Bleeder wide open, but only 0.75 bar

[dojobi]

I'm having a little trouble with this new GFB bleed valve I bought. I did all the gradual turns and it was slowly turning the boost up, but when I went to get 0.8 bar, I realised the bleeder couldn't open up anymore. Does anyone know why? I've got all the right breathing and cooling mods for the engine, so there should be no problem there. My boost gauge read 0.5 bar before I put it in, so I'm fairly sure it's accurate. Any ideas?

Cheers,

Michael

[Warpspeed]

Where and how is the bleed valve fitted ?

I assume you have teed it into the wastegate actuator line. You will also need to fix a restrictor of some sort into the line before the bleed valve for this to work properly.

[dojobi]

OK I'd say that's my problem then. I've got no restrictor. I've just removed the T-piece in the line and put the bleeder in it's place. I blocked off the other bit that goes to the metal thing (I assume this is the solenoid). So what do I actually need to do with this restrictor. Can you give me some more info please?

Cheers,

Michael

[Warpspeed]

Hi Michael.

It is difficult to explain, so check out this article from Autospeed:

http://www.autospeed.com/A_0028/page1.html

Cheers, Tony.

[Guest Chillgoon]

I'm sure I was reading the gauge correctly ....

but then again i was shitting my pants a little when u were hitting full boost

[Guest Chillgoon]

I'm sure I was reading the gauge correctly ....

but then again i was shitting my pants a little when u were hitting full boost

[dojobi]

Hmm I'd swear I didn't get a notification about a post here. Wonder why.

Anyway, sorry for not getting back to you earlier. I read that article, but I couldn't see anything about a restrictor. I realise my bleeder isn't quite the same as that, but it's just a standard GFB one, so shouldn't it just work like any normal one? I haven't heard of anyone not being able to turn the boost up because the bleeder couldn't leak enough.

It's really quite strange. All I want is a bit under 0.9bar and I'll be happy.

Chillgoon - you may have shat your pants, but we weren't even at 0.9bar. Wait 'til we hit that, then you can shit them.

Cheers,

Michael

[Warpspeed]

MIC33R, my apologies the article that I suggested indeed does not use a restrictor. So I will attempt to put it into words myself.

The wastegate actuator that is fitted to the turbo has a diaphragm and spring that opens the wastegate at a particular boost level set by the original design of the actuator.

What you need to do is arrange for the pressure fed to the actuator to be less than the actual turbo boost pressure by some fixed proportion. For example if stock boost is 7psi, and you want 15psi boost, then the actuator must still see only 7psi when the boost is actually at 15psi.

The way to do this is to fit an air restrictor into the control hose to the actuator, and an adjustable air bleed needle valve to atmosphere teed into the control line after the restrictor.

The flow path is, boost pressure, restrictor, tee fitting, actuator. The other branch of the tee goes to the adjustable air bleed out to the atmosphere.

If you close off the air bleed fully so it is completely closed, boost goes through the restrictor into the actuator and you will have the stock boost level.

You can then unscrew the needle valve a bit, and the boost pressure will rise above stock by some amount.

Hope this helps.

[dojobi]

mrthorpedo:

Thanks for the tip - I'll check the BOV out. I did install it myself, so there probably is a fairly good chance it isn't on properly

Warpspeed:

Thanks for the explanation. There's just one thing I'm not quite understanding though, and that's how the restrictor works. If the only bit that lets air escape is the bleed valve, then how can the restrictor cause the pressure to be any lower. You said that if the bleed valve is fully closed then I'd have stock boost, but if that's the case then how would it change anything when the bleed valve is open?

Acutally, I've read it again a few times now - here's how I'm seeing it. Please tell me if it's right. The restrictor is in there to force the air to use the bleed valve as that is the path of least resistance, right? I think my problem is that I just removed the t-piece totally and put the bleed valve in its place.

Cheers,

Michael

[Warpspeed]

The wastegate actuator only requires pressure to operate, it is a dead end. Unless there is a leak somewhere. Putting a restrictor in the line will not reduce the pressure IF THERE IS NO FLOW. Think about it.

Now if you add a needle valve that deliberately causes a controlled leak after the restrictor, there is going to be flow through both the restrictor and the needle valve.

