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First off I am not trying to start a discussion about the advantages or disadvantages, you can make that decision yourself.

I am mainly interested to hear if anyone has run without the factory bypass valve or blow off valve and experienced any negative effects in the long term.

I often talk to people who had a "mates car" that spun off the turbine or disintegrated a thrust bearing almost immediately after they had a blow off valve jam but I am not convinced.

FYI with a decent length of pipe for CAI and a longish pod it is actually quieter than the stock bypass valve (with a pod anyway) there is no need for hektic VL turbo dose.

hmmm

Hjt wrote:hmmm

Indeed...

So I ended up getting motivated to see if I could get the stock valve to seal (it worked ok when I first got the car but started leaking pretty quickly when it got some gt28 up it).
It is a very basic design, two halves of a plastic shell, diaphragm with a seal on the bottom and a preload spring (note that you do have to break them apart and reseal somehow).

Boost in the side port, exhausts out the bottom. Reference port on the top gets positive pressure when you’re making boost which pushes down and (theoretically) helps it seal then when you get off the throttle you will pull vacuum through the ref port lifting the seal and venting the intake.

So unless the case is leaking or diaphragm torn there is literally only one place in can be leaking pressure and that is past the sealing surface.

I ended up using an M16 bolt and some 800 and 1500 grit wet and dry to create a dodgy lapping device, use plenty of oil and very light pressure.

Used an M10 washer to preload the spring a little, it interference fits perfectly in the top housing and holds itself in place.

I am going to glue it back together and try it when I get a chance.

Two answers for the rpice of one...

Yes, I've run without a bypass/BOV on a few different cars (none being factory turbo MX5s though).
I personally never felt any negative side effects in terms of turbine life, or re-spool etc. Having said that, surely the factories who spedn millions on R&D wouldn't invest the few bucks into putting them in if they didn't think they did something positive?

Secondly, if you don't find your modded valve works acceptably, you'll find stronger sprung bosch units that are factory looking and a direct fitment - you can usually get them free from any fully hektic skyline owner you know who now has a wanky loud one installed...

Or brand new cheap on eBay has also been an easy option in the past.

Sean wrote:Having said that, surely the factories who spedn millions on R&D wouldn't invest the few bucks into putting them in if they didn't think they did something positive?

Oh they do make a huge difference to noise levels, I don't know what it would be like with a stock airbox but with a short pod filter it is loud as hell, it would never pass the sound tests. It is not so bad with a longer pod but I have to do a little relocating of some stuff near the passenger headlight to get it to fit properly. The GT turbos will spool up in a light breeze so even on light throttle shift at 2500rpm it is pretty obvious.

Sean wrote:Secondly, if you don't find your modded valve works acceptably, you'll find stronger sprung bosch units that are factory looking and a direct fitment - you can usually get them free from any fully hektic skyline owner you know who now has a wanky loud one installed...

Or brand new cheap on eBay has also been an easy option in the past.

It did actually work quite well, it bleeds a tiny bit of air all the time but held up to 20 psi (approx 1.2mm preload on the spring, i.e 1 washer) and still releases fine. In fact it worked so well that my mate gave me $50 for it and gave me one that looks (and leaks) identical to the old one, so now I have to do it over again.

I thought the Bosch units were found mainly on the euro VW and Audi etc.

i have never run BOVs in my aftermarket turbocharged cars. same goes with my current mx5. when they are working well then there is no problem but they always seem to play up and eventually get unpredictable over time. If manufacturers are spending mega bucks on R&D, how come so many cars still get compressor surge once all the intake restrictions are removed. My old s15 with a factory bov and pod filter would surge like mad.

vrmmmpshhh wrote:i have never run BOVs in my aftermarket turbocharged cars. same goes with my current mx5. when they are working well then there is no problem but they always seem to play up and eventually get unpredictable over time. If manufacturers are spending mega bucks on R&D, how come so many cars still get compressor surge once all the intake restrictions are removed. My old s15 with a factory bov and pod filter would surge like mad.

Because they design a whole system around a number of factors, none of which are likely to include fitting a pod filter?
I'd imagine a lot of people fitting pod filters also fit exhausts and maybe even different BOVs?

stock airboxes and associated airchambers mask the fact that compressor surge still happens if you have a bov or not. ive experienced so many sr20 cars make the ch ch ch sound through the filter when the pedal is lifted.

Like Sean, I didn't initially understand what you were getting at either but now I follow, and you make a very good point.

Dann

vrmmmpshhh wrote:stock airboxes and associated airchambers mask the fact that compressor surge still happens if you have a bov or not. ive experienced so many sr20 cars make the ch ch ch sound through the filter when the pedal is lifted.

I'm not debating that surge happens with a BOV, the physics make it essentially impossible to not encounter some level of surge, we all know it's the pressure differential that opens the valve, the differential means there must be excess pressure built between the compressor and tb, the BOV can't do away with that completely, but more minimises it.

I've run with and without a BOV, and to be honest I didn't notice a lot (any) performance difference - admittedly the seat of my pants dyno isn't that accurate... I could suggest there was less of the ch ch ch with the BOV fitted, but that'd also be open to my logical thought basis bias.

End of the day, I'm probably not going to convince you to fit one if you've decided not to - Each to their own - for me it was more about cheap insurance - A free BOV with the potential to extend the life of a $1000 turbo was a cheap bet.