Originally posted by WydRyd
Porschefile, if I punch the throttle, I can get full boost at ~3K... it spools very quick, just the way I like it. It may have to do with the 0.78 A/R divided inlet housing, not sure? I'm sure the bigger A/R housings would result in more top end HP, but I wanted it purely for street as my car is my daily driver, so I wanted something snappy on the road and that's what the GT35R delivered. I'm pleased. Once I sort out my twin plugging, it'd be even more responsive
I've heard reports of the GT35R spooling up as low as 2700rpm on a finely tuned motor with aftermarket engine management, pressure sensing, twin plugs etc...
Twin scroll housings do make turbos spool more quickly. Ultimately it's really simplistic in that they divide the total surface area of the inlet which has the effect of increasing airflow velocity and increased velocity = quicker spool. Depending on the exact turbo setup, you can couple this with pulse tuning to improve spool as well. All that means is you'd combine the proper exhaust runners to form two separate runners that stay completely separate all the way to the exhaust housing. For example, on a i4 you'd mate #1 and #3 together and you'd also group #2 and #4 together, though you'd keep each pair separate from the other pair. I hope that makes sense. I have some suspicions that simply running a divided turbo flange alone should provide 80-90% or more of the benefits of increased spool on most setups. Maybe on a motor with much shorter runners, like the typical i4 turbo setup, you might see benefits from pulse tuning a twin scroll setup (due to possible elimination of exhaust flow turbulence) though motors like 930's have decently long runners so I'm wondering if the divided flange alone is just "good enough" if you catch my drift. I'm sure Frank has much more hands on experience in this arena, so maybe he might be able to say for sure.
Personally, I'd say technically .78 divided T3 housing is a bit small considering your displacement, and a T4 housing should have some nice improvements in power however it sounds like it works perfect for your needs, and in the end that's all that really matters. Personally, I like a higher boost threshold of say anywhere around 3.5-4.5k for full boost. I don't mind the loss of some off-boost performance, and I prefer a powerband that flows plenty up top and holds torque/hp at least above 6-6.5k rpm before dropping off. I'll be going with Gt2 Evo cams and stiffer springs to support ~7.5-8k rpm so I don't mind a bit more lag.
The increased rpm is part of the reason I'm considering a larger turbo like the Gt4088r or possibly even the new Gt4094r (kind of a 40r/42r hybrid, about the size of a T4 T66). Either one of those should make full boost in the 3.8-4.5k range and no later, though they would both allow me to reach 600whp with quite a bit less boost than a 35r.