In the spring of 2017 I noticed that my turbo was making a slightly unusual noise, but I thought nothing much of it (it went away). 

I have done five sprints this year. It was my first full year of sprinting, although I did the Curborough 8 in 2016. I thought that I did a better job as a driver, but I noticed that my times were slower. Also my speed over the finish line was about 64mph, last year it was 77mph! And come to think of it, I can't hear the waste gate 'tshh' anymore.

The 160 is still fairly swift on the road,, but I'm clearly down on power.  I think that I just might have completed a sprint season without a turbo...

I decided to investigate. I sprayed the bolts on the unit with Halfords 'shock and unlock'. I understand that the turbo bolts can break if you are not careful (high temperatures, rust etc). The next day I took the cover off successfully.

The inside of the turbo looks like this

To my untrained eye, I think that the rotation is not a free as it should be...

Update 30 September 2017

I have since found that the fault was a split pipe (one of the thin silicone pipes that feed into, and around, the turbo).

Once reassembled the car was back to normal; there was a significant increase in power, and the usual turbo noise could be heard.

The following might be useful, if anyone does have turbo problems in future.

• The part number is HT06 VZ57 18 76JB1 (made by Hitachi)
• A replacement turbo might take a bit of effort to find - so treat it kindly! However, I understand from other posts (Neil Allen) that a fairly high mileage can be expected before turbo problems.
• Turbotechnics will inspect a turbo for free and can refurbish turbos for £200-£400 within a few days. I never used them, but my local Suzuki garage recommended them (and so did The_Ash)
• The Suzuki Cappuccino owners club maybe a useful source of information. (Same engine and drive train as a 160). Again, thanks to Neil Allen.
• Power Torque supply/prepare 160 engines for Caterham. They maybe worth contacting in the event of problems.