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#128511 - 8th Sep 2005 9:55am BOV's/DV's - Do you REALLY need one?
Anonymous
Unregistered


On a different board im in there's been quite a large discussion on the necessity of blow off valves and dump valves. I've heard before that you need them to prolong turbo life etc, but if thats the case then why dont cars come with them as standard? Some come with recirculationg ones but is that just to keep the noise of the turbo (wastegate flutter/chatter/whatever) down ?

Quote:
Originally posted by Some Guy:
The word 'Wastegate flutter' is often mis-interpreted for the actual wastegate opening and closing which it is not.

The correct term is compressor stall - but even that is slightly incorrect. As you take your foot off the accelerator the throttle body closes, the turbo is still spinning causing a build up of compressed air. This is why your hoses are made from silicone too, because they can expand. As the air compresses it'll force it back through the way it came and over the turbo compressor, it doesn't stall the compressor - just slows it down as it passes over it. It chops the air which is the flutter you hear.

Most cars owners put a dump valve just before the TB after the intercooler, which is a complete WASTE of cold/intercooled which is ready to go straight into the plum chamber if you change gear quick enough.


Dump valves are just a gimmic, they don't offer and performance increase. And more than often can cause problems by leaking etc etc. The only real reason you'd fit a dump valve is to help prevent strain on the turbo seals, but the difference in turbo life will be next to nothing. Its more customer satisfaction, and precaution for cars that come pre-installed.

Like what was said above you don't hear any rally cars with a dump valve do you.
So basically, will it harm your car by not using a BOV or DV? think

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#128512 - 8th Sep 2005 10:19am Re: BOV's/DV's - Do you REALLY need one?
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
Dump valves release the pressure on the turbo when you shut the throttle butterfly. As mentioned above.

This has its advantage and disadvantage.

Advantage is that when you let off, the valve opens due to the pressure change and dumps the air releiving the pressure from the turbo, disadvantage is that its let all the air from the pipes go, and this will need filling next time you get on the throttle making more lag between gears.

The reason you dont hear then on Rally cars is - the car is quicker without a dump valve, as lag is less between gears, and even with the pressure on the turbo, they are still tough enought to last a rally without letting go - they are after the performance rather than making the turbo last. Antilag also doesnt work as well with a DV as you are getting rid of air in the system.

Cars that have them fitted have recirc valves to keep noise down, and as it recircs the air keeps it all in the intake system which is better for economy and emmissions.

The cars that dont have them either dont produce enough boost in std trim to really harm the turbo and its more cost effective to not fit a recirc DV and live with a few 1000miles life off the turbo.
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#128513 - 8th Sep 2005 10:22am Re: BOV's/DV's - Do you REALLY need one?
Anonymous
Unregistered


So would you recommend running with one and prolonging the life of the turbo (if they actually make a difference?) or run without one and get less lag between gears and that lovely noise from the turbo laugh

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#128514 - 8th Sep 2005 10:25am Re: BOV's/DV's - Do you REALLY need one?
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
I killed a 2 T3s on my S13 (before going to a t34) within 8k miles due to not using a DV (Main oil seal went twice) - though it was pushing 20psi on a T3.

Each recon was circa 300, so 300 every 4000ish miles - depends how much value you put on the added performance and noise. For me it was well worth it laugh
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#128515 - 8th Sep 2005 10:26am Re: BOV's/DV's - Do you REALLY need one?
Anonymous
Unregistered


So it makes that much of a difference? What boost were you running and im guessing with your driving stu you were boosting quite a lot tease

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#128516 - 8th Sep 2005 10:32am Re: BOV's/DV's - Do you REALLY need one?
Scooby Offline
Forum Veteran

Registered: 9th Nov 2003
Posts: 5327
Loc: Birkenhead, Wirral.
I would have thought that running without a BOV would drastically shorten the lifespan of the turbo ??

Interesting topic, i know my own knowledge on BOV's and understand the Pro's & Con's of running with a BOV.

My Lag is so very slight expecially if your quick on the up-shift and the turbo keeps spinning up at stupid RPM therefore when i get back on the gas the turbo is already spinning its ass off and builds your boost up with minimal lag.

Surley if my turbo is spinning at 10,000 rpm and i close the throttle on it then the pressure build up will be quite severe and simply start blowing hoses wide open and putting the delicate turbo bearings under allot of pressure ??

Never ran a car without a BOV when its designed to have one think

More info Chewwy mate.... and anyone else with good knowledge on this.

