simonds1

Hey guys, have just been searching on here for info about dumpvalves etc.....and from what I've been reading, the general opinion seems to be that aftermarket ones are ****e and to stick with the original one. I however have recently found myself in a situation where the standard dumpvalve has proved to be ****e and an aftermarket Forge one has solved my problem! I never had any issues with my standard dumpvalve at all, until I had my car remapped. It's 290bhp/329lbft now and runs about 21psi boost. Whenever I accelerated hard, there was just a really loud sound of wooshing air escaping from somewhere, and not much acceleration from the car at all. I wondered for ages which bloody pipe was leaking the boost etc but all of them seemed fine, and then I suddenly thought maybe it was the dumpvalve opening slightly under the pressure and letting all the air out. I'd always been curious about fitting an aftermarket dumpvalve anyway, so I thought bugger it and bought a Forge FMDVV5013 recirculating one. Fitted it myself in about 5 mins, took the car out for a drive.......like a legend. No more leaking boost, just masses of acceleration! I noticed when I was fitting it aswell, the spring on the Forge was reallllyyyy hard to press in manually with my finger, but the one on my standard one was pathetic in comparrison and could press it in really easily. So no wonder it was opening under the pressure.

What boost should the standard dump valve be able to cope with? Had the spring in mine gone a bit weak over time do you think? The reason I'm asking all of this is that now, after nearly a year of using the Forge.....it's started doing exactly the same thing as the standard one. I think so anyway. Basically under hard acceleration I'm just getting a noise of loads of air escaping from somewhere (boost gauge reads normally while this is happening ??!?) and the car isn't accelerating as well as it normally does. It's not like I'm running a massive ridiculous amount of boost that no dumpvalve can cope with is it? At the moment I'm thinking of getting a HKS SSQV because of the way they work (using the boost pressure to keep the valve shut) so I shouldn't get any leaking then. But everyone slating aftermarket dumpvalves all the time etc is putting me off, even tho I have had one for a year with, up until now, no issues at all.

Sorry for the massively long post, your thoughts would be much appreciated!

Splitpin

Scheize! 21psi (aka 1.44 bar) is a hell of a lot on a TD04, assuming that's what you're running? Some will say that's above the usable envelope of that turbo - and they might have a point, as it'll probably be doing more to heat the air than compress it. Difficult to see why you need that much boost to get 290bhp either - makes me wonder whether you could get the same power with less pressure. Who mapped it, and was it mapped on the original DV?

Anyway, to answer your question, the springs on the late classic dumpvalves do have an occasional reputation for losing their temper so that may explain what happened to your OE one. As for the Forge, pass. Have you tried adding shims, changing the spring, or whatever method of adjustment is on them?

There's an element of HKS marketing bull there. Don't forget that when the throttle is open, the boost pressure in the inlet manifold will keep a "normal" valve shut too.

In your position, and without knowing any more about your setup than you've said, the best way forward may be to fit a newage STi intercooler and the dumpvalve that goes with it. You'll need a flipping good intercooler running the TD04 like that, and the newage dumpvalves are a lot better than the classic ones. Might need a map tweak to account for cooler (and hence effectively leaner) charge but it'd be a better solution than sinking all your wad into an expensive DV.

simonds1

I have talked to Forge about this and they said I am already running the correct spring, which is the blue one that the dumpvalve comes fitted with as standard, and is rated at 23 - 30psi. As for the escaping air, they said I could take the car to a specialist who could do a pressure check on all of the boost pipes etc cuz until I know exactly where the problem is....it's just guesswork.

I don't understand how boost pressure also keeps a 'normal' valve shut, when all it's doing is pressing against it all the time, which will cause it to open?

I am running a TD04 yes, and maybe I have got the boost level wrong. I'm pretty sure that's what it says on the gauge, and it holds at that level aswell when I'm accelerating, not just a quick spike like. I'll double check tomorrow! My car was mapped by Bob Rawle and I'm sure at the time he might've even said something about 23psi?? I was going to email him to ask him but I really don't expect him to remember something about someone's car that he mapped over a year ago.

I hadn't thought about the new intercooler & dumpvalve option, that makes a lot of sense! Thanks for your advice so far

midnight

iTrader: (10)

Good advice from splitpin , as a hks dump valve is around £240.00+, for that Sort of money you can get a good sti intercooler off eBay, which should allow more air into your turbo. The forge dump valve(as well as the baileys) is non adjustable,you can only change the springs, depending what boost your running. I must admit I too found the spring on my oe recirculating valve dead easy to push in, but as I am running standard boost I do not have any running issues with it fitted. I currently have a blitz bov fitted on mine which cost me £40.00 . I shall be getting it remapped straight after Xmas , so depending on the tuners advice I may end up putting the standard one back on, and the blitz may be on eBay .

simonds1

Just a quick question guys, will a newage sti intercooler go straight into a MY00 classic? Or will I need to do some modification for it to fit?

