WALKER

Bought a HKS sequential blow off valve today to see what it would be like. Ok, its fitted to a my99 uk, and it sounds ok, but when accelerating upto about 6000 rpm and then suddenley backing off on the gas the car backfires like hell. Sounds good, but is it right and is it doing any damage to my beloved engine. Also are the extra fins you can buy just a little bit quieter as it is a bit to loud even for me.
Help appreciated!

Paul

MR. Two

Doesn't sound as if it's doing much good. I prefer the atmospheric valves myself to these recirculating ones. I've got a Blitz valve on my '96 and it seems fine. It sounds great as well, better I think than the recirculating ones.

MorayMackenzie

Hmmm.

There have been many discussion threads on this subject, some quite recent ones to, so I suggest a search of the archives may help.

Anyway...
Cars that use the MAF sensor, e.g. cars running standard JECS ECU rather than link/motec, can suffer from running problems if a dump-to-atmosphere BOV is fitted. This is, as Rannoch says, because the car is fueling for X ammount of air and the BOV has released a chunk of it, so the car runs rich on lift off, hence more pops and bangs.

In most cases, these pops and bangs are harmless. There is, however, the risk that the valve may leak air constantly whilst running at high revs (4th on a motorway etc), you should hear the valve venting if this happens, this situation would cause rich running again, which in turn could possibly cause borewash (overrich mixture washing protective oil of the cylinder bores, causing premature wear and damage to the cylinder). This is a very Bad Thing (possibly TM of pat ).

If you are running a non-standard ecu that doesn't use the MAF (MassAirFlow)sensor, then there won't be the same problems with running an externally vented BOV.

I had an SQV on my previous car... I didn't like the high pitched squeek it makes as standard... I replace the "Vane" with an open one... this gave a deeper, more subtle sound that was better suited my tastes.

I only changed my BOV because the original equipment wasn't able to hold the boost level the JECS was achieving... there isn't much point otherwise, as the standard unit on later cars is generally up to the job anyway. Fit a cone filter and you get to hear the standard BOV work as well as all the new induction noises... nice (if that's your bag)

Moray

Gethin

Walker, make sure it's the proper kit for your MY otherwise you will have fuelling problems. My friend with a MY99 UK car fitted his old MY97 SQV on his car and had big problems with over fuelling....massive backfires, black puffs of smoke and down to 10MPG....be carefull!!!

Also the back fires can kill cats if you still have them in your exhaust system.

It would be worthwhile after any kind of mod like this to get it checked ona Rolling Road.

Gethin.

SecretAgentMan

...I've been looking at a BOV for my MY00 GT, but I've heard stories about engines running rich...? Can anyone explain to me why? Is the ECU aware of the air that's recirculating from the stock BOV...? I don't see why letting the preassure out in the atmosphere could increase the amount of fuel put into the engine.

*?*

/SAM - Sweden

Trout

iTrader: (1)

It sounds like it is an atmospheric venting blow off valve - I think that this correct for the HKS SQV - which is why it makes the noise (do you know you can buy different vents purely to get different sounds!).

Anyway - this is a BAD thing on Scoobs. As the air is vented it causes the Mass Air Flow meter to misread the amount of air in the system - basically the ECU is expecting X amount of air, fuels on that basis and the car is actually getting X minus what has been vented to the atmosphere.

Hence very rich running - 10mpg and lots of black smoke - if you have no cat then you will set fire to anything within twenty yards of your rear bumper

R

Gethin

It's wierd though, as I have the HKS SQV on MY97 WRX and my car runs lean higher up the rev range. 5% CO if I remember...whish is rather pushing my luck!!

I get good fuel economy as a result, but plenty of flames on throttle liftoff

Mind you, it's a bit of a mystery machine as it has an unknown jap chip in there....I must have a peek to see what chip it is so I can share my setup on this BBS.

Gethin.

MorayMackenzie

Mr Two,

The HKS SQV is an externally venting sequential piston type blow of valve. The blitz "super sound" valve is simply a high quality non-sequential piston type blow off valve with a brass piston and "2bar" boost capability, although RaceLogic were not able to confirm if that's 2bar absoulute or 2 bar relative to atmospheric!

IIRC Sequential valves tend to allow cars with MAF sensors to run better as they can be setup to ensure the valve remains closed on idle and still responds well when venting boost... conventional piston valves such as the Blitz are, IIRC, more tricky to setup properly to remain closed on idle whilst still opening when required. IIRC, this is why Bailey Motorsport designed the Piston Evo sequential valve, which could be fitted easily to Ford Escort RS Turbos without all the typical running problems these tended to suffer.

The long and the short of it is that, assuming you are using the MAF sensor, the HKS valve is better suited to the job than the Blitz... but then again, you probably prefer the "group A rallycar" sound the blitz gives on lift off, rather than the camp squeek the standard HKS makes, and that's the main reason most people fit dump valves anyway...

Moray

MR. Two

Moray,

Thanks.

WALKER

Cheers Guys

I have taken the SQV off now and all the backfires have disapeared accept for in the very high rev range ( think it did this before ), although it does now tend to feel as if it is running a little bit rough. After driving about 1 mile sedately i accelerated to about 5000 rpm, it held back very abruptley and then cleared itself. What could this have been, it then drove fine for the next 20 miles,i then stopped the car for about 5 mins. Started her up and drove off with it feeling as rough as hell, then cleared itself again
Am i just being paranoid or do you think that there could be something up.
Car is my99 ppp hks induction, decatted downpipes and centre.
Cheers
Paul

Gethin

Walker,

As Rannoch says, the ECU will take some time to sort itself out. My friends MY99 took around 100 miles for the ECU to relearn after the SQV messed his fuelling up.

Gethin.

Trout

iTrader: (1)

Paul,

I would have thought that the rough running, which cleared itself a bit will be a very confused ECU clearing it's head. A good example of when an ECU reset might actually be useful

Glad you have gone sensible - enjoy

R

Wreckleford

I have the Blitz valve fitted to my Evo, without any problems at idle or of not holding boost. I don't know if it has a WRC sound like they claim though. Just sounds like a "cchhhh" to me. The WRC cars sound like Flipper the dolphin to me.