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How can I get more boost?
What is a easy way to bump the boost pressure up?
*ANYTHING* if you know how to bump it 1psi from 20psi, Tell me how to get more.
Every one wonders how to get more boost
from a cheap and easy way..Tell your storys
But please Help
Kid-tsi
 

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Your boost level is controlled by your wastegate actuator. Let's look at the stock system. There is a vac line coming off a nipple from the output of the turbo (the start of the lower intercooler pipe). That vac line runs to the wastegate actuator (it also slpits off but I'll talk about that in a minute). The wastegate actuator on our cars is pnuematically activated which is to say it's pressure activated. That vac line from the turbo runs into the wastegate acutator and the pressure in that line is realative to the boost you are running since it comes from the output of the turbo. Okay... once the wastegate actuator sees about 7 psi in that tube it opens.

Pause

I need to tell you how boost works. Your engine is just a giant air pump. It sucks in air and pushes it out. The turbo takes advantage of that pushing and turnis it into more sucking. The exhaust someout of the exhaust manifold and goes thru the exhaust turbine of the turbo. The psuhing of the exhaust turns the turbine (much like those colorful pin wheels we all liked when we were kids... blow on them and they spin). Now that exhaust turbine is mechanically attached to another turbine on the intake side of the turbo. The intake air comes in through the air filter, thru the MAF and into the turbo. It then goes though the intercooler to cool it down after going thru that hot turbo and finally into the throttle body. Back tot he turbo... the exhaust is turning the exhaust turbine which is turning the intake turbine. The intake turbine works to suck more air in. Since more air is coming in the engine is working harder and there is more air coming out. More air coming out means the force of it is going to turn the exhaust turbine even faster.... which will in turn spin the intake turbine faster sucking more air in... even more air in means even more air out which means the turbines spin even faster..... This means an ever increasing boost. This will continue until something breaks.... which would be bad. So to restrict the amount of boost what they added was a wastegate door. This is a little door just before the exhaust hits the exhaust turbine of the turbo. The door is normally closed but once it opens it allows some of the exhaust to bypass the exhaust wheel of the turbine... resulting in the turbine spinning at the same rate but no longer increasing in speed. That's how you limit the boost to a certain amount.

Now back to the wastegate actuator... at 7 psi it opens which means it moves an arm that it attached to the wastegate door swinging it open. At that point the boost is then maxed out and it stays level at 7 psi. But you say your stock car does 10~11 psi stock... okay I'll eplain that. There is a T between the turbo outlet and the wastegate actuator that runs up to a part called the boost control solenoid. This part will leak about 4 psi of pressure from the line. So now it take 11 psi at the turbo for the wastegate actuator to see 7 psi (11-4=7).

As an aside your ECU can shut your boost down to 7 psi by shutting off the bleed thru the boost control solenoid. It will do this when it sees lots of knock from bad gas or whatever... that's another story. But just to let you know that's where it can do it.

Okay now I can explain how to modify your boost level. All you have to is reduce the pressure the wastegate actuator sees even more so it takes more boost for it to see 7 psi. For instance. If I add a 3 nipple aquarium bleeder valve into the line running to the boost control solenoid I can bleed off some more pressure from that line. Let's say I can bleed off 4 more psi from there. Now it would take 15 psi at the turbo for the wastegaet actuator to see 7 psi (15-4-4=7). That's how a bleeder type manual boost controller works... it bleeds off variable amounts of pressure so you can set your max boost.

The other way to do it is add a restrictor type controller into the line just before the wastegate actuator. What this does is it blocks all pressure from getting to the actuator with a ball bearing and spring mechanism. Once the boost reaches a certain point the ball will move out of the way and let the pressure past to the wastegate actuator. If the pressure is higher then 7 psi the wastegate solenoid will open. You can set these controllers to open at different pressures. If you set it for 16 psi then once the pressure reaches 16 psi the thing opens and 16 psi of pressure then hits the wastegate actuator opening it.

Electronic controllers work the same way but let you modify the boost level for different rpms and such for better tunability.

So that's how you boost level is adjusted.

But there are things to watch for when you raise your boost like fuel supply, fuel cut and such. When I have a few more spare minutes I'll write about some of those.

p.s. Forgive me I didn't have time to go back and proof read.

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Quadcylla
92 Laser RS-T FWD

[This message has been edited by Quadcylla (edited September 21, 2000).]

[This message has been edited by Quadcylla (edited September 21, 2000).]
 

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>. It will do this when it sees lots of knock from bad gas or whatever... that's another story. [/B]<HR></BLOCKQUOTE>

can i hear this story?
 

