It began with the addition of the Spearco Intercooler [IC] in late 1997. That major component installed, the remainder of the changes to the IC system have centered around the piping to & from the turbo/throttle body. This labrynthian maze of tubing is responsible for the transfer of ambient air to the combustion process: 1] air filter, 2] turbo inlet, 3] turbo outlet, 4] IC inlet, 5] IC outlet, & 6] throttle body inlet. Given this lengthy path, bolstering construction from stock plastic/rubber parts, to larger diameter aluminum pipes using stiff silicone hose connectors, is a proven method for increasing air flow, efficiency, & reducing pressure loss...besides being much more reliable under -triple of stock- boost levels.

The 1st gen setup consisted of a ceramic coated 3000 pipe [connects to the throttle body (TB)], a single 2.25" upper aluminum [T-6061] hardpipe, & a Bosch BOV. The original air flow meter was still in service, & there was an HKS Super Mega-Flow foam filter near the Cold Air Induction inlet.
No dyno of this interim setup, as an F-Con, & Gredy S-Type BOV were also being fitted at the time. The setup then did ~296RWHP running ~12.5 psi boost [on arcing spark plug wires].
Gen I-A included the addition of the weld mount for the Greddy S-Type Blow Off Valve [BOV].

The 2nd gen setup saw full 2.5" aluminum [T-6061] hardpipes in May '99. From IC to just pre-TB, the pipes were 2.5",then ramped up to 2.75" to match the TB diameter. The famous "3000" pipe, known by most as the final intake restriction, was removed in the process. Some other mods happened at the same time- those can be seen at: Dyno Runs #3 & 4, August 1998, on the Dyno & Performance Page.
Power came in at ~318RWHP on an unremembered boost level. That run had plenty of other problems, besides worrying about improvements from the IC hardpipes.

Gen III added a mild steel 2.125" elbow to the turbo compressor's outlet hose in May 2000. The Toyota pipe, is a cast piece, which is ovally shaped & a definite restriction. The replacement is a same diameter pipe that mates to the turbo & then to a silicone adapter hose that connects to a larger pipe leading to the IC. This was the final piece to the IC hardpipe puzzle.
About the same time as this pipe was done, the 6" K&N filter was replaced with a 9" version. At this point, I believe the intake has pretty much been taken care of for whatever the engine can handle; although enlarging the throttle body, & porting/polishing the intake manifolds would make nice finishing touches.

Besides the pipes, the T-bolt clamps on most of the connections serve to keep things together- so no more hose popping-off antics like the original piping. There's something those OEM parts don't like about running 15 to 20 psi- they do things like...blow apart into shreads.

Results

The Spearco Intercooler was installed with the 1st pipe upgrade, & the ECU was reset to relearn the new flow characteristics. The hardware gave back an estimated 35RWHP improvement on the dyno. Not bad for just an Intercooler, & a mere upper pipe. Not only a numbers game, the car became so much more alive. Throttle response greatly improved, along with quicker, more consistent boost. Anyone who's published test results proving the stock Toyota Intercooler is not-so-bad are of no consequence to me. I've witnessed enough quantitative data of my own to show otherwise. Your mileage may vary, but expect great results on a healthy emgine.

Subsequent to the intital hardpipe, & intercooler installation, a myriad of other mods happened simultaneously to doing the pipes in their variety of iterations, precluding a quantitative representation of any individual piping performance improvements. I can offer your basic qualitative Seat-of-the pants [SOTP] commentary.

Each step of pipe upgrade yielded a definite change in boost characteristics. Less lag, snappier throttle response, & more stable boost were all noticeable improvements. Ironically, one of the biggest improvements felt was with the replacement of the smallest pipe...the cast aluminum elbow right off of the turbos compressor outlet. I swear, boost came on stronger, faster, & pulled hard right through to revs toward red line after that little mandrel-bent pipe went into service there.

Image #2 - compliments of Spearco Intercooler kit documentation.

Here's a shot of a handful of parts taken during the upgrade.
It was late Dec 1997, & it was too cold to spend time taking more pics. Yes, even in SoCAL it can get burley-cold at times. The custom 2.25" aluminum intercooler pipe in the lower right, was replaced by larger 2.5" piping in 1999. The new pipe ramped up to 2.75" to meet the throttle body, eliminating the 3000 pipe altogether.

Spearco from above.

Spearco from above, pic #2.

Front portion of Gen I upper IC hardpipe.

Side overview #2 of Gen I upper IC hardpipe.

Overview of Gen I-A upper IC hardpipe.

Driver's side view of Gen II upper IC hardpipe.

Overview #2 of Gen III upper IC hardpipe.