Why are different size turbochargers used?
The size of the turbo dictates the response and maximum boost capacity. A small turbo gives quick response, and a big turbo has a high maximum boost capacity. Any turbocharger choice will be a compromise of these two considerations. As an indication, the T025 turbo used on the latest generation Escort Cosworth can produce 1.4 bar boost pressure from 2000 RPM, but by 5500 RPM, this is reducing acutely. The T04 turbo used on the RS 500 does not produce any significant boost pressure below 4500 RPM, but can still produce over 2.0 bar of pressure at 8000 RPM. (Both examples are with a 2 litre engine.
