spider wrote:
As a random thought: I was wondering the other day actually why the HDi injectors are clamped vs screwed in compared to an IDI unit, I thought about pressures but then again the actual compression / internal pressure in that cylinder is not that far different, unless the massively higher fuel pressure has a factor on it. I keep thinking I've overlooked something basic and obvious (as usual!) but nothing sprang to mind.
An interesting conundrum Andy. Pressures will be a little higher in an HDi than in an IDI engine but then the IDI injectors have some meaty old threads on them and threads are good at holding very high pressure back - look at Citroen spheres, they hold back up to 170 Bar with ease. Overall the pressures won't be that much greater overall and arguably the pre-chamber an IDI injector is screwed into most likely experiences greater instantaneous pressures than in a DI engine. Maybe that's why the majority of DI engines use clamps as the injectors don't have such pressure action on them so an economy can be made.
Also, DI injectors are a lot slimmer than IDI throttled pintle injectors so there's less area exposed for the pressures to act on.
In the end it all comes down to economy and ease/speed of assembly I expect. After all, it's a lot easier to push in an injector and then hold it in with a clamp than it is to screw in an injector to the correct torque.
It's a bit like the radiator bayonet connectors PSA experimented with in the mid 90s. Great for assembly but a right PITA whe it came to removing them. It's the same with push in and clamp injectors; easy in and bloody difficult out...
Odd the 2.0 8V HDi does not seem to suffer excessively from this issue despite using a similar sort of injector fitting...
I know it's an auto, but I was rather hoping for at least mid 30's, considering I don't drive much in town and rarely do trips of less than 10 miles across country.
I knew there was a thread around here but couldn't immediately find it. Glad that thread and my figures agree 
