Potential Causes of Overboosting

[Batmobile_Engage]

Just like the title says, what are some common causes of overboosting?

The ones I can think of off the top of my head are generally related to adding parts
without a proper tune, or a less than optimal tune.

I haven't changed one single thing on the motor/tune in a couple years, so my issue
is confusing me. I'm tuned for 19 psi and this morning, during a WOT jaunt on the
highway in 5th gear, I looked over and noticed my boost gauge reading about 23 psi.

I immediately lifted off the throttle but I didn't throw a code or notice any issues in
engine response, no noticeable knock, etc. I am running methanol, so maybe that
saved the motor. Who knows.

What could be causing this? Is it possible that my boost gauge is malfunctioning?

 

[Grinder34]

did it spike to 23psi, or was it steady at 23?

 

[Batmobile_Engage]

Steady. Rock solid at 23 psi.

 

[Grinder34]

and to rule out the simplest issue: if the key is turned on, but the car is off, does the gauge read 0 psi?

 

[Batmobile_Engage]

Yes. I will double-check though after work. It seems like it's accurate though,
because when my methanol system "active" light comes on, the gauge is reading
10 psi and my methanol system is set to come on at 10 psi. Of course the gauge
could still be a little off...idk.

 

[fuji_production]

based on your post i want to guess your scenario when this happened and tell me if this is true or not. You were cruising on the highway in say 5th or 6th gear at around 60 miles an hour and then you decided to go WOT and this is when you noticed the over boost right? are you using an EBCS? and you say your pro tuned?

 

[Batmobile_Engage]

I was getting on the highway, wanted to go into 6th and people were slowing down, so I stayed in 5th (55mph), moved to the left lane which was clear and ran it WOT up to 90-ish.
Factory Subaru boost control.
Protuned. Check my journal for mods list.

 

[fuji_production]

thats why you are overboosting. You cant go WOT throttle in 5th and 6th gear like that. even with a protune it is hard to change the turbo dynamic maps to make them aggressive enough to control boost like that with sacrificing some functionality of those tables. if you want to accelerate from 55mph you should be in 2nd or 3rd gear. 1-4 are always your hard acceleration gears. never 5th and 6th. If you dont like that then get an MBC. mbc=rock solid boost values in all conditions, i.e. selected gear, elevation, etc...

 

[Batmobile_Engage]

I trust what you are saying, but if that's the case, then why has every tuner I've had run dyno pulls from 2,000rpm up in 5th gear. I assume that would cause the same effect, right? Also, I have my Defi gauges set to alarm if I hit 20psi, letting me know if I overboost. My last tune was spring 2011, I drive like this all the time and I've never seen this issue before.

 

[HolyCrapItsFast]

High gear + High Load + low air temps = high boost.

The air is very dense compared to when it was originally tune, would be my guess. If you are tuned to maintain a waste gate duty of say 75% during WOT, the turbo will spin at a certian speed and it won't change much from that during the year. As the air becomes dense your turbo will output more air while miantaining the same speed, hence the increase in boost. Now add on top of that 5th gear high load. Now the ECU and turbo are striving to increase even more boost to keep up with the demand in load. You can easily run into an over boost situation under these conditions with out the proper compensation. There are compensations available for AIT in the GD and both AIT and Gear in the GR.

For tuners that don't really know how to use the factory boost control they accept that there will be changes in boost during the year and that the "Target" is just a guide line and not written in stone. They usually tune below target in the summer month to maintain a best range through out the year or tune to target or slightly higher during winter months. During spring and fall are the beat times to tune to target because you will swing marginally from +/- target during the year versus having it tuned in the summer to target and risk swinging to far above target in the winter. The other solution is to have a tune for summer tuned to target and one for winter tuned to target.

Since your issue is largely due to load related demand your situation is dificult to compensate for because the tables for per gear requested torque are not present in your year.

 

[HolyCrapItsFast]

I trust what you are saying, but if that's the case, then why has every tuner I've had run dyno pulls from 2,000rpm up in 5th gear. I assume that would cause the same effect, right? Also, I have my Defi gauges set to alarm if I hit 20psi, letting me know if I overboost. My last tune was spring 2011, I drive like this all the time and I've never seen this issue before.

