As a manifold builder in australia I have done a fair bit of work with the RB26, as also nissan is far more popular than toyota over hear. We have had great success with the 1.01 T4 flange rear housing, I've personally never gone under 1.01, although there is a .91 available, while some people will tell you you can't make power through small housings, we have made 520rwkw on a dyno dynamics dyno (800whp dynojet) through a .91 rear housing on a single cam RB30 motor.
The compromise is, the bigger you go, the more lag you incur. Often it may not show in outright spool rpm, so you might lose 100-150rpm between housings at which RPM they make peak boost, however transient response I have found feels substantially different than the peak rpm would indicate. I would be loath to go anuything above 1.15 on a street driven car, Geoff may be able to chime in here, as he has a GT4202 on his own car with a 1.15 rear housing from memory, I think from his dyno graph it made 30psi around 6000-6500rpm???
The 1.01 to me is the perfect compromise, a mix of big enough for power and small enough for spool. Also keep in mind that a 1.01 in the bigger frame turbo is much larger than a comparable T4 housing, so a 1.01 GT42 housing would be maybe equivelent to a 1.32 T4 rear housing, which, as you can see is quite big. Or, comparing to the GT40 you currently have, would be similar to the 1.15 rear housing on the GT40.
With a 1.01 rear housing GT4202 on a stock internal 2JZ we are making 27psi at 4900rpm, I'd expect 30psi on a RB26 at around 5500-5900rpm.
6BOOST
The compromise is, the bigger you go, the more lag you incur. Often it may not show in outright spool rpm, so you might lose 100-150rpm between housings at which RPM they make peak boost, however transient response I have found feels substantially different than the peak rpm would indicate. I would be loath to go anuything above 1.15 on a street driven car, Geoff may be able to chime in here, as he has a GT4202 on his own car with a 1.15 rear housing from memory, I think from his dyno graph it made 30psi around 6000-6500rpm???
The 1.01 to me is the perfect compromise, a mix of big enough for power and small enough for spool. Also keep in mind that a 1.01 in the bigger frame turbo is much larger than a comparable T4 housing, so a 1.01 GT42 housing would be maybe equivelent to a 1.32 T4 rear housing, which, as you can see is quite big. Or, comparing to the GT40 you currently have, would be similar to the 1.15 rear housing on the GT40.
With a 1.01 rear housing GT4202 on a stock internal 2JZ we are making 27psi at 4900rpm, I'd expect 30psi on a RB26 at around 5500-5900rpm.
6BOOST
