sweetttt replies guys!

I need to do more tech trails, I am not bad at them but not good either.

here are two things I'd need to improve:

1-There is one thing that I struggle to stay smooth and keep as much momentum as possible when I go through: 15-20 cm high roots/logs.

When I encounter this with other small roots, I loose all my speed. Not going fast enough to bunny hop it (and im not super good at bunny hoping). What it the right technique to go over such big roots at medium to low speed? I lift my front wheel but the rear wheel touches the root even if I try to lift it up. Should the rear wheel touch the top of the root/log? Should both wheels clear the obstacle completely?

Sounds like you need to learn how to manual, weight back, lift front wheel, then weight forward/back to roll the back over, it's a combination of weight transfer and momentum, easier said than done though.

2- Theres another thing that makes me loose a lot of speed: sharp 180ish turns. What the right way to enter these? Weight over the bars? Weight centered? Someone once told me to brake with the rear brake only when going through such turn to keep traction...

What kind of turns, are they flat or raised. Sort your speed before you enter the turn if you have to brake use the rear only, enter the turn high (wide)and come out tight, although this depends on the turn to a degree, Get your outside foot and press it down on the pedal as you make the turn, drop your outside shoulder and keep your head up and look where you want to go out of the turn.

What I like to do when I am on a nice wide quiet flat fire road is practice pressing down on the outside pedal and shifting my weight from one side to the other on the bike whilst making slow turns from one side of the track to the other. You are trying to carve a large 'S' along the track "slowly". It talks a while to get used too but if you trust your tyres you will be amazed how much grip you can get out of them if you load them up in this way, but you have to get used to really pressing down on the pedal as you turn and shift your weight and lean the bike otherwise the tyres wont hook up and you'll slide out. If you stop after a while, you should be able to see the line you have been carving along the track as you make the turns.


I ride a 26 HT BTW

5-any racing tips would be great too.
One pattern I have noticed... road racers new to MTB racing tend to fall behind on descents and catch up on the flats and climbs. I've nipped guys who would have crushed me on the road. Your technical skills will develop with experience, but you can compensate in the mean time by pushing even harder, especially on the climbs. Basically, use your fitness to bury the MTB'ers.

Also, a big +1 on afalts comment "Going for a hammerfest on the trails with [fast riders] can be some of the best in-season training, both technically and fitness wise."

One big question I ask myself is if training on the MTB on technical stuff will be as effective at rising my FTP then training on the road with steady power efforts.

No, technical mtb-riding will probably not be as effective at raising your FTP as steady-power road intervals. But doing steady-power road intervals will probably not be as effective at raising your trail-speed as technical mtb-riding So you should really just ask yourself what your goal is, getting a high FTP or getting faster on your mtb?

If you want to become faster/better at riding your mtb - just ride your mtb. XCO racing is full of short anaerobic efforts, and in my opinion you should therefore focus on repeated sprint ability and VO2max instead of FTP.

FTP training will not affect your VO2max and anaerobic capacity, but VO2max + sprint training will raise your FTP as well as your "high-end" power..

Use road bike for recovery- also do some interval training on road bike. Especially flat tempo. Many mtb racers are actually bad on the flats. Long steady climbs can be good on road bike too. I feel like I need to stay focused more and stay on the pedals more on long road climbs.
On the mtb work at what you are bad at. If it is technical skills train on single track.
If you need work on technical climbing, do that too.
There are enough days in the week to mix it up.