I've just bought a motor with a 4.0 V8. Theoretically, if I wanted to turbo it, would I be better going for something like a pair of TD05's (good for 700bhp?) or the big single route like big power Skylines and Supras? (Ignore minor details like fuelling, packaging, intercooling, ecu etc). I've just always find it weird that most twin turbo cars get converted to single when hunting for big numbers.

 

I guess it depends on what you want to get out of the engine.

If all you want is max power, then a honking great turbo would be the way to go, but obviously this would only come into full effect at high revs - at part throttle it would be pretty useless.

Two identical turbos (ie; one for each bank on a V8) would give more flexibility - there would be less variation in part-throttle and max throttle gas flow through each turbo. (I'm not sure if there could be issues with balancing the boost in each bank with this arrangement?)

I think the twin turbo arrangements on Supras and Skylines are staged - ie; a small turbo works at low rpm, the second, larger turbo at higher rpm. This allows each turbo to work at reasonable efficiency and gives the engine a better spread of power over the rpm range. As above, if all you want is max power, then the smaller turbo is effectively redundant!

PS, I'm not an expert on the subject, so you might want to wait until someone posts who is!

 

You need a book called 'Forced Induction Performance Tuning' by A. Graham Bell. It contains absolutely everything you will need to know and in a very accessible well-written manner. I seriously recommend it.