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Location:
Perth, WA
Registered:
February 2003
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Boost Changing
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Thu, 12 August 2004 08:39
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OK i have just noticed that when i floor it the boost goes up to about 13psi and then goes down to about 10psi... and in 2nd gear it goes down to 9psi. i was just wonding if this is normal as i am just using a home made boost controler (bleed valve thing).
engine is a 4agze MAP with a t25g turbo and on stock computer.
Please help
thanks.
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Location:
Hackham South Australia
Registered:
July 2004
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Re: Boost Changing
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Thu, 12 August 2004 09:02
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sounds to me you need an intercooler, if not a bigger one.
anything over 8 psi in my books is too much with out a cooler of some kind, whether it is intercooled via air - air, water - air, or the old skool water injection( be warey of this one i have herd good and bad things about it), also invest in an aftermarket bleeder valve as home mades are only good if you are one of the bush mechanics ( no i am not having a dig at you), there is nothing like quality parts to make a go good, ive learnt that one.
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Location:
Hackham South Australia
Registered:
July 2004
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Re: Boost Changing
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Thu, 12 August 2004 09:10
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by the way i forgot to mention that u should turn the boost to 5\6 pounds before you do damage, if not already.
What u are experiencing is that air gets so warm that when it mixes with the fuel it is bieng burnt before it makes it in the combustion chamber,coz the air is hot in 1st gr and you go in to 2nd the air is raising in temp due to the lack of cooling.
When air is compressed it gets warmer. this warm charge has to be cooled for it to be effective. I am soory i dont know much about this topic too much, hope this has helped in some way.
I would love to use liquid nitrogen as a cooling method, sure the cost would make it unviable but think of the BOOST!
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Location:
Perth, WA
Registered:
February 2003
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Re: Boost Changing
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Thu, 12 August 2004 12:33
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I have a VR4 intercooler and after a run all the pipes are pretty cold. but as i dont have a aftermarket computer i dont know the intake temp.
thanks for ur help.
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Location:
On your mum!
Registered:
May 2002
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Location:
South Eastern Subs
Registered:
March 2004
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Re: Boost Changing
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Thu, 12 August 2004 14:03
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What can you use to measure your intake temerature's and where should u mount it? I know after the cooler but where?
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Location:
Brisbane
Registered:
May 2002
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Re: Boost Changing
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Thu, 12 August 2004 23:31
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| doityourself wrote on Thu, 12 August 2004 19:10 |
What u are experiencing is that air gets so warm that when it mixes with the fuel it is bieng burnt before it makes it in the combustion chamber,coz the air is hot in 1st gr and you go in to 2nd the air is raising in temp due to the lack of cooling.
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Uh, dude, if that happened the engine bay would quite literally explode.
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soory i dont know much about this topic too much
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That much is fairly obvious, but if you don't know the answer why confuse the issue with incorrect information? 
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Registered:
May 2002
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Re: Boost Changing
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Fri, 13 August 2004 00:55
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To throw another idea in.
In my case I could hold 18psi in first, 18 psi in second, then it would start at 18psi in third and immediately drop to 12psi then 4th gear was the same as third and 5th was the same and so on.
Problem was that the wastegate flap was being forced open by the exhaust gases and hence the boost drop. It was only noticed in the taller gears because of the increased torque loading (more exhaust gas trying to bypass the wastegate flap) and longer time spent in those gears.
Increased tension on the wastegate actuator fixed the problem perfectly!
Your prob could be this but sounds much more like it is simply a bleed valve that needs to be better setup/located.
Ensure that the wastegate actuator line is as short as possible i.e. it should ideally be from the wastegate actuator to the compressor housing (or to the first few inches of piping immediately after the compressor housing) the shorter this line is the less spiking and more stable the boost. If your wastegate line runs from the manifold the the wastegate actuator then this will almost definitely be your problem.
Locate your bleed valve close to the wastegate actuator and ensure that there is a restrictor in the line before the bleed!! Otherwise you will be bleeding off a shite load of air and not gaining much boost or getting very good boost control.
If a bleed valve can't bleed enough then you will see low boost (because more positive pressure is able to force the wastegate actuator to open the wastegate flap). It sounds like yours can bleed off enough for around 9 - 10 psi but it spikes to 13 psi due to the delayed reaction of wastegate actuator then settles down to the boost level that the bleed valve can maintain.
I am assuming the bleed valve you made has no "gate" either?
A spike of a pound or so is not much to worry about, in fact some people like a spike to give a bit of oomph at the start as it comes on boost.
I have mine setup (4AGTE) to run a low boost of 13 psi and it does not spike or drop or flutcuate at all (no gate on the low boost). High boost (19psi usually) is gated and comes on with a 1psi spike (can be set up to spike higher or not at all too) then holds the preset boost perfectly!
Hope this helps.
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Location:
Perth, WA
Registered:
February 2003
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Re: Boost Changing
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Fri, 13 August 2004 03:11
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Thank you that was alot of help.
the current bleed valve does have a adjustable gate on it.. and is at about 2/3 open so i think ther isnt enought restrition in the line.
ill have a look at it now and see what i can do
thanks
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Registered:
May 2002
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Re: Boost Changing
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Fri, 13 August 2004 03:45
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From what you just described in the post above I think you mean you are going to adjust the restrictor ?? (in line before the bleed). The gate is (usually) after the bleed and will open once a predetermined pressure is reached allowing the pressure to move the wastegate actuator diaphragm.
The gate just allows boost to build a little quicker than not having a gate.
Sounds like you might be on the right track anyhow.
Let us know how you go.
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Location:
Perth, WA
Registered:
February 2003
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Re: Boost Changing
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Sat, 14 August 2004 05:06
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ok i have fiddled around with the bleed valve and it has got better. But still does it.
Now another thing that i thought might effect it is the brake booster... because on idle when i pump the brakes the idel goes up to like 1500rpm which i think is due to a dammaged diaphram in the booster. I dont know but this may effect the boost changing.
does anyone know if this could be the problem. and do i need a new brake booster??
cheers again.
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Location:
Perth, WA
Registered:
February 2003
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Re: Boost Changing
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Sun, 15 August 2004 10:55
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anyone?
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