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Old 03-01-2013, 01:24 AM   #1
jadawgis732
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Default Understanding PSI and Turbo (Beginner's Question)

I recently got a 2012 WRX, and although the pickup is good up to about 4K RPM, over that it is unreal. Since my car didn't come with a turbo boost gauge I was wondering if the PSI is limited until a certain rev point. Maybe someone has done an RPM vs Turbo boost graph. I'll check on Google.

Meanwhile, is it relatively easy to install one of those boost gauges? I see that the gauges are pretty inexpensive.

I guess, I was expecting it to peak later. Maybe this is a modified WRX, but I thought the 2012 had 265HP...
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Last edited by jadawgis732; 03-01-2013 at 01:41 AM.
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Old 03-01-2013, 02:46 AM   #2
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Im pretty sure the 2012 wrx is rated at 265hp, but not 265whp which is what your seeing on that dyno sheet. For my car at least my boost PSI can peek at 18 safely but will bleed out to around 8-10 after 5500rpm. My tuner told me I can run a constant 18-15 but run the risk of premature turbo failure. Your car should have a VF52 and you should be able to up the boost to 18-20 and be safe, or so ive herd but dont quote me on that.

Forgot to add, your boost is limited by your boost controller.
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Old 03-01-2013, 02:53 AM   #3
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PSI maxes out at about 3.5-4k rpms, around 15 for stock, then begin to taper down as rpms climb.

You feel the most power at 4k because thats where the torque is significantly climbing. Its easy to install a boost gauge and i would highly recommend it.

You should also get a cobb AP. does wonders on the powerband
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Old 03-01-2013, 04:11 AM   #4
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Quote:
Originally Posted by scx89 View Post
PSI maxes out at about 3.5-4k rpms, around 15 for stock, then begin to taper down as rpms climb.

You feel the most power at 4k because thats where the torque is significantly climbing. Its easy to install a boost gauge and i would highly recommend it.

You should also get a cobb AP. does wonders on the powerband

for beginners... i 100% agree.
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Old 03-01-2013, 09:05 AM   #5
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Quote:
Originally Posted by Godzillaclaw View Post
Im pretty sure the 2012 wrx is rated at 265hp, but not 265whp which is what your seeing on that dyno sheet.
To elaborate, that 265 CRANK hp is what it is rated at. Wheel hp is different... expect a 15-20% drivetrain loss.
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Old 03-01-2013, 10:56 AM   #6
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Quote:
Originally Posted by Mr Wrex View Post

To elaborate, that 265 CRANK hp is what it is rated at. Wheel hp is different... expect a 15-20% drivetrain loss.
Awd applications are typically 25%, with 2 wheel applications being 10-15%.
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Old 03-01-2013, 11:36 AM   #7
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Hate to admit it, but before I was on here and really started delving into these cars, I used to read How Stuff Works on a daily basis. There's a lot of great information simply explained on there.

http://auto.howstuffworks.com/turbo1.htm
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Old 03-01-2013, 12:59 PM   #8
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Cobb has a bunch of dyno plots. Plenty of RPM vs Boost graphs.

http://accessecu.com/dyno/
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Old 03-01-2013, 04:48 PM   #9
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Default WRX boost

The boost curve looks pretty normal for a stock WRX. If you're looking for more power I'd highly recommend a Cobb Accessport with standard off the shelf maps (warrning - it will likely void your warranty). If you go stage I (minimal investment in upgrade parts) you'll see some nice mid-range torque improvements. If you add a catted downpipe + Cold air intake you"ll be stage II with some really nice mid-range and top end power. You can do it all yourself for $1200 - 1400.

In general, Cobb OTS stage II programs will reach full boost around 3100 rpm and hold that until around 4500 rpm and taper off after 5000 rpm.

