From what I've read the VF-22 can deffinately run a 1/4 trap in the 110-115s.
The Vishnu stage 2 car ran a 12.8 1/4 @ 110.4 with a vf-30 which is smaller than the vf-22. (SCC aug 03)

Compared to the VF-22 the 18G has a 2mm smaller intake housing with a 2mm larger exhaust housing and, from what I've seen, it's flow #s are very similar to the VF-22s.

Forced Performance (www.forcedperformance.net) supposedly sells both, although I hear the 20G seems to be on perpetual back order. The 18T "as they call it" goes for $595 which is a good price but they want a core replace which leads me to believe that They are not useing the TD05 housing but the stock TD04 which is signifcantly smaller.

If you are just looking to save cash you may have to do some serious shopping around. AVO, APS and Power Enginering all make big turbos for the WRX that will run #s similar to the 20G, but they aren't cheap. But if your looking for "bolt-on" goodness they will be easy

 

You should ask if that 18G will bolt-on to the WRX's up-pipe and down-pipe. A standard 18G will not match up. It has different bolt patterns on both flanges. That being said, $912 doesn't sound too bad (18Gs are all over the DSM boards at less than half that cost, used most likely).

A VF-22 from www.gruppe-s.com goes for $750 shipped, and it bolts-on with out much hassle. I know, I've got one and put it on myself.

One more thought, the 18Gs can be rebuilt and lots of places can do it, the VF-22s generally cannot, although I have heard that deadbolt enterprises has done some (www.deadboltspeed.com).

Also, just so we understand one another. . . neither of these turbos will do much good without exhaust mods (up-pipe & down-pipe), fuel delivery upgrades (fuel pump, injectors) and engine management (utek, unichip, re-flashed ecu, ect.) Any of these can be pre-programed for a VF-22 without a dyno tune (it wouldn't hurt to have it though). You will most likely have to dyno tune for the 18G, unless there is a pre-existing map for it.

 

The 20Gs are massive units. I know many people with 20Gs who run in the mid-low 12s all day long on pump gas. They are all DSMs. There is probably someone out there who has one on his WRX, but I don't know any and I couldn't verify any data they might have, or what they had to do to make it all work. I can only imagine that the fabrications involved are not simple.

I have read many posts that indicte that an 18G / TD05 will out-perform a VF-22. According to a chart I once saw, the IHI VF-22 will push 490 CFM at 18 PSI While the 18G will push 500 CFM at 17 PSI, if I recall correctly. I assume that the difference will only increase with more boost. Although more boost doesn't always translate to more power on WRXs like it does on DSMs. The engines are VERY different. Some claim to loose power on WRXs above 20 PSI, even on big turbos.

In the oct. 2001 issue of SCC, Alex Shikmutadov's Vishnu WRX ran a 12.9 1/4 @ 104.6 with a VF-22 running at 16 PSI on stock injectors and stock intake and internals. That was with a TEC-II engine management system and was very early in the WRX mod days. I have no doubts that with bigger injectors and extra lbs of boost that a VF22 will safely run 110 mph traps (everyone claims the VF22 can support 20+lbs of boost) but it's "top end" potential should be less than an 18G.

I'm currently running STI injectors with a VF22 at a safe 17 PSI, and while I have not yet taken it to the track, it pulls harder than my previous DSM with a big 16G at 18PSI that ran high 12s low 13s @ 103-108 on pump gas.