Actuator preload

[YellowCar]

Following on from my pikey mod I tried a different spring. Shorter but about the same spring rate. Putting it on meant it was preloaded more. Consequence, too much boost, well above specified and stayed up there, was slightly scarey to say the least.

Just logged another run with all springs off again and same pattern as before (just to kind of reset and think through things again), keeps going down below specified from 5200rpm. However I realised I hadn't tried a run with n75 unplugged to check actuator and boosted to 4 psi. So it seems my cracking pressure is too low yes? Should be 5 psi? I therefore wonder if my issue is less about spring tension (some springs did help, but was a very slight over boost and still following same line albeit staying above spec for longer). But is actually more about the preload itself.

Can I therefore get away with winding the nut up the rod? I read somewhere that each full turn roughly equates to 1/3 psi? If so 3 full turns from where it is now could do it?

[Decender]

I had similar issue a while back. Turned out to be a weak actuator. In the short term I did the same as you are proposing and it worked fine. I didn't want to run it like that for long, just as a test really and until I got a new one fitted.

 

Fitted a Forge one in the end and the issue went away.

[YellowCar]

Thanks for that, yeah I've got a stock refurbished one which I'm just trying to put off fitting for as long as I can, means getting axle stands and gaskets etc too. You may have seen I tried adding external helper springs which makes it better but means it's boosting a bit too much. Don't have a problem getting to peak boost so I'm wary about preloading it too much, it's just that tail off I want to prevent.

Can I ask what was happening with your boost and how many turns preload did you give it? Did it rectify the issue?

According to CR Turbos it may not be just the spring, the diaphragm inside perishes too and looking at the angle it's fitted I'm not surprised, condensation can drip on it, crap can fall on it exactly where it's vulnerable.

[Liverpool-Lad]

Couldnt you fit a manual boost controller and set it with a gauge?

[YellowCar]

Couldnt you fit a manual boost controller and set it with a gauge?

 

Interesting idea, just starting to read about those and coming across some mixed opinions, giving it some thought...

 

Just had another look at my numbers, forgive my lack of graphs, but...in reference to my pikey mod with the helper springs my first effort (2 light springs) saw it spool effectively and peak to 20psi at 4000rpm, requested is 19.  20 is then pretty much held and then starts to drop gradually to around 15psi at 5500rpm.  Then it crosses requested and goes down to 12 at redline where requested is 14...so looking at that again, it's not too bad is it?

 

Here's a funny one though (well, in a way), I found a spring that was shorter and a similar spring rate, so I thought that this would be preloaded into a more effective tension, so I stuck it on, well, let's just say I created a monster.  It spooled like a bitch and hit 22psi...and held it on a dead straight line! Right up to 4760 where it then steadily went down to 16psi at redline, above requested all the way from when it came on.  Needless to say I'd like to keep my turbo, so I took that spring off...

 

What I plan to do is either give the nut one turn of preload and fit the original springs I tried, or add a bolt to pull them slightly longer (literally about 5mm) and that should see it stay with requested to redline. 

[Liverpool-Lad]

I use one on the Capri, it basically becomes your actuator, its a ball and spring which works against the boost pressure

[YellowCar]

Capri?  Nice wheels, I used to have a 3 litre

[Liverpool-Lad]

Heres a pic just for you

 

[YellowCar]

Sweet! Love it mate, zakspeed style!

[Decender]

Your boost will always tail off towards the top end. Unfortunately the K03 turbo just cant hold boost all the way through the rev range.

 

Here's a thought though. Despite what you do with the assister spring you have tried, should the N75 valve be adjusting/bleeding off boost the match the requested? I could be wrong, but I thought that was it's job?

 

That all said and done though, it does sounds like you may have a weak actuator, what sort of mileage has your motor covered? The Beach Buggy Turbo actuator seems to be the popular mod and not very expensive either.

[YellowCar]

I have been thinking n75 as well, it is going along the cycle it should be but not coming down low enough before going back up again. This can however be due to a weak actuator, boost leak etc. The fact it's driving and boosting smooth leads me to think n75 is ok, but it's still in the back of my mind. Especially as with the external helper springs it stays above requested (not by much though) and never really matches it, although the line does follow the same pattern until the drop off near the top.

I do fully expect the ko3s to tail off but it was going down by too much and only just making requested.

Cars only done 75k but I think that's part of its problem, it's had a history of fairly light use and was standing for a few months before I bought it. Think my use and remap and such shocked a few parts. I'm happy to fit a stock actuator, I have a refurbished one which should cope fine, just can't get to fitting it at the moment.

