perhaps i'm being a bit thick here(welshboy innit epic butty etc)but as long as the pressure downstream(engine side ) of the turbo is the same on venting with both types there should be no difference as the upstream(maf side) air will always be uncompressed so will always have the same volume.
in fact the atmo dump should be quicker to recover because airflow through the maf wont have stalled due to the upstream reinjection of pressurised HOT and less dense air.
perhaps the differences between the two are down to the rate at which air is dumped(speed of pressure drop) final pressure and ability to flow a lot of air with low restriction.
or like i said earlier i may be wrong but i do like to think about these things cos i've got an inquiring mind(or was it too much caffine first thing)
richie

 

I changed to a Forge Recirc type on my Sti iii because the original gave the classic blowing across a milk bottle top sound.I did not notice any difference to performance.For flames on a trackday Just use 102 octane repsol/carless race fuel with usual suck and blow mods!

 

I'm impressed guys - thanks for all the comments. Peter, just to echo what Nick has said - welcome to the board, it is always good to have some suppliers on here. As you can see, dump valves are one of those things that are often misunderstood and as a result, a lot of misinformation is in circulation.

If any one else has any comments, please feel free to post them.

Chris

 

UPDATE!!!

I've received a maintenance kit from Forge (cheers Peter!), and after cleaning the BOV thoroughlly...changing the piston (from the blue plastic one to the ally one), o-rings and greased it up...it seems to work as it should! WOOOHOOO

The erratic idle (stepper motor value all over the place), and hot start problems (directly linked to the erratic stepper) have totally disappeared.

I'm now a very happy Turnip, with a working car...and the MaxP BOV still in place.



/J

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>This valve also has a larger internal diameter that allows you to release more air between gear changes , giving you a better turbo response.<HR></BLOCKQUOTE>

Dump valves <B>do not</B> aid turbo response, they actually reduce it. You will not find a dump valve on any WRC engine. You wont find one on any race engine unless it is using very large turbo like a full race T4 running high boost.

Dump valves are installed on production cars for one reason and one reason only. To allow the manufacturer to use 300 degree thrust bearings in the turbo and give a long service life.

If you want max response from your turbo, remove the dump valve and block off the hoses. You will have much faster spool up. You will reduce the life of the thrust bearing though.

If you want to gain the max response have a turbo with a 360 degree bearing installed and get rid of the dump valve.

 

john

what is your thoughts about removing the dump valve when using a IHI VF turbo ( vf23 ) ? i was told that they are no as strong and if anything i need to uprate the dump valve.

you comments are appreciated.

cheers

sam

 

I dont know sam is the honest answer.

You need to ask an IHI turbo specialist about the construction of the turbo.

What the dump valve is doing is reducing the thrust load that is seen on the compresor thrust bearing. When you remove the dump valve the presure waves in the piping/intercooler between the compressor and throttle buterfly try and press the compresor wheel into the housing when you close the throttle whilst you are producing boost.

Most turbos use a bearing that covers just 300 degrees of the 360 degrees around the shaft and so they tend to ride up at an angle and wear. The 360 degree bearing ensures the shaft runs true even under high presure waves.

I have run standard turbos with 300 degree bearings in high boost/ no dump valve specs but they are not ideal and do fail in time.
I am a Garratt person though, i am not certain how the IHI's are built so wont bull**** you.

 

Sam, as you may know I have a VF23 as well...

Because of the rumours of the standard dumpvalves not coping (which is true for the older models - see "blowing bottle" threads), I had an "uprated" recirc one installed for a month or so.

Long story short, I'm now back to the original item, and will remove it once I have a blanking plate done for the IC.
It copes without any problems with the boost the car is making now though.

The "uprated" valve used a rubber O-ring for the seal. That needs special grease. After a month, that grease was washed away (probably due to some oil you will always find in the intake route) and the dumpvalve started to behave irratically. Sometimes it wouldn't close at all (giving me a whopping 0.2 bar of boost up to 5000 rpm, thing would then close, very funny (not).

That's how I found out how true JF's statement actually is: it sometimes wouldn't open on lift off, keeping enough boost at the ready (quick gearchange) for the next loud pedal application

I then experimented with just blanking off the recirc pipe, and indeed, response is a lot better *without* the DV being able to get rid of the boost. So it's gonna go ...

