Boost Guage at high altitude

[A1337STI]

the stock 05 STI turbo should boost 15.5 psi , or .105 bars IIRC

on uphills in 2nd/3rd from 3500 to 6K i'm not seeing .105 , i'm seeing like .08 or .075 Is this due to being at high atitude ? since the guage also shows - .1 bar of vac ( - 14.7 psi)
Is basically showing a range from 0 to 30.2 30.2 is 15.5 psi + 14.7 (at sea level) ??? so that the less air pressure the lower total your boost will show OR should the display guage always be able to show .1 bars ?

I do belive i've seen .1 bars on my guage. before i installed my K&N and reset the ECU. (after which i babied the car big time, was hoping to see a big jump in my gas milage) i've read on a diff forum that how you drive directly after an ecu reset affects how it maps . This forum seems to have better expertise so figured i'de bounce it off the pros

[Kevin M]

Your gauge reads in mPa, not bar. 14.7 psi is 1 bar, not .1 I forget the conversion from mPa to psi, but your gauge isn't too far wrong. Also, I thought STi peak boost was 14.5 psi?

[A1337STI]

Ooops i ment Mpa
http://www.chapelsteel.com/psi-mpa.html
14.7 = 0.10135295857559792
15.5 = 0.10686876584501823
In either case i should definatly hit 0.1 Unless its measuring atmospheric + boost ??
(and odd the boost amount is not in the owners manual or on subaru.com )

[doubleurx]

I was getting 1.4 bar consistantly today.

[doubleurx]

Well if you count the Bar of America - 1.5 bar

[A1337STI]

Bar not Mpa ? 1.5 Mpa would be 22 psi of boost . i'm guessing you are not quite stock ? hehe ah but you are in truckee. do you see more boost in sac ? sea level ? Could using 91 octane be forcing some sorta knock correction and or my ecu is using less boost to avoid knocks ? (can't seem to find 93 in tahoe, or carson and the owners manual actually says speically to use 93 and states that 91 is an acceptable compramise doens't sound ideal at all though )
well what the heck. ECU reset , added octane booster, gonna drive to carson and back (i want some Del taco anyways) and see if i don't hit that .1 mpa mark on the first few uphills 3500 to 5500 ish on an uphill in 2nd should be enough to tell ?

[doubleurx]

Originally Posted by A1337STI

Bar not Mpa ? 1.5 Mpa would be 22 psi of boost . i'm guessing you are not quite stock ? hehe ah but you are in truckee. do you see more boost in sac ? sea level ?

I see 1.4 in Truckee Max. 1.5 down in Sac where I am now afraid to bring my car!

[A1337STI]

Oh okay, so it is a measure of Atmospheric pressure + boost , and less atmospheric pressure means you will read lower ? so i'm all normal ? sweet. ( i think) well i'm still going to get some del taco lol 42 miles for tacos !

[Nick Koan]

No, boost gauges doesn't measure atmospheric pressure + boost. You just make more boost down at lower elevations because the air is denser to begin with.

If you had an absolute manifold pressure gauge (atmospheric pressure + boost, effectively), you should be making ~2bar because 1 atmosphere of pressure is closeto 1 bar.

[sperry]

1st and 2nd gear don't make as much boost as the rest on a stock car, the ECU limits it to a lower peak. At least that's true on the WRX, I'm assuming the STi is the same. Boost also tapers at the top end of the rpm range. A 2nd gear pull up a hill won't tell you what your max boost is, it will tell you what your max boost in 2nd gear up that hill is.

[A1337STI]

Ah so it just shows turbo boost, and the thinner air leaves you with a bit less boost ? well i did a few 3rd gear pulls up highway 50 but i couldn't watch my guage the entire time . didn't ever see that .1 I did see about .09 ish but it felt good and fast lol and yes i noticed a taper off at about 5500 . so is there no point in pushing it past 6k ? Sounds like i should ask subaru at my next service ... i'm at 12,200 so 15K is coming up.

