Weird boost issue I'm lost
 

Hi all so I have a 03 S that I just recently have gone through and made mechanically sound again and still have a weird boost issue. My setup is 17% pulley 380cc injectors and a DT bypass valve along with a intake and bigger intercooler. My issue is that it seems to max out at about 10psi at 5500 rpm and nothing after that according to my ultra gauge. Now before the 17% I had a 15% and that only made 10psi at around redline. I have already smoke tested it with no leaks found except for a small leak at my oil cap. I smoke tested via the intake itself as well as the map sensor port on the front of the intake. The bypass valve is brand new. Is my supercharger bad? Or do I have the smallest boost leak known to man. Thanks!

MTB, I'm new to the R53 world. I just purchased an '06 MCS; the check engine light was on "low airflow". I found a post on the internet for my specific DTC (P1688), and sure enough, my harmonic balancer was coming apart. When I removed it from the crank, it came out in three pieces. Since the supercharger is belt driven, you will loose rotational speed of the compressor if the harmonic balancer is slipping. Look for a gap between the grooved pulley and the outer section; there should be no gap.

Go to the 1 minute mark.

That is a very good guess however unfortunately it's not that easy in my case since I have a brand new pulley on there already. Appreciate the input.

Have you pulled any codes?
When I had installed my mechanical boost gauge (after 15% sc pulley),- everything went great. I loved watching that needle hit 15psi. A few days later (according to my gauge) I started only boosting 10psi.
At idle the needle had risen to -12hg. Smoke tested revealed nothing. The vacuum leak/ low boost/ high -hg was the result of a crack in the tiny vacuum line under the right side (passenger side) SC horn.
It's a pain to see and even more of a pain to get to.

Of course this was just my experience and is merely anecdotal.
It may or not pertain to your symptoms.

No codes are thrown.

Do you have a tune? Maybe chat with Adrian. He seems to be able to find all sorts of things. Told me about a vacuum leak that I was not aware of. The tune is reasonably priced and easy to do. (and I am computer challenged- so that's saying something)

I also wanted to know that, thank you for the suggestion.


So is the consensus that a 17% pulley should put out 15 psi of boost?

I recently installed a mechanical boost gauge (Autometer) on my R53 with 17% pulley, ATI Super Damper (stock diameter), DT bypass valve, 380cc injectors, DDM Works CAI, BMW V12 throttle body (about 3mm larger diameter than stock), ported plastic air feed pipe to the S/C, ported S/C outlet horn, GRS Motorsports intercooler, ported intercooler outlet horn, ported intake manifold and Miltek resonated cat-back exhaust. I hit 10 psi fairly early and then boost continues to climb to about 13 psi (according to my gauge) where it seems to top out by the time I shift at redline. I was kind of disappointed because I was expecting 15 psi.

Gail Banks has some interesting videos on YouTube, and he has a lot of experience with forced induction. His point ... forced induction devices like turbochargers and supercharges are air density machines. Power doesn't come from air pressure; power comes from air density.

Here's another good one.

Go back to your stock intercooler and see if you get boost back. I’m running intake, full milltek exhaust no cats or resonator, 15%, 380’s, tuned by Adrian and see 16 to 17 lbs of boost depending on temperature. I had a racing dynamics intercooler and would see 15-15.5 lbs, went back to stock and picked up the extra boost.

I also think you need a tune. I was going back through my build thread, With no tune and a 17% pulled and a 2% crank I was getting 14lb boost (granted I had new injectors installed with no tune AND I thought that they were 380cc but turned out to be 550cc) so that could have contributed to the issue. After the tune I am hitting 17-18 psi boost and the car moves like a rocket. I am not sure where it was before the injectors or the exhaust work but it's definitely faster. More efficient, needs less boost?

There's been a fair amount of responses since I last saw ghost's post.
I can offer this as another comparative "data point" to the mix.

15% reduction pulley
Modified stock airbox w/ 2-1/4" un restricted CAI intake hose(s)
3.7"x 5.75" K&N cone filter
380cc Siemens/DEKA jcw injectors
NGK BRQ7 colder plugs and wires
PRW fluid filled crank pulley (stock size)
Factory throttle body
Factory BPV (unmodified)
Stock manifold(s) & catted exhaust
Adrian tune

Although not indicative of my driving habits-
I can easily reach 15psi (within a reasonable amount of time) pulling 5,800-6k rpms @70mph in second gear.

I don't drive it like that often; but have taken my eyes off the road for a moment to see for myself.

I'd currently had a P0171 "lean condition" trip my SES. Cleared the fault and have addresses a few possibilities that may have been responsible. Waiting to see if the fault comes back before driving the car in an abusive manner.