As an example of whp on a dyno, my stk 2005 STI had a max hp of torque of 247 ftlbs at the wheels (factory rated at flywheel 300 ftlbs) and 236 whp (factory rated flywheel 300hp). That is an uncorrected 20% + or - difference between wheel and flywheel readings.
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Old 03-01-2013, 06:05 PM   #10
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Originally Posted by jaboyd View Post
The boost curve looks pretty normal for a stock WRX. If you're looking for more power I'd highly recommend a Cobb Accessport with standard off the shelf maps (warning -you will likely have your warranty claim denied). If you go stage I (minimal investment in upgrade parts) you'll see some nice mid-range torque improvements. If you add a catted downpipe + Cold air intake you"ll be stage II with some really nice mid-range and top end power. You can do it all yourself for $1200 - 1400.

In general, Cobb OTS stage II programs will reach full boost around 3100 rpm and hold that until around 4500 rpm and taper off after 5000 rpm.

As an example of whp on a dyno, my stk 2005 STI had a max hp of torque of 247 ftlbs at the wheels (factory rated at flywheel 300 ftlbs) and 236 whp (factory rated flywheel 300hp). That is an uncorrected 20% + or - difference between wheel and flywheel readings.
Intake is a waste of money at stage 2. Unless you want more noise. Then go for it!
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Old 03-01-2013, 06:33 PM   #11
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Wow, great information here guys. Thanks.

I really was considering getting an AccessPort until I read that it nullified the warranty. That sucks. Also, that torque at 4k RPM is most likely what I was feeling.

Finally, is there any safe way to adjust the boost controller without voiding warranties, or messing something up? Would the MPG drop with an increase in PSI?

EDIT: Oh, wow that Cobb Dyno Database page is great. Getting bookmarked. Are their HP graphs WHP or just regular HP? Also, how costly is it to get your car tested?

Last edited by jadawgis732; 03-01-2013 at 07:01 PM.
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Old 03-01-2013, 06:39 PM   #12
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One more thing, on the turbocharger vs supercharger HowStuffWorks page, there is a video, where the guy is talking about Turbos. He says that turbochargers can actually improve MPG because they are atomizing the air going into the engine, causing all the fuel to burn, but if you are driving around with the boost on all the time, you use 25-30% more fuel. How does one switch on or off the boost on the fly like that?
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Old 03-01-2013, 07:02 PM   #13
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Quote:
Originally Posted by jadawgis732 View Post
Wow, great information here guys. Thanks.

I really was considering getting an AccessPort until I read that it nullified the warranty. That sucks. Also, that torque at 4k RPM is most likely what I was feeling.

Finally, is there any safe way to adjust the boost controller without voiding warranties, or messing something up? Would the MPG drop with an increase in PSI? After reading the HowStuffWorks on turbocharger vs supercharger (yes, I wound up there too), I would imagine not, since turbochargers get their power from the exhaust stream.

EDIT: Oh, wow that Cobb Dyno Database page is great. Getting bookmarked. Are their HP graphs WHP or just regular HP? I assume the latter because it's a dyno database?
AP doesn't nullify the warranty. It raises your chances of getting a warranty claim denied. For example, if you go in for warranty for a broken headlight bulb, they're not going to deny it. If you go in for engine problems and they somehow found out you were using an AP and the AP likely gave cause to it, then your warranty claim can be denied. If you stay at Stage 1 and don't beat the car up, you're not going to run into any problems.

Some people say MPG's go up, some say they go down. But, yes more PSI = more fuel consumed. If you're not boosting, then you'll save the most gas there.

Cobb dyno database are all WHP because they are dyno'd on the wheels. Where as manufacturers just dyno only the engine right at the crank. It'd be pretty crazy to take your engine out just to dyno crank power anyways...

Turbocharger's are "fuel-efficient" because they are recycling the energy from the exhaust. It doesn't make something MORE fuel-efficient, it just makes it so if you wanted more power from an engine, you could obtain it without sacrificing as much fuel mileage.

For example, the 2011 Impreza's 2.5L non-turbo are rated at 20/27 city/hwy @ 170HP
the 2011 WRX's 2.5L turbo are rated at 19/25 @265HP

See how much the MPG's dropped? If you were to increase power on the impreza in any other way.. supercharging, increasing displacement/engine size etc.. would result in a much more noticeable MPG drop.
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Old 03-01-2013, 07:09 PM   #14
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Quote:
Originally Posted by jadawgis732 View Post
Wow, great information here guys. Thanks.

