RB25GUY

^ correct anything under 20 psi with any reputable turbo you will be fine i called COMP TURBOS about running a 5562 TBB without a BOV he said it was fine unless you plan on running more than 20 psi but he did suggest on the bigger turbos to run a BOV

joe645733

Alright so after investigating the second BOV, I removed it and it's most likely a knockoff (from Tial). Opened it up and didn't see anything visually bad, but the spring inside is super tight. As soon as I found this out, I did order a real Tial 50mm BOV.

So I did some research online and some people cut the spring to loosen some tension. So I did this just for the hell of it until my BOV comes in.
So after cutting, under boost, I'm finally hearing it open up and make noise. My question is...why am I hearing the BOV slightly delayed AFTER my surge from the turbo? Still too tight of a spring? And I was only giving it maybe 5psi from the turbo.

Thanks, guys

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E85 1j SC300

Kingtal0n

This is a common problem when placement is too far. move the bov closer to the compressor and the pressure drop created by it will "get there quicker". Again think of my example of the bypass on the cold side- you have to empty the intercooler volume as you empty the hot-pipe. Any pressure drop that registers in the hotpipe will also have to be recorded in the cold pipe and intercooler.

Other things that may improve response:
Make the bypass easier to open (adjustments to spring/diaphragm)
Increase vacuum signal (use large vacuum line, sole dedication to the bypass, short as possible)

I go through this debate constantly and have provided 10 examples over the years. Another example would be:
Imagine your hot pipe length was adjustable and that there was no intercooler or cold side at all. Please the bypass as far away as possible from the compressor- 20 feet away for example. Now fill the plumbing with 10psi of air pressure, and open the bypass and measure how long it takes to empty the tube. Now repeat the test with the bypass 30 feet away, then 40 feet away, then 50 feet away, 1000, 50000, infinity. As the length of the tube approaches infinity, the difference in pressure drop per unit time (change in pressure per millisecond is how we measure response) approaches zero, in other words, there is no relief whatsoever when opening the bypass since there is an infinite amount of air to evacuate. You therefore see the important of keeping volume as far from infinity as possible, that is, as close to zero (as short and small of a bypass tube connecting the compressors outlet with the bypass as possible while still meeting minimum size requirement for anticipated flow).

To put this another way, as you increase the distance from the compressor, and increase the air volume that needs to be evacuated by the bypass, the result is that it takes longer and longer to empty the plumbing, which means the pressure remains elevated for longer and longer periods of time (while it is elevated, it is causing surge condition) Whereas, if you install the bypass directly on the compressor the response is instantaneous, since it doesnt need to empty gallons of air volume from the plumbing. Indeed many manufacturers are installing their bypass directly on the compressor these days. The running engine helps evacuate what is left in the remaining plumbing, but if we consider the entire packaging together then it would also make sense to have a bypass on the cold side as well. This isn't done normally since the cost and additional complications (another place for something to leak or break, etc...) and that many systems do not need an extra bypass. I throw this out there only to make it clear what I am suggesting- that the first place I would put the bypass is on the compressor and then close to it as possible. For sure. Absolutely if possible. And then if I exhausted all the different styles and designs of bypass available within my budget (for example, if this is a budget application without access to any brand new parts) there is a niche category of cars that fit the bill for this double bypass situation no doubt. I myself run twin bypass valves on my budget street application, because it just happened that way I never planned it to be that way and it works magically, and this is not my first car with twins, so I am all for additional bypass complexity and fancy recirculate tubes if the fates have steered you there by coincidence. You should be able to get twin ill-placed bypass valves to work as effectively as one single well placed bypass.

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5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

joe645733

Your first couple parts is what I needed. I understand the further it is, the greater the pressure drop will occur.
Appreciate it.
This knockoff BOV is actually before the intercooler, roughly 2ft away from the compressor side of the turbo.
I've cut the spring in two parts and I'm almost getting there.

BUT, what's too easy of a tension spring? I'm cutting increments of maybe a half inch at a time. But again, I did get it making some noise.

Thanks again, dude.

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E85 1j SC300

R3b

The tail springs are based on vacuum pressure, make sure you get the right one because if you get too light of a one it will be a massive leak and too heavy it wont open nicely.

Kingtal0n

So this is how the adjustment goes. Ideally, a bypass will hang open at idle. The one on my hotpipe in the picture on page 1 of this thread hangs open all the time at idle. So I have the spring setting adjusted fully loose. This is how the OEM bypass operates, and this is what you want on a MAF car. Allowing the bypass to recirculate at all idle will minimize noise at the maf sensor. The maf is very sensitive to the incoming air, and if the bypass shuts as the engine returns to idle, the compressor wheel's mild surge behavior will be detected at the maf sensor, even if you cannot hear it (I can hear it easily because I run OEM exhaust but many do not). In other words, to keep the incoming air signal to noise ratio consistent at the maf sensor, you want the bypass to open very easily under all situations and stay open- except wide open throttle of course. Too loose of a spring/diaphragm and it may leak under boost situations. So there is a borderline between a weak setting that allows the bypass to open easily- and stiff enough to hold boost pressure.

If the bypass is not recirculated, then you cannot run an open bypass at idle. The only time you can allow it to open is when RPM > 1400 and TPS voltage < 0.5v~
In other words, above idle, full throttle lift situations. This is when the ECU pulls 100% fuel (complete fuel cut) so it is safe to blow up the maf signal with an atmospheric bypass. This is what the HKS SSQV shines at doing- it generally mixes very well with MAF engines because of it's inherent characteristic of only opening during this scenario.

R3b

Or you can run a blow through setup with the maf or go towards map tuning so you dont have to worry about leaks and recirculating 24/7 like a normal maf setup. Just my .02, I love my blow through ka-t, could basically run with no bov, turbo or even a blown coupler. There is downsides but im loving it.

fatduece

bovs are for suckers