GRIFF007

Or are all the views simply, technical snobbery - looking down on 'dimwitted chavs?'

Last week i visitted a very highly regarded tuner and was surprised to see a forge dump to atmos on the IC - naturally I queried the wisdom, and was told ' well it works for us' - This tuner also uses huge cone filter induction kits in the engine bay - again - 'it works for us - the larger flow afforded by non inner wing cone offsets the 3 or 4 deg temp drop - MAF re-scaled for 80 mm pipe'

Experienced observations please.

If it is simply techo snobbery and then using very iffy theory to 'proove' a DV dangerous, I would consider one, provided:

better turbo performance
no real danger
noise is controllable (I believe you can get units which semi re-cyc and proportionately dump, rather than full sigh every time even a light throttle is lifted)

Comments?

NotoriousREV

As for the so-called "3 or 4 degree" temp drop, having measured underbonnet temps I can guarantee you that there's a bigger difference than that. In summer the air temp by the air filter on my HKS induction kit can reach 60 degrees regularly. Under the wheelarch doesn't seem to get much above 30 even on the hottest days.

"Works for us" is hardly the greatest argument in the world. "Proper" tuning isn't about fitting bolt on parts, it's about selecting an overall set-up for your car and getting the details right. 10 little things that make a 1hp difference is worth 10hp. "Works for us" suggests fitting a few bolt-ons, upping the boost and very little else. All IMHO, of course

xvw

the import wrx i have just bought has a k&n induction filter, i also have the standard airbox, am i gaining anything or is it best to go back to original box,it also has a dump valve but is very quiet and only really pssssssshhhh when driving hard so its not to bad

GRIFF007

i hear what you say and dont disagree - however this is one of the top pro-tuners (ie 450 bhp P1 upgrade - full internals)

so are we to conclude that these make not a lot of difference?

Incidentally Bob does his re-maps..

GRIFF007

This dump valve & induction kit issue isnt going to go away until we get all the heavyweight engineers to slug it out on line for us all to see the resultant pros and cons

If anybody knows an 'oracle' - please invite him / her to the thread...

EddScott

Personally I have no idea!

However, if you look at most of the early WRX imports chances are they have an induction kit and VTA valve. These cars are 11 years old and more than likely had these things fitted early in life. Given that most of these cars are still running its reasonable to assume that induction kits and VTAs aren't actually too damaging to an engine.

I dont have an induction kit but that only becuase my car is the one with the fragile MAF. I do have an HKS VTA for no other reason than I like it. If it could be proved to be damaging then obviously I'd take it off.

GRIFF007

good man, keep all the helpful comments coming - lets try and make this thread on the subject a proper reference, not some target for jibes as has happened before

STI-R/A

Here we go again......

Aztec Performance Ltd

iTrader: (234)

Indeed some of the top scooby-tuners do use VTA d/v as they believe them to be better than OE.

It will probably be said that the ecu is expecting the air to re-circ etc and the top-tuners which use VTAs probably use ECU which dont expect it to re-circ or is mapped not to expect it.

I use a HKS SSQV and its build quality is excellent and you cant hear it when you're taking it easy (it uses multi valve sys). Very happy with mine.

Induction kits are much more clean cut than that. Most (if not all?) med/highly tuned cars use induction kits as they do flow more air than the OE airbox.

Just my 2ps worth

Bob

GRIFF007

please try and keep the thread educational, we have already had the 'beer jousting' version thanks! (fun in its own way, but not educational to tuners considering all possibiliities)

As I mentioned the approval was from one of the top ranked tuners in conjunction with BR's mapping & scaling so I for one am prepared to consider the subject seriously...

Soulgirl

I have an sti2 and when I had a new exhaust fitted they recommended full decat with the hks induction kit. Immediately felt faster and more responsive and have had no trouble in the 18 months since being fitted. I know, not technical information - just waffle from an end user Oh, and I get the pwshhhhh noise but only when eccelerating fast changing up through the gears

STI-R/A

WTF!? Mate I am in total agreement with you I run a vta on my STI and have no problems, I find your post very interesting reading and it has totally restored my confidence in using a vta so I thank you for that

It was just a sarcastic comment - sorry if I offended you....

