Measuring boost level?
- Thread starter poprock
- Start date
poprock
New member
As far as I understand it there's a ten percent tolerance on the standard boost gauge. That means that the boost gauge should read 1.85±0.185 bar. I know that includes atmospheric pressure, so knock that off and you get between 0.665 and 1.035 bar. If 1 bar = 14.5 psi, then that's between and 9.6 and 15 psi.
That's a massive amount of variance. I think I can see why people want to fit aftermarket boost gauges.
I'm still learning the basics of how turbo systems work. Am I right in thinking that wastegate modifications do not affect the boost pressure, but only affect what percentage of that potential boost is applied at any given time?
That's a massive amount of variance. I think I can see why people want to fit aftermarket boost gauges.
I'm still learning the basics of how turbo systems work. Am I right in thinking that wastegate modifications do not affect the boost pressure, but only affect what percentage of that potential boost is applied at any given time?
poprock
New member
My wastegate's already been replaced with an adjustable one, which I currently have set to 17psi of resistance (as opposed to the standard Porsche units being set at seven or ten).
I'm about to fit a manual boost controller and want to figure out my current boost pressure so that I know what baseline setting to begin with"”but I don't want to go to the trouble of buying and fitting a "˜proper' boost gauge to do so. A rough estimate will do me fine.
I'm also wondering whether having a wastegate which opens at a higher pressure than standard means I should dial up the manual boost controller to match, or whether it isn't a consideration.
I'm about to fit a manual boost controller and want to figure out my current boost pressure so that I know what baseline setting to begin with"”but I don't want to go to the trouble of buying and fitting a "˜proper' boost gauge to do so. A rough estimate will do me fine.
I'm also wondering whether having a wastegate which opens at a higher pressure than standard means I should dial up the manual boost controller to match, or whether it isn't a consideration.
poprock
New member
As I understand it, a boost controller does not alter the maximum boost achievable.
Your wastegate opens gradually, filtering off air and dropping the amount of boost getting through to the engine. This is one contributor to your turbo lag. The wastegate valve pressure (7psi standard) is the pressure it takes to fully open the valve, not the pressure it starts to vent at. I think"”I'm still not 100% sure on this stuff.
A boost controller is a more "˜switch-like' valve, preventing air from venting through the wastegate until a set pressure is reached. This has the effect of reducing the lag you feel, because the turbo is kicking in as soon as it can, rather than immediately leaking some of it's power out through the wastegate.
Promax have a fairly good explanation here.
Your wastegate opens gradually, filtering off air and dropping the amount of boost getting through to the engine. This is one contributor to your turbo lag. The wastegate valve pressure (7psi standard) is the pressure it takes to fully open the valve, not the pressure it starts to vent at. I think"”I'm still not 100% sure on this stuff.
A boost controller is a more "˜switch-like' valve, preventing air from venting through the wastegate until a set pressure is reached. This has the effect of reducing the lag you feel, because the turbo is kicking in as soon as it can, rather than immediately leaking some of it's power out through the wastegate.
Promax have a fairly good explanation here.
Suffolk944
Moderator
The boost setting for a 250BHP Turbo is as Nags suggested 0.85 bar. Think a 220BHP is marginally less.
Are we talking about a Boost Enhancer as shown in the Promax link or a Boost Controller ? They aren't one in the same.
Are we talking about a Boost Enhancer as shown in the Promax link or a Boost Controller ? They aren't one in the same.
appletonn
New member
The Manual Boost Controller (I have a Lindsay Racing one fitted) and the LR/Promax boost enhancer are not the same thing. The MBC does directly control the point at which the wastegate opens, thus directly controlling the maximum boost - there is a vacuum hose that runs from the MBC directly to the wastegate.
I have an additional boost gauge and I can turn the maximum boost up or down from the comfort of my seat!
I thought the MBC dictated the point at which the wastegate begins to bleed of the boost, thus protecting the engine.
With an old/tired wastegate, the valve will begin to open too early thus reducing the max boost available and increasing the lag.
poprock
New member
It's the enhancer as linked to that I'm going to fit; a Lindsey Racing product sold by Promax.
So "¦ I think I understand what this enhancer does. How is a boost controller different? Aren't they both just adjustable valves that prevent flow to the wastegate until a desired pressure is reached?
