Basically you plug up the turbo inlet with this boost leak tester, clamp it down, blow it up with an air hose, and listen for hisses where air could be leaking out of the intake system. Injector seals, throttle body shafts and gaskets, idle screw, couplings, BOV, intercooler and IC pipe welds, vacuum hoses, etc... If you hear it, but can't find it, you can spray soapy water on the area where you hear the hiss, and it will blow bubbles from where it's leaking. Boost leaks are bad because vacuum won't be correct if it's after the throttle body causing idle problems, wasting fuel, and sealing up the leaks will prevent you from over-spooling your turbo, and will improve throttle response. On cars that have MAF sensors, it's especially bad, but cars that rely on MAP sensors and engine speed aren't as affected fuel-wise.

Bottom line is, boost leaks are wasted energy.

Before someone says "but won't some of your valves be open preventing it from holding boost?" the answer is no. The intake and exhaust valves aren't ever opened simultaneously. Some air may leak past rings, and poorly adjusted valves can cause problems, too, but those are easy to diagnose with this test, too, buy determining how fast the air pressure leaks down.

As for the MAF sensor, the stock DSM sensor is a Barometeric MAF and it's located before the turbo's compressor, creating drag on the compressor wheel because it's restricted during spool-up from having to draw air through the MAF. The 1g 90-94 sensor can meter up to 380 cfm. The 2g 95-99 sensor can meter up to 500 cfm.

The GM LS-1 series of engines use a hot-wire MAF that doesn't rely on air pressure, but rather applies voltage to a wire, heating it up, and as x amount of air crosses that hot wire, it cools down. The amount of air drawn through the MAF is determined by how much the wire is cooled down at a given voltage.

I have Ramcharger's MAF translator that allows me to set my baseline fuel curve, run any size injector and tune my Idle, Mid and WOT fuel trims. ($200) It translates the GM MAF's output to match the frequency of my DSM MAF. It lets me also move the MAF sensor so that it meters air AFTER it's been compressed by the turbo, so there's no drag on the compressor wheel anymore. It can also meter 500cfm more than the stock 2g DSM sensor, so it's not much of a restriction anyway. The MAF translator is plug and play, too, you only have to tap one wire. A tripple-whammy. Great product.

The IC pipe hack was done because the IC kit I bought wasn't a good fit. I told them when I bought it that I would be running the LS-1 MAF in a blow-thru setup, and they said it was "easy" to do with the pipes they were sending. It wasn't. There were bends where it should have been straight, the BOV would have hit the fuse box if I didn't hack it up. So I cut the pipe, clocked the BOV flange about 20° clockwise, and then cut 4.5" off the pipe to eliminate a bend and make room for the sensor. The throttle body elbow got chopped off the flange, clocked 30°, and welded back on so the upper IC pipe goes almost straight from the IC end tank to the throttle body, ensuring no turbulence impedes it's job. These IC pipes are almost 5 feet shorter than the ones I had. They flow GREAT.

I can't wait to take it to a dealer (with my own oil) for an oil change and put a Mic under the hood. I'd love to hear what's said when they see that GM shiz. That's the only reason I'd pay a dealership for anything service related.