Bypass V Blow Off valve operation

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-Nemesis-

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Are these the exact same thing? What's the difference if any?


I have one of those Bosch type bypass valves (adjustable) which is vented to the atmo at the moment. Fitted to a centrifugal blower system.

I love the blow off sound at high revs, but I hate how the thing opens constantly on a closed throttle. So if I change gears at 1500rpm it still goes pshhhh... And worse than that, if you are slowing down under compression the valve is open constantly so you have a constant SSSHHHHHHHHHHHHHHHHH on deceleration.

Just wondering if a 'blow off valve' is any different, in that it won't do this (why doesn't a turbo)? Or is it just a characteristic of a centrifugal system?


I had considered plumbing the bypass back to intake, then running a blow off for high boost revs, but just realised it's probably going to do the same thing?
 
Nem- I finally got my TIAL 50mm blowoff working flawlessly (contrary to popular belief) but it makes a lot of noise also. Not ricey, just a SHHHHH like you stated. Mine needed a 3psi spring to function correctly... now anytime I have vacuum at under 10hg it slams shut and for the most part isn't too bad. I get lots of looks because it's not like a typical turbo but I absolutely love mine. I scared a camaro SS driver in freeway traffic when I pinned 1st gear and let off... SHHHHH was so loud he weaved off the road.

Anytime your off the gas pedal it's supposed to pop open, you could try putting a sock/wristband around it to muffle some sound. Recirculating BOV is much quieter than venting. Also, if your rocking a bosch type BPV, it has a 1'' port and if you throw a breather filter on it's port it will shut up some more. Hows your procharger treating ya? So far 7,000miles w/o any hiccups.
 
So if vacuum opens them like a bypass valve, why can you get blow off valves with different 'psi' springs?

I would like one that only opens when the throttle closes and there's boost in the system, not from only vacuum. Impossible?
 
Maybe adjustable blow-off will be OK. You can than make a spring harder or softer. When the spring is harder then vacuum by itself can`t open the valve
 
TIAL motorsports do not list it's 3psi supercharger spring but it's only 3psi. Mine is open at idle and shuts once i apply 1/4 throttle. I had an issue with when it was closed at idle but since I moved mine about 4'' from my blower on the other side my idle was corrected. I tested mine with a straight pipe and no BOV/BPV alltogether and the car ran fine, weird right? MAF doesn't like having so much air being dumped so close. If you rcked a 7psi spring i bet you'd love it. It would be silent at all times except for mid-high rpm deceleration. the real trick is mounting it on the driver side(hot side). I noticed increased throttle response tho with the 3psi spring... since centri's pump so much air at idle it is working against the impelelr and actually increases parasitic drag at low rpm, not such a big deal that you MUST run one but this is coming from experience changing out virtually every spring TIAL makes.
 
Nem,

Just so you're aware venting direct to atmosphere is illegal and coppers listen for the blow off in action.

You could try muffling it with a filter or small muffler off a bike.
 
Illegal hey, didn't think of that. What's the legaility, noise pollution? Guess I'll plumb it then either way, rather not be cop bait (more than an obviously supercharged V8 sound is heheh)
 
Basically, a custom turbo or supercharger system is also illegal in the U.S. However, guys like us still vent the air out for fun. Anyway, I'm not sure about the bypass valve, which I think is more suitable for root supercharger, but I know the blow-off valve works wonderfully either with turbo or centrifugal supercharger. I'm using the adjustable blow-off valve and I could make it open soon or late. I made it open late so it only opens under hard deceleration.

With centrifugal supercharger and if you don't want to vent it out to the atmosphere, you can route the outlet pipe back to before the supercharger's inlet. This is what most factory turbo cars do. It's quiet this way.
 
Yeah Steve's right.... if you rock a recirculating BOV/BPV just pipe it to the procharger inlet and adios all sound. TIAL's are 360 degree vent so it's out of the question for me.

I used a thick Wilson streachy wrist band over the whole unit and it muffled a few Db.
 
Or.....you could just do without it altogether.:wink:

I do know for a fact that a Vortech will chatter. I have also read that chatter is really bad for an internal belt driven (rather than gear driven like Vortech) supercharger.

Putting a filter on it does muffle it quite a bit.

KC
 
Both Nemesis and I have prochargers which are gear driven units, not belt driven internals. I thought Powerdyne was the only "belt driven centri"??

I really had issues with my serpentine belts shredding but a stronger tensioner healed that.


Nemesis-Hows your 4 runner doing? get your problems resolved?
 
Yeah I sorted my LPG problems and it's running surprisingly good at the moment. Boost loves 108octane LPG!

The only problem is the LPG injection seems to emphasize that MAF problem where it changes from vacuum to boost. Are you still running the MAF spf?

I put a filter on the end of my bypass today and it certainly shut it up.
 
Yeah still running MAF. I realized my issue was just fouled plugs and once I swapped out my old NGK v-powers for iridium it was like nothing ever was wrong

Geeze, 108 octane must be a fun daily fuel lol
 
So you dont get that weird miss at those revs now? I hardly notice it at all on petrol but lpg is bad at anything other than full throttle.

I think it's because the LPG ECU piggy backs the petrol injectors, so it amplifies whatever goes wrong.
 
Yeah I have not had a miss in the past 4000 miles. Very smooth power down low. My best friend out here races his EVO X against me and we are good competition for each other... neck and neck! I plan for a real tune in a few weeks when I get off for sumemr break but OEM everything is proving very reliable so far.


Think I could pick up some extra hp by raising my octane? I always run 91 premium out here but wondered if octane booster would help? I only notice considerable power loss when i'm climbing elevation... 5,000ft out here and a few hundred at home!
 


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