Just a a little theory crafting here; I'm not certain if this has been done as I couldn't seem to find any info on it or find out whether or not it would work.

So since I'm going to be boosting my stock b20b and everyone says to keep it under 300whp (which btw, don't know why people don't stress the torque more than whp, but w/e)

So I was wondering if it is possible to have a slightly larger turbo than what I need for 300whp, and let's say it boosts to X psi by around 3k or so (hypothetically, doesn't have to be realistic)...
Then let's say X psi would net me like 450whp (remember, hypothetical here) at around 6k rpm or so, and that would be unsafe to run obviously so could I taper off the PSI as the rpms increase using an electronic boost controller?
Why?
In order get more torque at lower rpms then adjust accordingly for rising rpm and hp. I find this may be possible to do on say, one of the t3t4s. Thoughts? Shodan?

 

It would take a lot of fiddling with the solenoid duty cycle for the boost control solenoid... honestly probably more than it's worth.

Size it right, build it right, keep it simple

 

Boost taper is mainly from lack of cylinder head efficiency, even with good boost control. It would just occur later in the powerband. Make the head more efficient, follow the philosophy that was just posted above and keep the turbocharger small and simple. Going too large of a turbo just makes the powerband peaky and driveability garbage.

 

Yes in theory you could engineer boost taper if you used a small wg spring so most of your boost curve was increased by use of the ebc thus giving you the ability to dial back the curve all the way down to the wg spring whenever you wanted - assuming you had enough wg bypass.

However you're over thinking this. Peak cylinder pressures are going to be where the torque peak is and not at redline. You can't "cheat" the safe limits by fattening up the mid range and softening the redline boost. Let your tuner worry about reducing ignition timing if they feel its unsafe.

 

If you want to manipulate boost like that aem does a good job of it

Boost by

Gear
Speed
Tps
One more I'm forgetting

 

I dont get it. You want a larger turbo so you can use none of its advantages and all of its weaknesses?

Aka slower spoolup, and trying to choke it up top where it will want to make more power. With my GT2560R on a stock LS I made 300 ft-lbs by 4000 rpm

 

Of course not, my thoughts were more along the line of
A. I was originally planning to use a t3 super60/maybe 16g (somewhere along those lines) for quick spool and good power but then I thought...
B. Since T3/T4s seem to spool not much later than the two above^ (with the correct a/r and trim of course) I theorized using this method so I could get a higher torque in the midrange, then taper it off so I wouldn't exceed the prescribed 300 whp limit of b20b sleeves.

After reading the responses however it seems that option A is the better of the two.

 

Well, the EVO has a great stock flowing head but they have the boost tapering down because the turbo is too small. The stock Wrx sti also has boost tapering down.

 

An Evo is decent for a flowing head. But for the WRX STI, those have 2 things against it. A lower flowing head, and the fact that most users keep UEL headers that hurt the exhaust energy stream in higher rpm settings.

I've dealt with more Subarus than I care to even mention.. I actually don't like the damn things.

 

Its a torque limit. I know b18 blocks are safe to around 300wtq, not sure b20 sleeves. 300wtq at 3000rpm is just as damaging , if not more, as 300wtq at 7000rpm

 

you are seriously over-thinking and over-complicating this...

it's not like it's a rock solid limit where 301hp equals blowing the motor into pieces. with stock rods and pistons you won't get near the torque/cylinder pressure limit of the stock sleeves, a piston or rod will let go first.

besides the longevity of a motor is all in the tune and how you drive it.

 

Well I care to differ with the pistons or rods giving first, there are plenty of b20's i have seen with cracked sleeves on stock pistons and rods. That being said, I agree, anything around 300whp is probably pushing it.

As always, thank you Shodan, wantboost, Muckman, Lightningteg, maxwellmurder, and turbo hatch dude for your input : D
Will be going with option A btw, just letting you know you steered me the right direction

 

What is option A?

I can post a log of my high comp b20v with an 18g

Spools pretty quick. Nice tq down low

 

Option A i think was using a properly sized turbo to meet his power goal, rather than a larger turbo to run higher boost down low to have a high mid range torque, then taper boost to keep the power down

 

^^ correcto.