Suffolk944
Moderator
I think the difference is that the Enhancer is a device that allows the car to achieve its normal levels of boost without it bleeding out prematurely from the weak wastegate. Effectively bypassing the function of the wastegate I would deduce. Having re-read the Promax explanation which says
I would say that is the case. On the other hand the controller when combined with different engine management chips is the system for increasing boost. I would think the standard chip will limit a car to what boost it will run up to.
Certainly when I had the L2 kit fitted (which includes chip and controller) Promax removed the boost enhancer I had on the car.
*Caveat - am no car mechanical so am expecting someone to be along presently to shoot me down [
]
I would say that is the case. On the other hand the controller when combined with different engine management chips is the system for increasing boost. I would think the standard chip will limit a car to what boost it will run up to.
Certainly when I had the L2 kit fitted (which includes chip and controller) Promax removed the boost enhancer I had on the car.
*Caveat - am no car mechanical so am expecting someone to be along presently to shoot me down [
]
appletonn
New member
I thought the enhancer simply delayed (slightly) the onset of the wastegate opening and thus reduced some of the lag and slightly increased the boost level at which the wastegate opened.
Here's the detail from Lindsay Racing...
Boost Enhancer Explanation and Adjusting
EXPLANATION:
The following is an explanation of how and why the Boost Enhancer works. Once you understand the basics of the 951 waste gate system, you will see the necessity for the Boost Enhancer.
First, let's explain the basics of turbo charging. Since a turbo is an exhaust driven device, the more pressure you build in the exhaust system, the faster the turbo spins up and the less lag time there is. Keep in mind that the typical turbo spins over 50,000 rpm at full pressure. The turbo takes time (lag) to reach this speed so the more exhaust pressure we can put to it, the faster it will reach the necessary rpm to produce full boost.
The waste gate is the device that regulates the speed of the turbo, otherwise with enough pressure the turbo would over-rev. This is a bad thing! There is a diaphragm in the waste gate that contains the pressure and opens an exhaust valve inside that relieves excess exhaust gas pressure to slow the turbo down. This basic concept is used on virtually all turbo charged applications. The waste gate has a connection to the intake system that feeds boost pressure to it. This is the basics of how the system works. The "Banjo Bolt" on the boost tube is where this connection to the waste gate takes place.
Most people, even factory mechanics, are not aware of this fact: The factory design of the 951 waste gate opens it as soon as any pressure is introduced. It might be barely open, but open none the less. The higher the boost pressure goes, the more it opens. The problem is it is dumping valuable exhaust pressure to drive the turbo, before it has to! More boost at a lower RPM means more torque and horsepower in that RPM range.
Who knows why Porsche did this! Personally I think they did this so the car would be slower and a little easier for the average person to drive. Remember the 951 was the bottom end of their line of cars, they didn't want it to be the fastest!
The solution to this problem is to slow or completely stop the air signal to the waste gate as long as possible. Most of you with stage 2 software have the modified "Banjo bolt" that was supplied. This device has a restriction jet that slows the boost signal to the waste gate. It works well, but it only slows the boost reaching the waste gate. Why not stop it all together?
That's where the Boost Enhancer comes in. This device does exactly that, it stops the boost signal until a preset pressure is reached, then full boost is applied to the waste gate and factory systems operate normally from that point on!
It's not intended to allow you to build higher boost pressure, but to give you your normal level of boost much sooner. Once the Boost Enhancer is fully open, the factory controls for timing, fuel, knock control and maximum boost are still there, it is not intended to over ride them.
Factory setting on the Boost Enhancer is 10psi. It requires 10 pounds of boost pressure to start to open it. The higher the pressure it receives, the further it opens and the more it flows air to the wastegate.
We highly recommend that if you have the "Banjo bolt" with the air restrictor, remove it and install the factory bolt! The reason for this is that once the Boost Enhancer opens, you need to get the boost to the waste gate as soon as possible. There is no more reason to delay it any longer!
For street applications, there is really no advantage in changing the factory setting of the Boost Enhancer. We have already set it at the optimum pressure for safe operation. The speed of the turbo increases exponentially. In simple terms, the time it takes the turbo to build 4psi, it can go from 4 to 16psi just as fast. So if you set the Boost Enhancer to high, the turbo can spin up so fast that it could over-boost. The Factory computer will shut the engine off if this takes place, so you won't blow the engine. The 10psi-factory setting gives the waste gate time to regulate the turbo like it needs to.
