So I recently installed boost gauge on my 03 S, and I’m beginning to wish I hadn’t . Here’s my setup:
• 43k miles
• 15% pulley
• Miltek cat back
• Dinan CAI

Vacuum looks great – 17 in hg at idle, around 25 in hg on engine overrun. My problem is, I’m seeing much lower boost than I expected. The max I’ve seen is a little under 12 psi, and that’s WOT in 3rd @ 6000 RPM.
Typically I see more like between 5 and 10. From what I’ve read, I’d expected more in the 15 PSI range.

I don’t see any leaks in the supercharger boots, what else should I be looking for? (I’m suspecting bypass valve, but that sounds like a bear of a job)

Ideas most welcome!

 

Some extra info in case anyone replies (please!!)

I'm in Seattle. Temp today was aroun 52-55, with humidity of 83% (at least accoring to weather.com!).

I also have the MTH tuner file installed, adjusted for my mods.

I'd really like to figure out why i have such pitiful boost numbers...

 

Stock is about 10 WOT, 12 souds pretty darn close to right, humidy kills these cars but I always took that to be much more of an IC issue, that may be playing a factor. It's an 03 have you done anything to the BPV? Or considered or even inspected it. (If you search for BPV there are many options, if its not closing right you may be getting a little bit of boost robbed), but doesn't seem like you're too far off ethier, 15% and intake is about 12psi, cat-back and ECU don't effect boost but to play into the Bhp and ultimately WHP.

 

Thanks Motor On. No, I’ve not looked at the BPV; to be honest after some of the horror stories I’ve read about breaking off tabs, and the difficulty removing the BPV, I’m trying to avoid it!

Perhaps I’ll just have to bite the bullet and take a peek. I think if I put the MFE in “service mode” things might be easier.

Of course, I could just wait till the weather gets drier in the summer (pretty
rare here in the pacific northwest! ). Decisions, decisions.

Thanks for the reply.

 

According to my ScanGaugeII, I see a max MAP of about 22psi, which when atmospheric pressure of 12.3psi is subtracted, I get about 10psi boost. I don't seem to be able to get more, and I have new boots, DT-BPV installed. Altitude is 5000ft as indicated by the atm. pressure reading.
Randy Webb once said to me I'd rarely see more than 10psi at altitude.

 

Assuming you're not up in the mountains around Seattle, you should be at 14-15psi at WOT with a 15%. Could be the BPV, but I had a problem a little while ago with low boost readings. As you describe, the vacuum was good, but the boost gauge tube had gotten a crack in it due to the way I routed it. Apparently, under vacuum the crack didn't leak, but it did under boost. Maybe not too likely, but something to check.

 

On my car, boost keeps rising up untill I tag the rev limiter. I see my max indicated boost of around 15 p.s.i. at 6800 rpm. You still have some more rev's available after 6000, what do you see for boost just before you hit the rev limiter?

Jason

 

but it doesn't sound that bad. If you're really worried about your BPV, wire tie it shut and give it a run.... But 12 PSI at 6000 sounds about right....

Matt

 

Thanks for the replies.
I'll check the boost guage for leaks, but i'm pretty sure it's leak free. Worth looking at tho.

I'm not in the mountains, so altitude shouldn't be an issue.

As far as how the boost builds, when i go to WOT, i see an initial boost reading of 5 psi, then it slowly builds to around 10 or so. If i keep beyond 6k, i see maybe 12 psi on a good day. At anything other than WOT, boost drops right off.

I guess it's wire tie time!

 

Thats about what I'm getting when I reach the 7000+ rpm. I can do that since I raised my rmp limiter by about 500 with th cpu programing.

 

Well, problem solved
After a run home from work this evening I confirmed I was only getting around 10psi of boost @ 7k rpm. I decided it was time to retrace my steps installing the boost gauge:

• Vacuum tubing run without kinks?.....Check.
• Teflon tape on all brass fittings?....Check.
• All T pieces & joints secured with clamps/wire tires?......Check
• All IC bolts tight and to the right torque?…Check.
• Really sure about that last one? Err, yeah of course…

Out I go with the trusty torque wrench:

• Clamp 1: good
• Clamp 2: good
• Clamp 3: good
• Clamp 4:ah!

Yep, the problem is that I’m an idiot. I’d completely forgotten to secure one of the IC boots.
Torqued it up and off for a spin – great! Around 15 PSI of boost. I knew it was there somewhere!
So the moral of the story?

1. Always double check your work
2. Assume you messed something up
3. Try and avoid making an idiot of yourself in front of everyone on NAM

Thanks very much to everyone for the help. I guess I’m my own worst enemy!

 

w/ yr set-up you should see 14.5lbs of boost.

Before doing anything else - confirm yr line is good and try another guage. Just buy a different guage, hook it up temporarily and test. If you get the same results then package it back up and return it.

 

Speaking of boost gauges, has anyone found a digital display in a rectangular housing, as opposed to all those analog circular ones?

thanks,

 

rectangular? and you were thinking of putting it where?

 

Next to all the other rectangular gauges I have (ScanGaugeII, airbox temp gauge)
Yes, I know I'm supposed to have round ones to match the MINI gauges, but I'm trying to gather data, and if all the telemetry is digital and rectangular, it will all fit on my dashboard!
I found one, but it's $160. Seems like a lot for a simple boost gauge. Oh well...

 

i never had any issues removing the BPV. i just followed the directions from Detroit Tuned and it took about 2 hours from start to finish, and that included the adjusting of the valve... as i saw lots of light shining through...when it was supposed to be closed

 

I have a MTH tuner file with a 15% Pro Mini pulley, i see 16lbs believe it or not. Now i have issues, my check engine light is along with my DSC which come off, i think i have a vacuum leak which i will investigate once the temp get into the high 30's, what is the stock vacuum range...i forgot. The car breaks cuts out once i hit 6 lbs of boost.