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So what heppens when people like me are not using the BCS from Mitsu. When Profec was installed, GReddy provides another BCS looking box (2 nipples) and said to cap off the Mitsu BCS.



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'99 GST
http://www.geocities.com/mospeed9844
Akimoto Air Fitler
GReddy BOV
GReddy Intercooler Piping
GReddy Cat-Back
GReddy Profec B
GReddy Boost and EGT Gauge
Autometer Air/Fuel Meter
Front and Rear Strut Bars
 

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Then the ECU can not touch your boost. So you won't suffer pre-fuel cut and won't have your boost turned down under high knock. It will still kill your timing though when you're knocking.

I think having the knock LED is even more important for those who no longer have the BCS hooked up so that at least you know when the ECU has 'done everything it can' to stop the knock it sees.

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Quadcylla
92 Laser RS-T FWD
 

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Okay so you want to know about knock. Let's see... where to begin.

Heat causes knock. Once you start puching your engine hard you'll have to start worrying about heat. Now one point to make is that when you go to a higher octane fuel it will take more heat to cause that knock. That's why everyone suggests going with higher octane gasses in our cars... because there will be less knock for the heat being generated. That's also why race gas is even better when you are really working your engine at the track. Now let's look at why less knock means better performance.

Your ECU likes your car and really wants to keep it in one piece... so it has some self preservation abilities built in. Knock is bad and can lead to engine damage. So the ECU listens for knock and tries to prevent it. The ECU uses the knock sensor and some other circuitry to monitor knock. The knock sensor is basically a microphone listening to all the noises the engine makes. Knock makes a specific sound, so it has a specific frequency. The ECU has a listening circuit that listens for just that frequency (band pass filter). When it hears that characteristic knocking sound it keeps track of it. This is where the infamous knock sum comes into play. Knock sum is how the ECu keeps track of the amount of knock over a period of time. It counts the number of knocks per given time frame and constantly updates this value. So as knock increases knock sum will increase... and then say if you shift the knock goes away and the knock sum will gradually reduce. The time period it watches over is pretty short so it's very close to a real time representation of the amount of knock taking place.

So what the hell does that have to do with performance? Well as I said the ECU lieks your car and so wants to prevent knock. How it does this is by controlling your timing. Your ECu has direct instant control of your timing advance. So if it hears enough knock it will index your timing to less of an advance then is dictated by the timing map. Reducing the advance will ensure a better combustion and will reduce the power and thus temperature of each combustion. This lower temperature will reduce the amount of knock. The ECU will continue reducing the timing advance until it sees that the knock has been reduced to a safe level. Once it sees that the knock sum has reduced past the safe level into a very safe level it will start indexing the timing advance back up towards the proper map determined value.

Okay so it effects timing what does that have to do with boost? Well let's say the knock sum does not decrease and the timing is going lower and lower and it's not solving the problem (due to bad gas [gas with water in it or low octane] or overworking the engine). Eventually the ECU will say it's done all it can with timing and it's still not helping... so it then decides to cut your boost down. This is when it deactivates the bleed thru the boost control solenoid (BCS) which reduces your boost by about 4 psi. This reduce in boost reduces the work the engine is doing which reduces the temperature. This will greatly help the knock problem. This is the ECUs last resort... it can do no more after this.

This is where the knock led comes in. You can hook up and LED into the circuit that goes to the BCS to activate and deactivate it. The light being off means that everything is fine and the boost should be at 10~11 psi (stock system). But once the light comes on you know that the ECU is at witts end and just exercised it's last line of defense. That is why the knock LED so so valuable. I recommend everyone do this mod. You don't want to keep pushing the car once that light comes one... the ECU will not be able to stop the knock with timing anymore and it will just get worse.


Aside: The actual timing advance indexing done by the ECU is not just based on knock sum... it also takes into account an ECU calculated value called octane. Octane is really the same as knock sum but over a longer period of time. I do not fully understand how it uses each of these to calculate how much to lower the advance and if you understand control language and want to learn more ask Todd Day about it. It's enough to know that higher knock sum will reduce the timing advance.

Any questions?

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Quadcylla
92 Laser RS-T FWD
 

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One other time that the BCS is activated by the ECU is for the pre-fuel cut defense mechanism. Pre-fuel happens when the ECU sees that the airflow (not air-mass) is above a preprogrammed value set in the ECU. What the ECU does is it turns the BCS on and of in pulses to reduce the boost somewhat. In a lightly modded 1G running 15 psi you will see your boost start to drop when your rpms go above about 5,500... that's the EUC reducing airflow. If you ahve the knock LED mod you'll see it flashing at this point.

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Quadcylla
92 Laser RS-T FWD
 
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