Turbo sizing...T4, 13BT SP, 9.4 rotors.

RotaryProphet · 11-19-2008, 11:32 AM

Have you given thought to an individual throttle body setup (ie, what I was running on my 12a) coupled with a water-air intercooler? For 9 minutes balls out, you're going to have a lot of heat to move, so being able to start with ice water, or even a heat exchanger in the back with dry ice in it might just get you there. (particularly when you're at altitude and the heat output from the turbo is going -up- while cooling efficiency from the air-air intercooler is going -down-)

The intake'll let you make use of more power from less boost as well as keeping the intake path nice and short so that lag is virtually eliminated. You still have to size your turbo for the boost threshold you want, but I find that if you port the exhaust to open ten or so degrees earlier, you'll spool it much faster. (ie, the turbo 12a I had would make positive pressure at 3000rpm and was boosted at about 4500; the same exact setup on the bridgeport made positive pressure as soon as I floored it and boosted at 3000)

Also, have you considered any kind of swanky anti-lag setup? For a real rally car setup, you'll need a ceramic exhaust wheel in the turbo to handle the EGTs, but for 9 minutes all out on a rotary, you probably want that anyway, no?

I would think that a T3/T4 hybrid is what you want for the response, but are you worried about the top end? It'll really suffer if you force the engine to exhale through that tiny exhaust wheel full time. A gigantic wastegate set to ~9-10psi would help alleviate that, though. More boost than that and you'll have backpressure issues no matter what you do.

11-19-2008, 11:32 AM	#8
RotaryProphet Rotary Fanatic Join Date: Sep 2008 Posts: 147 Rep Power: 18	Have you given thought to an individual throttle body setup (ie, what I was running on my 12a) coupled with a water-air intercooler? For 9 minutes balls out, you're going to have a lot of heat to move, so being able to start with ice water, or even a heat exchanger in the back with dry ice in it might just get you there. (particularly when you're at altitude and the heat output from the turbo is going -up- while cooling efficiency from the air-air intercooler is going -down-) The intake'll let you make use of more power from less boost as well as keeping the intake path nice and short so that lag is virtually eliminated. You still have to size your turbo for the boost threshold you want, but I find that if you port the exhaust to open ten or so degrees earlier, you'll spool it much faster. (ie, the turbo 12a I had would make positive pressure at 3000rpm and was boosted at about 4500; the same exact setup on the bridgeport made positive pressure as soon as I floored it and boosted at 3000) Also, have you considered any kind of swanky anti-lag setup? For a real rally car setup, you'll need a ceramic exhaust wheel in the turbo to handle the EGTs, but for 9 minutes all out on a rotary, you probably want that anyway, no? I would think that a T3/T4 hybrid is what you want for the response, but are you worried about the top end? It'll really suffer if you force the engine to exhale through that tiny exhaust wheel full time. A gigantic wastegate set to ~9-10psi would help alleviate that, though. More boost than that and you'll have backpressure issues no matter what you do.