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C900 Performance, Mods & Tuning Covers Tuning & Performance modifications for the Classic 900 (C900)

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  #1  
Old 17th December 2002
Sy-Downes Sy-Downes is offline
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Default overboosting lpt

hello
does anyone know how much boost i can get from my lpt turbo
im having trouble getting it over 10psi and it drops back to 7psi
im using a wastegate bleed valve system but its already maxed out shall i just keep the wastegate shut?
surely it must be able to produce more?i'm not even into fpt territory yet!
its a 1993 16 valve
thanks sy :P
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  #2  
Old 17th December 2002
Carl Hernandez Carl Hernandez is offline
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You really cant run hig boost levels w/o becoming an fpt car.
you could try water injection as well as a fifth injector to keep the boos from knocking.
Even by just adding the apc computer / system and not the intercooler you can probably still run about 13 psi.
remember too much boost w/o some control will blow the engine and possibly a hole through a piston.
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  #3  
Old 18th December 2002
Sy-Downes Sy-Downes is offline
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knock prevention isnt the issue here i just cant get the boost to get to a level even near a fpt it seems the turbo just wont blow hard enough yet i am told the unit should be good for at least 15 psi
Has anyone every messed about with the wastgate spring tension on these?
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  #4  
Old 18th December 2002
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ask alex fer sure. :-? but 1 of the mods is to shorten the wastegate actuater rod 2 give a stronger spring tension
which means the plate stays closed longer, also u could replace the spring with a stronger 1 !! (dont quote me on this but i think thats the answer)
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  #5  
Old 18th December 2002
Johann F Johann F is offline
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Remove the hose to the actuator and go for a drive - very very briefly see if the boost improves - if it does then the actuator is letting the pressure off. If it still does not boost you have a pressure leak in another part of the system. Cranking up the WG arm is not a good idea if you want to increase boost a lot as all you are doing is reducing the travel of the arm and therefore the maximum opening when it does eventualy open - this means you can't dump boost at all and you go bang
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  #6  
Old 18th December 2002
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Does anybody know if the lpt actuator is weaker than the fpt? because if it is, then maybe this is the reason for your lack of boost. Or the actuator could be old/weak!!
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Old 18th December 2002
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Only running a little more than standard boost in my LPT, but what I found was the wastegate needed winding in a long way just to get this. It was almost loose when I started adjusting. Need about 5mm off the end of the rod so you don't run out of adjustment.
No problem with wastegate not dumping the boost like this, but I'm not running high boost.
The exposed thread of the rod gets rusty, so clean this up well before attempting to wind back the lock nut. The lock nut has a fine metric thread, and isn't 'off the shelf' after you've sheared it.
Overboost switch cuts in at about 9.5 so set this higher as well.
Fred
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  #8  
Old 18th December 2002
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i havent tried running at higher boost. but my boost is currently set at 0.4 bar. when gradually going at higher rpm the boost eventually drops by 0.1 bar due to presaasure. best is to get an additonal boost controller like the evc(hks) or the avcr(apexi). get a intercoller installed, and maybe some water injection to reduce knock.
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Old 18th December 2002
Sy-Downes Sy-Downes is offline
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Thanks for the comments guys
I am still not sure why i cannot develop high boost levels but i have some ideas to try, the first being to disable the wastegate completely and see what i get
i will keep you posted with the result
:wink:
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  #10  
Old 18th December 2002
Johann F Johann F is offline
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Please - only disable the actuator for one very quick boost check - it's very easy to burn a piston! (
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  #11  
Old 18th December 2002
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I'm having the same symptoms in my 900T. I can only get to about 10psi. The engine does not seem to be knocking at all, but my boost drops back to about 7 psi, then cycles back up to about 10. If I disable the wastegate and it holds boost then the actuator is bad?
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  #12  
Old 18th December 2002
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So, I disconnected and plugged the vacuum line going to the wastegate actuator. I took in on the highway and gradually increased boost. It held steady boost at the beginning of the red and I heard no knocking or pinging. I didn't want to push it any farther for fear of burning a piston, but this was well past the point that my boost usually starts dropping. Maybe my actuator spring is weak? Is there anything else it could be?
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  #13  
Old 19th December 2002
Johann F Johann F is offline
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Raub, This tells me there are no leaks in the system and that there is nothing actualy wrong with the turbo in the sense that it can actualy produce boost.However this is not to say that it's the actuator that is bad. The next test is to reconnect the actuator but to disable the APC (pull the fuse or connection to the solenoid) See what boost you get now - it should be around 1/3 - 1/2 in the yellow zone but if you can get an accurate boost guage and get the reading - all the better. If you are substantialy bellow this then yes you can point to the actuator as being at fault but if this is within limits then it tells you that the APC is doing it's job and reducing boost because it is detecting knock ( and remember you can't hear knock at high speeds) you must look elesewhere; fuel enrichment and ignition timing (particularly the retard under boost) After that you may have to look at the APC ECU -old electonics do go off!
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  #14  
Old 19th December 2002
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I set my base boost before I started messing with anything else. I think I may have a vacuum leak despite the higher boost with the actuator connected. Maybe the knock is related to this?
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  #15  
Old 20th December 2002
kie kie is offline
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Niko who posts on this site runs well over 1bar, I ran 1 bar on my lpt

u need the actuator the one i had ran a base boost of 12psi .8 bar ish

Kie
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  #16  
Old 20th December 2002
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A good piece of advice I had from a Saab mechanic friend is that a good starting point for setting the wastegate actuator is to set its length so that it needs to be extended by half the diameter of the hole in the end of the rod before attaching to the wastegate arm.
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  #17  
Old 21st December 2002
Keith Keith is offline
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Quote:
base boost of 12psi .8 bar ish


My engine melted with base boost at about 7~8 psi :!

But that was without water inj.
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  #18  
Old 22nd December 2002
Sy-Downes Sy-Downes is offline
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ok so I disabled my wastegate actuator pipe and took it for a drive
when i floored it i saw the boost hit 18 psi,lost traction in 3rd! and blew one of the intercooler pipes off, all within the space of 5 seconds
the good thing is that this proves that the turbo can at least produce the boost when it wants to.
Ithink the problem is the bleed valve cannot bleed fast enough, does anyone know where you can buy a better one?
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  #19  
Old 23rd December 2002
kie kie is offline
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get yourself a decent actuator from abbots !!!

I have one but there are a few names on it already
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