Smaller pulley = Lower boost????
 

Replaced my 2.365" pulley with a 2.2", new belt. Tested and had 1.5-2lbs lower boost on my s1 L67. WHY????

Two short runs on dirt registered approx 8lbs vs. 10 lbs with the LARGER pulley...

Does your custom setup utilize the knock sensors? Can you scan for KR? If it's like the stock PCM it will take time to learn the new level of boost, and for the initial break-in it may run lower boost until it learns to compensate for the added boost.

The computer could be pulling boost due to KR. It also could be the belt slipping as well, yes it is new but its possible that maybe you needed to actually go with a smaller belt for that pulley size so it wouldn't slip.

I believe he does not have a BCS. So my guess is belt slip. IMO, a larger SC belt tensioner pulley will work better by increasing belt wrap and keeping good tension. You can get it from ZZP.

I installed a new smaller belt. I'm sure there is no belt slip. I am not using a stock computer - LYNX engine management, is using engine speed, CPS and O2. I do not have a KR sensor.

What does that leave? Nothing else changed?

I still think a larger tensioner pulley works better.

If he's sure there's no slip, no need for a larger tensioner. As well...most regular parts stores sell pullies. No need to buy one and pay shipping.

My point was if the PCM can't dump boost and you don't have any belt slip, what else could cause lower boost with a smaller pulley.

Did you blow a gasket out? Did you ever unplug the lower port of your boost control actuator? Although I see a plugged lower chamber not allowing as much vacuum at idle and coasting.

Maybe you developed a BCA leak?

If it's not a boost dump issue, it could be an issue with creating FAR too much heat. Hot air is less dense. That pulley is very likely hurting your performance greatly, and running the risk of popping a piston or a valve.

There's only one car here that has succesfully run smaller than a 2.4" pulley on a Gen3 94/95 top end. And I had to do ALOT of work to get it to run the 2.2 and the 2.0".

The air wouldn't be hotter till it was already in the LIM, though, right? Ideal gas law tells me that would INCREASE pressure.

The heat is created during compression. And the boost-stacking he's getting is going back up through the system, pushing the heat up into the SC. He's losing efficiency in the compressor in a big way.

In what conditions do you get higher boost readings? Cold or Hot weather?

Cold, but that's because the air is denser to begin with.

Take air of the same temp, heat it up more on the way in... wouldn't that increase pressure?

Not if you're boost-stacking already. You have to take into account boost stacking, reversion, and heat transfer. It's a complicated mess.

Regardless, that's WAY too small of a pulley for his setup, particularly since we don't even know how his PCM is managing anything. We know the limits of the stock PCM in our cars, and what needs to be done to get a pulley that small to actually work (with MUCH higher octane, I might add), but on his, it's a crapshoot, and a BOOM waiting to happen.

Not to mention..he's near the equator and while it's been cooler, it's not that much cooler to reverse the effects B1 is talking about.

Let's also not overlook the fact that he's probably got MAJOR belt slip. That's why I added another idler. ;)

UPDATE
 

Took the car to the dunes with better results.

Only ran 110 race fuel.
Ambient Temp 60-75 degrees.
Elevation 600 feet!!
2.2 pulley with NGK 7IX plugs.
New Belt.
De-carbon the motor and injector cleaning. - Which resulted in me having to lower my idle after the cleaning. (Involving a 15 minute spray from a machine directly into the plenum, followed by attaching the injector cleaning machine tapping into the fuel rail with the fuel pump off, and running for about 8 minutes)

I experienced no belt slip, no knock, no ping.

Max 10lbs of boost, but it comes on right now!!! Much better throttle response. I have 10lbs of boost at 1/3 throttle, but it never exceeds 10lbs.

My previous reading was actually, consistently 9.5 lbs, so there was a small net increase. Just not what I expected.

I think the smaller pulley helped me burn more fuel. I estimate about 20% more than the other pulley. Not sure if the computer has anything to do with it.

I'm now considering changing back to a larger pulley to improve fuel consumption. On our long rides, I am the first to request heading back to camp because of low fuel.

I appreaciate your thoughts and comments.

110 octane? Leaded or unleaded? Are you running an O2 sensor? Or do you have some other method to determine fuel ratio?

That 20% decrease in fuel mileage is way too much loss. Most of us only see 5% or so if we're hammering it.

There has to be some reason you get full boost at 1/3 throttle and it doesn't go any higher. Maybe a vac leak between the BCA and SC inlet?

15 minutes of cleaner in the plenum may have removed some of the coating from the rotors.

Gas
 

110 Octane unleaded. My Comp utilizes the O2, I'm not aware of any leaks.

Agreed, Shouldn't I have more boost? I have 3 vacuum lines from the boost diaphram, can anyone verify where they should go?

What is a BCA? I would guess is is a boost control actuator (the diaphram thingy?)

I have a feeling the wastegate is dumping all boost over 10 lbs.

BCA, Boost control actuator... diaphram thingy, same thing. On mine, the vac line to the top of the BCA goes around to the back side of the black 1" square vacuum manifold on top of the SC inlet. I'm not sure how it would dump at 10 psi, seeing as you don't have the solenoid that makes it dump.

Did you ever unplug the lower chamber of the BCA?

If your BCS isn't wired up to the computer, you're not dumping boost. It's not possible.

Boost
 

I did unplug the lowest vacuum line and fashioned a custom filter.

Why only 10lbs?

Stripped rotor coating from your solvents, high temps, belt slipping, any number of factors.

Go back to the stock pulley (or the one you had on there before) and see what you get. Smaller pulleys don't always get you more power. Sometimes they KILL power. Or gain nothing. There's alot of factors involved here.

With it idling, pull the vacuum line off the top of the BCA. Does the rod extend all the way so the foot on the end rests against the base of the SC?