Hey everyone,
After reading a ton, I have been slowly narrowing down the possible culprit behind the fact that I'm only making a max of 12.5 PSI (using Torque app). I have a 17% pulley so I figure I should be making at least 15PSI (I live at about 2,000 ft)

-I have replaced the intercooler boots back to the stockers which are in good condition (my previous ones were Alta)
-I have checked the BPV spring (good tension)
-I performed a pressure test to the intake system which revealed some weak rubber fittings for the two vac hoses under the left IC horn. I have replaced them.

Everything else held up great with the pressure test. So I'm stumped!

My 03 R53 has 103k miles, so the only thing that's left that I can think of is SC wear that causes a lack of pressure.

Anything I might be missing?

 

Few things, Crank pulley failure, poor compression, slipping/wrong sized belt, slipping supercharger pulley are a coupl3 that spring to mind.

also a bad/sticky gauge that reads wrong which happens.

 

For comparison, I'm running a 15% pulley and regularly top out at 15.5 psi boost @ 7,000 rpm. I would guess that your BPV is not sealing properly and/or you have air leak somewhere. A smoke test might be in order.

 

Thanks everyone.
I can safely rule out all of these suggestions except for one: wrong size belt.
I looked and have a Continental 6pk1388 belt.
I believe this would work for a stock or 15% pulley, but not 17%.
Correct?

 

What I’ve found is stock belt doesn’t even work on a 15 nor an 11(JCW). Despite people sayin* it does.

that’s why I had to swap belts on the PW before I even drove it back.it was slipping ie screeching under boost.

this is right size for a 15% and fine on a 16%.





iirc the chart, on 17 you go down to k060532?

 

Great! Ordered one, should be here tomorrow. I'll check back in to share my findings.

 

Well I successfully installed the K060532 belt (much tighter, can now see half the hole on the tensioner)
Still max 12.5 boost (although it feels like it comes on sooner).
Next will be BPV replacement I suppose. Darn it!

 

The K060532 should be the correct size for a 17% with a stock crank pulley, but a half a hole is on the loose side. Brand new before stretching you should be seeing a complete hole or more.

What is the history of your car… have you owned it for a long time and felt a noticeable loss of power, or is it new(er) to you and you decided to check the boost pressure?

Were the supercharger or crank pulleys checked for slipping?

 

I know this will sound weird, but when's the last time you changed the fuel filter? And have you ever had the injectors rebuilt? I've had them done on all my cars (about $10-15 a piece) and they are refitted with new filters, o-rings and flow matched. Just to get them out of the equation. Might be worth the effort to eliminate them from the list of possible issues. And it's cheap!

Also, vacuum leaks. There's lots of gaskets and rubber hoses on these cars, I even had to replace my fuel filler hose as it was rotten. (it was not leaking yet, but all the rubber would rub off if you touched it)...

One last thing, how's the catalytic convertor? One that is broken or plugged will keep you from realizing boost.

 

I’d suggest a smoke test, to check for leaks.

 

I agree with the smoke test AFTER you slap a new bpv down in there, the new ones operate on a close-ended system (my stock one had built-in boost leaks.) Has the supercharger ever been oil serviced? Judging from the year and mileage, it is also a common problem, the gear boxes tend to go completely dry, causing enough extra friction to start grinding teeth smooth. This can also start wearing out the lobe bearings and cause just enough slippage in the rods to cause tolerance reduction. This is one of the worst case scenarios, but if you don't catch it soon enough, the sc has to be removed and rebuilt/replaced.

PS - clean those MAP sensors while you're in there.

 

I did an intake pressure test, so leaks can be ruled out (it revealed one tinyleak in a vacuum line fitting which I replaced, everything else was sealed up like a drum)
Supercharger was just serviced 1.5k miles ago, but is still original from 03' so it might just be getting tired with 103k miles on it.

Next up is BPV! I'll report back what I find. If that doesn't do it, I'll just have to settle for 12.5 max PSI as I'm not going to tear everything apart.

Thanks everyone for your input

 

It may sound silly; but you may want to try and clean your T/MAP sensors.
I had a very similar symptom. My MAP sensors were super clean but I replaced them anyway (with OEM) and my particular troubles were resolved.
Those OEM T/MAP sensors aren't cheap though.

Ignore.
Replied to the wrong subject.

 

Not gonna be the supercharger. All of min3 have over 145k one has 160k and no issues. But bypass valve could definitely cause this.

 

How about the intercooler itself, any signs of corrosion / leaks / compromise?

Also, any codes? Supposedly BPV will throw at least one if that's the issue:

 

Stock cam and head?