Splitpin

Guesswork, or a process of elimination. Other than the DV there aren't that many things on the pressurised side of the inlet tract that can leak. Just the y-pipe, dumpvalve mounting flange and the throttle body connection. Hopefully an academic question given the power level you're running but can we assume you've got a silicone or STi y-pipe instead of the cruddy original moulded plastic one?

It's a bit more complicated than that. Yes, the boost pressure is acting against the face of the valve from the inside of the intercooler. However...

As you know there's a vacuum pipe between the inlet manifold and the DV. This leads to the chamber in which the diaphragm or piston (and spring) sits. When you back off the throttle under positive boost, the sudden vacuum in the manifold travels down the pipe, acts on the diaphragm, overcomes the spring and literally sucks the valve open.

Conversely, when you're on the throttle and the inlet manifold has positive boost in it, this will, again, travel down the pipe into the DV chamber and pressurise the diaphragm, so in addition to the spring, the boost pressure itself is, as mentioned above, holding the valve shut. Make sense?

The spring tension comes into play a lot more when you're on part throttle and there's a pressure differential either side of the butterfly.

Whatever the actual number, if Bob did it, it should be good. Certainly worth emailing him to ask - he may well have both your details and a copy of the final map he flashed.

No probs! The newage STi IC does need a few mods to fit a 99/00 optimally. Brackets and cutting the bonnet scoop undertray (and making a new seal), lower the coilpack mounting pillars so it clears the dumpvalve. You'll need to do something with the recirc pipe from the DV back to the inlet too. Easiest way to take care of that is to fit a newage one.

Nothing particularly difficult and you have a far more effective solution, so if nothing else it'd be worth dropping Bob a line to ask if the expected reduction in charge temps would suggest a map check or tweak.

joz8968

iTrader: (13)

When throttle is open, there's the same boost pressure acting on both sides of the valve (that's what the vac hose is there for). So it remains shut regardless of boost pressure, as the forces either side are the same, but opposite, therefore cancelling each other out.

When the throttle is shut off, then you still have residual boost pressure acting on the 'turbo' side of the valve, and now has nowhere to 'escape' to but travel backwards from the TB/plenum, to whence it came. Plus there's now a vacuum in the inlet manifold (as the throttle is shut off). The boost pushes on one side; the neg manifold pressure pulling on the other - hence the valve popping open, and relieving the boost pressure to atmosphere (VTA DV)... or recirc back to intake (OEM recirc DV).

joz8968

iTrader: (13)

LOL at the post at the same time SP!

simonds1

Haha, cheers for your simultanious replies guys! Yes your explanations of why the DV stays shut do make perfect sense......altho.......this doesn't explain why my old standard DV was letting air escape because it's spring had gone a bit crap? If there is pressure both sides then surely the spring wouldn't just cave in under the boost pressure of acceleration? Sorry if I'm being an idiot lol

Yes Splitpin, I have got the samco silicone intercooler hoses. So I've got the y-pipe, intercooler to throttle body, and then the one that comes off the DV. I bought a load of mikalor supra clamps to replace all my crappy jubilee clips on all the hose ends when I first had this problem, so they are all properly well tightened on there! Cuz the single end of the y-pipe used to come off every now and again after I'd had the remap (not right off, just kinda loosen itself off a bit) with a jubilee clip on it, and that would give exactly the same symptoms as the cars got now.......sound of lots of escaping air but no acceleration. Put it back on again, and the car was sorted like. Job done. But it kept coming off eventually, I just assumed because I was now running more boost pressure than before. So I bought the mikalors.......which sorted that problem out, but still had wooshing air and no acceleration......even tho the pipe was now staying on. That's when I looked at the DV and decided that might be the issue. So yeah, I guess what I'm trying to say is that unless there is a split or problem along one of the pipes, all the actual end connections should be pretty much as secure as they can possibly be! Will have to take em off & have a check tho, but I'm guessing those samcos are pretty resilient to splits etc?

I'll give bob an email now and see if he can remember the boost figures etc, and also ask him about whether he'd recommend another map for the intercooler etc.

Cheers for your help so far guys, much appreciated

simonds1

I just went to email bob but I found a previous email from him because I've asked him this question before! My gauge was showing 23psi and I was asking him if he thought this was a bit high. This was back when I first had the problem of boost leaking and was trying to get to the bottom of it. He replied "The boost is not actually that high as your gauge is going to over read, it's mapped to hold 1.4 bar if it will"