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To Blow or Not


Guest freemchr

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Guest freemchr
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One of the first mods for my car Im thinking at the moment is a blow off valve.

What do you guys think? Then again I dont want to be on the same level as some idiots in old corolla's wooshing around.

Should I leave it stock or add one? Im not even too sure about the benefits of having one or if their is any at all. I dont want to be seen as some tosser driving around a nice car. ;)

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Guest shorsfall
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I think you should blow. Im not a ricer by any means but I do like the sound of a blow off valve. The purpose of the valve or waste gate is to stop back spin on the turbo. If you accelerate heavily and then deccelerate the turbo is obviously winding up then down. The valve just realeses this build up insted off the turbo back spinning.

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  • Member For: 22y 2m 18d
  • Gender: Male
  • Location: South Coast NSW

As far as I know the XR6T has a blow off valve incorporated - the ones that you hear on ricers are highly illegal - you must not exhaust gasses to the atmosphere which is what they are doing. The correctly operating valve opens into the inlet plenum not to the atmosphere and this is quite OK.

It has nothing to do with the wastegate - but it has everything to do with keeping positive manifold pressure during gear shifts when the turbo naturally spools down for a second. With an auto this is not necessary as boost remains constant during the upchange.

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  • 2 weeks later...
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  • Member For: 22y 2m 10d

On this subject, I believe the XR6Ts use a MAP sensor, not an Air-Flow Meter, can anyone confirm this by any chance?

If a car already uses a BOV (plumback, eg. 200SXs and WRXs have factory plumback valves, excess air is recirculated into the inlet tract), replacing it with an external vent valve can cause overfuelling problems on gearchanges, however I believe it only affects cars which use an Air-Flow Meter, hence my question above :)

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  • The Noble Leader
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  • Member For: 22y 2m 17d
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  • Location: Sydney Australia
On this subject, I believe the XR6Ts use a MAP sensor, not an Air-Flow Meter, can anyone confirm this by any chance?

If a car already uses a BOV (plumback, eg. 200SXs and WRXs have factory plumback valves, excess air is recirculated into the inlet tract), replacing it with an external vent valve can cause overfuelling problems on gearchanges, however I believe it only affects cars which use an Air-Flow Meter, hence my question above :)

Sorry but I have no idea about Turbos what does that mean?

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  • Member For: 22y 2m 10d

Well, just quickly, there are two main ways (to my knowledge, anyone who finds any errors please correct me :)) that the ECU can calculate the volume of air which is being pushed into the cylinders, either via an Air-Flow Meter (AFM) or MAP (Manifold Absolute Pressure) Sensor.

The Air-Flow Meter actually sits in the path of the air-flow (usually just after the airbox) and measures the volume of air flowing through the air intake.

A MAP Sensor measures the pressure of the air inside the intake manifold and combines that with the intake temperature to work out the volume of air in the manifold.

Because the MAP sensor doesn't take it's measurement of the air until it's actually inside the intake manifold, it shouldn't be affected by whether the excess air is vented to atmosphere or back into the inlet.

I'm going to have to finish this in the morning, I'm too tired to think straight now, plus I still haven't finished my TAFE assignment, sorry :ph34r:

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Guest DZ.
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There's more than a few people that believe it uses a MAP sensor - so that's probably a safe bet - we were having a discussion relating to performance mods in Performance Forums a few weeks ago.

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  • Member For: 22y 2m 10d

Thanks DZ., I might have to have a proper squiz under the hood at the Motor Show if possible I think B)

Oh yeah, AFAIK, the reason you have problems when replacing a plumback BOV with an external vent unit, is the ECU assumes there is a lot more air after the AFM which has been recirculated when you open the throttle again for the next gear, so it pumps in more fuel, however because your external vent BOV has just released all this air into the atmosphere, the engine momentarily runs rich until you start pumping a lot more air through again to even up the mixture.

That's my knowledge of it anyway :)

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