Just wanted to ask the group who ever is running a larger turbo such as the S42 or 43mm's....

I have been playing around with the wastegate preload setting over the last month trying to dial in the cars full potential on RPM Stage 3 and a JMTC S42. At first it seemed like it was overboosting so I backed it off until I was registering no more than 22.5 psi on my Torque Pro app (bare in mind I can only see up to 22.5psi due to the limit of the stock map sensor)

At that point the car felt more driveable and better at part throttle boost as it wasn't so eager to get up and go without being at WOT. BUT as the weather warmed up I noticed my max boost was hitting around 21.8 psi and only brief spikes of 22.3 psi here and there.

So a couple of days ago I decided to check all of my Charge hose clamps and tightened them down while also adding another 1 full turn of preload on the wastegate. Now the car feels pretty good and strong and I'm able to hold "22.5" psi almost all the way to redline. It drops to 21.9 just before my auto trans shifts.

NOW! the one thing I never took into consideration while trying to make sure I was getting the full 23psi of Stage 3 Map C was WHEN full boost was arriving. That is no my real full question....at what RPM should a S42 hit FULL boost??? On my drive into work this am I noted I am hitting Full boost right around 4000-4200RPM. The stock Turbo when I was Manic Stage 2 would spike 21PSI in as little as 3000rpm. I know the S42 was designed to spool "just as fast" as a stock turbo...So should I be dialing it in now to hit Target Boost earlier?!

 

You need to look at more than just rpm and boost. If the EBC is fighting you then that can create a whole host of weird behavior. Also, the rpm of peak boost is not a measure of turbo lag - the time in seconds it takes to get there is. BMW has some published literature on the N20 where they held rpm at peak torque rpm and went from 0-100% boost and measured that time. I forget the actual number, but it was like 1.5s. This also means lower gears have less time to reach peak boost, so you may not see peak boost at lower rpm until higher gears where it spends more time at that lower rpm range

 

Thanks for the input. I know when it was definitely too tight the car would misfire really quick sometimes during a WOT pull. I might just go another 1mm up and see how it reacts.

 

Have you tried adjusting the EBC parameters though (PID, pre-control, boost target, etc)? Tweaking the spring may help, but that's a case of two wrongs making a right. If the R56 is set up like some other production turbo cars, then the EBC is using boost to control torque in conjunction with the throttle. The pedal position just gives the ECU a torque request, and then it tries to meet this request by adjusting the throttle, boost, timing, cam phase, etc. A major change to the turbo without calibrating the EBC parameters and torque management will give you driveability issues compared to stock.