Right... To start.. as far as I know, only one guy here has had his Murena converted to use the peug engine.
That would be Lennart, and he didn't do the work himself, but paid a garage to do his "dirty work", so I'm not sure he will be a reliable source of more tedious technical information.
But now..
Before I bought my Murena, I had EXACTLY the same speculations as you have now.
I also thought of other engine options , but came to the conclusion that the xu series is the most suitable engines considering cost, effort and performance.. IF an engine swap is whats wanted.
In the end , I decided to buy a 2.2 and put a turbo on that engine instead.(I just havent gotten around to it yet
)
If you decide that you definitely want to convert to an xu engine, the 1.6 is the murena to go for.
The 1.6 shares a couple of the engine mounts with the xu, where the 2.2 is completely different.
Apart from that the 1.6 SHOULD prove the cheaper to buy, and the difference form the 2.2 is so limited that is (in my mind) doesn't make any real significance, as apart from the slightly wider tracking of the 2.2, you'd have to improve it anyway. (brakes, suspension etc)
The swap itself will require the use of the BE3 gearbox that comes with the xu engine.Fortunately This gearbox is superior to the Citroen bx one used by matra.
I don't know if the gear linkage can be used without modification, but the propeller shafts needs to be cut to measure and then welded up again and balanced.
Right hand engine mount needs to be custom fabricated to fit.
You will need the wiring harness form the xu , the efi fuel pump and some way to feed it.
Exhaust needs modification as well... especially the down pipe.
And lots of other "small" things I can't think of now.
Now... the xu turbo from the 405 was NEVER renown for durability .. and add to that .. its an extremely rare and sought after engine..... like the 1.9 mi16 it will be very hard to find.. and if you do, it will certainly need a complete rebuild... witch is much the same as it will need extensive and expensive modifications to get anywhere near 350 hp for more then a short time without the bottom end going south.
And seriously..... 350hp in a murena?.. hope you have your life insurance paid! because it WILL kill you mate!.. no doubt about it!!
ps: What's with this hp craze we see today!?
When the murena hit the street in the early 80'ies the 911 turbo had about 250hp.. and that was PLENTY to get you killed twice over!!..
The calibra turbo 4x4.. had 204hp.. and it went like a stabbed rat!!!..
Now anything with less then 300+ hp is regarded as weak.. I just dont get it..