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The mkiv Supra Owners Club

Think i need a dump!


Andy Metcalfe
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It's a device that makes a big whoooshing noise as you lift off the throttle. Great for scaring animals and young chilren. :biggrin:

 

Yours,

J

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Ash has given you the real answer, it is great for whoosh.

 

The official answer is that it releases excess pressure in the turbo system which avoids 'slamming' the turbos when the throttle is closed due to all the boost still being in the system, and also ensures the turbos continue to spin due to the pressure being released.

 

Its another one of these 'air filter' scenarios. Nobody can say for sure that it helps or hinders the engine. Numerous people have said it doesnt really help, at least one has said it is detrimental to performance, and some say it is worth having as it does help in some small way.

 

I have one, it makes a whoosh, my car is quick, but then at 19psi it bloody well should be.

 

As for the best one, well the HKS and Blitz are both nice units. The blitz is a little quiet, the HKS is slightly louder, and the Apexi is adjustable and on the loudest setting is just NUTS. RJ has one on his Supra so he can tell you just howloud the Apexi one is.

 

Not cheap items, ranging from about £280 upwards, but combined with the air filter it makes the induction noises amazing. HKS price available in Shop!! is you are interested.

 

JB

Shop!!

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So does this mean that the stock BOV not do as good a job as a dump valve

 

I thought that the aperture opening on a most dump valves was about the same as the stock BOV tubing..  I assumed that pressure release would be governed by the minimum opening diameter of the system.

 

The USA guys run a mod with two BOV’s mounted together, presumably to almost double the amount of pressure that is allowed to escape.

 

This route may not make the amazing  sound of a dump valve.

 

But might it give better protection?

 

We need an expert opinion here.

 

The must be one somewhere......

 

Ash your thoughts...

 

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It depends how the air is metered into the engine.

 

The UK spec supras shouldn't have a dump to atmosphere valve because the air being dumped out of the system has been accounted for in the fuel/air ratio.

 

The Jap specs don't have so much of a problem with this because they have a MAP sensor instead of a MAF sensor, but having had a Dump Valve go south on me before I just stick to the standard BOV with an induction kit to make it sound louder.

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I cannot really add any more than what Branners has said in his post. Except to reiterate the technical reason why they are fitted is to stop the axial compressor going into what is called a surge condition when the throttle is suddenly snapped shut.

 

Under such conditions there is much turbulence developed within the compressor housing. This has the effect of placing a lot of drag on the compressor wheel, just at the time when exhaust flow has stopped due to the throttle having closed.

 

The basic theory behind the BOV is the moment the throttle closes, you blow off the boost-pressure in the intake to atmosphere. This is meant to then reduce turbulence and, therefore, reduce the drag on the compressor wheel. The idea being, momentum will keep the compressor wheel spinning between gear-changes if, as I say, you cut the drag on the compressor blades to as small a degree as possible.

 

To my mind, though, it's a case of swings and roundabouts. Okay, the compressor wheel may well continue to spin faster than if there were no BOV fitted. But what about all that pressurised air you have just blown off to atmosphere?

 

After a quick gear-change, where there would normally be pressure remaining in the intake. Now you have to charge the whole intake from scratch. But you have the advantage the turbo is spinning faster.

 

Without a BOV, the turbo would be spinning more slowly after a gearchange but, then again, there will be more pressure in the manifold as you quickly get back on the gas.

 

So, as I say, it could well be a case of swings and roundabouts when looked at from the point of view of overall efficiency.

 

I imagine that the stock BOV will technically be adequate. But there are instances, like with the air-filter, for example, where what has been fitted is *technically* adequate but lacking in other features like a great intake sound.

 

Not that the sound is everyone's cup of tea. Same with the whooosh-type BOV's... some people like them and some people loath them.

 

Personally, I love them. There's nothing like making a big whooosh during gear-changes. :biggrin:

 

I fitted the HKS sequential BOV just after I got the car. I already had the stock valve fitted which was in good condition. Out of curiosity I removed it and really didn't notice any change. Though I didn't engage in any exhaustive tests: just went for a quick blast up and down a few fast A-roads. Then I fitted the HKS BOV and went for a blast and, apart from making a big whooosh during gearchanges, performance-wise the car felt the same.

 

Yours,

J

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Quote: from Paul Booth on 6:26 pm on July 19, 2001[br]
Quote: from branners on 5:08 pm on July 19, 2001[br]...... RJ has one on his Supra so he can tell you just howloud the Apexi one is.

 

JB

Shop!!

 

Is that RJ as in "I'm driving an Integra" RJ?

 

 

Yes and the the answer is BLOODY loud. When blipping the throttle from the engine bay, perople used to comment how my hair used to stick up straight in the air when the pressure was released, because as I lent over my head was directly above the BOV, and I cthen couldn't hear what they were saying LOL. Matt (sorry didn't catch last name) will probably be able to tell you more once he has it fitted mine to his hardpipe.

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