Thank you for your advice…to take your points further..
So a MHD flash of a 35i will yield the same result as a 35is?
So you say the charge pipe and air inlet are more than adequate for a MHD level tune…what evidence / experience / support is that based on pls ?
Finally apart from a VSRF down pipe what other mods would you recommend?
uprated dv
air box to turbo pipes
uprated boost pressure control valve
I assume a FMIC is still a good idea..I’ve got a Wagner Evo 1 already from a previous project
Yes, it's the same engine and hardware. Overboost is just a marketing term.
BMW allowed a temporary uplift on boost pressure in the 35is to achieve higher peak engine output but didn't upgrade the intercooler so to avoid over stressing the small standard intercooler they limited the increased boost pressure to short bursts so after you've had your temporary power boost the engine will revert to 35i boost levels.
With a tune you just ignore the overboost logic and target as much boost as you want (and your fuel/mods can support) without it becoming unavailable after a few seconds.
As far as proof that chargepipe, diverter valves and dual cone (hot air) intakes are useful. I'd be asking the inverse question, what makes you think you need to change your chargepipe or that diverter valves are a problem? Stories of shattering chargepipes come from 335i users which have different pipework.
I've had my 35i for 9 years now. I've driven 80,000 miles in it, most of which are tuned. It's still on stock turbos but I'm running 20PSI peak boost tapering down to 16PSI at the top end. My stock chargepipe is still intact. My stock diverter valves seem fine as my WGDC is exactly where it should be for the boost.
Dual cone intakes are contentious on the 335i, I've seen no good data showing that they are beneficial but plenty to suggest that they provide inadequate filtering. I'm more concerned about getting clean cold air into the engine than worrying about 1 or 2 best-case scenario horsepower. On the Z4 it has been well documented that the air intake box flows better so I don't see any merit for changing that.
The problem with car forums in general, and why I like spoolstreet more than the other BMW forums, is that most of them are run by greed. You have a load of vendors selling tat that will jump in on any new user (just look at any E90post thread) and tell them that they need a billet oil filter cap and some huge ricer air filters. In general you want to avoid any tat from the likes of BMS, they are the kings of pointless engine bay bling.
If you want to make more power with your 35is then you just need MHD, some downpipes and a good intercooler. That will have you at a nice easy 400hp. If you want more then a custom tune might get you another 20hp. After that you'll need bigger turbos as the UK has no E85.