Induction

Does the 52mm Throttle body cause any problems? I've heard of cars running lean?

Ive just changed mine to an Ally throttle body. I choose 48mm for a few reasons. The 52mm apparently can cause some engines to run lean. IMO if you put a 52mm one on, you would have to declare it as a mod for insurance purposes. The 52mm also causes a bit of Kangarooing at low speed in traffic. The BHP increase would be small. I would go for a 52mm as part of an upgrade package, ie head ported, better exhaust manifold etc etc. HTH

Has anybody put a 56mm throttle body on?

Can't really add too much concrete information to this, however I will add the following thoughts:-

As far as I know, the only benefit of a lot of power boost valves is to stop the fluctuations in pressure during rapid changes in demand (e.g. when you snap the throttle open). Therefore its my understanding that peak power is unaffected. I don't think anybody has reported problems with the standard regulator. You can tweak the standard regulator to give more flow, but more flow does not necessarilly mean more power if your engine does not require it - this mod is only performed when you've modified you engine to the point at which you cannot program the ECU to supply enough fuel under the standard pressure. Too high a pressure can make it difficult to control the idle fuel demand accurately.

If it is a 56mm throttle then it is very large. The standard ECU has an adjustment for air flow by measuring the speed of the air. This assumes a known area of throttle. By putting on a 56mm from a 48mm the std ECU will underestimate the amount of air, and therefore potentially run lean. Also, the rate at which the throttle lets air in as you press the pedal will also greatly increase. Whether you consider this good or not depends on the individual - it reduces the ability to control power at low throttle openings but increases the feeling of response. You would definitely get away with fitting the 56mm throttle body if you also fitted an aftermarket ECU that can be programmed to compensate.

If you are serious about power increases then put your money towards some cylinder head work - this will yield significant improvements in peak and (at a medium state of tune) mid range torque. For less money, a lot of people say good things about changing the exhaust headers/manifold for smoother transitioning aftermarket item - again these give reasonable improvements in midrange power as well as a potential small peak power improvement.