Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 8 of 8 Posts

·
Registered
Joined
·
26 Posts
Discussion Starter · #1 ·
Gents (and lady(s))

I've got a little boost instability at part-throttle on my NG900 with stage 1 ECU.

WOT and @20PSI is fine and dandy.

Contacted the manufacturer and they reckon 0.75 bar (10.8 PSI) base boost (eek!).

I've got bog stock 6PSI.

I know that if the actuator is adjusted much beyond 8PSI, then it cannot then open the gate enough at max RPM.


What's anybody else running? Do I need a stronger actuator and do I really need 10.8 PSI of base boost. Seems a bit dangeroos to me.
 

·
Registered
Joined
·
14,305 Posts
I can't believe that's right. Stage 3 or 4 tunes normally only require a max of around 8 psi base boost.

11 psi will be outside the range that a stock actuator can reliably achieve.

Also, a figure of 20 psi (nearly 1.4 bar) is too high for any stage 1 I've heard of. Around 1.2-1.3 bar would be the max I would expect.
 

·
Registered
Joined
·
11,343 Posts
Originally posted by hunt.dogshome:
[qb]Contacted the manufacturer and they reckon 0.75 bar (10.8 PSI) base boost (eek!). [/qb][/b]
They do


Standard base boost is 0.45bar.

I wonder if this is the same supplier that tells people they need to upgrade their actuators on stage ones

With a standard wastegate actuator you should set it at the Saab specification base boost. Even with an uprated actuator I would not expect anything as high as 0.75bar.
 

·
Registered
Joined
·
26 Posts
Discussion Starter · #4 ·
That's what I was thinking. Thanks people.

I've replied to their tech help in case something got lost in the Swedish translation. Don't think so though.

Yes it really is getting to 20PSI. Mind you it's -1C outside.

Big Saab Roller.
 

·
Registered
Joined
·
494 Posts
on the topic of base boost and actuator settings, would anyone know offhand approximately how much base boost is raised by for each turn or half turn of the actuator rod?

tbh, i never checked my base boost before or after installing my stage1. my supplier reccommended an adjustment of 3-4 complete turns on the actuator rod.

edit: duh! open the shop manual... "One complete turn of the end piece roughly equates to a 0.04 bar (0.6 psi) pressure change. turbocharger basic boost pressure is listed as 5.0 +/- 0.4 psi. four turns would equal a 2.4 psi increase. that would put base boost at around 6.8-7.2 psi. the stock maximum turbocharger output is listed at 10.2-11.6 psi.

i would certainly have to agree that a base boost setting anywhere near 10 psi would be rather high (atleast in the case of a stage 1)
 

·
Registered
Joined
·
26 Posts
Discussion Starter · #6 ·
Yep it's high (for me at stageo uno).

Tech Emailed me back: "This was a wrong info the correct info is 0,40-0,45bar". Phew!

Doesn't explain my instability at part openings. I'll leak check again and maybe see what spring my BOVs got in it. Can't hear it, but could be bouncing about.

Oh, don't adjust your actuator more than say a couple of turns away from stock pressure: With too much preload, it won't open enough at the top end of the rev range. Certainly does that at 5 turns. Exciting, but risky.

Having looked and thought: If you need more base boost, but still want to have full wastegate operation (yes!) then a stronger spring in the actuator is the way forward.
 

·
Registered
Joined
·
1,086 Posts
Hunt, when I got my ECU custom tuned, it wound up having a wavering or pumping boost problem. The fix indeed wound up being a stronger wastegate. Also, something to note, they told me to set the actuator the same length as stock and it should be fine, and it was. They said finding the actual base boost pressure did not matter as long as there was the same preload length as the stock actuator.
 
1 - 8 of 8 Posts
Top