NotoriousREV

I personally don't beleive that a dump valve other than OE has any advantage unless you're running stupidly high boost (i.e. enough that your either forcing the valve open under boost or it can't cope with the airflow when dumping). What that boost figure is, I'm yet to find out.

As for VTA or re-circ, then yes, if your mapper knows it's a VTA he can change things accordingly.

Your tuner may well be correct that a larger filter may offset the advantage of cooler air, but surely a large filter AND cool air is the way to go? I personally don't like the inner wing kits as I get paranoid about all the road crap etc. but a big cone filter in an airbox fed air directly from outside is surely the best solution?

GRIFF007

Thick skinned - no offense taken!

GRIFF007

agree on all points

also just had another famous name confrim that Dump Valves are fine - no danger, no bad fuelling - no advantage! - Only come into thir own well above 350 bhp - however if it is the sonic character that is desired - then the concensus is use highest quality and enjoy (possibly scuppers IM warranty though)

Andrew Dixon

I remember reading a post on this subject many moons ago. Not sure if it's still there in the archives?

Seem to remember that the general consensus amongst the informed contributors at the time was that any dump valve was of questionable performance benefit, and only fitted to reduce stress on the turbo and associated pipework - which then permits the fitting of less highly specified (and therefore cheaper) components. It was suggested that the whole 'reduced turbo lag' thing was a myth supported by the tuning industry!

This was borne out by my own experimentation. Having ran my MY97 both with and without the factory valve (for a brief experimental period), I found it to have less lag when running without the DV. It seemed that boost pressure was maintained between shifts rather than being 'dumped', and this massively offset any 'stalling' of the turbo that may have occurred. Oh, and it also made a WRC-alike chirping sound!

I was advised that if I wanted to run the car without the DV on a longer term basis that it would be advisable to fit a turbo with a 360 deg. thrust bearing, and to upgrade my boost pipework.

Going back to that thread, it was suggested that dump valves were only absolutely necessary when running super huge amounts of boost. Seem to remember RS500 touring cars being mentioned ...

Anyone?

SiHethers

Dump valves are there to reduce shock-loadings to the thrust bearings in the turbo, and to protect the compressor itself when closing the throttle on boost. DVs don't reduce lag, if anything they create it because, as is mentioned above by AD, it allows the piping between the turbo and throttle to de-pressurise on throttle closure. This deadspace has to be filled when the throttle is reopened before effective boost pressure reaches the manifold. Running without a DV or using an aftermarket one where you can adjust the pressure at which it opens will reduce lag, but is likely also to shorten bearing life on some turbos, and risk damaging compressors on others (VF2x being the classics). Rally cars (or any car with antilag) do not use dump valves because they need to maintain a positive manifold pressure at all times.

As for induction kits, you need to understand how the compressor works, what an adiabatic process is, the effect of changes in compressor efficiency and how to interpret compressor flow maps to truly appreciate why what GRIFF has been told by his top-tuner is absolutely correct.

Jeff Lucias' articles will illuminate those who wish to know more

http://www.stealth316.com/2-3s-compflowmaps.htm

Cheers

Simon

NotoriousREV

Simon, I'd still be suprised if an induction kit with 80mm inlet pipe is enough to overcome what is sometimes a 40 degree temperature differential between underbonnet temps and outside temperature

Andy.F

Agree with Andrew above, to an extent !

There are a number of issues to consider when using a VTA or blanking off the OE recirc valve.
VTA (and recirc) DV's come in a range of opening pressure settings. Whether high or low pressure, with a VTA there can be issues.