Can a vf23 stand the shocks ... don't know, and I will probably find out Can give you a definite answer in 2 years LOL

HTH,

Theo

 

Sam,
I have been advised from the suppplier of my VF22 , that the IHI range of turbos have a 360 degree bearing.
I'm taking my BOV off.

 

theo, and Rob
keep us posted please. i have no doubt that it will work however i have been told by quite a number of tuners that the VF series are not very strong . so it is not really a good idea to put extra strain on it by removing the dump valve. but since you guys volunteered, i will ask you in couple of months if your turbo is still in one piece then i will follow suit. call me a chicken but i have paid enough on my car lately

 

OK - I have isolated the outlet side of the BOV and capped off the air hose.
So effectively the BOV is now non operational.
After a quick test drive , I have noticed a significant increase in noise from the engine bay when backing off the throttle.
Now I'm not sure whether it is from the turbo or from the air box.But I'm a bit uncomfortable with it.

 

Rob

The noise will be your turbo stalling - when you close the throttle the pressure builds until your turbo stops spinning....or you open the throttle again.

Best (for turbo life) is a quick change - that way the system has more pressure available that when you closed the throttle. Should make for stunning pick-up

Not brave enough to do this with a td-04 though

Richard

 

If any Forge valve users have any problems at all , Please contact me direct . worst case you get all your money back!!

In our experience running with no valve will cause your turbo to stall.

I do not think that Ford , Fiat, Mitsubishi, Nissan, Audi, would not use a Diverter valve if there was no purpose.

FYI
The Mitsubishi WRC runs with an OEM valve that vents to atmosphere

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Peter Miles:
<B>
FYI
The Mitsubishi WRC runs with an OEM valve that vents to atmosphere [/quote]

Really ?
I didn't think the ALS were compatable with BoV's.

 

It isnt your turbo stalling. the noise you will be hearing is probably waste gate chatter and the presure waves hitting the compresor, although making statements on noises is a dangerous thing to do without hearing it yourself. You get more chatter without a BOV because the airflow from the compressor through the solenoid to the waste gate actuator is higher and causes it to bounce. (I wont go into why in this thread as i wrote a book on that before.)

Like i said before, BOV's are used to anable manufacturers to use lower spec components in road cars and get a good service life. They are not interested so much in performance if the costs escalate. Lets face it too, most road users are never going to make any use of the extra performance either.

As to using a BOV on a WRC engine. They are not used. The modern ALS systems generally use air valves that bypass the throttle buterfly. These devices, in conjunction with the ECU ignition timing enable to turbo to keep holding boost without producing any torque.

If you take a look at the engine bay of Brian Bells WRC Escort Cosworth (this is the last Escort WRC car MSport built) you can see the air valve on top of the inlet plenum. Its the valve that looks like an idle control valve with the blue piping to it from the inlet to the throttle buterfly hosing.

Quite simply without going into how these systems work again (do a search, i wrote a book on it in here) they dont function with BOV's on the car.

Dont get me wrong, i am not slagging off BOV manufacturers, if you are running high boost and want to retain the extra protection a BOV will give you then <I>some</I> of the aftermarket BOV's work better than standard. None of them give you better response though, it's a complete myth. The standard BOV's can leak when aged or when asked to work in more extreme conditions. My current car had a Bailey BOV installed when i bought it, i melted that, but thats another story entirely. It was coming off anyway.

 

Hello JF!

A little Q on the subject...I'm going for a 360 bearing turbo as my next mod...would it be harmful for anything else besides the turbo itself to remove the BOV altogether?



/SecretBoyRacerMan

 

nope

 

Cheers!

/J

 

John
I respect your opinion.
However I will try and post a picture of the 2000 Evo with the OEM blow off valve fitted.

Thanks

 

sure pete, i would be more interested than most to see what you have to show.

Just make sure its a groupA car OK.

 

Picture i took of a GroupA Evo. If you look to the right of the cylinder head you can see they are using the same webber valve that is on the Escort WRC car. This is what controls to a large extent the ALS system.

It is in fact an Idle control valve from a Cosworth YB series engine that is modified internally. They replace the small sliding air valve with a valve that looks just like a normal engine inlet valve. This is pulsed by the ECU on closed throttle to keep some airflow yet in conjunction with ignition control produce no torque. Its clever stuff.




[This message has been edited by johnfelstead (edited 20 July 2001).]

 

John

Thanks for your re assurance. After more testing/evaluation I agree with you -The noise is from the wastegate.
Pick up is in a different class .

Sam,
Just do it mate ! You wont regret it,