Boost leak test and the BPV

Hi guys,

I've got a newly built engine and am currently tuning with mike@stratified. An issue I have had since before the engine was built and still after, is a hesitation when accelerating moderately at around 3000 rpm. If I plant it it is nice and smooth and strong. Mike told me it is not tune related. So I did a boost leak test up to about 18psi and found that the stock BPV was leaking all the way down to about 3psi, so I bought a second hand stock one, felt the same and was leaking the same. I then purchased a corksport BPV and installed it, this seemed to smooth out the hesitation quite a bit. I then did another boost leak test and found that it is leaking much worse. Strange thing is that the car feels quite good, but I don't understand why they are leaking so much. I've attached some videos of the leaking and some logs.

Video of Stock BPV
https://youtu.be/mN-6O9vmmck

Video of Corksport BPV
https://youtu.be/DYDE3ibjxwY

Logs:
Part throttle hesitation - With stock valve. If you look at sheet 2 I have made some graphs which highlight the issue.
WOT3rd Stock - A WOT log with the stock valve
WOT3rd Corksport - A WOT log with the corksport valve

Do you have a leak in the top vac line perhaps? That might explain why multiple are leaking.

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I thought that too. So I replaced that line. Do these things typically have a 100% seal? There doesn't appear to be any kind of rubber seal on the stock or Corksport one.


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Stock uses an O ring. Not sure about CS, but it should be the same or a gasket. If you have air coming out of the bypass hose, it suggests an internal seal (unlikely on 3 different ones) or a problem with a reference line somewhere (like the barb on the manifold perhaps). If you cap of the bypass hose (the one you are covering with your hand in the vid) so you still have leaks elsewhere (soapy water is good for finding them)? Also, where is your boost tester attached?

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I never had much success proving anything with a home made boost leak tester. There will almost always be valve or two opened that can bleed pressure out of the engine or into the crankcase past the rings.

The best boost leak test will be with smoke machine and/or soapy water while running the motor under load on a dyno.

Soap helps to find leaks, but you are right, you can't put much stead in the actual PSI figures. I always have slow leaks from the crank case but I could diagnose a leaking TMIC gasket and a BOV line leaking using a home made tester.

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Thanks for your help on this guys.

When I was refering to the seal, I meant should there be a rubber seal on the piston. Both BPV's use the stock gasket between the mating surfaces which is there, but neither seem to have anything to provide a perfect seal where the piston seats on the body.

This afternoon I double checked the vacuum line and it has no leaks. The nipple on the manifold is not leaking, confirmed with soapy water. I even pushed a plastic tube through the nipple to confirm it wasn't obstructed. The thing is, I don't think either BPV is opening to let the air out. I think it is just leaking past the piston.

When testing I used 2 methods
1. Boost leak tester on the hot side of intercooler, so pressurising all lines that typicaly see boost, with bypass hose disconnected
2. Boost leak tester on the intake with only the VC breather hose disconected and blocked off at the intake. With this method I only get leakage through the crankcase and out the breather. Have sprayed soapy water on all lines.

The stock has a diaphragm which seals with pressure on both ends, and corksport uses a pressure seal http://images.tapatalk-cdn.com/15/09...8078c1754d.jpg so neither should leak with pressure applied to both sides. Something else seems wrong. Could the line be blocked maybe?

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There has been a superceed pcm, might be worth a read in msf for any related topics?

I've replaced the line, checked the barb for blockages. I've even removed the BPV with the line still attached, blocked off the hole in the intercooler, pressurized the system and then tried to push the valve open, which I couldn't. I'm at a bit of a lose to understand why it is leaking. I've emailed corksport to see if they have any suggestions.


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I've been in contact with Corksport about this, and they have given me permission to post their response here. I'm keen to get people's opinion. Particularly about my comment regarding the turbo needing to work harder to make up for the lost air.

Corksport:
Gavin,

Our CS Bypass valve does naturally leak air around the seat as most aftermarket units do. And as you have already noticed it occurs around the bottom of the piston where it seats against the body. This is due to the fact that the two machined surfaces cannot make a perfect seal against each other in this regard. This is there for several reasons in respects to design, cost, complexity, and much more.

The cut of the piston allows the valve to be able to create much less turbulence. Which in turn allows it to operate much more efficiently and push all the air where it needs to go. The guys who have really loud recirculated valves also have very inefficient valves. The noise actually comes from air hitting sharp bends and or corners in the unit that create noise. Another aspect is the speed of the unit. If an O-ring was there it would cut down on response time which reduces efficiency as well. That being said the unit will not cause any hesitation due to the recirculated nature of the MAF system on these cars. No air is ever vented out and lost so no changes in the fuel curve will exist.

Another really interesting thing that most people miss is the fact that your OEM BPV is supposed to leak from the factory.


Notice the hole in the OEM unit?(blue arrow) But that’s a long story for another day. In an nutshell unless there is some physical damage to the unit rest assured it is working as needed.

Me:
Hi Vinny

Thanks for your response. That does clear up a fair bit. However, if you look at the videos I linked, it seems your BPV leaks significantly more than the oem. While I understand that all of this air is being returned to the intake post MAF and is not being lost. This allows for the car to drive smoothly and perform as normal. I question though, how much harder the turbo needs to work in order to make up for this "lost" air from the boosted part of the intake tract.

My first option for a BPV would have been the Synapse valve, which offers lightning quick response and has an O ring for a perfect seal. I decided on the Corksport as from what I read it seemed to have the best of both worlds for a cheaper price. I didn't expect it to leak so much though.

Regards
Gavin

Corksport:
Gavin,

From the testing we put on the product we did not see any dramatic changes in turbo efficiency. Nothing showed us the turbo was working extra hard compared to normal. It was not till higher boost pressure where it became more of a concern and at that point the turbo was starting to lose efficiency it-self.

The synapse BOV is a great valve. I have personally used it and may others before. The biggest draw-backs with the Synapse are its price and much larger size. One of our great outcomes was able to deliver a quick response while creating a smaller package which helped for fitment with larger FMIC piping. It’s quite the challenge to get the perfect of everything in regards, to price, function, size, sound, etc. But we feel with deliver a product that offers the best value.

Vinny.




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