1 - Overfueling due to excessive venting to atmosphere
2 - Stalling the turbo
3 - MAF revertions and System volume
4 - Repressurisation time
5 - High pressure damage


Looking at the issues one at a time,

1 - Overfueling due to excessive venting to atmosphere

If you run a standard pressure vent to atmosphere dump valve (BOV, VTA, Atmo DV) with a mass air flow monitoring ECU such as the OE Subaru, then you can have problems when the DV opens under cruise conditions. The DV allows air to escape from the system during the high vacuum conditions during cruise, The reason for this is the signal side of the DV is subject to vacuum and the flow side is subject to slight boost pressure (the difference across the throttle valve) If this exceeds the spring pressure then the valve starts to vent.
This airflow has been monitored by the ECU and fuel is added accordingly, the result is too much fuel for the air being consumed by the engine.
Best case - You just waste fuel but who cares when you get that 'pschhhht' you've always wanted
Worst case - You cause bore wash, increase oil consumption and reduce engine life.


2 - Stalling the turbo

The term turbo stall refers to stalling the airflow across the compressor blades, not physically stalling the rotor (common misconception)
This is a case of what happens if you don't use any DV or use a valve with too strong a spring.
When you lift off the throttle on full boost, the compressed air has no where to go and blasts back across the blades giving that (lovely ) sharp 'cacho' or WRC chirp as some call it. Very taxing for the turbo, all this backwards flow.
Best case - Runs forever (TD series generally tougher than VF series)
Worst case - Shatters compressor wheel or thrust bearing fails


3 - MAF revertions and system volume

This is not such an issue with a TMIC but when FMIC's are used the system volume is so large that when the throttle is brought back from power (boost) to cruise, if a strong spring DV is used (strong enough to eliminate issue 1 ) then you can get a sudden pulse of pressurised air back out of the MAF, this is measured as an airflow (the meter can't differentiate) and the engine overfuels giving a hicup/jolt
Best case - Slightly jerky drive as you come off throttle
Worst case - Very jerky !


4 - Repressurisation time

This is where the stiff spring DV or running without DV scores a point. The system holds more pressure between gearshifts as the DV isn't venting it. Boost recovery in the next gear is improved (slightly)
Best case - Improved response after a gearshift
Worst case - Issues 2 and 3 above.


5 - High pressure damage

If you use no DV or a high pressure DV spring then when the turbo is spinning at high speed and the throttle valve is snapped shut, there is a pressure pulse in the system
which can be high enough to damage the intercooler etc.
Best case - At boost below 1.5 bar you will probably be ok
Worst case - Bigger turbo's/ higher boost may pop hoses off or 'balloon' the intercooler core.

Options ?

A light pressure recirc valve (just like std) overcomes all of the above issues but sounds a bit boring

Sequential dump valve. At light pressure it recircs, at high pressure lift off it still goes Pssshhht

You pays your money, you takes your chances.

Andy

RoRu

Andy

So are you saying that a badly set up recirc d/v could be as harmful to the engine as vta d/v?

Andrew Dixon

Thanks for the informative post Andy. It's good to learn stuff.

SiHethers

NotoriousREV

That may be the case when stationary, but not when moving at a reasonable speed, say over 20mph (unless you're on a track I suppose). On the other hand, I've seen temps on a MY03 with standard induction hit 60 degrees when stationary, as the intake inlet resides directly over the radiator.

As you've mentioned above, ducting cool air to your cone filter is very important, but it is also dead simple to do, so people shouldn't be misled by "it's just sucking in hot air from under your bonnet" arguments. As an example, my MY99 UK turbo, when it still had a td04 gained 5-10lbft torque at the wheels above 5000rpm (measured by deltadash road dyno) as a direct result of fitting an induction kit, even without any cold air ducting. This was because I gained 1.5psi boost over 5000rpm, due to freeing up some of the restriction the airbox was causing and because I was running the td04 on its choke line.

Your supporting mods will also play an important role. If you have a very efficient intercooler, the intake temp is not going to influence charge temps so much, compared with an inefficient IC. Also if you've got an aftermarket exhaust, wrapping it will help keep under bonnet temps down, as will insulating the hot-side of the turbo.

