First, have twins vs. a single does not guarentee better spool or driveability. There are a lot of different turbos and since the efficiencies are different, so is the spool. Using Supra as an example, a ball-bearing T61 with an O-trim turbine wheel will spool as fast as stock twins(in true twin mode), but make 600 rwhp on pump gas where as the stock twins can do a maximum of 485 rwhp. It will also spool a lot faster than HKS big twins, but not make as much peak power on race gas. This whole topic is very application specific. There are of course many V-engines with single turbos. Grand Nationals, Regal T-types, Z31(300ZX) turbos and even Nissan Bluebirds with VQ30DET's sold in Japan today. The spool rate is going to be based on the efficiency of the turbine wheels and the weight/friction of the cartridge.

You also have to define spool. You could have 2 turbos on a engine that can make 500 hp or a bigger single. If this is a 3.0L, we'll say it needs 18 psi of boost to reach that. If the twins are run sequential where all the exahsut flow bleow 3500 rpms runs to 1 turbo then it may only be able to make 10 psi of boost on the single turbo adn does it at 2500 rpms. Then at 3500 it switches over to the second turbo and hits full boost at 4500 rpms. By comparison, the big single may not spool until 3000 rpms, but have 18 psi at 4000 rpms, 500 rpms lower than the twin setup. The bottom line is that there isn't a single rule for this.

04' G35 Coupe(on order)
6-sp Diamond Graphite/Willow w/Premium

 

Typeing corrections for the above post(the system won't let me edit it):

First, having twins vs. a single does not guarentee better spool or driveability. There are a lot of different turbos and since the efficiencies are different, so is the spool. Using Supra as an example, a ball-bearing T61 with an O-trim turbine wheel will spool as fast as stock twins(in true twin mode), but make 600 rwhp on race gas where as the stock twins can do a maximum of 485 rwhp on race gas. It will also spool a lot faster than HKS big twins, but not make as much peak power on race gas. On pump gas, stock twins are limited to 440 rwhp while a good single turbo can put out 525 rwhp on pump gas.

This whole topic is very application specific. There are of course many V-engines with single turbos. Grand Nationals, Regal T-types, Z31(300ZX) turbos and even Nissan Bluebirds with VQ30DET's sold in Japan today. The spool rate is going to be based on the efficiency of the turbine wheels and the weight/friction of the cartridge. Twin turbos will always cost more than a single turbo setup for the same type of turbos, i.e: ball bearing, GT series, etc. The main reason why there are both is packaging. Good luck trying to package a single turbo in a Z32. The stock turbos are very tightly packed in there and all the aftermarket kits have to work on the same constraint. Most Supra and RX7 owners when making big upgrades switch away from the factory twin turbo setup and go to a big single. These are quite efficient and simply a lot more reasonable in cost than twin kits.

You also have to define what you consider spool to be defined as. You could have 2 turbos on a engine that can make 500 hp or a bigger single that makes the same power. If this is a 3.0L, we'll say it needs 18 psi of boost to reach that. If the twins are run sequential where all the exhaust flow below 3500 rpms runs to 1 turbo then it may only be able to make 10 psi of boost on the single turbo and does it at 2500 rpms. Then at 3500 it switches over to the second turbo and hits full boost at 4500 rpms. This would be like have a single TS04 turbo on a Supra versus stock twins. Even in sequential turbo mode, the TS04 spools as fast on the low end as the twins and at higher rpsm easily beats the twins to boost levels of 18 psi of above. Also by comparison, the bigger single may not spool until 3000 rpms; but have 18 psi at 4000 rpms, 500 rpms lower than the twin setup and simple make boost/power levels well above the stock twins. The bottom line is that there isn't a single rule for this.

Looking at a G35 and how the exhaust manifolds are, obviously twin turbos would be the better choice. You ideally want the turbo as close to the exhaust port as possibly. For a single turbo, you want the tubes that feed the turbo to be as equal in length as possible. The only mounting position for a large single will be in front of the engine compartment, far away from the exhaust manifolds. This tubing alone would add a lot of lag. There is on the other hand room to mount a smaller turbo on each side close to the exhaust port...hence the twin turbo kits in development.

04' G35 Coupe(on order)
6-sp Diamond Graphite/Willow w/Premium<P ID="edit"><FONT class="small"><EM>Edited by Loren04Coupe on 06/11/03 10:09 PM.</EM></FONT></P>