You should replace the cam seals at the same time... you'd be crazy to not replace them, then find you have to do practically all the same work again in a few months because they have started leaking.
There are a few good youtube videos on how to fit the cambelt.
What gap did you set?
So coil on plugin is it?
It sounds a bit like it could be mis-firing from what you have described. 4000 rpm is where the boost will be coming on very quickly, so peak torque... possible over boosting a bit and the spark is breaking down. Though I'm not sure how likely that is with coil on plugin.
ok so looks like with the single avcs heads, those are biggest cams you can get without head modifications. I have the same cams and turbo but with the non-avcs heads.
They are a good choice for the turbo, because the turbo is a bit on the big side for the motor. I am making 330kw with E30 and 27 psi boost... I seriously doubt it would
make 400 kw with these cams... they are aimed at throttle response and not high rpm. What size turbine housing do you have?
And it's not bigger ports you need for the higher lift cams... you just need some metal removing to allow for the larger lobes to rotate without hitting things. I would
get it done if you really want 400kw. It's not a lot of work in the grand scheme of things and you could do it yourself with just a dremel.
You should think about drivability before deciding on what cams... is it a track only car or something else?
You can go bigger to bigger cams before you need to modify the heads... but you'll need shimless buckets most likely.
The turbo choice is going to be more important than the cam choice.
Diesel and Turbo for a stock equivalent replacement. http://www.dieselandturbo.co.nz/
Upgrading is a whole can or worms... you'll need to do a whole lot lot more research and spend a whole lot more money.
It could be a gearbox issue, not the clutch. If it's a clutch issue it could be over-throwing rather than not disengaging. When at a standstill, try putting it in first gear with the clutch pedal only about 75% down... move the gear shifter slowly, and if you feel any crunching, press the clutch down a bit more until it goes into gear without crunching.