If you use the previous example, with 14 psi boost, and a 7psi rated actuator. If the restrictor AND needle valve have EXACTLY the same flow areas then the same air is going to flow through both.

There will be a 7psi drop across the restrictor, and a 7psi drop across the needle bleed valve (if they are set to have identical flow areas).

By adjusting the needle valve you can vary the relative pressure drops across each restriction.

[dojobi]

OK, I understand what you're saying about how it all works, I think. The concept of bleeding off the air is quite clear in my head (I hope), but I think I may not be understanding what a restrictor actually is. Is it just something in the tubing that reduced the cross sectional area of the pipe. If so, then this all makes sense. The t-piece shouldn't be need at all if everything is inline, as long as the bleed is after the restrictor.

Thanks for explaining all this to me btw

Cheers,

Michael

[rob77]

Becareful with bleed valves make sure you dont let the car spike to much over 1bar of boost. Anything more than that with the stock intercooler will cause detonation on a warmish day and the ceramic wheel on the turbo will drop off and fly down your exhaust if not too careful. I would say be safe and set boost to ~ 0.8bar. I have an electronic boost controller restricting it to 0.8bar boost max. I havent dyno'd it but the car should be over 200HP @ rear wheels and its fairly quick. I've found my stock clutch and crap tyres are the main problem with traction issues and my front mount is on order from japan.

Rob

[Warpspeed]

rob77 is quite right.

Be very careful after making any changes, that the boost does not suddenly and unexpectedly rise above a safe level. So gently does it, while watching the boost gauge after any adjustment.

A restrictor is just a small hole. You could solder up the inside of an existing brass fitting and then drill a small hole. Or push a round piece of metal/plastic with a small hole up a rubber hose.

I would start out with a fairly large hole maybe 3mm, you may then find that you cannot get enough boost even with the needle fully open. Go a bit smaller, and see what happens.

If you do it this way, the needle when fully closed gives stock boost, fully open will give some safe maximum, with lots of adjustment inbetween.

[dojobi]

Cool, thanks for the advice guys. I've got a big front mount, so I should be fairly safe I feel, but I'll make sure the turbo is well protected from spikes.

I think I'll try and make a restrictor tonight. Once again, thanks for the help Warpspeed.

Cheers,

Michael

[Warpspeed]

Let us know how it all goes Michael.

Cheers, Tony.

[Ender]

Why do you need a restrictor?

Isnt this what a bleed valve does...it controls what goes to the actuator. I thought that was the whole idea of a BLEED valve. If you just run a variable restrictor like a needle valve...then yes you need a vent or alternate route for the air for it to work...

If you look at one side of your bleed valve you will see a little hole....this is the "restrictor" you talk about with the hole in it...this is a built in one...

Russ

[dojobi]

That was my take on the point of a bleeder too, but since this one can't bleed enough air, I have to use other methods to lower the presssure the actuator sees. So the restrictor will give me a lower starting point to bleed from.

[Ender]

Excellent...I understand...by the way does air escaping affect the A/F ratio at all...I gather it is too small an amount to make any difference..is this right?

You don't normally need this restricter though...I know of numerous cars with up to 230 rwkw without needing this mod..they just use standard bleeders, I wonder what is causing this to happen on your car..let us know if you find out.

Russ

[dojobi]

It does affect it slightly, as the standard tubing off the intercooler piping returns the air the same way the bov does, but a bleeder will just vent it.

I can't work out why I need a restrictor, but I would say the GFB bleeder is just not designed for Skylines. I believe GFB primarily make their products for WRXs. I would say they use a very small amount of air to open the wastegate (light spring), so the GFB bleeder would only have to leak a small amount of air to open it, hence making it not work correctly on a Skyline.

[dojobi]

OK, well I had to get my HKS cam gear installed by my mechanic, so I got him to have a look at it while it was in there. It turns out my bleeder is screwed. I don't think I did this, as I think it's a bit hard to do that. Anyway, I'm sitting happily at 0.9bar with a replacement GFB bleeder. The acceleration is awesome now - I can't wait to get my cam gear and SAFC tuned. I also experience the R33 flat spot that everyone talks about too. While I'm still accelerating heaps, the stall in the acceleration is quite noticeable, and does take a bit of the fun out of it.

Cheers,

Michael