From someone who has tracked this PS2 setup multiple times running anywhere from 18 to 22 PSI on the turbo, I have to say the "lag" component seems to be way over exaggerated in this thread... Even moreso when discussing track (road racing) performance.
The PS2 turbo makes 400 ft/lbs of torque at 3500 RPM if you look at my dyno graph. If you look at the dyno graph SeanWRT posted and compare that to my PS2 dyno graph you can see that it's really not that much different. Let's just take two points into consideration here when comparing the two graphs. One on spool up, the other as a "peak" value.
- SeanWRT makes 500 Nm (368 ft-lbs) of torque at 2600 RPM. I make the same torque value at 2900 RPM. That's a 300 RPM difference lol. You're not going to feel that on the track.
- SeanWRT makes his peak torque of 540 Nm (400 ft-lbs) at 3500 RPM, and at 3500 RPM my PS2 turbo is making 664 Nm (490 ft-lbs)
Now yes, I am running way more air through my manifold than SeanWRT is, so it's not an exact apples to apples comparison but it just goes to show that the two turbos are really not that much different in the low end with regards to how much power they make and how responsive they are.
Where the turbo really shines is the top end power which is definitely felt on a road-race track. If you compare the two graphs again you can see that by red-line, SeanWRT's turbo is barely making 300 ft-lbs of torque to the wheels. The PS2 on the other hand is making 400 ft-lbs. This difference is even more in the mid-range of 3500 - 5500 RPM. Yes, there is definitely a difference in how hard the torque hits at low RPM (< 3000 RPM) but how often are you really at that RPM on a road-racing track? Not to mention, should you really be going wide-open-throttle at such a low RPM in a turbo vehicle? If you're driving appropriately and down-shifting into the corners and coming out at higher RPM, the added "lag" of the PS2 turbo is never felt.
Let it be clear, I am definitely not arguing the fact of efficiency when running "high" boost through a hybrid turbo - I personally feel that 18 - 22 PSI is the sweet spot with the PS2 turbo, anything more and you're probably going to gain some power, but ultimately end up throwing way more heat into the mix as well as back pressure. That's been proven on hybrid turbos across multiple platforms. No argument there.