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Discussion Starter · #1 ·
https://app.gfb.com.au/storage/uploads/1656481931_T9010_Instructions.pdf

I'm looking to purchase the GFB Respons BOV for my VN. Upon looking at their instructions linked above(page 3), it appears that the spring preload adjuster doesn't affect how much boost holding under throttle, unlike many BOVs out there. But rather, it affects how quickly, and for how long, the purge valve opens and closes on throttle lift. Since the boost control solenoid controls when the BOV actuates, the BOV operation is not 'direct' from vacuum lines.

So my question is, does the spring pre-load still need to be 'tuned' for the VN? Would leaving it in the 'softest' position just purge air any time I get off the throttle? And would leaving it in the tightest position cause compressor surge because the pressurized air would have nowhere to escape besides rushing back in to the turbo? I assume that tuning the spring preload would be best to reach optimal operation, but I wanted to hear peoples' take on it.
 

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So I don’t have the Respons, but I have the Mach 2 and I have been playing around with the preload tension. I don’t have any definite answers yet though.
 

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Discussion Starter · #3 ·
So I don’t have the Respons, but I have the Mach 2 and I have been playing around with the preload tension. I don’t have any definite answers yet though.
After doing some digging on other Hyundai forums, comments on YouTube, Reddit, etc., it does seem that the preload spring affects turbo operation and has a direct effect on compressor surge. The idea is to use enough preload so that you don't hear the fluttering noise when coming off throttle at high RPM, but also not have the BOV open at idle or at low boost conditions. One can definitely screw up their turbo in the long run if one sets the preload spring way too tight. From what I've gathered, a good baseline would be to have a buddy or set up a camera at the BOV opening and stab the throttle. The valve should close back before the tach needle goes back down to idle speed. I've also read that you can tighten the preload all the way, which would cause compressor surge. And rev and loosen the preload until the surging is gone. Then go for a drive to make sure. In any case, it'll take a few hours to get this just right.
 

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Discussion Starter · #5 ·
GFB has a video to properly adjust their BOV. 👍🇺🇸

I don't have someone to help me do this so it's going to be a pain in the ass to setup. I'm hoping I can rest my iPhone in there somewhere and view the iPhone screen through my iWatch in real time.
 

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Discussion Starter · #6 ·
I installed my GFB Respons BOV and it was easy, especially with the Forge boost pipe that sets the sensors and BOV within easy reach with the airbox removed. It's all right there. Thanks Forge, for making this easy.

As far as the preload goes, I set it about 3 turns in(tightening) from the screw head being flush with the surface of the top plate.

As far as sound goes, I'm a bit underwhelmed. Not by the BOV, but by how the ECU controls the BOV. The GFB BOV sounds great on any other car besides the VN. It's weird. I had it set to 50/50 VTA and recirc and the purging noise is so brief. It doesn't sound like what I expected. It sounds like my dog sneezing. I set it to different ratios. I settled for 10/90 VTA/recirc and I still didn't like the sound. So I'm just going full recirc until my N75 boost solenoid arrives. I read that this could perhaps mitigate these BOV issues.

It also likes to purge air when I go WOT on 2nd gear. I think I have an idea why it does this, and why we don't get that long venting PSSSSHHHH noise from other turbo cars.

I think the ECU uses the electronic wastegate AND the BOV to regulate boost, especially in lower gears to maintain traction. Not only that, the purge noise is brief probably because of the anti-lag tuned in to the ECU. Think about it. The pops and burbles still need an air and fuel mix to go in to the cylinders and combust in the exhaust manifold. The throttle plate would stay slightly open to let some air through at throttle lift off, air is still getting in to the intake manifold for a split second, then the throttle plate shuts. So in essence, the compressed air goes through both the BOV/Recirc AND through the throttle plate to make sweet, sweet pops and burbling. But the time the burbling and pops are over, all or most of the air in the piping has either been turned in to pops and burbles and/or went through the BOV/recirc valve. If ALL the trapped air went through to the the BOV, then we'd get the long, pronounced PSSSSHHHH noise we all crave.

In a turbo car without this form of ALS, the throttle plate would close upon lift-off, so the air would have nowhere to go besides the BOV(or back in to the compressor wheel) which is why the PSSSSSHHHHHH noise is so apparent and long lasting.

I have the Forge Intercooler installed, as well as larger piping. So there's a lot of air volume stuck in those pipes. Probably more than double compared to stock. I've noticed that the pops and burbles are a lot more apparent and it happens all the time now. Probably because that extra air volume being sucked in to the engine at throttle lift to make sweet, sweet noise. I also think that recirculating that air rather than full VTA, is the better choice, at least for the VN. The turbo already compressed that air so to VTA all of it, you'd be basically 'throwing away' all that work done by the turbo. With the extra volume of a larger intercooler and piping, that's a lot of air to VTA. Recirculating all that air could mean that the turbo may not work as hard. Yes, I know the VN has a MAP sensor so that air isn't 'expected' to be there like a MAF car would. But that air is still physically going in to the intake pipe and turbo. And that has to account for something right?

Obviously, I don't have the equipment and lab to test all of this, so I can't provide definitive proof. But the theory and reasoning seems sound to me.

Or maybe the stock boost control solenoid just completely sucks and the N75 Motorsports solenoid will give me the sweet, long lasting PSSSSSHHHHH noise I crave.

Thoughts anyone?
 
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