robski

Would like to know if you have seen any evidence that a VTA makes for a more tunable or better torque than a recirc valve.

Also does this show via a faster spool, more control etc etc...

Just interested I've heard the mechanics versions just wonder if the ECU guys agree

robski

john banks

My preference is recirc because of the MAF system on all the ECUs I tune.

Theoretically I prefer recirc for conservation of effort.

Bob Rawle

VTA is a real pain in the backside, it vents air outside the "system" which sends the mixture rich, if you are using a maf based ecu then it can send reverse pressure pulses back to the maf causing it to read low, that coupled with the loss of air can confuse the ecu, if the car is running reasonable boost then its also possible to nearly stand it on its nose during high rev/boost gear shifts due to the loss of air.

Bottom line is you can't beat a properly set up recirc.

bob

Dizzy

by that do you mean a specific manufacturer or the way its plumbed in?

if so which in YOUR oppinion is the best

john banks

Overall I haven't had a lot of success with the Forge recirc on my setup so far - I have to use the red spring (strongest) to stop the car juddering when lifting off from light throttle (particularly after the FMIC), and even then with a few different turbos it doesn't let the air back into the intake (and hence the back end of the MAF) smoothly but farts it out in juddery parcels that upset the MAF sensor. The stronger spring is better (because it hardly ever opens except on full lift off and then does it smoothly enough) but still not as smooth as stock. Seems to be a balance between not letting it fart too easily by having the spring strong enough, and not being too jerky and surgey. Certainly with the stronger spring you can't seem to get away with a Dawes so easily because it isn't aware of part throttle condition, and part throttle or lift off from part throttle easily throws it into surge. So with JECS you have to map the part throttle boost more carefully. With a weaker DV you can have the turbo ready to go by already recirculating some boost on part throttle. Obviously you don't want to overdo it and make a load of hot air.

I hear the Link guys play off dump valve spring strength against actuator pre-load or strength to get the part throttle response they want without surging the compressor. Maybe they could confirm.

Certainly you can get horrible surge with a compressor size biased hybrid, lots of part throttle boost and a strong dump valve.

The red spring in my Forge did not let the DV open with the vac line disconnected until 22 PSI.

Now running on the standard DV and it is far smoother and sounds more sensible, although it is the metal bodied valve you get on the later cars not the plastic bodied one. I need a simple method to check if it leaks although at part throttle with a Dawes you can hear it recirculating but I can't hear anything at WOT. There is a possibility I oversped a previous turbo on the OEM DV so I need to look into this to make sure it is not leaking. Like clutches some get them failing easily and others hold the pressure well.

I suppose the farty opening of the Forge would not matter if I wasn't running a MAF sensor as it is the MAF misreads that seem to make it judder.

Jake

Why is it then that so many people run the HKS SQV with no problems?

john banks

Some people go for DVs based on looks and sound, flames or pops. Personally I went for it as I was told the original one would leak at high boost.

The overfuelling (on a MAF system) from atmospheric dump valves during their operation is what puts me off. John Felstead pointed out that this could degrade oil quality which would be my worry, as well as the effect Bob describes at high boost (presumably from suddenly going rich). Maybe it is even more of problem with FMICs since there is more volume under pressure to be vented and hence really mess up the MAF readings. So on a high boost car with a FMIC you have a massive amount of air leaking away so the enrichment would be huge hence the braking effect?

nom

The HKS SSQV is a good one, remembering of course that it's good when it's set up as a recirc rather than VTA...

Jake

Nom do mean setup the HKS SQV as a recirc?

Dizzy

I'll probably stick with my OEM one (even though its obceenly loud due to blitz )then as I'm only running with standard fuel cut. However I do like the idea of being able to adjust the timing of presure release.

Sorry John do you have the oil degredation thread to hand anywhere? Would like to read up

nom

Yup the HKS set up as a recirc. But only really worth doing if the standard one isn't working. I think there's a marginal but noticeable improvement 'between gears' with well-design aftermarket BOVs, but really not worth the £.
Basically, it's just a toy for 95% of people.

john banks

Compressor surge is dangerous to your turbo and engine, so perhaps it is best if people don't mess with dump valves unless they are broke? I wonder if the pursuit of flames and noise compromises this sometimes, and can make the car orrible to drive.

Sorry Dizzy don't have the link, but uncombusted fuel from overfuelling can end up diluting your oil. Petrol does not lubricate bearings as well as oil

Bob Rawle

The noise John describes is air chittering back through the turbo as you lift off, I usually use a red spring ... and then shim it and it makes no difference wether its with a Link or oem ecu I still use the same approach.

Can't agree about the SQV, it had one of the worst effects due to not having the capacity to flow enough air.

Bob

robski

Wow!

a big thanks to John and Bob.

I guess a standard subaru recirc dumpy is ok for me then.