I really was considering getting an AccessPort until I read that it nullified the warranty. That sucks. Also, that torque at 4k RPM is most likely what I was feeling.

Finally, is there any safe way to adjust the boost controller without voiding warranties, or messing something up? Would the MPG drop with an increase in PSI? After reading the HowStuffWorks on turbocharger vs supercharger (yes, I wound up there too), I would imagine not, since turbochargers get their power from the exhaust stream.

EDIT: Oh, wow that Cobb Dyno Database page is great. Getting bookmarked. Are their HP graphs WHP or just regular HP? I assume the latter because it's a dyno database?
Dynos spit out WHP. Stay out of boost to obtain maximum MPG (a boost gauge tells you whether you're in boost or not). BUT, if I understand it correctly, if you are in boost then a higher target boost requires more fuel to maintain the proper air/fuel ratio (someone please correct me if I'm wrong). This means lower MPG's.
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Old 03-01-2013, 07:16 PM   #15
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Quote:
Originally Posted by jadawgis732 View Post
One more thing, on the turbocharger vs supercharger HowStuffWorks page, there is a video, where the guy is talking about Turbos. He says that turbochargers can actually improve MPG because they are atomizing the air going into the engine, causing all the fuel to burn, but if you are driving around with the boost on all the time, you use 25-30% more fuel. How does one switch on or off the boost on the fly like that?
Boost is controlled by throttle response (aka how far in you're pushing the gas pedal). You can't obtain target boost without going wide open throttle. Want boost 100% of the time? Drive around with the gas pedal mashed in 100% of the time.

Just a couple of tips I picked up driving around in my old WRX:

-Don't go wide open throttle when you're cruising in 5th gear on the highway. Your engine won't like that. If you feel the need to accelerate quickly just downshift.

-Learn how to double clutch when downshifting.

-When coasting downhill don't put the car into neutral. Keep it in gear. If for some reason you do go into neutral. Rev match before popping the appropriate gear back in (learn what Rev Matching means and how to do it)

-Read this:

http://forums.nasioc.com/forums/showthread.php?t=533787

Edit: Fixed first bullet point.

Last edited by jhmr; 03-02-2013 at 09:37 AM.
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Old 03-01-2013, 09:15 PM   #16
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You get peak boost/torque at 4k because of turbo lag and compressor efficiency.

The lag is why you dont hit peak boost the instant you hit the has at 1krpm. its caused by inertia of the compressor and turbine and the intake charge and the lower volume of exhaust at low rpms.

the reason it tapers of is due to the efficiency range of the compressor. as the compressor gets further out of the efficient range more of the energy goes to heat. this is why a bigger turbo can actually produce more hp at a lower boost. To keep the compressor in the efficient range the boost needs to taper off. using water meth or better intercooler can help take the heat out of the intake charge then you can turn up the boost and operate more outside the efficient range.
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Old 03-01-2013, 11:42 PM   #17
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Quote:
Originally Posted by jhmr View Post
-Don't go wide open throttle when you're cruising in 5th gear on the highway. Your transmission won't like that. If you feel the need to accelerate quickly just downshift.
That was a laugh out loud moment for me.

Also, seems like I need to install a boost gauge. I mean, looking at the Cobb Dyno results, it seems like no matter where in the RPM spectrum you are, you're getting some kind of boost.

Quote:
For example, the 2011 Impreza's 2.5L non-turbo are rated at 20/27 city/hwy @ 170HP
the 2011 WRX's 2.5L turbo are rated at 19/25 @265HP

See how much the MPG's dropped? If you were to increase power on the impreza in any other way.. supercharging, increasing displacement/engine size etc.. would result in a much more noticeable MPG drop.
Yeah, I went from a 2006 stock 2.5i to my 2012 WRX, had to start buying the premium gas at the tank, and am only averaging 19.8MPG, over my first 3 tanks (so far 800 miles put on the car). I did show off a little for friends during the first few days I had it, but since then, I haven't gone over 4500RPM 3 times. But still, my annual gas bill probably increased by about 50% when I signed the financing papers.
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Old 03-02-2013, 12:06 AM   #18
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Cobb dyno plots are all done in WOT

If youre in 3rd gear 3500 rpm, youre not at 15psi or anywhere near that if youre not WOT
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Old 03-02-2013, 12:50 AM   #19
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Gotcha. Okay, so the gas pedal throttle has the biggest impact on boost.

On another note, according to this article Car and Driver, the AccessPort voids your powertrain warranty. But how could they tell if you flashed back to stock and unmarried the AP from the vehicle when it went in for service?

Also interesting was this:
Quote:
The AccessPort connects to the OBD II plug and automatically saves the factory engine programming. It also has preset engine maps for various states of tune, but none that accounts for an aftermarket intake. Cobb says there are too many variables to have a single program, so we got a $460 custom engine tune.
So flashing to new tables is not something you want to do on your own? The appeal of the AccessPort has declined significantly for me in the last few hours.

Last edited by jadawgis732; 03-02-2013 at 12:56 AM.
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Old 03-02-2013, 12:57 AM   #20
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Look up Checksum. They can tell when you've flashed your ecu.

You can flash new off the shelf maps all you want. It's not a good idea to use maps for parts you don't have. Cobb doesn't make maps for every intake out there. Why would they make maps for other people products? The have maps for a few intakes, and Stage 2 maps. Other people make maps you can buy on line.

Seems like you need to do more reading. If you want to get the most out of your parts get a custom tune. If your just getting an in take an off the shelf map is fine.

Last edited by hillsboro; 03-02-2013 at 01:04 AM.
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Old 03-02-2013, 01:03 AM   #21
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Quote:
Originally Posted by jadawgis732 View Post
Gotcha. Okay, so the gas pedal throttle has the biggest impact on boost.

On another note, according to this article Car and Driver, the AccessPort voids your powertrain warranty. But how could they tell if you flashed back to stock and unmarried the AP from the vehicle when it went in for service?

Also interesting was this:

So flashing to new tables is not something you want to do on your own? The appeal of the AccessPort has declined significantly for me in the last few hours.
This has been talked to death, search on this one.
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Old 03-02-2013, 03:27 AM   #22
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Quote:
Originally Posted by jadawgis732 View Post
Gotcha. Okay, so the gas pedal throttle has the biggest impact on boost.

On another note, according to this article Car and Driver, the AccessPort voids your powertrain warranty. But how could they tell if you flashed back to stock and unmarried the AP from the vehicle when it went in for service?

Also interesting was this:

So flashing to new tables is not something you want to do on your own? The appeal of the AccessPort has declined significantly for me in the last few hours.
Yep, exactly (in relation to your boost answer)

once again, nothing is voided. They can't void your warranty. They can deny a warranty claim. Off the shelf maps are made so they can run very safely on all our cars - otherwise.. the cobb ap wouldnt have such a great reputation.

They can't tell you had an AP, they CAN tell if you've reset the ECU, when and how many times. However, you can just say the battery died or you took the battery out.. etc.

If you're really worried about the warranty thing, just ask the service techs / advisors at your dealership. They'll let you know what they're cool with. However, SOA makes the call at the end of the day.
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Old 03-02-2013, 05:52 AM   #23
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Quote:
Originally Posted by jhmr View Post

-Don't go wide open throttle when you're cruising in 5th gear on the highway. Your transmission won't like that. If you feel the need to accelerate quickly just downshift.
Where do people come up with nonsense like this?

Going WOT in 5th while cruising without a downshift has ZERO negative effect the transmission.

However, it is very hard on the ENGINE.
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Old 03-02-2013, 08:24 AM   #24
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Originally Posted by Spenk View Post

Where do people come up with nonsense like this?

Going WOT in 5th while cruising without a downshift has ZERO negative effect the transmission.

However, it is very hard on the ENGINE.
Whoops, my mistake! What this person said! Rule number one, take everything said on here with a grain of salt haha.

Last edited by jhmr; 03-02-2013 at 08:32 AM.
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Old 03-02-2013, 10:47 AM   #25
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Rule number one, take everything said on here with a grain of salt haha.
In the newbies forum, general, or interior exterior because you have people who have no clue attempting to answer questions they are clueless about.

CN: don't answer a question unless you are pretty damn sure of the answer.
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