok well its just FYI about the double edged sword you speak of, a tight non leaky BOV causes this surge (which doesnt seem to be too much of a problem or is unnoticeable for most) but the loose leaky BOVs eliminate/reduce it. Using the smaller bung on the type S will make it react much faster, but make it less performance oriented too. I still need to refer to your fix for the HKS to get a better understanding, but are you saying it now reacts faster + doesnt leak at all now?

Rob

Originally Posted by jeff97vr4

Rob,

This was over a year ago, , and I think I may have tried just capping the nipple for the lower chamber. Both of my Greddy S valves were sold before I confirmed that the problem wan't caused by leaking valves. The problem revolves around being able to lose or bleed off pressure at the right time and still not leak at high boost pressure.

Incidentally, I had thought about various schemes to keep the wastegates open below some rpm and throttle position to control the pressure in the IC pipes. But the potential solutions were too complex so I didn't even see if that could have solved the problem.

Jeff