Well, what a piece of junk! Just before my historic rolling road session last week, I went to my local Saab dealer (well, one of them) and bought a brand new dump valve. The ones they sell now are an uprated version originally fitted to the Viggen, I think, and now sold as a replacement on all Saabs with a dump valve. The Bosch part number ends in "-110". Anyway, it's supposed to hold 20psi which is a lot more than the old one is supposed to hold, but I can't remember how much more exactly. All the people on the TSN Performance Board say that's what you need if you're going to have a lot of boost. Then they say a lot of things there...

Well, it lasted about 3 days, then my boost dropped to normal levels (NO!!! NOT NORMAL AARGH!!!). Still pretty quick, but not blazingly so. After a couple of evenings looking for loose hoses in the dark, I decided to backtrack all the things I'd done over the last week or so. The dump valve is easy, so that was the first thing to try. I took it off and had a look inside and could see a split in the edge of the diaphragm, just by the low-pressure outlet. I fitted the old one (not very old) and went off to test it. I could see almost immediately that I had all my old boost back. All 1.6 bar of it! Luverly!

Until someone convinces me to spend loads of dosh on an expensively hand-crafted piece of forged ally with high-quality innards, I think I'll just keep using these old-style standard valves (Bosch part "-103"). Actually, I haven't had one of these fail, but if I do, I can get a replacement from Euro Car Parts for about £17.

Anyone know any better? Am I talking ball-cocks?

[edit] P.S. the new one is £37 from the dealer!

BillJ,

Running standard dump valve on your setup !!! blimmey :o

I would of thought that it would have launched itself into orbit :)

As far as my experiance goes; running max boost that a cse turbo will run on std ecu with dawes device at max , my bosch dumpvalve couldn't cope at all, when i put on the forge unit i could tell straight away, in gear boost held (ie no leakage) and between gear changes the boost/turbo spoolup was much quicker - the lag was reduced a fair bit.
Im still running with cat - as per my comments on the top post.
but i could still notice an improvement

Damo

I'm now pushing 24psi max. with standard dump valve. No signs of leakage yet!

Alanb

Yeah that may be the case, But the point is the std unit does not react as quickly as an aftermarket motorsport valve, after all that's why they make em!

The point of a dump valve is to protect your turbo from backwash pressure so that the compressor fins don't flex and keep it spinning by instantly allowing the pressure to vent back thru the system or out to the atmosphere.
Any delay (and im talking milliseconds) in this process will result in lost spindle revs and the turbo will have to spool up to it's optimum efficient rpm i.e. LAG.

I speak from bitter experience of overdoing a turbo without having the correct protection - result blown turbo :cry:

In my honest opinion if you’ve spent the sort of money on your trionic upgrades and what not, it seems a bit silly to skimp on one item that in it's very nature is designed to protect your investment.

Damian

PS the uprated Bosch units ARE a waste of time.

Just before the Abbott track day, I borrowed MarkE's spare Bailey dump valve. I noticed the action sounds much quicker and I think there is less lag between gearchanges. There certainly didn't seem to be any on the day. Trouble is, it's hard to compare on public roads: I can't get much boost running in 1st or I'd spin the wheels, so the 1st-2nd change can't really be used as a reference. If I'm really giving it some stick, then I don't need to change into 3rd until 70mph. By that time, I've reached the legal limit, so the 2nd-3rd gearchange isn't under full throttle and doesn't tell me anything.

Now, when changing from 2nd-3rd under full power at 70mph while crossing the starting grid at Goodwood (the only place I ended up being in such a low gear, just after the chicane) there was no discernable lag. Likewise when changing from 3rd-4th at 110mph :o on the Lavant straight.

Now that's a handy place for checking out all this performance stuff!

Anyway, perhaps I'll make Mark an offer for the valve. He likes his atmospheric one (PFSSSHHH!!!)

But the point is the std unit does not react as quickly as an aftermarket motorsport valve, after all that's why they make em!
And here's me thinking they did it because they wanted to make money :cheesy: