Low Boost Issue

Akalawur77

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I know A LOT of people aren't hitting the advertised boost on their Si, but I bought my car a few months ago (new with 30 miles) and I was hitting 15-17psi and its been gradually dropping to where I'm getting 12-13psi now. I called the dealer today to tell them my situation and they were less than helpful. Off the bat the service advisor said "so you were racing your car and blew it up" and later in the conversation "so who were you racing when you blew the turbo". He called me back after talking to a tech and said "First of all I don't understand how you are measuring a boost pressure" and I had to tell them that the car can read boost on the cluster.. Anyway the tech is blaming the issue on "winter gas" saying that it has lower octane and lower octane = lower boost and that if I had a leak that I would be losing a lot more boost. I didn't realize that only hitting 60% of your boost was not low enough to constitute having an issue. They told me to put octane booster in my car to see if it helps and if not then they'll schedule an appointment for me. The only mods I have are a different muffler (cut it off and welded a new one), short shifter, CDV removal, and an intake. I took the intake off to see if there was any difference and I was actually hitting about 1psi more with the intake on (13-14 instead of 12-13 with stock intake). The advisor called me back again and left a voicemail with more excuses saying that the built in boost gauge is inaccurate because it's electronic and not getting its reading from an actual vacuum source, and the car has an electronic wastegate and the ECU will limit boost in cold weather to protect the turbo because it gets very hot and I have to be driving for 20-30 minutes for the oil to be at operating temp, et cetera. What do you guys think? Car has 5k miles and I have a lot of knowledge and experience with turbos and manual cars, and a little experience with tuning.

TLDR; boost dropping from when I bought the car, only getting 12-13psi. Dealership is being arrogant and giving me excuses and now trying to say its normal.

PS I have the voicemail saved if you guys care to hear it I might be able to upload it
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jakabony

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Could the stupidly intense cold we’ve been having have something to do with it? I’m not sure if the atmospheric pressure and temperature would have that much effect or not.
 

charleswrivers

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If what I keep reading about (there's several threads on this) I'd the car adjusts boosts based on trying to make a specific power output, it would lower boost as IATs drop as the air would be more dense and there would be more O2 content for the volume of air. It would do this to keep power constant. That is not to say it isn't worth look. Every 5F is supposed to affect air density around 1%. Going from 80F to 30F oughta cause about a 10% bump in power (from something I read a long time ago... but it shouldn't be car specific). Because the act of compressing air raises temperature in a turbo/SC, low ambients are doubly effective w/an intercooled car. Someone who knows more tuning oughta chime in as I'm still learning. On another thread, there's a lot of discussion about how the car will pull boost to just hit power targets. I didn't realize how much you could do/see w/a tuner until I got mine last week.

I was also weirded out about the lower than spec'ed boost pressure. I have a Ktuner so it runs the boost I put on the targets, right on the nose. Before, in 50ish degrees it was getting about 16-17 out of the 20.3 it was spec'ed for.

On my old dumb Z32, the colder it is, the more boost it gets with the same solenoid duty cycle. I might run 15 lbs in 70f weather and 17 at 30f. It is massively more powerful cold because of it. I mean... spinning through 2nd at 70 mph faster.
 

HRC

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Could the stupidly intense cold we’ve been having have something to do with it? I’m not sure if the atmospheric pressure and temperature would have that much effect or not.
Dense air (cold air)=More boost. However, more than likely the ECU will pull boost/timing to protect the motor from blowing up.

Hot air=hot air going into the engine, making less boost thus making the car slow. Imagine a blow dryer sucking in hot air.

Humidity=Heat soak, hence the need for a good intercoller. Generally heat soak will result car in being very sluggish.
 

ChinStrap

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I keep my cluster on the 'MPG' screen. I don't currently track the boost numbers, with that said i'll change it on the way home tonight and see what kind of boost i'm getting.

It's been pretty cold in IA this winter (current: 8*f w/ -17*F low, tonight). I have noticed lower MPG, but I think everyone is dealing with that in this weather.
 


Scarlet

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Like others basically stated, the car's ecu is smart and will adjust boost levels based on varying factors, fuel type, fuel quality, temperature, etc. The stated oem boost level is just a "target boost" level the ECU works toward achieving.
 

2tone

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I have noticed lower boost levels since my area has had a cold front recently(Florida) but it only seems to be the first 10-20 minutes of driving. I also haven't been pushing the car hard or trying to reach peek boost but I did notice it since the dramatic temp decrease
 

batman900

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Never paid attention to my level before. Watched it today on a few good pulls, seems it likes to stay around 14 and will peak at 16 briefly. 91 octane 50 degrees F very dry.

What bothers me a tad is that sometimes it will have the power to break the tires loose in 2nd and other times it feels sluggish and no where close to spinning a tire. It’s very inconsistent.

On my 3rd pull today it felt like it bucked a few times while climbing in rpms, like it was choaking. Maybe knock was detected?

None of it really bothers me a lot but the inconsistency does make me miss my cvt hatch a tad, it was entirely predictable and pulled crazy hard on stage-1 ktuner, haven’t flashed my Si yet because I worry about clutch issues. Still a fun car to drive and I enjoy it.
 

tapakidney

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I just want to give my current boost level experience and see if it's normal.

It's 20 degrees here, FYI. 93 octane (my only option for premium around here).

While idling, I'm at -10 PSI.

I have to get to about 2500 RPM to get to 0 PSI

When I REALLY hit the gas, I top out at 14 PSI.

I'm new to turbos....Is this normal behavior?
 

boosted180sx

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I just want to give my current boost level experience and see if it's normal.

It's 20 degrees here, FYI. 93 octane (my only option for premium around here).

While idling, I'm at -10 PSI.

I have to get to about 2500 RPM to get to 0 PSI

When I REALLY hit the gas, I top out at 14 PSI.

I'm new to turbos....Is this normal behavior?
when you are at idle, you are in vacuum so its normal.

when you are accelerating, your gauge would be different depending on amount of load you put on the car.
 


10gCiViC

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What is the advertised psi? I run 94 octane. 1200ft ASL, and it's been well below 10°C (50 ish °F).

I've only seen 15psi
 

charleswrivers

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For an SI, 20.3 is the number given as 'Boost Pressure's under specs on the Honda website for an SI.
 

17siturb0

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Don’t worry to much about what psi you are making. If the cars running properly. It’s probably the outdoor temperature, it’s been as much as -30 where I am, all the cars around here aren’t acting right, because it’s to damn cold.
 

10gCiViC

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So if its advertised at 20.3, and I'm getting 15, I'm not experiencing what its capable of ? What's the point of a Ktuner then ? The dual sport mode ? 19.5/23 or whatever.
 

charleswrivers

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From experience, whatever boost targets you have with Ktuner, you reach them every time.

I'd get 17-ish at full throttle, ~50F, full throttle in 2nd and 3rd at best prior to flashing with Ktuner. I made up a 19/21.5 dual basemap. In sport, I get 21-22 on the digital boost gauge every single time I do a pull.
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