Wastegate setings

[valjo]

Hi !

I have one questation regarding wastegate setings. What is difference if i use stronger spring or if i just tighten WG screw ?

[Rusty]

There are 2 functions here - WG cracking pressure and mechanical boost profile. From my testing last year, I have found the following:-

WG cracking pressure is down to the pre-load. The stock spring is approx 3N/mm spring rate, 1.9 and 2.2 bar springs are 7/8/9 N/mm. This means that the maximum crack pressure attainable before the spring binds is much higher on a larger spring. It also reduces the chances of binding the spring and forcing the WG to remain shut or partially shut.

The mechanical boost profile is related to the spring rate. If you unplug the N75 you'll see what I mean - after the WG has opened at the desired pressure, the boost starts to drop off. A softer spring will give lower boost up top, a larger spring higher boost up top. The stock spring cracks at 0.4 bar and drops to just under 0.3 at the redline. On a '2.2 bar spring' I was running, crack was 1.2 bar gauge dropping to ~0.7bar. This drop off is also related to the turbo and other factors but we're discussing springs here and for one setup different spring rates will have an effect.

Tighteneing up the stock spring has little effect so don't bother. If you go over 0.7bar crack pressure then you need to remap the ECU as it'll run rough. Be careful on an RS2 turbo if you decide to run a silly high spring as it could cause issues on stock rods.

[GazzaG60]

so from your tests andy what did you think was optimum for cranking down on the spring.

[Rusty]

Firstly, if your car is mapped for a certain spring and pre-load then you need to leave it at that level, don't mess about, especailly on Motronic - it certainly didn't like big deviations: 0.4 to 1.1 for example and it coughed and spluttered on boost build-up! It was noticeably faster spooling though and for a track car it would be worth mapping with a 1.9 or 2.2 bar spring just for the part throttle performance and corner exit pickup.

Secondly, as I said above, there are many things that will affect the mechanical boost profile on any non-standard car, turbine flow characteristics, WG flow characteristics, EM... etc. etc. If you're running a big spring and it's mapped for that spring then leave it so, there's little to be gained as the N75 or boost controller will sort the boost, to a point (too waeka spring wouldn't give the pre-load so there is a workable range here).

If you wanted to be a bit old skool and go fully mechanical then that's when some experimentation is required to choose the correct spring for your requirements. You could model the system but I think it's just as easy to test a couple of springs and choose the best one for your requirements.

I modelled the OE WG and so can recommend pre-load to give a WG crack pressure. The bit after that is a bit more experimental and unfortunately big springs aren't cheap, something like £10 off the shelf, so you'd have to take a best guess. When using stock springs, there's also what's available in the diameter and useable length and that can determine what you use as much as anything else...

[S2central.net]

Reminds me to find some time to play with one of those big springs you sent Andy. Someday maybe...

[Rusty]

That would be nice thanks Paul but I understand that other things get in the way...

I think you'll find it bloomin' good fun to sort a little map out In my layman's terms I'd hope that the current map will only need the 'expected boost' and 'N75 duty cycle' tweaking a little to give some nice results for part throttle response*. The chips I tested a while ago were nice also and won't need much to work well on my car. The extra little 0.1/0.2 Bar up top certainly liked the cold air of last Autumn, as did the actual 1.5 Bar (vs. 1.3 Bar) through the RS2 IC - for sure .

Happy to oblige with testing again, if there are some to look at. VAG com is here now too. The current cooking HF that I have is sublime and I've never found it anything other than polished but we're all guilty of wanting a little more and my car is getting more aggressive in teh chassis department all the time...

* 1.0+Bar @ half throttle is a bit of a shock but it's so much more like NA and you don't have to mash the right pedal to the bulkhead to get proper performance. The S2 is a blunt device and the digital throttle does not help one bit.

[GazzaG60]

so whats the best place to get springs. i want to help out my boost controller in its older age. make life a little easier.

if factory is 0.4bar id like 1 bar and 1.5 bar and i will bleed the rest with the eboost.

[S2central.net]

'bleed the rest' - ahhh the sacrelige

I didn't source the springs - Rusty did - they can be expensive for what they are.

[GazzaG60]

i figure that when we spend x amount on the car a little spring aint gonna blow the bank and may help get the benifits nailed.

would you prefer "Modulate the rest" sir?

i know however tight i get the controller mechanical assistance is an advantage.

[Rusty]

Is it a stock WG Gaz? Off the shelf springs require adjustment on the WG cap. The one I have sent to Paul will do 0.8 to 1.2 Bar, I'll have a look and see what will do a 1-1.5 Bar range

[HPmuirt]

Surely going from 0.4 bar to 0.9 bar is the best and safest option as then mechanical boost can never be above what the stock turbo can produce, even at redline?

That reminds me, must get a new WG diaphram and change to my 0.9 bar spring

Cheers n

Si

[Rusty]

The headline figure is the WG crack pressure, pressure at the redline will be less, when I tested a 1.9 bar spring, it produced 1.5 bar at the redline so isn't going to be an issue. This is what I refered to as 'mechanical boost' profile above - it's not a constant boost!