If you have a racecar running significantly higher than normal boost pressures, a slight gain might be had by "Tweaking" the setting.
ADJUSTMENT:
The following is an explanation of how to adjust the Boost Enhancer.
The inner working of the "Boost Enhancer" is as simple as it's function. It contains a valve and a spring. The more pressure you apply to the spring, the more pressure it takes to open the valve. It is factory set at 10psi. Otherwards, at 10psi of boost, the valve starts to let air through the "Boost Enhancer" and down to the waste gate.
We like to see the Boost Enhancer pressure set at 5psi less than the total boost you normally run. Lets assume you run 15psi of boost, thus we set it at 10psi. This allows a 5 pound window of time for the signal of air to open the wastegate properly and eliminate overboosting or boost spikes.
The housings of the Boost Enhancer screw together like a nut and a bolt. Right hand threaded. Once you loosen the "Jam" nut (the thin red nut) from the Inlet Housing (Blue Housing) you can screw the Outlet (Red Housing) in and out freely. One revolution equals approximately 1 psi of pressure. Tighten in (clockwise) one turn for one additional pound or pressure and loosen (counter clockwise) one turn to lower one pound of pressure. Two turns equals two pounds, etc... etc...
After turning the housings to desired position, you need to tighten down the "Jam" nut back against the Blue Housing. This locks the two housings back together again.
So it would appear that the MBC and the enhancer both delay the wastegate getting the signal to start opening - the MBC allows you to change the maximum pressure, whereas the enhancer is primarily aimed at reducing the lag and allowing the turbo to deliver boost earlier.
Here's the detail from Lindsay Racing...
Boost Enhancer Explanation and Adjusting
EXPLANATION:
The following is an explanation of how and why the Boost Enhancer works. Once you understand the basics of the 951 waste gate system, you will see the necessity for the Boost Enhancer.
First, let's explain the basics of turbo charging. Since a turbo is an exhaust driven device, the more pressure you build in the exhaust system, the faster the turbo spins up and the less lag time there is. Keep in mind that the typical turbo spins over 50,000 rpm at full pressure. The turbo takes time (lag) to reach this speed so the more exhaust pressure we can put to it, the faster it will reach the necessary rpm to produce full boost.
The waste gate is the device that regulates the speed of the turbo, otherwise with enough pressure the turbo would over-rev. This is a bad thing! There is a diaphragm in the waste gate that contains the pressure and opens an exhaust valve inside that relieves excess exhaust gas pressure to slow the turbo down. This basic concept is used on virtually all turbo charged applications. The waste gate has a connection to the intake system that feeds boost pressure to it. This is the basics of how the system works. The "Banjo Bolt" on the boost tube is where this connection to the waste gate takes place.
Most people, even factory mechanics, are not aware of this fact: The factory design of the 951 waste gate opens it as soon as any pressure is introduced. It might be barely open, but open none the less. The higher the boost pressure goes, the more it opens. The problem is it is dumping valuable exhaust pressure to drive the turbo, before it has to! More boost at a lower RPM means more torque and horsepower in that RPM range.
Who knows why Porsche did this! Personally I think they did this so the car would be slower and a little easier for the average person to drive. Remember the 951 was the bottom end of their line of cars, they didn't want it to be the fastest!
The solution to this problem is to slow or completely stop the air signal to the waste gate as long as possible. Most of you with stage 2 software have the modified "Banjo bolt" that was supplied. This device has a restriction jet that slows the boost signal to the waste gate. It works well, but it only slows the boost reaching the waste gate. Why not stop it all together?
That's where the Boost Enhancer comes in. This device does exactly that, it stops the boost signal until a preset pressure is reached, then full boost is applied to the waste gate and factory systems operate normally from that point on!
It's not intended to allow you to build higher boost pressure, but to give you your normal level of boost much sooner. Once the Boost Enhancer is fully open, the factory controls for timing, fuel, knock control and maximum boost are still there, it is not intended to over ride them.
Factory setting on the Boost Enhancer is 10psi. It requires 10 pounds of boost pressure to start to open it. The higher the pressure it receives, the further it opens and the more it flows air to the wastegate.