Thats 1 less item to worry about prior to the remap

So the ECU tuners response is opposite in must of their reasoning to the mechanics view.

Now I can pair them up and let them fight it out

robski

john banks

You're welcome, in fact your thread has been a good catalyst for me to try and understand this a bit better as I still have issues with it.... (plus a good chance to pick Bob's brains )

In thinking this through I am trying to classify the two airflow/dump valve related problems I get with the Forge recirc DV:

1. Compressor surge (can get rid of by RPM vs TPS boost mapping no problem although the stronger the spring the more careful I have to be on part throttle so cannot use a Dawes at least when using a big compressor wheel) - this certainly causes a shudder or a bang and can happen on steady part throttle or lift off, the shudder also causes MAF misreads which additionally mess up the fuelling as well as the airflow, so truly horrible to drive and not nice to the compressor wheel.

2. A Forge quirk? : the farty pulsatile opening of the dump valve (at least it feels like it) even when you map it without surge, this also causes the car to judder bodily and audibly and the MAF to misread, this happens typically from a less abrupt backing off the throttle from part throttle 5 PSI or so boost. This is worsened by the extra volume of the front mounted intercooler and pipework, worsened by a weaker spring, and improved by a stronger spring.

The standard dump valve causes neither of these problems, whilst number 1 is mainly a part throttle boost control issue the stronger dump valve spring makes the problem far worse. The standard dump valve is also totally smooth with any speed of lift off from part throttle or full throttle boost. I have to see if it leaks - propose to take off the recirculating vent and vent to atmosphere to see if the mixture richens on WOT full boost or whether I can hear it venting. In addition I have to live with a slightly slower rate of boost rise during gear changes if it seems not to be leaking, but the smoothness seems worth it to me. I suppose I could shim the red Forge spring and conservatively map the part throttle boost if I want the aggression back. But then on part throttle I would need to open the wastegate more so the turbo lag would be increased.... the original DV being so weak with say a Dawes with small bleed hole is going mad (too mad) on part throttle but the lag is tiny on stamping on it as the turbo is already up to speed you are just diverting it, although relying rather on the intercooler There has to be a trade off between part throttle waiting to overtake for example and lag during gear changes as a more closed wastegate on part throttle with big recirculation would favour the former, and a strong spring not allowing this so much without surge (at least on some turbos) would favour the latter?

Tell me if you agree Bob, but the farty noise and shudder with the weaker springs in the absence of compressor surge seem to me to be a sticky opening and closing venting through the dump valve rather than back through the turbo? Alan says when this happens on his car (Link) that there is only the sound not the actual shuddering which makes me think the MAF is misreading, although I'll have to log and see. Hence my suggestion about the difference depending on ECU? If it was air going back through the turbo why does it IMPROVE with a stronger spring? Maybe we are talking about different farty noises LOL?

[Edited by john banks - 4/15/2003 7:58:11 PM]

nom

Well, personally - with the link - the farty noise (my farty noise anyway ) doesn't come with any shuddering; the shuddering comes on its own without the farty noise Farty noise OK (& very rare), shuddering not fun (& common!).
All in all, I should make the effort to go & find an unbroken (ie not like mine) BOV, although somehow it just seems like too much effort

dowser

Good timing I wanted to fit a Forge recirc on mine last night - but it's too big with my APS tmic (also tilted slightly), it fouls with the coil packs.

So we whacked it on a friend's car with vf23 and Dawes - difference was amazing, running through the gears you get a much better response; no delay to boost returning when you get back on the gas. It's got the red spring, and there's a slight chuffing (a quiet fart? ) noise on full lift off. However, car is as smooth as ever.

He wont give it back to me John - do you want to sell yours? I will look at machining the base plate where it bolts to the i/c to make it thinner (I need 3-4mm) - either that or move the coil-pack thingy.

But this raises another question - who's run a td05 for an extended period of time, and no adverse affects, with no DV? I guess, but don't know, that the best system would be to be able to switch the DV out of the system for power work, but use it for 'normal driving'....I'm sure Andy has tried/is doing this?

Richard

Dizzy

John are you saying that your NOT expecting the OEM DV to "leak"?
I thought the DV (@WOT and full boost) deliberatly recirced air? which was another reason why VTA was bad.

btw who manufacurers the OEM item?

That'll be your passangers wondering why your looking @ your laptop / boost gauge while trying to pass another car @ 110mph

[Edited by Dizzy - 4/16/2003 8:56:32 AM]

john banks

Andy F ran his TD05 without a DV with good effect. He put a DV on with the TD06 because it surged on cruise at higher speeds otherwise.

I believe the valve is only SUPPOSED to leak when there is a pressure difference across the throttle sufficient to overcome the spring with the setup of the various areas presented to the different pressures, so not at WOT.

I need to check to see if the OEM one leaks, but I don't think it is supposed to. Think it might be made by Denso.

