I guess I still don't understand why a turbo at 5psi would absolutely require a tune, and a TRD blower at 7psi wouldn't. The blower at 7psi is pushing more CFM than the turbo boosting at 5psi. The blower at 7psi would make more power at the CRANK than the 5psi turbo would, but at the wheels, the turbo could be making more power than the blower because of significantly less parasitic drag. If you set both the turbo and supercharger at 7psi, then they should both move about the same amount of CFM of air, and make similar power at the crank. But at the wheels, the turbo makes more power (again, the whole parasitic drag of the blower).
I know I keep referring back to Clownmeat's rear mount turbo build... but I think he's pretty much proven that you can run a turbo at 7psi, and not require tuning any more so than the TRD supercharged guys do. He's been doing it over a year now. Check out his thread and look at his videos. Pretty impressive.
What you need to do is figure out how much CFM the SC'r flows @ X psi. Then find a turbo that flows the same amount of CFM @ X amount of PSI?? I'm not saying any turbo will do because it doesn't matter which size turbo you get they will all flow different CFM's @ the same PSI at the same RPMs? Make sense? A lot of variables will come into play here. You wan't to find a turbo that flows X amount @ 7psi like the SC'r and be in the turbo's most efficient range. You can look @ turbo maps which I doubt some people will not know hot to read on here because lack of turbo knowledge etc.
Lets say on my Supra IE: I boost my 6766 Turbo @ 18psi and make 600hp @ the wheels? Now lets say I slap on a smaller turbo like a 6266 and boost it @ 18psi.
Now the torque and hp curve will come on a few hundred RPM's sooner than the larger 6766 but the turbo only puts down 500hp @ 18psi so that's 100hp less then the larger 6766 at the same PSI level.
This means the larger turbo is forcing more air in at the same boost level as the smaller turbo.
Now in a perfect world lets say you get a turbo to match the SC'r for CFM's @ say 7psi. Both put out identical Horsepower.
The SC'R will put out it's peak HP # sooner than the turbo because you'll have to spool the turbo. Now you're getting into a dyno graph and you can see where the torque and HP curves are on both turbo and sc'r and make your mind up what you consider is the most usable of both in the RPM range you'll be at most of the time.. But yes you will make more hp up top with a turbo than you will with a roots style SC'r.
Long story short the smaller turbo will come on sooner than the larger turbo and put out less hp @ the same PSI of the larger turbo. But the smaller turbo will be more efficient @ 7psi than the larger @ 7psi.
There's more to it than just slapping on a turbo and it putting out the same CFM as the SC'r.
Intercooler sizing and pressure drop, Intercooler piping sizing and routing, heat soak like any other engine N/A or Boosted, Down pipe and exhaust sizing...
There maybe some holes in this but forgive me as I'm at work and I'm going between this and other things lol
