Originally Posted by motorola222 (Post 9169209)

Yeah exactly most of u elders do know it's just usefull for us newbs who don't. My main concern is everyone claims to think or know that vta valves damage the cars. Whernis the proof?

Originally Posted by Someone

On many cars, the air is metered by a device called a MAS/MAF before the turbo inlet. If this is the case on your car, venting your BOV to the atmosphere can result in an inaccurate count of the air entering your engine, resulting in a rich condition after each shift, damaging performance. On some cars it won't be noticeable, but on some cars it will cause the engine to stall instantly. On all cars with pre-turbo MAF/MAS, it is officially "incorrect".

If this is the air metering method in your car and you want the "PSSSHHHH" noise, you would be better off installing an open-element air filter, since it is the airbox on most cars that stifles the blow off noise.

If this does not give you the desired effect, you might try changing your BOV to one of our aftermarket BOV's that is capable of recirculating to the turbo inlet pipe.

Originally Posted by +Doc+ (Post 9169274)

It is proven that some DV blow Maf's which blow engines, the DV doesnt do it on it's own.

Originally Posted by motorola222 (Post 9169233)

Yeah ok, but it could aslo mean fitting a dual port bob meaning it's recirc unroll full throtle then it's a vta. Or have I missed summit

Originally Posted by +Doc+ (Post 9169274)

It is proven that some DV blow Maf's which blow engines, the DV doesnt do it on it's own.

Originally Posted by motorola222 (Post 9169281)

Yeah ok I get that but surely ud notice if ur MADD had gone way before the engine failed.

Originally Posted by +Doc+ (Post 9169274)

It is proven that some DV blow Maf's which blow engines, the DV doesnt do it on it's own.

Originally Posted by Splitpin (Post 9169311)

What do you mean by "unroll full throttle"? You've missed the point that atmospheric venting is undesirable on a suck-through MAF equipped car, full stop. On that basis, a valve that does recirc part of the time and VTA part of the time is just as undesirable as a pure atmospheric one.

If you don't like the taste of a sh*t sandwich, are you going to like a cheese and sh*t sandwich any better?



That's correct, but the key point to make there is that a properly adjusted dumpvalve (whether VTA or atmos) will not damage the airflow sensor. MAF damage only results when the valve is set too stiff and does not dump, causing compressor stall and resulting in pulses of air travelling backwards through the induction tract.

This is one of the biggest arguments for sticking with the standard dumpvalves, as at least you can be confident that they are calibrated within the correct range. The problem with adjustable aftermarket valves is that there's a tendency on the owner's part to set them too stiff - although the article linked above does give a good explanation of how to set the release pressure correctly.



Sometimes, but more often than not you'd notice it's failing after your on-boost mixtures have been leaning off for some time - with consequent risk of engine damage from the resultant cylinder temp increases and detonation.


Same place it is on all Imprezas - in the pipe immediately after the airbox. If you have an MY00, you'd be even further advised to avoid aftermarket valves, as the 99/00-type MAF is particularly prone to vibration damage of the sort outlined by Doc.


The short answer is no. Someone might pop along later telling you about a test that involves unplugging the sensor with the engine running and seeing if it stalls. Unfortunately that "test" is based on complete bullsh*t and can pass dangerously degraded sensors as "good", so is best avoided.

The only way to be certain whether or not they're good is to test them on a bench airflow rig, although you can get a pretty firm idea from datalogging the car under boost and looking at the sensor's output. By the time they are far enough gone to cause idle stability issues, the response at high airflow levels tends to be all over the place.

Originally Posted by motorola222 (Post 9169330)

Srry I'm on an iPhone and the autocorrect is giving me grief.

Unrollis actually untill and mapp is maff.

Originally Posted by Splitpin (Post 9169350)

All of this "dual mode" bollocks is ultimately just a way to sell shiny bling tat to people who don't know better.

Originally Posted by RA Dunk (Post 9169641)

I would assume so, but then again theres that stupid f,ing chav noise it makes[/quote

people had dumpvalves well before the chav was invented so i dont know why people keep refering them to chavs and i know lots of well off people who have them fitted.

Originally Posted by Jamie Bird (Post 9169595)

So if VTA valves are no good on Scoobies because of the maf does that mean if your using an aftermarket ecu e.g Simtek which isnt using the maf then a VTA will be o.k to use ?

Originally Posted by RA Dunk (Post 9169641)

I would assume so, but then again theres that stupid f,ing chav noise it makes[/quote

people had dumpvalves well before the chav was invented so i dont know why people keep refering them to chavs and i know lots of well off people who have them fitted.

Originally Posted by Roger.m. (Post 9169853)

yea but they all go pshhhhttttt and ya weally need the loudest egzaust to go with it to mint innit! :cuckoo:

Originally Posted by Roger.m. (Post 9169853)

yea but they all go pshhhhttttt and ya weally need the loudest egzaust to go with it to mint innit! :cuckoo:

Originally Posted by RA Dunk (Post 9170290)

nah mine goes pppiiiiiisssshhhhh:D