reducing my waste gate spring to .6 bar

[gorskined]

Its been a while 3 winters into this project. winter is just around the corner here in the North East time to put away the outside toys and start wrenching in the garage.
getting close to finishing up on my 3.0L 76 row turbo build in my 80 all metal no rust widebody targa . im looking to down size the spring to a .6 bar ( from what i understand i can always adjust up from there if i feel the need but probably never will, can anyone recommend a boost controller ) . can i simply swap out the spring to a .6 or do i need to do anything with the blow off / diverter valve also .. pretty much everything is new or re-machined
fresh build less than 10 miles on it. new mahle 3.0l low compression6.5:1 turbo p&c with machined heads making a whopping 6.8:1 , sc cams evergreen k-27 raptor turbo long neck intercooler twin 044 bosh fuel pumps, ss high flow exhaust, carrera tensioners a balanced fuel distributor# 2and #5+5%. 3 way adjustable wur still looking to iron out the wur settings running a little rich when warm and chasing a few oil leaks . . This will be my fun fair weather beater . built to be reliable not so concerned with horse power . new to turbos but quite versed in 911,s and 356's so im learning the turbo stuff as i go. thanks for your input any help is greatly appreciated. i would also be interested in purchasing a .6 spring if anyone has one for sale or know where i can get one
thanks

Regards Ned

[spuggy]

Originally Posted by gorskined

looking to down size the spring to a .6 bar ( from what i understand i can always adjust up from there if i feel the need but probably never will, can anyone recommend a boost controller )

Problem you're likely to encounter is that wastegate spring pressures are specified as the pressure at which they will be completely open.

Most wastegates aren't entirely gas-tight. So they will leak boost anyway, even when shut (through the guide/past the seat). But with a relatively light spring and a large valve diameter, the valve tends to crack off the seat, leaking even more boost, long before that "fully-open" rating. Some even "chatter", resulting in uneven boost readings (and possibly messing with the fueling).

Also, spring rating is only an approximation; some will open earlier. Or later. Your header design can affect this too.

Ordered my Tial with a 0.5 bar spring, figuring I'd use Motec boost control. Very underwhelmed with the result, and switched to a 0.8 bar spring. Huge difference in spool - and overall driveability, even when you didn't think you'd be making boost (surprise! - atmo blow-off valve is a real tell-tale).

The best result is very likely to be to use boost pressure to actively, in conjunction with the spring, hold the wastegate shut until desired set pressure is achieved. Probably much more noticeable with lower spring ratings.

JakobM explains exactly why in this thread https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/1034993-tial-46mm-external-gate-ebc.html

I was convinced, but have yet to fit the 4-port MAC valve I bought