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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 05-22-2009, 02:36 PM   #1
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Base boost difference?

Thought these two graphs were pretty interesting. First one is stg 3+ with base boost left stock 5psi or so.

Second one is the same exact tune, but base boost was increased to 9psi.

Quite a difference

There is some thoughts on if some cars need it and if some cars don't. I have found some need it and some don't. I have been round and round, checked everything under the sun and for me it came down to having a weak actuator.

Some people prefer the nice forge actuator, its smoother and more consistant. Some people bock at the idea of a helper spring, but my first tuner recommended it to me and I have been using them for years, it does the same job basically, its only 5 bucks as opposed to 180 bucks, but some people do consider it ghetto.

John
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File Type: jpg stg 3 stock actuator.jpg (77.9 KB, 138 views)
File Type: jpg stg 3 9psi base boost.jpg (86.8 KB, 130 views)
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Old 05-22-2009, 03:05 PM   #2
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Hey John, instead of adding a screen door spring, why don't you either fix the actuator if it's bad, or tune for a stronger response from the actuator if it is good?

You never did answer my question, what is the maintenance interval on one of these springs? Can you get 5,000 miles out of one?
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Old 05-22-2009, 03:12 PM   #3
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Quote:
Originally Posted by Drew in Houston View Post
why don't you either fix the actuator if it's bad,
Just commenting on this point, I agree with the rest, but you ever price a new W/G actuator for a saab? They are shockingly expensive.
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Old 05-22-2009, 03:36 PM   #4
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Just commenting on this point, I agree with the rest, but you ever price a new W/G actuator for a saab? They are shockingly expensive.
yeah at GS the forge is like $180... if i could fix something for $5 and have it last for a decent amount of time i would rather do that.
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Old 05-22-2009, 03:57 PM   #5
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And the forge is quite a bit cheaper than O.E.
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Old 05-22-2009, 04:02 PM   #6
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or...fix it right with an external wastegate.
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Old 05-22-2009, 04:36 PM   #7
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Originally Posted by DeLorean View Post
Just commenting on this point, I agree with the rest, but you ever price a new W/G actuator for a saab? They are shockingly expensive.
I agree, if I had a lot of good actuators, that is option I would take, but like said here, they are very expensive and the forge is about the same.

This is a cheap easy fix and its an advance auto spring, not home depot


People have tried both and I admit the forge actuator delivers smoother boost, but the helper spring is dirt cheap and works just about as well.

Drew, I have tried doing everything, turning up the reg kon as far as it will go, when you can hear the flapper going pst, pst pst under boost at high rpm, no sw is going to fix that.

In the first dyno I posted, the wast-gate was blowing completely open at 4500rpm. 5 bucks later and maybe 15 minutes, it was a whole new car

John
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Old 05-22-2009, 06:05 PM   #8
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Adjusting base-boost is mostly just pre-loading/shortening the wg arm.
I can't see how tightening/preloading it more WOULDN'T yield these results.


If any of you guys REALLY think that an external wastegate is needed on a td04, you're high.
The best thing, would be to port/machine the turbo outlet, to make it easier for the exhaust to pass through there, than through the wastegate.
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Old 05-23-2009, 07:04 AM   #9
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Shortening the rod a hair is ok, but you also shorten the travel of the waste-gate and that is the whole point of running a helper spring, you can retain full travel of the waste-gate and get the base boost where you want it and its adjustable by simply increasing or decreasing the hooked end for a change in spring tension.

When you crank the rod all the way in to get say 10psi for a t28, you have almost no waste-gate travel left and that could be bad.

John
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Old 05-31-2009, 04:23 AM   #10
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Quote:
Originally Posted by DeLorean View Post
Just commenting on this point, I agree with the rest, but you ever price a new W/G actuator for a saab? They are shockingly expensive.

But there are other options too.... I have seen one of these used where the rod was cut/threaded with a threaded piece to use for adjustment and it worked just fine.

http://www.cimotorsports.net/motor-s...n-sr20det.html
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Old 05-31-2009, 10:41 AM   #11
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how do you install a helper spring?
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Old 05-31-2009, 10:46 AM   #12
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Would the differences be this drastic on stock software?
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Old 05-31-2009, 11:13 AM   #13
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my stage 3 software was only making about 12-14 psi, i uped the base boost to 8 and wow that made a huge differance. automotion reccomended this to me when i got my tune to check and make sure it was around 8
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Old 05-31-2009, 11:15 AM   #14
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Quote:
Originally Posted by dcr99vig View Post
my stage 3 software was only making about 12-14 psi, i uped the base boost to 8 and wow that made a huge differance. automotion reccomended this to me when i got my tune to check and make sure it was around 8
You should not have needed the base boost adjustment to make the power though... thats the point of software..it handles the adjustments for you.


I am pushing 20PSI with no issues and no base boost adjustment on my 9-3 SE HOT Automagic. And no helper spring.
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Last edited by stevehayes01; 05-31-2009 at 11:23 AM.
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Old 05-31-2009, 03:04 PM   #15
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This issue of whether or not a base boost increase is required, or advisable, is another example of a topic oversimplified.

There are many variables in the exit of exhaust through the turbine housing and wastegate flapper and these variables are complicated and compounded by the variables associated with the wastegate actuator itself.

When flow is limited, pressure is created. As boost pressures are raised from SW or an MBC the WG remains closed more of the time allowing the exhaust gasses to "power" the turbo for the increased boost. At the same time, pressures inside the exhaust manifold begin to rise because the turbine flow (among other things) is not able to exit the, now much larger, volume of air being moved.