[TeflonTom]

Subscribed, i'll post my thoughts later when i have more time to formulate a reply.

[Mankee]

If you are sticking with the standard turbo, a new stock actuator (if you can get one) is the best bet. I have the 10 psi BBT actuator and it is/was a sod to map as it makes the little turbo spool up incredibly quickly. If it isn't mapped properly, you will end up with an on-off, no boost-all the boost throttle pedal, which I had the first time round. Little bit rampant during the slippy winter.

 

It is a million times better now that Niki at R-tech has refined the map and taken preload off the actuator. I set it up with the usual "three turns of preload, innit", but just one turn is enough for a K03S and this actuator. If the flow of your setup can't cope, a K03S just turns into a hot air pump at high revs and with the actuator slammed shut, which is what I found with my setup, hence the reduced preload

 

Having said all that, I don't regret fitting the BBT actuator at all. With the N75 unplugged and running just actuator pressure, it made over 217bhp and 229ftlb. Obviously it's much more fun and tyre-shredding goodness with the N75 plugged back in.

[YellowCar]

Sounds like fun, as I said I have a stock refurbished one from CR Turbos. My flow had been improved with this big side mount I fitted and don't seem to be getting any lag. Plus my peak intake temps have come down 20 degrees to just over 40 near redline (WOT 3rd gear), so I'm not suffering with retarded timing and high temps really now either. 217 with n75 unplugged? Lol that's funny.

[TeflonTom]

Yes you can get new actuators, but not from vw, there are no oem spares from vag, but if you can find a turbo repairer that deals with borgwarner turbos you can get them and the mounting brackets too.. on mine i fitted the 6psi actuator from a garrett t2 but that needs the mounting bracket to be modified.

Yellow, i think you have misinterpreted the function if the wastegate actuator preload, its mainly there to keep the wastegate closed on vacuum conditions, if you crank it up too far you will get turbine surge at high boost outputs and risk seriously damaging the turbo and engine.

the other thing to consider is internal cracks around the poppet valve, ko3 housings are prone to cracking around that area, and if it extends around the seat of the poppet it wont matter how much preload you apply, it will always leak.. both of the ko3 turbochargers on my audi s4 cracked internally and it made some really strange results.

[YellowCar]

I was thinking of winding the nut up to increase the cracking pressure as in my op it is at 4 psi, I didn't plan to use preload to keep it shut/increase boost. I'd much rather use the helper springs I found to help it shut when it is supposed to at top end. The way the springs are set up they aren't strong enough to keep it shut, just help it to shut again.

As the guy from CR Turbos says and as you say it may not just be the spring it could be perished internally, but the springs have helped, it holds peak boost for longer and meets specified later when it starts to fall away. Doesn't seem to be any surging.

I think I need to fit my refurbished in all honesty, but this has helped in the interim. I just don't have axle stands and such at the moment so difficult/impossible to do it on the driveway. Plus me and ceased bolts don't get on well.

[TeflonTom]

its quite tricky to change the turbo, oil and water feed and return lines you can't get without taking the exhaust manifold off, occasionally the bolts holding the turbo to the manifold snap off when you undo them too. You will need to remove the drivers side driveshaft too.

[YellowCar]

I've read of people leaving most of the lines on the turbo and just allowing it to drop a little to get to the manifold? Or is that just ridiculously wishful thinking?

[2stroke]

On 29/04/2015 at 22:15, TeflonTom said:

Yes you can get new actuators from BorgWarner but not from VAG-dealers.
On mine K03 I fitted a 6 psi actuator.

The main function of the wastegate actuator preload is to keep the wastegate closed on vacuum conditions,
if you crank it up too far you will get turbine surge at high boost outputs and risk seriously damaging the turbo and engine.

 

On 29/04/2015 at 22:25, YellowCar said:

I was thinking of winding the nut up to increase the cracking pressure to 4 psi,

I have trouble to understand what is going on with the actuator on my K03

My cracking pressure with the actuator arm connected to the wastegate is only:   0,21 Bar  /  ~3.0 psi

...So if I change/adjust the setting of the lock nuts on the actuator arm so cracking pressure rises to factory setting:  0,37 Bar  /  ~5.36 psi   it will automatically also change the preload of the spring.

How should I think about this ?
🤔 Should the focus be on getting the correct preload at rest or should the focus be on getting the right cranking pressure ? 🤔


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Edited 21 July, 2023 by 2stroke