Ah these... I thought I had answered earlier
1. Why m3 e36 3.0 with 286hp use long runners and m3 3.0 GT's with 290hp and m3 3.2 with 321hp use sort runners? some 3.0litre people upgrade the runners with EVO ones.
3.2 engine revs little bit higher so to tune intake for it, runners must be shorter. Also, 3.2 engine has double vanos (I think) which should give more power in low and middle range so intake system can be more optimized to give more power on high revs.
2. e30 m3's have 8.5 litre intake plenum for 2.0-2.5 litre engines. We need big intake plenums?
Intake plenum size has some effect on power curve but I have not seen too many ways to calculate it. Personally I would try to copy race car designs which usually are as large as possible permitted by the available space.
3. Why metric mechanic in camber pulse intake make tha tube so sort ?it wasnt better if the make them longer ? or make more distance from the intake valve ?
I think MM pulse intake is ordinary E30 itnake with one pulse chamber in each runner. It seems to work in a way that on certain rpm's pressure waves going away from intake valve up in the intake runner goes to chamber and is reflected by the dead end.
4. dbillas desing use short runners and small plenum and far away the butterfly from the valve . what about this?
Well I think they work ok but I suspect they are not 100% as optimized as for example BMW Motorsport intake designs. Dbilas uses same components in different models from different car manufacturers so there is going to be some compromises.
5. every m3 have the Maf in the center of the plenum (dbillas too) CSL;s and every other plenum i have see it have the maf boot in the front. which is better?
I think again is best to look at race cars, they have tried most things out to see what works. And usually the intake plenum opens towards front of the car to give shorter path to air and smaller angle for air to turn while entering plenum.
I would personally go for CSL design
6. some engines uses metal runners and some others use plastic ones . which is better?
I think plastic might be better. It conducts less heat so air entering engine is cooler and gives more power (thats why S50 engine has ceramic insulators between cylinder head and ITB's I guess). I think plastic is also lighter. But metal runners might be easier to make iuf you have tools.
7. how long it has to be the runner in to the plenum ? does it matter ? dbillas does not put the runner in the plenum why?
Usually race car runners end to the plenum wall, on road cars runners enter plenum maybe 50 - 100 mm. I would again go with the race car design
