David_Long

I think the reason Caterham, and their agents, had trouble getting the diff quiet was two fold. The worst examples relate to 'pattern' parts produced under license (and stamped with the Ford logo) that simply were not of the same design quality as the OE part. Secondly, the genuine Ford parts where not fitted as intended by Ford. The Sierra diff was developed after quite a lot of R&D and this technology was closely guarded and limited to a small number of production lines. The contact patch pattern we see widely shared on YouTube videos is an engineering interpretation of what is correct - not necessarily wrong in an engineering perspective, but not what was used by Ford. If you dig into the history and available archives, you see their production process used an offset pattern. This pattern dispersed the oil from between the teeth in way that reduced the whine. But the 'non factory' techniques, although arguably correct, can override these subtle design features. The relevance to this thread is that adjusting the backlash to the extreme limits can reduce noise - the trick is balancing noise reduction against reliability and service life.

Here's a video showing how the Ford manual recommends setting it up. The important thing is that the bearings are preloaded correctly, otherwise you are wasting your time at the case flexes under load. This was one of the issues with the Caterham supplied diffs around 2008 - they set the backlash without pre-load on the bearings.

For what it's worth, my thoughts are the pictures indicate a bearing failure rather than a driveshaft problem. It could be through ingress of water as the corrosion on the splines and threads is not what you'd expect on a Caterham of this age. The staining could be overheating, or it could be rust, or even a bit of both - it needs closer examination to be sure. I would suggest it has had a history of being run under torqued at some stage that this has stressed/worn the bearings an allowed seepage of moisture (water from rain or washing) to ingress the splines around the driveshaft and bearing. Edit to add there is some evidence in the picture to suggest polishing of the bearing which may indicate movement (under torqued).

It's interesting what was said about driveshafts. We had some issue with racing Minis where the bearings kept failing. It turned out to be a badly machined driveshaft that was not seating properly/squarely and seemed to be stressing the bearing. If the problem persist with new bearings, I'd look at the driveshafts.

The MAP sensors do fail but seldom cause serious problems as they are simply fine tuning the map settings. The problem is that they tend to give erratic readings to the ECU when faulty. Unplugging it will set the default value that's a 'constant' value and may give smoother results. Either disconnect it (and accept that some conditions may be less than optimum), or get a new one.

IIRC the minimum MBE ECU tacho pulse generated is 1200 rpm (1250 rpm?), so it is not possible to see RPM below that unless you use an external tachometer on the pulley, or use Easimap.

The reason the Caterham Duratec is more prone to vaporisation than the Ford equivalent is that it is a longitudinal installation and the fuel rail and pipes runs hotter as a result. The fuel rail is also a single feed, so the only way for any vapour to escape is via the injectors. But only some cars do it and the reason for that is unclear. Re-mapping does seem to remove it but I suspect thats because the Caterham map is sensitive to the condition (posibly due to emissions requiremnts on the generic map, rather that best running that a custom map gives).

Sounds like classic fuel vaporisation, which some R400s suffer badly from. It's difficult to cure without fitting a fuel pipe return system, but a little time spent heat shielding fuel pipes may help reduce it. Premium brand fuel (shell, BP etc) are also less problematic.

In terms of oil and noise in differential, it is an interesting subject that goes back to the earliest days of automotive engineering. Much of the whining noise generated is caused by the oil being squeezed from between the teeth in pulses. It resonates at particular frequencies dependent on the oil, design of the casing, and other factors such as oil quantity. The noise was engineered out (to a degree) by introducing helical gears that had continuous mess. Ford took it a stage further by adjusting the tooth profile, housing shape, and using calibrated tools to 'adjust' the mesh pattern to further help reduce the intensity of the oil ejected and noise generated. So it is perhaps not a surprise that any re-working of a diff can upset 75 years of refinement. But a noisy diff is not necessarily an unhappy one. Choosing an oil to reduce the noise is personal choice, but I suspect older technology oils are quieter simply because they are less inclined to adhere to the surfaces (they get thrown off the crown wheel) - additives are likely to have a similar effect. Another trick used is to add additives that help to aerate the oil which provides dampening. It is all about what is important to you - the noise, or the oil performance.

As soon as the oil enters the engine it will be quickly get up to the engine/water temperature, and then much higher in the bearings and when it's squired onto the pistons - probably well above a 100c locally. If you see 60c in the tank then I'd say that's fine (and 56c is not far from that for winter driving). The sump looses quite a lot of the oil temperature while the oil is waiting to be pumped to the tank, and more is lost in the plumbing and tank itself.

FIA Homologated CAT's are essentially designed for racing and meet minimum standard the racing authorities will accept. They differ from road car CAT's in that the core is not as fine and they are less restrictive and generally more robust - I suspect they are less effective too. As far as I'm aware, all Caterham cars fitted with factory exhausts are using this 'racing' spec.

It actually the CAT that does that.

The final results of the BTB exhaust, mapped by Troy at Northampton Motorsport are below. BTB have made two other copies of this exhaust that I know about - both have had good results, but it would be wrong to quote any particular figure that can ce atributated to the exhaust as there are so many factors involved. The cost was not cheap - over £3k IIRC but it's BTCC/F1 quality, basically as good as they get. Contact Joe Ellis at BTB https://www.btbexhausts.co.uk/

Here's the original R500 graph with torque - with (blue), and without (red) the BTB exhaust. Also it's worth saying that all these runs were not mapping sessions but power checks, for competition reasons - hence wheel power and engine RPM on the graph is estimated from wheel speed. And yes, the BTB was a 4:2:1 and slightly larger bore. It was responsible for transforming the mid to low range of the R500 graph. What was a surprise to us was why the R400 was so good with the standard exhaust. Best guess was that the exhaust was just a little undersize for hotter cams of the R500. Although the 4:1 is seen to kick in above 6000 rpm, the whole curve seems to be pulled down by some exhaust issue. The BTB exhaust wasn't cheap and was designed by Simon Armstrong who did all the R500 heads. I think he knew what was required, but was probably restrained by Caterham's resources at that time. It has a racing Cat in the silencer box, but I've never put it through an MOT .

That question is a bit of a can of worms. I don't know if this is of any help but it's the evolution of an R400 engine to the R500 spec and then beyond. Although not a factory R500, it was based closely as we could to that engine (red on the graph). It's all wheel BHP, so you need to add the losses to them for flywheel BHP. It also just a representation as it is a compilation of several dyno runs on different days. WRT the R500, it was disappointingly poor at the low end with the R400 spec doing better. What became clear during the development was how bad the Caterham's exhaust was at the time.