944 Turbo & boost pressure
04-29-2003, 05:03 PM
#1
Three Wheelin'
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944 Turbo & boost pressure
I was looking at turbo products and saw <a href="http://www.smartcart.com/Paragon/cgi/display.cgi?item_num=PP993.110.337.50" target="_blank">this</a>, which made me wonder about my boost pressure.
When I shift, while driving hard, the boost gauge drops from 1.6+ down to 0.4 almost instantly, then when I get back on the gas it goes up, but not as quickly.
Is this normal behavior, or is there something wrong?
When I shift, while driving hard, the boost gauge drops from 1.6+ down to 0.4 almost instantly, then when I get back on the gas it goes up, but not as quickly.
Is this normal behavior, or is there something wrong?
04-29-2003, 06:46 PM
#2
Burning Brakes
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If the car doesn't boost properly then look for:
-A mechanical problem with the turbo
-A leak or other problem in the air intake system
-The wastegate sticking open
-A leak in the exhaust system
-Other mechanical problems
Engine computer problems
-A mechanical problem with the turbo
-A leak or other problem in the air intake system
-The wastegate sticking open
-A leak in the exhaust system
-Other mechanical problems
Engine computer problems
04-29-2003, 06:58 PM
#3
Nordschleife Master
ERr...yeah..anyway
If in doubt you wanna yank the CBV thats pictured on the Paragon site and inspect the diaphragm.
Also try sucking on the vac line part of it...if you hear air hissing out and whatnot...you need to replace it.
Does the car boost strong otherwise?
If in doubt you wanna yank the CBV thats pictured on the Paragon site and inspect the diaphragm.
Also try sucking on the vac line part of it...if you hear air hissing out and whatnot...you need to replace it.
Does the car boost strong otherwise?
04-29-2003, 07:00 PM
#4
Okay - I'll assume that you drop the throttle pedal (not powershifting) and that you are reading the factory boost guage. In this case, the car is normal, because when you are shifting, you are closing the throttle butterfly, which will instantly create vaccum in the manifold.
The bypass valve has zero affect on this because it's events are before the throttle butterfly.
<img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" /> <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />
The bypass valve has zero affect on this because it's events are before the throttle butterfly.
<img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" /> <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />
04-29-2003, 07:02 PM
#5
Drifting
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I'd say you're losing too much pressure when shifting (of course you have to do that quickly, but I assume that's not the problem 
)
My chipped 951 drops from 2 bars to somewhere around 1.2 or so when I shift (accelerating hard, of course) (absolute numbers from the stock gauge)... goes back to full boost in maybe a second or so, fast yet slow enough to notice it... I'm thinking I need to replace the CBV as well...
)My chipped 951 drops from 2 bars to somewhere around 1.2 or so when I shift (accelerating hard, of course) (absolute numbers from the stock gauge)... goes back to full boost in maybe a second or so, fast yet slow enough to notice it... I'm thinking I need to replace the CBV as well...
04-29-2003, 07:17 PM
#6
Three Wheelin'
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I can feel the turbo kick in as the boost gauge approaches 1.0 bar, and grow even stronger as it goes to 1.6+ bar. I was just wondering if the gauge was supposed to drop so abruptly during shifting.
04-29-2003, 07:59 PM
#7
Race Director
Check the bypass valve.
My turbo would drop off boost when shifting. Now that I have replaced the valve it drops to about 1 bar.
Remember also that 1 bar on the stock gage is ambient pressure (0 psi boost)
The car generates .6+ bar of boost.
running below 1 bar is running the manifold under a vacuum. A NA car will run from vacuum to ambient at full throttle.
My turbo would drop off boost when shifting. Now that I have replaced the valve it drops to about 1 bar.
Remember also that 1 bar on the stock gage is ambient pressure (0 psi boost)
The car generates .6+ bar of boost.
running below 1 bar is running the manifold under a vacuum. A NA car will run from vacuum to ambient at full throttle.
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04-29-2003, 09:38 PM
#8
Three Wheelin'
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I was wondering about that, cuz I saw it in another thread recently.
So when I'm driving on the freeway, and see ~0.5bar on the gauge, am I getting less intake air than I would be without the turbo? I guess that would be a good thing, since I'd be spending less fuel to go the same speed. But what about when I start from 0 and the gauge isn't up to 1.0 yet?
I'll see what it's like Thursday night (or Wednesday if UPS is quick) when I go from a dirty paper filter, to a K&N filter.
Would one of those <a href="http://www.smartcart.com/Paragon/cgi/display.cgi?item_num=944BoostEnh" target="_blank">boost enhancers</a> help keep the boost up? And does that replace the CBV? If so I might as well get one instead of a new CBV.
So when I'm driving on the freeway, and see ~0.5bar on the gauge, am I getting less intake air than I would be without the turbo? I guess that would be a good thing, since I'd be spending less fuel to go the same speed. But what about when I start from 0 and the gauge isn't up to 1.0 yet?
I'll see what it's like Thursday night (or Wednesday if UPS is quick) when I go from a dirty paper filter, to a K&N filter.
Would one of those <a href="http://www.smartcart.com/Paragon/cgi/display.cgi?item_num=944BoostEnh" target="_blank">boost enhancers</a> help keep the boost up? And does that replace the CBV? If so I might as well get one instead of a new CBV.
04-30-2003, 01:17 PM
#9
Race Director
Ag951
Remember that boost is generated by exhaust gas. On the freeway you run low boost since you are not using very much power to acclerare. Just enough to keep the car at constant speed. When cruising at 70 mph I like to see my boost gage at .4 to .6. I typically accelerate at 1 bar.
