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When do you need / not need a BOV?


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They are not essential, however, they do serve a purpose. You will probably find that whatever FMIC kit you buy will have a port in the piping for a DV.

Its personal preference whether to run a DV or not, i like the sound of my HKS, but some DVs (baileys) are prone to leaking boost which is never a good thing.

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Worth running one IMO chatter is nice but on bigger turbos the lag is noticeable on gear changes when you dont have one fitted. However a good adjustable DV is perfect as you get chatter at low boost and no shit noise, and dump at high revs when needed.

A bit of positive pressure on shut throttle is actually goid for response but difficult to achieve!

Edited by The Toffinator
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Worth running one IMO chatter is nice but on bigger turbos the lag is noticeable on gear changes when you dont have one fitted. However a good adjustable DV is perfect as you get chatter at low boost and no shit noise, and dump at high revs when needed.

A bit of positive pressure on shut throttle is actually goid for response but difficult to achieve!

My pal ran no DV on his VF28 and then put it back on, he said there was a noticeable difference in spool time, it was better and less lag.

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My pal ran no DV on his VF28 and then put it back on, he said there was a noticeable difference in spool time, it was better and less lag.

Possibly mate. But as i said i ran back to back on both the TF035 And my VF24 And could notice it both times. Possibly if your very quick with gearchanges it may be less noticeable but normal fast driving it was mega noticeable. Properly slows the turbo down and is well documented. BUT as i said a small amount of charged air in the system does help. Hence why i now have my R2D2 Set up to only dump very quickly and when flat out.

Try it yourself dan ;)

And im not sure unless you set up some sort of system it may be possible, possibly using a forge Split r or whatever they are called

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Unless i'm getting mixed up and he ment the other way about lol.

Yeah man i'll defo be trying it out in mine when its done :) Ive only got a crappy HKS rep but it didnt leak in the GT so that was a bonus lol.

I do prefer that idea of only dumping at high boost thats why i mentioned it up there ^^^ How do you rate the Sard DV then Toff ?

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Hahaha easily confused mabye! And i also have a hks rep and cant fault it really just wanted a proper adjustable one so got the Sard.

Really impressed with it makes an awesome sound and at low revs/boost is pretty quiet but when pushing on a bit its louder but a different noise, then full boost is awesome sounds fantastic and keeps the turbo on song! Deffo recconend one

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Possibly mate. But as i said i ran back to back on both the TF035 And my VF24 And could notice it both times. Possibly if your very quick with gearchanges it may be less noticeable but normal fast driving it was mega noticeable. Properly slows the turbo down and is well documented. BUT as i said a small amount of charged air in the system does help. Hence why i now have my R2D2 Set up to only dump very quickly and when flat out.

Try it yourself dan ;)

And im not sure unless you set up some sort of system it may be possible, possibly using a forge Split r or whatever they are called

So would this just be a case of running a stiff spring setup?

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I'm running a Zisco TD04 kit externally gated. 0.7spring.

I had a baileys DV on my CT9 but having got rid of the long route pipe work, I had no place to fit it. So basically no DV currently I don't THINK it's laggy... But I've never had a DV fitted an I don't think I particularly want one as I'm enjoying chatter. I do plan on mapping mine at 1bar without one so were see how that goes...

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what about if you run an external wastegate ?? And if you don't have one could you use a bov instead or will I need a wastegate ??

BOV and wastegate are not related, the BOV is on the inlet side, wastegate is exhaust side.

A wastegate (whether it is internal or external doesn't matter) is what controls your boost, it opens to let excess exhaust gases bypass the turbine wheel once you have reached full boost (this will either be down to your boost controller, or the wastegate spring itself if you don't have a boost controller).

A blow off valve releases pressure from the inlet side, when you lift off the throttle the turbo will still be spinning but because the throttle is shut the air can't go into the engine, the only way it can go is back the way it came - through the turbo. It isn't good for the turbo, so the blow off valve releases the excess air.

Edited by ste91
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i use the original recirculating bov and get chatter from compressor stall, ive always reckoned it was because it's too pussy to depressurise the whole intake fast enough, but im not certian. kind of a safer middle ground to not running one at all if it is.


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BOV and wastegate are not related, the BOV is on the inlet side, wastegate is exhaust side.

A wastegate (whether it is internal or external doesn't matter) is what controls your boost, it opens to let excess exhaust gases bypass the turbine wheel once you have reached full boost (this will either be down to your boost controller, or the wastegate spring itself if you don't have a boost controller).

A blow off valve releases pressure from the inlet side, when you lift off the throttle the turbo will still be spinning but because the throttle is shut the air can't go into the engine, the only way it can go is back the way it came - through the turbo. It isn't good for the turbo, so the blow off valve releases the excess air.

Technically they are the same and you can use a BOV as a means of controlling boost pressure, look back a few years to the frenzy turbo era of rally engines and you will find they used a BOV to control boost pressure on the compressor side of the turbo.

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Technically they are the same and you can use a BOV as a means of controlling boost pressure, look back a few years to the frenzy turbo era of rally engines and you will find they used a BOV to control boost pressure on the compressor side of the turbo.

Sounds like a poor way of controlling boost to me, letting the turbo spin much faster than it would if it was controlled by a wastegate, would surely put the turbo out of it's efficiency range and then keeping the BOV open to release air you've essentially just got a massive boost leak...

Technically they may be the "same" as they are just valves that allow air through them but in that sense you are just going to confuse people.

Edited by ste91
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Not at all a poor way of controlling boost pressure, there are still many people that use this method because its cheaper, simpler, accurate and responsive. The BOV's are modified with the use of much stiffer springs, some even utilise a twin BOV arrangement.

The only downside is that those using air flow meters, may upset the AFR's if routing back into the inlet as the incoming air has already been accounted for.

Some people have numerous trophies to back up this system, so it works well enough. But hey thats the world we live in where external wastegates are considered the best thing since sliced bread, when infact it couldn't be further from the truth :)

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