Assuming the t3 and the t3/t04e are of the same specs, only difference is one being a t04e compressor- the t3 turbine will make power faster, and the t3/t04 will lag more cause of the larger compressor.
A while ago, i said that if everything is constant- then at a set psi level on any turbo then the cfm's will be the same- and here is what calesta told me:
given all factors constant- engine @ constant RPM, intake manifold pressure the same... yes the flow rate (CFM) will be the same.
The main deal with relating flowrate vs pressure is in how MUCH flow the turbo can maintain at certain pressures. Your small turbo will start to "run out of steam" at higher revs, while the larger turbo will still be able to maintain pressure.
Let's say that you have two turbos... one is capable of 600cfm @ 15psi, and one is capable of 300cfm @ 15psi. Now let's take a theoretical engine that chugs 50cfm of air (naturally aspirated) per 1000rpm.
At 2000rpm, the engine only uses 100cfm at atmospheric pressure. The small turbo can maintain 300cfm at 15psi, and the larger turbo can maintain 600cfm at 15psi... both only need to supply 200cfm total (engine wants 100cfm at atmospheric, then add another 100cfm to boost 1 bar/atm) to maintain a +1 bar positive manifold pressure (or 14.7psi), so both will produce the same amount of power at that engine speed and boost level.
At 3000rpm, the engine wants 150cfm at atmospheric, so you need 300cfm to maintain 15psi of boost. No problem for either turbo here either- they can both maintain 300cfm at 15psi.
Once you step the engine up to 4000rpm, it wants 200cfm. To maintain 15psi of boost, you'll have to flow 400cfm into the intake manifold- and here is where the small turbo starts to choke. It's now operating outside its efficiency range, and it can't supply 400cfm of air to the engine. It can try- but it'll be spinning so fast that it does more work heating the air charge than compressing it. You start running into supersonic blade tip speeds, cavitation, etc- then a turbo that starts caramelizing its oil supply and starts to die. The larger turbo has no problem- it's still well within its efficiency range. It can flow 400cfm with no problems.
Since it can go to 600cfm at 15psi, it can maintain boost on that engine all the way to 6000rpm. It's supplying the 300cfm to satisfy the engine's atmospheric pressure needs, then another 300cfm to increase intake manifold pressure to 15psi (well 14.7 really).
Understand how it works? I could draw you some diagrams, but I don't really feel like it right now... the downside to using the bigger turbo is that it takes longer to 'spool up' and start producing positive intake manifold pressure against your engine. Your power curve will start later, but you'll be able to flow more air at those higher revs, and ultimately make more power. Go with a smaller turbo and you'll have your power sooner, but you could be choking your engine off towards redline.
This is my somewhat shorter version of that
CFM's is what makes HP not PSI. All the PSI does is move the air. You need the move the air efficiently though. You want to run the turbo at about 70%-80% of its potential. The intake system will only handle so much flow. Say the flow is maxed out at 12 psi and you are running 15-16 psi. That will create a lot of heat. The boost pressure may indicate 15 or 16 psi but there are no more air molecules in the intake charge than a cooler 12 psi intake charge. After a certain point, increased boost gives decreased intake charge density plus more heat and detonation plus increased ignition retard. Increasing the boost begins to give rapidly diminishing returns until a point of negative return is reached.
So if you increase the flow of your intake and you were already running the turbo at 70%-80% of it's potential at 15 psi before, you may be running it at 90% at 15 psi now. That's going to create heat and inefficient flow. You need a bigger turbo to get back down to that 70%-80% range.
Basically, these are the reasons to use a larger turbo.
1. More lag (benefitial sometimes)
2. Cooler intake charge, not overspinning the turbo at high rpm, larger turbos generally can support more psi than the smaller ones.
the larger turbo will make more power due to the lower intake temps, and it wont fall out of the compressor effeciency range when the revs increase.