They don't... They tune in fourth gear because it is your 1:1 gear

 

[Batmobile_Engage]

With the slight wiggle room in the tune being considered, could I be hurting anything? I assume yes, but still wondering.
I will CAREFULLY try to hit peak boost when I leave work today, but at mid rpms in 2nd or 3rd gear. If I see anything different, I will let you know.

 

[fuji_production]

High gear + High Load + low air temps = high boost.

The air is very dense compared to when it was originally tune, would be my guess. If you are tuned to maintain a waste gate duty of say 75% during WOT, the turbo will spin at a certian speed and it won't change much from that during the year. As the air becomes dense your turbo will output more air while miantaining the same speed, hence the increase in boost. Now add on top of that 5th gear high load. Now the ECU and turbo are striving to increase even more boost to keep up with the demand in load. You can easily run into an over boost situation under these conditions with out the proper compensation. There are compensations available for AIT in the GD and both AIT and Gear in the GR.

For tuners that don't really know how to use the factory boost control they accept that there will be changes in boost during the year and that the "Target" is just a guide line and not written in stone. They usually tune below target in the summer month to maintain a best range through out the year or tune to target or slightly higher during winter months. During spring and fall are the beat times to tune to target because you will swing marginally from +/- target during the year versus having it tuned in the summer to target and risk swinging to far above target in the winter. The other solution is to have a tune for summer tuned to target and one for winter tuned to target.

Since your issue is largely due to load related demand your situation is dificult to compensate for because the tables for per gear requested torque are not present in your year.

BOOM! knowledge... couldnt have said it better myself. and yea, tuners use 4th gear for the exact reason stated above.

 

[Batmobile_Engage]

They don't... They tune in fourth gear because it is your 1:1 gear

That makes sense, but I could have sworn it was 5th. Man, I must be confused today

 

[Batmobile_Engage]

Thanks for all the input guys! I'll keep an eye on everything and see if I can notice any other symptoms.

 

[HolyCrapItsFast]

With the slight wiggle room in the tune being considered, could I be hurting anything? I assume yes, but still wondering.
I will CAREFULLY try to hit peak boost when I leave work today, but at mid rpms in 2nd or 3rd gear. If I see anything different, I will let you know.

Keep an eye out for AFR and knock at this level. If you maintain safe AFR around 11.3 - 11.5:1 and no knock then I would say "Bonus Power" and leave it alone

 

[fuji_production]

With the slight wiggle room in the tune being considered, could I be hurting anything? I assume yes, but still wondering.
I will CAREFULLY try to hit peak boost when I leave work today, but at mid rpms in 2nd or 3rd gear. If I see anything different, I will let you know.

I would assume no because your shooting meth and the iat's have the potential to be cooler. but you cant say for sure unless you log some data. like i said the boost can be controlled if you accelerate in the proper gear. so try recreating that with lower gears and i would predict that you wont have that problem. the ecu has better ability to control the boost with a shorter gear so if it sees >19psi (target boost) it will use the values dictated in the turbo dynamics maps to keep it there.

 

[Batmobile_Engage]

Keep an eye out for AFR and knock at this level. If you maintain safe AFR around 11.3 - 11.5:1 and no knock then I would say "Bonus Power" and leave it alone

Unfortunately, my ability to monitor AFR is non-existent at the moment :banghead:.
(My Cobb AP recently shit the bed.)

It sure feels like free power I tell you what!
I briefly thought about putting a couple gallons of turbo blue (for more knock protection) in with the 93 I use and hitting full boost EVERYWHERE.

 

[Batmobile_Engage]

Before my AP shit the bed, I was looking at IATs. I was seeing around 70*F. Is that for real?! I know its cold outside, but jeeez. Seems too good to be true.

 

[fuji_production]

Before my AP shit the bed, I was looking at IATs. I was seeing around 70*F. Is that for real?! I know its cold outside, but jeeez. Seems too good to be true.

Is that low or high? what was the temp outside?