Maybe you get away with the red spring (at least that one is strong enough to stop the farty business, but do you still think it is as smooth as stock?) with Dawes on the VF23 because it has a relatively weak actuator, relatively large exhaust side compared to the compressor side, so it doesn't go mad on part throttle boost? Would think the TD05 would be fine as well since Andy ran without DV and using Dawes type MBC.

[Edited by john banks - 4/16/2003 9:49:18 AM]

WREXY

I have the Blitz DV on mine, (MY00, VF23), as John saw when he came out here to map my car and I have no problems. No farty noises.

However at half throttle at around 4000 rpm and up, I get a high pitched whistle noise. It's not there at WOT though, only at half throttle as boost comes on. Is this normal or do I have a problem?

Cheers,

Wrexy.

john banks

It is just venting a bit on part throttle not a problem as long as it doesn't vent too much.

dowser

Hmmm - time to try without one then Do you know what boost can be held with the vacuum line at atmospheric with the stock DV? I guess I'll need to replumb it somewhere postive until I've had a plate made up.

Re. the vf23'ed car - too early to say really; it was 01:30 this morning by the time we tested (preparing for track Monday). It just constituted warming the car up and then enjoying the between gear response (raar-raar-raar, instead of raar---raar---raar ) - we only played a little with part throttle but it seemed OK, and certainly no juddering with lift off. The guy (note: word 'friend' is long gone) has also just confirmed, "there's no f*cking way you're getting this back" I hope it kills either his vf23 or gearbox on Monday, lol! (joke...).

Richard

paulwadams_my99

When I first fitted the Forge I took it off because it was very jerky on sudden lift off and made all kinds of high pitched noises. I wasn't sure it was right. I put the OEM one back on which was much much smother and didnt make any of the noises the forge one did.

I then put the forge back on and learnt to live with it coming off throttle a little easier, almost always with the chatter noise. This isn't particularly noticable through the boby for me though. Its only if i lift off very quickly does the car jerk. I would love to improve the whole smothness of the valve but I assumed it was the trade off for having the stronger spring to run with the higher boost pressure? would a slight shim help the situation then Bob?

john banks

My FMIC made it a lot worse too, was fine without, but there is quite a large volume of pressurised air to handle

WREXY

John,

When you say as long as it doesn't vent too much, what do you mean? How would I know if it's venting a little or a lot?

We know there is no whistling at WOT, just at half throttle. Are you saying that it is not venting a lot because it's at half throttle?

At half throttle it whistles from 4000rpm to say 6000rpm which is where I've taken it to at half throttle. I also hear the whistle for a split second after releasing the gas pedal slowly after having floored it till say 6800rpm, say in 4th gear. Is this OK?

Cheers,

Wrexy.

JamesS

John,

As you may know I have exactly the same problem with the Forge recirc. Running the red spring + 2 shims. Quick full throttle lifts are fine. It`s the partial lifts / modulating the throttle for corners - shuffles and shudders all over the place. Also have the HKS FMIC - The BoV attaches at 90deg to the pipework; not great flow......

On mine the std dump valve could not handle the volume of air released. The forge has made it better but it is still there and very anoying. Might try shimming the BoV some more so it ONLY opens on a full lift from full boost????......

john banks

Sounds OK WREXY. With your VF23 and ECU boost control I don't think you've got an issue. By too much, you would probably have the turbo surging and it would be obvious. In addition with a VTA I don't think you want to throw away lots of part throttle boost - a bit is OK as it lets the turbo run at a higher speed and makes it friskier when you go WOT.

James, you have a VF30 right? Not fiddled with one of these but the P15 version (VF35) is quite surgey. Can you exclude surge as a possiblity? If I use a red spring and a fairly closed wastegate on part throttle with the 20G it surges on part throttle. If it is not surge perhaps even more shimming will help? Bob?

DubaiNeil

Not an expert on the subject [by a very long way], but I am aware that 'respected' tuning houses such as APS include dual vent valves in their performance 'kits'. My assumption is that this vents internally at low pressures, and externally at WOT. They may include this for a number of reasons, the ones that spring to my mind are:
1) The customer would expect this kind of 'toy' (and associated noise)
2) They need it to enable the fitting of CAI systems.
3) They need it to avoid their TMIC/FMIC pipework
4) It actually gives some benefit
5) They make more money!

As to noise, smoothness etc I cannot comment on, I am still waiting for mine to arrive from Australia!

http://www.airpowersystems.com.au/wrx/blow.htm

john banks

The only one I ever came across leaked and completely screwed the idle. Maybe that was bad luck.

JamesS

Must admit I had not considered surge as a potential cause. However the 1st time you lift you vent all the boost pressure and slow the compressor, so even a high volume of air flowing over the compressor from the BoV would not be enough to cause surge?