We highly recommend that if you have the "Banjo bolt" with the air restrictor, remove it and install the factory bolt! The reason for this is that once the Boost Enhancer opens, you need to get the boost to the waste gate as soon as possible. There is no more reason to delay it any longer!
For street applications, there is really no advantage in changing the factory setting of the Boost Enhancer. We have already set it at the optimum pressure for safe operation. The speed of the turbo increases exponentially. In simple terms, the time it takes the turbo to build 4psi, it can go from 4 to 16psi just as fast. So if you set the Boost Enhancer to high, the turbo can spin up so fast that it could over-boost. The Factory computer will shut the engine off if this takes place, so you won't blow the engine. The 10psi-factory setting gives the waste gate time to regulate the turbo like it needs to.
If you have a racecar running significantly higher than normal boost pressures, a slight gain might be had by "Tweaking" the setting.
ADJUSTMENT:
The following is an explanation of how to adjust the Boost Enhancer.
The inner working of the "Boost Enhancer" is as simple as it's function. It contains a valve and a spring. The more pressure you apply to the spring, the more pressure it takes to open the valve. It is factory set at 10psi. Otherwards, at 10psi of boost, the valve starts to let air through the "Boost Enhancer" and down to the waste gate.
We like to see the Boost Enhancer pressure set at 5psi less than the total boost you normally run. Lets assume you run 15psi of boost, thus we set it at 10psi. This allows a 5 pound window of time for the signal of air to open the wastegate properly and eliminate overboosting or boost spikes.
The housings of the Boost Enhancer screw together like a nut and a bolt. Right hand threaded. Once you loosen the "Jam" nut (the thin red nut) from the Inlet Housing (Blue Housing) you can screw the Outlet (Red Housing) in and out freely. One revolution equals approximately 1 psi of pressure. Tighten in (clockwise) one turn for one additional pound or pressure and loosen (counter clockwise) one turn to lower one pound of pressure. Two turns equals two pounds, etc... etc...
After turning the housings to desired position, you need to tighten down the "Jam" nut back against the Blue Housing. This locks the two housings back together again.
So it would appear that the MBC and the enhancer both delay the wastegate getting the signal to start opening - the MBC allows you to change the maximum pressure, whereas the enhancer is primarily aimed at reducing the lag and allowing the turbo to deliver boost earlier.
poprock
New member
Yep, that all tallies with what I have learned so far"”the text from Lindsey is what's quoted on Promax's website.
I'm still not sure how the MBC is different though. How does it change the maximum boost pressure? By preventing exhaust gases from flowing through to the wastegate until a point past where the wastegate would usually be fully open? Thus making the wastegate redundant?
Suffolk944
Moderator
My guess would be witchcraft. [
]
Diver944
Active member
First of all the standard car should boost to 0.85bar (12psi) which will be 1.85bar on the dash gauge. However, it is very inadvisable to use the dash guage when increasing boost. Just look at how close together the graduated marks are, 0.8 bar and 1 bar is a few mm apart and if the needle is on or past 1 bar it could actually be 1.5 bar [] because 1 bar is as high as it will measure.
Hopefully the following diagram should explain how the standard wastegate works (left) as well as an aftermarket in single port mode (centre) and also in dual port (right)
Dual port is the most effective way to control the wastegate because the valve is kept shut not only by the default spring, but also by pressure from the upper port. The valve will not open until the set boost is reached which vastly decreses turbo lag.
I measured my old factory wastegate on a workbench and it started to open at only 4psi of boost which bleeds off valuable exhaust pressure way way earlier than you want and increases the lag. In Dual port mode with an MBC you 'could' set it so the wastegate NEVER opens which would be brilliant for building boost, but possibly catastrophic if your fueling and tuning do not match those levels []
] because 1 bar is as high as it will measure.Hopefully the following diagram should explain how the standard wastegate works (left) as well as an aftermarket in single port mode (centre) and also in dual port (right)
Dual port is the most effective way to control the wastegate because the valve is kept shut not only by the default spring, but also by pressure from the upper port. The valve will not open until the set boost is reached which vastly decreses turbo lag.
