ScoobyDoo69

iTrader: (17)

Hey guys,

An honest question to all those in the know about how these cars work. I currently have a HKS SSQV, otherwise known as a dumpvalve. I bought it because I like the noise - but this is not what I want to discuss

Now recently I've been thinking over in my mind how these different valves affect things. I've also recently read a magazine article which compared the 3 ways.

To me I can see how if you block off the dumpvalve, you leave the air in the intercooler/pipework, which would mean there's air available for when you next open the throttle after lifting off/changing gear etc. But you could potentially stall the turbo as it has no where to push the air? Thus slowing the spool, but which is compensated by the air in the pipework already ?? (Bare with me)

If you have a vent to atmosphere dumpvalve, then you lose all that air all together, but the turbo hasn't been stalled therefore can create boost quite quickly again? The negative effects of this are that the car still thinks there's air in the system and so therefore overfuels..right?

And if you have a recirc valve, then you get a mix of both? Just to mention that the magazine test showed the blanked off valve quickest in a 1/4 mile sprint, but I can't remember the other tests.

So what are peoples views on this? I'm leaning towards blanking off my dv.

Thanks for reading..

jef

iTrader: (13)

ive tried all three on my car

can honestly say in real world driving it makes fck all difference

aslong as the d/v doesnt affect your idle or give any other issues - which does seem to be quite common,

then just do what you want - if you want it loud get a loud vta

think the general consensus tho, is the standard one works best

ScoobyDoo69

iTrader: (17)

Thanks for you input.

Can I ask what kind of intercooler you did these tests on? A front mount or top mount?

Thanks

TimH

iTrader: (11)

Doesn't the air simply flow back through the turbo and thence to atmosphere via the air filter/induction?

ScoobyDoo69

iTrader: (17)

Well unless it suddenly spins the turbo the other way to force it back down..? I'm not sure though if I'm honest, hence wanting some of the guys in the know to answer!

jef

iTrader: (13)

i dint real;ly do test mate, i was trying to aleviate an issue with judder on light throttle lift off.

so ended up trying all three.

was a fmic

my fav(for noise) was the dumpvalve delete tbh, but scared of eating mafs, ive just got a re-c forge on.

Splitpin

You're kinda right. The key point with that scenario is that as soon as you reapply the throttle (provided you haven't waited too long), there's a slug of pressurised air in the intercooler that'll go straight through the engine and spool the turbo back up PDQ. If there's too long a delay between you lifting off and going back on the throttle, the advantage is lost.

You can also get the same sort of fuelling errors from a DV delete as you do from running VTA, due to the fact that some pressurised air in a delete situation will try and escape backwards through the turbo and out through the inlet tract as the compressor slows down. The Subaru ECUs (and all the MAF designs bar the 99/00) are unable to tell the difference between air travelling the "right" way down the MAF tube, and air travelling the "wrong" way, so you can end up in a situation where the ECU measures the same air twice - once when it was inducted, and the second time when it went backwards out past the sensor.

This can cause transient overfuel and bogging down on reapplication of throttle - which of course negates the benefits of deleting the DV in the first place.

Again all depends how long you wait before reapplying the throttle.

That's the main one on a standard location MAF-based system yes. Although there are further potential complications arising from the fact that the use of a third party dumpvalve (and especially an adjustable one) opens the possibility of the wrong crack pressure being selected. If you select too low an opening pressure then you can run into problems with the DV opening on part throttle. If you select too high a pressure (which is the common mistake VTA owners tend to make when trying to control the amount of noise), you effectively create the same situation as having no DV under certain combinations of throttle and manifold pressure/vacuum.

Not quite. The key point with the recirc system is that the air dumped out of the pressurised side of the intercooler is dumped back into the induction pipe - where it can re-enter the turbo and go round again. Hence the term recirculating.

This removes the airflow measurement/overfuelling error because the ECU is able to keep track of the amount of air in the system, due to none of it being externally vented.

The other point with the standard Subaru valves is that they're correctly calibrated for the engine, which removes the possibility of opening pressure errors as outlined above.

What type and model year of car do you have? Some turbos can be broken pretty quick by a DV delete, especially older IHI ballbearing ones. In addition the air pulses emitted down the induction tract by the surging turbo cause a lot of buffet and vibration to the MAF sensor, which is a very sensitive electronic part. They can all eventually be damaged by this, but the MY99/00 version in particular can be compromised very quickly, and the consequences of driving around with a vibration damaged sensor can be very serious for your engine if you don't pick up on it quick (you will almost certainly not get a CEL til it's too late).

The common reason people ask about deletes on here is because they want their car to sound like an Impreza WRC, and while you do get a semblance of that noise, it's pretty pathetic in comparison simply due to the fact that the rallycars are running over 4 bar of boost and aggressive anti-lag.

If you want to try a delete, it's your car, but in practice the performance difference between that and the OE recirculating DV is so small and so confined to specific scenarios that the disadvantages can easily outweigh any benefit. The only time a delete really stands to benefit the car is in flat out acceleration with the quickest gearchanges you can manage - which is why the report you read about the 1/4 mile makes sense.

For a daily driver though, the potential downsides need some careful thought.

sy.

iTrader: (8)

i too have been messing with this and have come up with my own middle ground i have a part blanked/flutter & part re-curc setup. This is done by fitting a blanking plate behind the ome re-curc valve (bolt on to intercooler type 02 sti) as a way of blanking off the d/v the clever bit is a 10mm hole allowing part pressure from the intercooler to re-curc via the d/v in the normal way...

53

iTrader: (41)

Out of part necessity and part convenience I deleted the DV when having a FMIC. The DV pipe I had welded and tapped for the Simtek temp sensor. TD05 turbo V2 STi mapped mafless obviously. I like it performance wise, but then I tend to drive it hard on the close ratios.

ScoobyDoo69

iTrader: (17)

Car is an 04 STi. My plans were to go Simtek or similar in the future, so by the sounds of things I best wait until then so as not to destroy my MAF...

harvey

iTrader: (48)

Do not delete the dump valve on a fragile turbo eg. VF22. As per post 2 from Jef, unless there is already something wrong with your dump valve you are unlikely to see much gain from deleting the DV but the sound might be nice, perhaps.

badbaz

iTrader: (17)

I've an 05Sti, MD321T, no potential for recirc due to intake pipe having no intakes!

I have a forge vta and wondered about removing it and the consequences of such?

The reason I'm asking is I'm having issues with setting it up. It previously was on my car with the VF35 and worked fine, dumping as and when it should. Now the MD is on I have dump from light throttle(closing) up to about 0.4bar, above that I hear the WRC chirp and either no/can't hear dump, I believe this is compressor stall?

TimH

iTrader: (11)

Based on comments from Simon/JGM in relation to my setup, if the engine was mapped with a VTA and you then delete the DV, you may need a map tweak.

I'm pretty sure the MD321T is fine with no DV though, from what I've gathered.