IMO, if you want to make your power as efficiently as possible, you want to have as little restriction in the intake as is possible (ie the pressure at the compressor inlet close to atmospheric). You'll therefore be working in more efficient areas of your compressor's flow map, heating the charge less during compression, and have more scope to run more boost at greater airflows.

Simon

Andy.F

Not so harmful to the engine regards overfueling but the stall/reversion issues can still arise if the lifting pressure is too high with a recirc valve.

I can't imagine any "top pro-tuners" recommending a VTA for a daily driver if the car retains the original ECU.
I certainly wouldn't settle for being fobbed off with "well it works for us" ? that doesn't sound too technical to me !

Andy

SiHethers

Andy

I think the advice given on induction kits may have been based largely around Bob's experience and experimentation with his JDM twin-scroll, so does have some technical basis. Suprised about the VTA advice, knowing where this advice originated

Simon

Andy.F

Si

What you need is the highest possible air density at the compressor suction.
You need low pressure drop across the induction AND low temperature to achieve this.
Cold air feed is critical, sucking it from under the bonnet is not the work of a "top tuner"

Andy

SiHethers

I agree completely Andy.

I thought I'd stressed that point in my post above, but obviously it must have got lost in amongst the rest of my ramblings

I've got plenty of cold air ducting to my cone filter

Simon

Andy.F

So you did I read too fast

Andy

Bob Rawle

All the high power cars we do are fitted with charge temp sensors and so temps are easily monitored, I certainly do not advocate the use of vta bovs and if you were speaking to RCM they don't fit them to any cars I get involved with up there, they do fit MY98 forge recircs and they can look like a vta the way they are installed, on a GC8 car underbonnet temps are 3 degrees above ambient in the air intake vicinity on the move with cruise charge temps sat at the same, on a GDB car its a differnet kettle of fish and the sealing at the front of the car does increase temps, which is why cold air cooling is routed in. A feed to the inner wing merely delays the onset of heat soak, it still happens, all the associated pipework etc from induction and intercooler pipework attracts and retains heat long after a car has started to move again.

So yes "it does work for us" ... if other tuners can't get their heads around it then they have some research still to do. No one sensible (ie me) is going to risk running an uprated engine at 2 bar under conditions of high under bonnet temps. Bear in mind that all the highly uprated cars that we do with RCM run Motec management.

My own cars are testament to what works or not as the case may be, thats where the R & D is done and thats what the induction system is based on, the STi9 version was a spin off.

BTW my own forge recirc (MY98 type) fitted to the STi5 is set to crack at 1.5 bar, and thats using the factory ecu with maf, Motec M800 without or Link ecu without. What would your views be on that as it certainly does "work for me". There is no performance gain by changing dump valves, however a response improvement on part throttle and between gear shifts can certainly be seen if correctly matched to the cars set up. As a matter of comment I have reverted to the std bov on the STi9 and see no reason to switch it back to aftermarket, its a far better item than the GC8 equiv's apart from the MY97-98.

cheers

bob

SiHethers

Hi Bob

I'm glad you've had the time to share your experience, as I think it was me that recommended GRIFF to go to RCM to consider their ind kit in the first place

So do you have any experience with the MY99/00 DV, as I had a stiffly setup forge recirc but found some MAF reversion issues, with mild lift off det so have reverted to OEM. The OEM seems to do the job ok despite running 1.4bar boost.

Andy, I reckon you were just spoiling for a rumble

Simon

GRIFF007

Yikes Andy, Simon & now Bob (welcome to the party) - I have created a monster...! - This thread is indeed steering away from the 'pass me a pint' brigade!

Doc - that link is seriously heavy going for first thing in the morning - or anytime for that matter..

Every time I delve a little deeper into car tuning away from the pub banter level, I start to regret it! - I am science based too, but the theoretical interactions of varying h/w & s/w gets truly scary...

If DVs can create so much technical debate, I dont really fancy swotting up on say combustion swirl efficiency - effect there on, when modding pistons, c/r , timing, fuel mix, valve size, head porting etc...........

I think I am going to sit back and try and pick up a few facts from the wizzards joining the thread - keep it up guys