Stock boost a bit low

[decathect]

I need to keep my boost control stock for the purposes of autox/rallyx. However, my boost is lower than it should be. I have a 93 talon tsi, and the boost is typically only between 7-8 psi.

I want to squeeze out a few more psi, I've heard people hitting about 11 or so, but i'm not entirely sure why i'm not already hitting it.

Turbo is in good working order, zero boost leaks (even replaced the compressor housing O-ring). No exhaust leaks. I have put an MBC on it, and it was boosting very nicely up to 17 psi... so its capable of boosting just fine.

Is my BCS bad or something? Is there any little discreet way I could up my boost to a reliable 11 psi, on the cheap and free?

Thanks!

 

[Dsmj89]

Take out the tiny littly bcs restrictors on the nipples of the bcs, they are very small rubber restrictors, use a toothpick or needle.
Take the car for a spin and see if that upped the boost a pound or two.

 

[decathect]

I thought that was only a 2g thing. I have a 1g.

 

[Dsmj89]

I had a 1g as well at one point and yes they do have the restrictors just like the 2g's.
Go see for yourself.

 

[cgmtboarder]

wow your boost is low... i have a 91 tsi and my car boost 12 psi. only thing ive done is ported the exhaust manifold and i may have a small leak but i dont think so. if your using ## stock boost gauge it may be bad

 

[decathect]

nope, aftermarket boost gauge.

 

[cgmtboarder]

hmm... not sure what would cause that. usually people have a problem with over boosting. the only thing i can think of is maybe there somethin wrong with your gauge. what is ## stock one reading compared to ## aftermarket one? stock 1g psi is around 10 or 11

 

[tunethis]

My Talon was boosting 10psi completely stock with the bcs mod. I'm not sure what the boost was before the bcs mod since I got a gauge at the same time I modded the bcs.

 

[decathect]

I really doubt its my gauge. Its a reliable unit, brand new prosport with their improved boost sensor. I just did the bcs mod, its sitting here on my desk. I'll post up results!

 

[decathect]

Results: at first I thought there was a difference, but peak boost hasn't changed. The turbo feels like it spools a bit quicker, but that also could be my imagination, I have nothing to back that up.

I really think the BCS might be bad. How do I determine that?

Another question: the point of the BCS is to *raise* the boost a bit over stock wastegate pressure, right? So, on a car making 11 psi, if we took the BCS out of the picture and connected the turbo right to the wastegate, it would only make about 8 psi?

 

[allthrottle]

I have a big 16g on my car, stock everything else, and the most boost I've seen with the BCS mod is maybe as high as 10lbs, usually a hair above 9lbs. I do have a slight boost leak at the tb shaft seals though, so I'm hoping to see another lb or two when I fix that.

 

[Dsmj89]

Back when i had previous gst and my t25, i had a boost gauge and managed to see the difference before and after the bcs mod.
The first time i tested it out with the stock bcs on and my car read only 10 psi, so i brought the car back to my driveway, ran a hose straight from the turbo to the wastegate, and took it for another spin.
To no surprise, it boosted the exact same 10 lbs.
I left it like this as there wasn't really any gain having all that clutter there.. who knows maybe my bcs was bad. Just my 2 cents.

 

[jeffo]

Do you still have the factory Wastegate Solenoid installed? The job of the Wastegate solenoid (also called BCS or Boost Control Solenoid) is to bleed off 3-4 psi when the ECU sees that everything is OK. If you aren't running high enough octane pumpgas or too much timing advance, that causes knock, so the ECU closes off the BCS, dropping your boost down to the wastegate spring pressure of only 7-9 psi.
One wasy to find out is to disconnect the battery to reset the ECU, and then take the car for a quick drive. If you have full boost for a while, then that is the problem. Do you have a logger? It will allow you to watch knock and the "octane value", which will tell you if you are dealing with a knock or octane issue.
keydiver

 

[decathect]

thanks for the input. Jeff, I do have a logger, but i'm unfamiliar with this 'octane value'. I'm using mmcd, any hint as to what it might be called in there?

I do have some phantom knock issues, so that could make sense. The BCS might be choking off the boost cause it thinks the car is knocking.

I wonder if there's a way i can just fool the BCS into thinking all is well and allowing the maximum boost possible... Any ideas?

 

[AWD_Hybrid]

I don't think the autox/rallyx inspectors would notice a pin hole in your
vac hose 1/2" before your actuator Cut 1/2" off & replug it in afterwards !
This red wine is not bad btw Jokes aside, ^ easy few lbs undetected.
Cheers !