When looking for the boost amount in the manual, I did notice how many times the owners manual mentions 93 octane specifically. the manual only had one entry about using 91 as a substitute, but the wording definatly makes it sound sub-optimal . so i added some octane booster after i reset the ecu , it does feel more powerful now. (maybe just the added octane though?) i bought like 6 of em at wallmart so i'm gonna use 1 per tank for how ever long that lasts. and see what affect it has on my mpg after a few tanks . @ 1.97 on top of a $37 fill up it won't have to help much to be worth it. will this make my engine run significantly hotter?

thx 4 the info

[sperry]

High octane doesn't add power... in fact higher octane gas is harder to burn, and burns cooler, which is why the car can advance the timing and make more power w/o detonating. High altitude has the same effect as octane boost... up here 91 is more like 93. Chances are your car will advance its timing as much as possible w/o pinging on 91, so octane booster is a waste of money, unless you get the ecu retuned for it.

[A1337STI]

found out on car and driver the sti is only 14.5 psi
7-2 2.5L turbo model
The 2.5 liter turbo engine is designed to operate using super-premium unleaded gas with an octane rating of 93 AKI or higher. If super-premium unleaded gas with an octane rating of 93 AKI or higher is not available, premium unleaded gas with an octane rating of 91 AKI can ube used. For optimum engine performance and Driveability, it is recomended that you use super-premium grade unldeaded gasoline with an octane orating of 93 AKI or higher.

not gonna type in the next section but it again warns about low octane fuel, and that you are more prone to hear knocking while accelerating up a hill. (which i do daily)

but as usuall. i dunno sounds like this experiment is going to waste $12 over the next 6 fillups. lol

when Cody and i used his AP and ecuexplorer he mentioned something about the knock correction number. don't recall what it was, and what it means i still have the logs though.

[cody]

Alex, I asked Ed about that collumn in the logs. It turns out that higher numbers of "knock correction" are a good thing. I was worried because I was seeing "knock correction" of 7,8, and 9 through most of my rpm band. Apparently this is actually an indication of the ECU advancing timing which is good. I think negative numbers are what would indicate the ECU is pulling timing.

[Double Phister]

Originally Posted by sperry

1st and 2nd gear don't make as much boost as the rest on a stock car, the ECU limits it to a lower peak. At least that's true on the WRX, I'm assuming the STi is the same. Boost also tapers at the top end of the rpm range. A 2nd gear pull up a hill won't tell you what your max boost is, it will tell you what your max boost in 2nd gear up that hill is.

The WRX has the gear based boost correction. On the STi there is a speed reference that is around 25 MPH. Anything below this gets a fixed percentage drop in the WG DC. Above that all gears are treated equally. I'd rather see a linear correction based on speed. Not just a fixed threshold.
/hijack

[A1337STI]

Okay well i know my Knock correction numbers were a lot lower then Cody's were. like 0-3 , so my ecu must have been pulling the timing a bit . and maybe still is. Although this may be partly due to my K &N air intake kit as indicated on a diff thread...

well going from 42 to 60 in 3rd on a steep up hill only seemed to yeild .08 or .09 If the ecu is detecting knocks would it decrease your max boost at all ? or does it only affect your timing?
(i've never heard any engine knock, but i'm rather tone deaf and i don't think i'de hear it over the wind / ski rack noise anyways)

Suggestions at this point ? well since i have 5 more bottles of octane booster already , i'm tentively planning on just using 1 per tank, and hopefully i can test my knock correction number in a week or two and see if the added octane helps at all?

Also Should i leave in stock air intake - plastic tubing that goes from the front of the hood into the fender? will that assist in moving cold air towards my short ram air intake ? (i was thinking I could maybe mod that further and fix up a proper elbow peice (where the resoninator goes) and fix on a Bell like peice directly from that elbow to the K&N (if the placement of the stuck intake really does get a lot of air flow might be worth it ? or a fun waste of time i dunno)

Again thankx want to get every pennies worth out of my car , and yall seem to know every bolt in a subaru

[cody]

I think any positive number is okay. The number indicates how much the ECU has decided is safe to add on top of the basemaps. I'm pretty sure only negative numbers would indicate the ECU pulling timing, but I'll get a confirmation on that. Ed said your intake should be fine since it's the Typhoon.

I don't know if the ECU pulls boost.

[A1337STI]

so any postive knock correction is okay? aah Thought i saw a -1 at one point but maybe that was when we had over 17 items checked. Thanks for asking Ed about the K&N [its a bit sentimental now cuase my dad bought it for me and he's not the type to buy me a car mod! + i LOVE the noise]