Blow-off Valves & Dump Valves for Impreza 2005
Discussion
Hi all,
I've been looking into the HKS Blow-off Valve because apparently when you change gear in a scooby, the excess pressure in the pipe stops the turbine blades from spinning, then when you slot in the next gear the turbo has to spool up again The HKS Blow-off valve says that by releasing the pressure in the pipe the turbo can keep spinning so when you slot in the next gear you don't have to spool up from zero again - is this true?
Does anyone run a dump valve or blow off valve here?
Cheers,
John
I've been looking into the HKS Blow-off Valve because apparently when you change gear in a scooby, the excess pressure in the pipe stops the turbine blades from spinning, then when you slot in the next gear the turbo has to spool up again The HKS Blow-off valve says that by releasing the pressure in the pipe the turbo can keep spinning so when you slot in the next gear you don't have to spool up from zero again - is this true?
Does anyone run a dump valve or blow off valve here?
Cheers,
John
Jockster said:
Hi all,
I've been looking into the HKS Blow-off Valve because apparently when you change gear in a scooby, the excess pressure in the pipe stops the turbine blades from spinning, then when you slot in the next gear the turbo has to spool up again The HKS Blow-off valve says that by releasing the pressure in the pipe the turbo can keep spinning so when you slot in the next gear you don't have to spool up from zero again - is this true?
Does anyone run a dump valve or blow off valve here?
Cheers,
John
I've been looking into the HKS Blow-off Valve because apparently when you change gear in a scooby, the excess pressure in the pipe stops the turbine blades from spinning, then when you slot in the next gear the turbo has to spool up again The HKS Blow-off valve says that by releasing the pressure in the pipe the turbo can keep spinning so when you slot in the next gear you don't have to spool up from zero again - is this true?
Does anyone run a dump valve or blow off valve here?
Cheers,
John
I would say that is a load of bull, everytime the dump valve releases pressure you have to build that up again. You can get a more aggressive dumpvalve that does not release as much pressure but you will be putting more pressure on the turbines.
The only reason for some of these mods is sinmply to have the psssssst noise, Unles you are running high boost/bhp and you need a more agreesive dumpvavle to hold the pressure.
On a seperate not the Turbo will always be spinning as when you hit full boost the turbine will be spinning in excess of 80000 RPM. and that is not going to stop in an instant.
Steve
With no dump valve at all the excess pressure can be forced backwards through the compressor and this can stall the blades and potentially damage the turbo. A dump valve / blow-off valve will prevent this. An atmospheric one will give you a pssst sound and potentially cause fuel/air problems (though not always) and a recirc will dump the air back into your intake and be a bit quieter. I'm sure most turbocharged cars come with some form of dump valve already.
Jockster said:
Hi all,
I've been looking into the HKS Blow-off Valve because apparently when you change gear in a scooby, the excess pressure in the pipe stops the turbine blades from spinning, then when you slot in the next gear the turbo has to spool up again The HKS Blow-off valve says that by releasing the pressure in the pipe the turbo can keep spinning so when you slot in the next gear you don't have to spool up from zero again - is this true?
Does anyone run a dump valve or blow off valve here?
Cheers,
John
I've been looking into the HKS Blow-off Valve because apparently when you change gear in a scooby, the excess pressure in the pipe stops the turbine blades from spinning, then when you slot in the next gear the turbo has to spool up again The HKS Blow-off valve says that by releasing the pressure in the pipe the turbo can keep spinning so when you slot in the next gear you don't have to spool up from zero again - is this true?
Does anyone run a dump valve or blow off valve here?
Cheers,
John
The 05 WRX has a recirculating valve so as said the air is passed back to the other side of the turbine. A dump valve is only for show and in some cases can cause fuel to mix with the oil (dont ask me how).
What you said is true for Cossies like the Escort which needed a dump valve to improve spool up because it didnt recirculate the air.
Cheers,
Ian
They sound cool though!
What you said is true for Cossies like the Escort which needed a dump valve to improve spool up because it didnt recirculate the air.