 

[decathect]

I woudlnt do that... thats a very unreliable way to raise boost. Plus, leaks like that just cause boost spikes, boost won't hold at a consistant level.

 

[AWD_Hybrid]

The spike is the gain on others who are std & the gentle manifold bleed (with a small hole)
is consistant. My post was a quick cheat with only a pin hole absolute manifold boost leak
to help the actuator spring. Ok a very hard to detect bc I have setup before. Weld a tube
right through the inlet mani to conect a vac hose both sides. Run the std looking vac hose
to the actuator. The vac hose behind (hiding) you run into the cab & conect an oxy valve
to to adjust the bleed rate. From that valve you run a vac line back into the bay to hook
up to the rear of the mani to pickup manifold pres. Unless you climb into the bay, you will
not find the hidden hoses. If the law sees a rear hose, you say it's for your boost gauge.
The pin hole method is a quick fix, not a permanent one. Illegal is a sick bird.
Cheers !

 

[decathect]

I heard rumor that I could just grounda pin on the BCS and it'll allow maximum boost... anyone know anything about this?

EDIT: After some research, I believe that if i just ground the orange wire going to the BCS, then the BCS will be fully open all the time, allowing for the max boost possible thru the stock BCS. I'll give this a try and post up results.

 

[Mr PopUps]

I heard rumor that I could just grounda pin on the BCS and it'll allow maximum boost... anyone know anything about this?

EDIT: After some research, I believe that if i just ground the orange wire going to the BCS, then the BCS will be fully open all the time, allowing for the max boost possible thru the stock BCS. I'll give this a try and post up results.

Which is 11.1-11.6 lbs. If you are seeing only 7lbs, like jeffo said, the ECU is limiting it via the BCS. The BCS is only a solenoid, not a controller in the true sense.

Fix whats wrong and the ECU will give you the boost you are missing. It could be the caps, it could be that something threw a code once and the ECU remembers that and the problem is actually fixed, it just doesnt know it and a reset would fix it. if you reset the ECU and you see an increase, then it pulls it back to 7lbs, then you know you have a problem that you NEED to fix.

 

[Bluesideup]

A long time ago I installed an LED to tell me when the ECU was pulling boost due to low octane. This was of course all before people had loggers and such. I think the ECU grounds the BCS to take out boost.

My GSX was really sensitive to octane and would pull boost all the time.

One thing to check is to make sure your wastegate actuator rod is not bent. I installed an EVO III 16G once and it wouldn't make stock boost. Turned out the rod was bent during installation.

 

[decathect]

A long time ago I installed an LED to tell me when the ECU was pulling boost due to low octane. This was of course all before people had loggers and such. I think the ECU grounds the BCS to take out boost.

My GSX was really sensitive to octane and would pull boost all the time.

One thing to check is to make sure your wastegate actuator rod is not bent. I installed an EVO III 16G once and it wouldn't make stock boost. Turned out the rod was bent during installation.

ECU grounds the BCS to open it up -- allowing MORE boost.

Mr. Popups - as I mentioned earlier, I am having some phantom knocking issues. It has been confirmed that it is in fact phantom knock. And while I would like to ultimately eliminate it, so far I have been unsuccessful. For now I would just be happy being able to make the stock maximum boost - and also eliminate the boost curve limitation that the stock ECU does between 2500-3500 RPM (Most people notice with those LEDs that they flash in that rpm range, to limit the quick torque onset of the turbo spool - lame!)

So at least this way i know it will make stock boost all the time. My car shouldn't have real knock - ever. Completely bone stock with stock fuel system, all maintenance is completely up to date and nothing else should be causing real detonation. I still want to fix it, because its still pulling timing, which is another big performance hit.

 

[decathect]

ok, I did this, but soon after i realized that my BCS is completely dead. Resistance across the terminals is just about 0. Great. gotta find a new one before I can post up results. I'm thinking the dead BCS may have been contributing to this problem in the first place.

 

[Dsmj89]

Just run straight wastegate pressure for now until you get a mbc.

 

[Mr PopUps]

ok, I did this, but soon after i realized that my BCS is completely dead. Resistance across the terminals is just about 0. Great. gotta find a new one before I can post up results. I'm thinking the dead BCS may have been contributing to this problem in the first place.

I just found one in my garage tonight. But seriously you dont 'need' it. You can cut a length of vac hose to about 15" i think start there and see how much boost it produces, going straight from elbow to WG. Shorten it to reach the 11lbs and route it in such a way that it looks stock.

He cant run MBC in stock class.

 

[decathect]

straight wastegate pressure is what i'm getting. The stock BCS actually *raises* boost pressure a bit over wastegate. Ugh, so much heresay and misunderstanding about these things.