I measured my old factory wastegate on a workbench and it started to open at only 4psi of boost which bleeds off valuable exhaust pressure way way earlier than you want and increases the lag. In Dual port mode with an MBC you 'could' set it so the wastegate NEVER opens which would be brilliant for building boost, but possibly catastrophic if your fueling and tuning do not match those levels [
]
sawood12
New member
It is alot simpler than you might think. Wastegates are a pretty simple and crude device and basically just act like a governer valve on steam engines. The wastegate regulates boost pressure by bleeding off exhaust gasses and not by bleeding off boost.
The stock single port wastegate has a spring loaded diaphram that actuates the valve so that as the pressure signal on the diaphram increases as boost builds it will eventually open the valve by overcoming the spring pressure. In this case the spring rate will determine the amount of max boost you will achive. Ideally you want the wastegate to remain shut until your desired boost pressure has been achived then it will open to maintain that boost pressure - i.e. it will regulate.
There are two problems with the stock single port wastegate seup:-
1. springs are not on/off devices so the valve will be opening before you hit your intended max boost pressure. Therefore this will increase lag as you will be bleeding exhaust gasses early. This will happen in a brand new stock wastegate.
2. Over time the spring weakens off and as such the valve will open earlier and earlier increasing turbo lag. This can be combated by shimming the wastegate where you use washers or shims to pre-load the spring, however this is a sticking plaster solution at best. The Lindsey Boost Enhancer gets around this by completely blocking off the pressure signal to the wastegate diaphram unitil a pre-determined boost pressure has been achived upon where the valve will open and expose the wastegate to the full pressure signal and it will immediately open. If the spring is good enough to hold the wastegate valve shut against the exhaust gasses this is a very effective device (as proved by Mark Koberle's dyno run at the last dyno day where he got +50hp over stock).
An MBC in a single port wastegate setup will allow boost to rise to a preset level after which it will hold the output of the MBC will be a constant pressure. This doesn't get around the weak spring problem.
A dual port wastegate is by far the best solution for controlling boost pressure. The second signal is exposed to the other side of the diaphram so you have control via pressure balance either side of the diaphram. This allows the wastegate to be positively held shut until the intended boost pressure is achieved. However with a DPW you need a boost controller, which is what the MBC is. With an MBC the boost pressure will build equally either side of the DPW diaphram until the desired boost level is reached. Once reached the MBC will maintain this boost pressure whilst on the other side of the diaphram the pressure will continue to increase and hence the wastegate will be opened to regulate boost.
The stock single port wastegate has a spring loaded diaphram that actuates the valve so that as the pressure signal on the diaphram increases as boost builds it will eventually open the valve by overcoming the spring pressure. In this case the spring rate will determine the amount of max boost you will achive. Ideally you want the wastegate to remain shut until your desired boost pressure has been achived then it will open to maintain that boost pressure - i.e. it will regulate.
There are two problems with the stock single port wastegate seup:-
1. springs are not on/off devices so the valve will be opening before you hit your intended max boost pressure. Therefore this will increase lag as you will be bleeding exhaust gasses early. This will happen in a brand new stock wastegate.
2. Over time the spring weakens off and as such the valve will open earlier and earlier increasing turbo lag. This can be combated by shimming the wastegate where you use washers or shims to pre-load the spring, however this is a sticking plaster solution at best. The Lindsey Boost Enhancer gets around this by completely blocking off the pressure signal to the wastegate diaphram unitil a pre-determined boost pressure has been achived upon where the valve will open and expose the wastegate to the full pressure signal and it will immediately open. If the spring is good enough to hold the wastegate valve shut against the exhaust gasses this is a very effective device (as proved by Mark Koberle's dyno run at the last dyno day where he got +50hp over stock).
An MBC in a single port wastegate setup will allow boost to rise to a preset level after which it will hold the output of the MBC will be a constant pressure. This doesn't get around the weak spring problem.
A dual port wastegate is by far the best solution for controlling boost pressure. The second signal is exposed to the other side of the diaphram so you have control via pressure balance either side of the diaphram. This allows the wastegate to be positively held shut until the intended boost pressure is achieved. However with a DPW you need a boost controller, which is what the MBC is. With an MBC the boost pressure will build equally either side of the DPW diaphram until the desired boost level is reached. Once reached the MBC will maintain this boost pressure whilst on the other side of the diaphram the pressure will continue to increase and hence the wastegate will be opened to regulate boost.
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