At some point the pressure inside the exhaust manifold will exert enough force on the wastegate flapper to open it from inside with absolutely no regard to the SW targets and BPC action. The point where this occurs is determined by the strength of the WGA itself, to some extent, but to an even greater extent it's determined by the actual volume of air being moved by the engine. The later cars, like SteveHayes and Drew in Houston own, are running T7 cams and TD04s. The T7 cams do not move as much air past 4500 RPMs, right where most "helper spring" activity is experienced on T5 cars. Also, both Steves and Drews cars run turbochargers with slightly higher flow compressors than a stock Garrett T25.

Even though the T25 has a decent hot side for a small unit, it will still create enough backpressure in the exhaust manifold to require an increase in base boost. It requires the base boost adjustment just to reach it's rated max flow rate from Garrett. By the same token, a later car with the T7 cams and a little higher flowing compressor wheel might not need as much base boost to keep the flapper closed and at the same time make similiar power. I believe that Vigge reported that one of the turbos that he used (maybe the GT2860RS) had exhaust manifold pressure that EXCEEDED his boost pressures up high in the revs. The reason many tuners use the FORGE WGA is so they can utilize the turbochargers full range of flow. The more CFM the engine moves the harder it gets to flow the exhaust out through the turbine nozzle. The harder it gets to flow the exhaust through the turbine nozzle, the higher the exhaust manifold pressures go. The higher the exhaust manifold pressures go the harder it is for the flapper to stay closed no matter what the BPC is doing. As a matter of fact, if you are going to push a smaller turbo (IE less than about 600CFM) to it's max with T5 cams and decent supporting HW you're very likely to need more base boost.

Another thing to remember is that the boost level is really not the key point in what necessitates the higher base boost. The key point is really the flow volume as relates to the turbine nozzle area.

I have mentioned some variables but others would include the actual size of the flapper, (which I've never actually measured.) the flow characteristics of the exhaust, the EGTs etc. A smaller flapper, for example, would require more pressure to open than a larger one with more surface area.

Just my $0.02

David

Last edited by David in Tallahassee; 05-31-2009 at 03:08 PM.
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Old 05-31-2009, 06:00 PM   #16
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Quote:
Originally Posted by stevehayes01 View Post
You should not have needed the base boost adjustment to make the power though... thats the point of software..it handles the adjustments for you.


I am pushing 20PSI with no issues and no base boost adjustment on my 9-3 SE HOT Automagic. And no helper spring.
What software? I have 3+hardware but only pushes to hold around 15 and by then I'm at 90sh, spikes to 17 at times when i first floor it atfirst, drops to around 11/12 and then rises to 15
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Old 05-31-2009, 07:26 PM   #17
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Helper spring or higher pressure actuator is only required if wastegate actuator will not hold flapper shut under high boost.
You want just enough to keep the flapper closed, but not too much pressure that it interferes with boost regulation.
Watch your EGT's if you go with either stronger actuator or helper spring, as increased EGT's lead to higher risk of detonation (knock).
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Old 05-31-2009, 09:02 PM   #18
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Quote:
Originally Posted by soccerrplyr View Post
What software? I have 3+hardware but only pushes to hold around 15 and by then I'm at 90sh, spikes to 17 at times when i first floor it atfirst, drops to around 11/12 and then rises to 15


I am using my own software that I tuned....... I spike to 20-21 and settle to 18-19psi on hot days and on cold days i peak and hold 20psi steady.


Your drop is due to limiters in the software for your gearing more than likley.
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Old 05-31-2009, 09:12 PM   #19
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Quote:
Originally Posted by David in Tallahassee View Post
This issue of whether or not a base boost increase is required, or advisable, is another example of a topic oversimplified.


David

I am not trying to oversimplify but the wastegate and turbo are sized for each. But the fact is to run a stage 3 at 17-20psi you should not have to change base boost if your actuator is in good shape.

The other issue is that in the software it is controlable to maintain boost and hold it at the levels you set it to. I think Drew's tune is case in point for that... stock wastegate running 4.5PSI base boost and peak and holding 24PSI at full boost.

So instead of raising base boost to meet 8psi to get a max 18PSI and only get an increase 11psi.....when if you set your software up right you can get the same gains to 18psi with a 5.5psi base boost and have a solid gain of 13-13.5psi and no need for a helper spring or an increased base boost setting.

just my opinion..
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Old 06-01-2009, 02:41 AM   #20
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Originally Posted by stevehayes01 View Post
I am not trying to oversimplify but the wastegate and turbo are sized for each. But the fact is to run a stage 3 at 17-20psi you should not have to change base boost if your actuator is in good shape.

The other issue is that in the software it is controlable to maintain boost and hold it at the levels you set it to. I think Drew's tune is case in point for that... stock wastegate running 4.5PSI base boost and peak and holding 24PSI at full boost.

So instead of raising base boost to meet 8psi to get a max 18PSI and only get an increase 11psi.....when if you set your software up right you can get the same gains to 18psi with a 5.5psi base boost and have a solid gain of 13-13.5psi and no need for a helper spring or an increased base boost setting.

just my opinion..
Yeah, but this is only valid if the flapper is not being forced open before reaching 18psi. No amount of tuning can hold the flapper shut if the BPC is not routing any air pressure from the compressor to the wastegate actutator.
It really comes down to turbine housing restriction vs. wastegate actuator spring pressure.
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