Cheers,
Ian
They sound cool though!
stevieb said:
I would say that is a load of bull, everytime the dump valve releases pressure you have to build that up again. You can get a more aggressive dumpvalve that does not release as much pressure but you will be putting more pressure on the turbines.
The only reason for some of these mods is sinmply to have the psssssst noise, Unles you are running high boost/bhp and you need a more agreesive dumpvavle to hold the pressure.
On a seperate not the Turbo will always be spinning as when you hit full boost the turbine will be spinning in excess of 80000 RPM. and that is not going to stop in an instant.
Steve[/quote]
The dump valve doesn't release all the pressure, just the excess pressure. If it released all the pressure, you'd never get any boost.
The turbine may be spinning at 80000RPM, but its pretty light, and you're probably taking 20-30HP from it to keep the air compressed; it will slow down pretty quickly!
The dump valve releases all pressure, the noise it makes is the air escaping, I.e the pressure inside the pipe is equalising to the pressure of atmospheric (outside of the pipe). If it's recirc, it's still doing the same thing, so the pressure inside the pipe is going to drop to no lower than that of the intake, which with the throttle plate closed will normally be atmospheric, give or take.
There's a huge amount of myths about dump valves, for's and against's.
As mentioned most t/c'd engines have them in some form or another as standard, always as the recirc type.
Basically with atmospheric valves you're dumping air which has already been accounted for by the ECU (usually via the AFM or equivelant). Obviously, as the ECU monitors and maintains air/fuel ratio the air that has been accounted for already has suddenly gone missing, and this means you get some overfuelling. In the long run the overfuelling can apparantly be bad for catalytic coverters, never seen one die myself but anything's possible I guess.
Most people fit aftermarket valves purely for the sound they make. They're fun at first, but you soon realise you sound silly and it gets on your nerves
A lot of people also confuse wastegate chatter (the fluttery noise to those who know it) as turbine stall.
Basically, if you're going to do it get yourself a decent recirc valve, and bypass or remove and replace the standard valve with the aftermarket jobbie. Not sure about Imprezas, but there's a few cars out there who's valves don't deal well with mega boost pressures etc, so it can be beneficial if you're modding it in some instances.
If you want a bailey DV I've got a spare sat here you can have for 35 quid delivered that's of no use to me
There's a huge amount of myths about dump valves, for's and against's.
As mentioned most t/c'd engines have them in some form or another as standard, always as the recirc type.
Basically with atmospheric valves you're dumping air which has already been accounted for by the ECU (usually via the AFM or equivelant). Obviously, as the ECU monitors and maintains air/fuel ratio the air that has been accounted for already has suddenly gone missing, and this means you get some overfuelling. In the long run the overfuelling can apparantly be bad for catalytic coverters, never seen one die myself but anything's possible I guess.
Most people fit aftermarket valves purely for the sound they make. They're fun at first, but you soon realise you sound silly and it gets on your nerves
A lot of people also confuse wastegate chatter (the fluttery noise to those who know it) as turbine stall.
Basically, if you're going to do it get yourself a decent recirc valve, and bypass or remove and replace the standard valve with the aftermarket jobbie. Not sure about Imprezas, but there's a few cars out there who's valves don't deal well with mega boost pressures etc, so it can be beneficial if you're modding it in some instances.
If you want a bailey DV I've got a spare sat here you can have for 35 quid delivered that's of no use to me
The Recirc Dump vavle on the Impreza Dumps the air out in the intake system which is prior to the MAF. So converting this to an atmospheric system will not change any of the Air:fuel mixture ratios.
The ECU does not measure the amount of air that it is recirculating so can not inclde this in the calculations to get the Air:fuel mixture correct.
If you dont believe me than look at the where the intake system vents the air back to.
The ECU does not measure the amount of air that it is recirculating so can not inclde this in the calculations to get the Air:fuel mixture correct.
If you dont believe me than look at the where the intake system vents the air back to.
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