Push you foot down more and you will suck more air into the engine. As more air goes in more fuel is delivered. This means more exhaust gas is released and therefore more is avalible to drive the turbine end of the turbo. As the turbine end is driven more the compressor end compresses more air thus sucking more through the intake thus more fuel and even more exhaust gas and therefore more compression and boost from the turbo.
Boost enhancers attempt to maintain boost at WOT (wide open trottle) and will not do anything at partial throttle. The CBV is used to maintin boost when you lift off the trottle for an up shift. The air filter wont do much unless you have a very dirty paper one. I still use a paper filter on mine.
Get a new CBV and it will be better, but you will only have boost when you step on it. That is one of the nice things about turbos is that they are an "on demand" system. keep the boost low and you will be excellent gas milage. Step on it and get power, but less milage. Remember a postive 1 bar boost (2 on the gauge) is in theory equvalent to doubling the displacement. So at 1 bar boost you basicly have 5.0L motor. Nice thing is that stay at low boost (below 1 on the gage) and you have small fuel efficient 2.5L motor.
Remember that boost is generated by exhaust gas. On the freeway you run low boost since you are not using very much power to acclerare. Just enough to keep the car at constant speed. When cruising at 70 mph I like to see my boost gage at .4 to .6. I typically accelerate at 1 bar.
Push you foot down more and you will suck more air into the engine. As more air goes in more fuel is delivered. This means more exhaust gas is released and therefore more is avalible to drive the turbine end of the turbo. As the turbine end is driven more the compressor end compresses more air thus sucking more through the intake thus more fuel and even more exhaust gas and therefore more compression and boost from the turbo.
Boost enhancers attempt to maintain boost at WOT (wide open trottle) and will not do anything at partial throttle. The CBV is used to maintin boost when you lift off the trottle for an up shift. The air filter wont do much unless you have a very dirty paper one. I still use a paper filter on mine.
Get a new CBV and it will be better, but you will only have boost when you step on it. That is one of the nice things about turbos is that they are an "on demand" system. keep the boost low and you will be excellent gas milage. Step on it and get power, but less milage. Remember a postive 1 bar boost (2 on the gauge) is in theory equvalent to doubling the displacement. So at 1 bar boost you basicly have 5.0L motor. Nice thing is that stay at low boost (below 1 on the gage) and you have small fuel efficient 2.5L motor.
04-30-2003, 02:00 PM
#12
Race Director
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by '86 944 turbo:
<strong>whats CBV?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Check this link..
<a href="http://www.smartcart.com/Paragon/cgi/display.cgi?item_num=PP993.110.337.50" target="_blank">Compressor Bypass Valve</a>,
<strong>whats CBV?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Check this link..
<a href="http://www.smartcart.com/Paragon/cgi/display.cgi?item_num=PP993.110.337.50" target="_blank">Compressor Bypass Valve</a>,
04-30-2003, 04:14 PM
#13
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AG,
I just had a similar problem, once I replaced the CBV, everything was fine again.... Upon inspection, the diaphragm had a nice sized tear in it. I think you can pick up the 993 valve (direct replacement for a 951) @ paragon for $34.
I just had a similar problem, once I replaced the CBV, everything was fine again.... Upon inspection, the diaphragm had a nice sized tear in it. I think you can pick up the 993 valve (direct replacement for a 951) @ paragon for $34.
04-30-2003, 04:20 PM
#14
Three Wheelin'
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That boost enhancer I was looking at (linked in the first post on this thread) was supposed to increase boost at lower RPMs.
I want to get the turbo to spool up quickly, so when I come around a low speed corner in autoX I get boost sooner, rather than later.
I want to get the turbo to spool up quickly, so when I come around a low speed corner in autoX I get boost sooner, rather than later.
04-30-2003, 05:04 PM
#15
Race Director
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Ag951:
<strong>That boost enhancer I was looking at (linked in the first post on this thread) was supposed to increase boost at lower RPMs.
I want to get the turbo to spool up quickly, so when I come around a low speed corner in autoX I get boost sooner, rather than later.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Won't happen
Sorry to say but the 951 is crappy autocross car since you are rarly on boost. You often have two options. 1) Work first gear and hang on with power oversteer from too much boost and shift to second 2) wait it out in 2rd gear.
Of course option 3 is best.. Get a 944 NA or S2. Less power overall, but no lag and better low end torque.
That is primialy the reason I built my 944-spec car. I was tried of fighting my 951 at the autocross.
You really need to visit road course at AMP. Here you will feel what the Turbo was made for!
The CBV in your post is a stock part that often fails. I does nothing to improve performance of the car except to bring it back to stock if you exising CBV is broken.
Remember below 3000 rpm you will never have any boost anyway.
<strong>That boost enhancer I was looking at (linked in the first post on this thread) was supposed to increase boost at lower RPMs.
I want to get the turbo to spool up quickly, so when I come around a low speed corner in autoX I get boost sooner, rather than later.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Won't happen
Sorry to say but the 951 is crappy autocross car since you are rarly on boost. You often have two options. 1) Work first gear and hang on with power oversteer from too much boost and shift to second 2) wait it out in 2rd gear.
Of course option 3 is best.. Get a 944 NA or S2. Less power overall, but no lag and better low end torque.
That is primialy the reason I built my 944-spec car. I was tried of fighting my 951 at the autocross.
You really need to visit road course at AMP. Here you will feel what the Turbo was made for!
The CBV in your post is a stock part that often fails. I does nothing to improve performance of the car except to bring it back to stock if you exising CBV is broken.
Remember below 3000 rpm you will never have any boost anyway.