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#128517 - 8th Sep 2005 10:47am Re: BOV's/DV's - Do you REALLY need one?
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
Lol, on full chat the turbo is spinning at 100000rpm on some turbos, up to 250000rpm on others eek

The momentum in the turbo keeps it spinning when you you shut the throttle and still pushes the air at the closed throttle housing for a split second - a DV gets rid of this, otherwise if has to go back through the turbo, causing the chatter noise and putting a lot of load on the turbo.

The DV empties the intake pipes of most of the air which must be refilled by the turbo when you go back on the throttle before you can make decent boost pressure again.

Without the DV, there is still some pressure in the pipes which makes the time to fill them again less - and less lag.

Best compramise is an adjustable BOV, which gets rid of a limited amount of air, taking some strain off the turbo, but leaving some air in the pipes.

Scoobys have quite low lag as the IC and pipe work is close to the turbo and inlet, and the distance the air needs to travel to get to the engine is quite minimal.
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#128518 - 8th Sep 2005 11:05am Re: BOV's/DV's - Do you REALLY need one?
Anonymous
Unregistered


Thats about as much as i know, i also though it'd be good to have a technical topic on the board too laugh

So basically its mainly stressing the oil seals on the turbo? and not worth the hasstle of not running one by the sound of it!

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#128519 - 8th Sep 2005 11:22am Re: BOV's/DV's - Do you REALLY need one?
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
Another thing an atmospheric BOV does is run the car rich when it releases the air. As all the air in the intake has passed the AFM, the car thinks it has "x" amount of air in the system, you get rid of it and the ECU doesnt know, and is still putting fuel in for "x" amount of air when you have just vented it to atmos via the DV and it runs rich - though only until the engine has cought back up.
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#128520 - 8th Sep 2005 3:24pm Re: BOV's/DV's - Do you REALLY need one?
Anonymous
Unregistered


Quote:
Originally posted by Some Guy Again:
If I was to fit a BOV to my car it would reduce performance, infact many GTti owners have disowned their 'loved' BOV. The best place to fit a BOV is close to the throttle body, this means on a gear change the BOV would vent the air pressure that has passed into the intercooler (been cooled) and waiting to go into the plenum via the throttle body. If you change gear quick enough without a BOV (As you do when driving fast) the air won't be wasted, on the piston stroke the throttle body will re-opened and the cylinder will be quickly filled with already cooled air, minimal air will pass back over the compressor.

So back to the BOV, if the air in the intercooler and inlet hoses is vented, the turbo will have to start spooling again to fill the intercooler and hoses, which is quite alot of air mass to replace - AND that will cause more lag.

My car never came with BOV, thats because it doesn't need one. My car is 16 years old, the turbo is original and has done 85 thousand miles worh of compressor stall - and whey its still quicker than starlet.
I know rally GTti's that have competed in events for five years boosting at 29psi with the wastegates welded shut and never needed a rebuild.

I'm just quoting from alot of people that have removed BOVs on the daihard forums. We're all anti BOV =P Besides, turbos can spin at speeds of 130,000rpm - the air flowing over the top of it really isn't going to slow it that much.
He drives a cherade turbo btw**

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#128521 - 8th Sep 2005 3:34pm Re: BOV's/DV's - Do you REALLY need one?
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
Firstly, I find it had to see how a std turbo with a 270 degree bearing would last for 5 years at 29psi with or without a BOV - that is some serious punishment eek

Secondly, the GTTi's use tiny turbos, meaning the volume (not pressure) of air is very small, meaning there is less air coming back at the turbo when the throttle shuts, and the compressor housing blades are also very small and provide less surface area for the air to back up against causing less stress on the bearings. Therefore the smaller the turbo, the less damage it can physically cause.
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#128522 - 8th Sep 2005 3:35pm Re: BOV's/DV's - Do you REALLY need one?
Anonymous
Unregistered


So basically he's chatting shit? smile

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#128523 - 8th Sep 2005 5:32pm Re: BOV's/DV's - Do you REALLY need one?
DavidB Offline
Wiki Guide

Registered: 7th Dec 2003
Posts: 5608
Loc: Bebington, Wirral
Quote:
plum chamber
Is that a plenum chamber??

think
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#128524 - 8th Sep 2005 8:32pm Re: BOV's/DV's - Do you REALLY need one?
rossi-foci Offline
Smartchild

Registered: 4th Oct 2004
Posts: 467
Loc: Wirral
Intersting........ think

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