Yea, I read a bunch but also there's a lot of threads that seem to end abruptly before the last piece of information. A few i noticed were regarding some turbos through APS that would fit and flowed something like 55 or 60, but nothing was ever said what they were. I've heard different things about cartridge sizes like -11 vs. something about a -12 that would fit?

 

the -12 is the biggest size that will fit.

 

If you upgrade the GT2871R's to a -12chra you really should stay at 346ci. The 44lb GT28's turbines pretty much max out the backpressure on a 427ci. since the turbine ar is maxed. If you go to a 50-55lb compressor the turbine will max out faster and you'll be shifting under 6000rpm as the power will nose dive. Now with a 346ci the PR will be better and you will extend the hp another 100 but will lose a ton of low end torque over the 427......never easy huh? All depends on what you want and your budget. Build a 427 for massive torque and use the GT28's....or save some money by building a forged 346 with a stock crank and spend that savings to upgrade the turbos to a -12 chra. Either way a meth kit is needed and a LPE cam is needed since they know how to size a cam for a turbine that is too small....part of the secret to making that kit work well is their GT series camshaft.

 

Damn man a LME 427 with those specs and a FLT 4l80e with a transbrake just seems way too nice of a setup to settle for small turbo's but again not familiar with the incon kit. Upgrade them to the largest possible to matter what it will cost, since you've spent this much already, or either ditch the kit and easiest route would be a F1 procharger on it. It would be great for the street and the most basic setup and not to mention not much wait time. Either way with that killer setup I'd like for you to have a mean ride, but the incon kit with upgraded turbo's to the max sounds like it might suffice for you. If not you could easily sell it in the future and upgrade if desired.

 

I am running the stage 2 turbos on a 370 iron, unported 6.0 heads, baby cam, 9" rear, and am quite happy with it. Hit the dyno yesterday and encountered some problems, but at 11.5psi on 91 octane it was somewhere around 625rwhp/670rwtq (dynojet). Would have pushed it further, but once we got to around 10psi something funny started happening, heard a weird noise and boost dropped 2psi for an instant and then back up, very apparent on the dyno graph. After going through all the possibilities the only thing we could come up with is that a cold-side hose is collapsing.

This is of course on a 370, I'm leaning in the direction of the others, backpressure on a 408 is going to become a problem, I think it's impacting me to a certain extent as well.