Actuator take off position
Turbo Mini Forums

A recent thread stated that the actuator take off should be on the atmospheric side of the throttle plate rather than taken from the manifold.

Why ?.

The actuator will open the wastegate at the pre determined pressure,which will be achieved with the throttle almost wide open, so that the pressure each side of the plate will be almost if not exactly equal, surely ?.

If the throttle is closed there will be a large differential in pressure each side, but that wont matter because we dont mind if the actuator opens the wastegate or not with a closed throttle.

I can see that it MIGHT affect the speed from which the compressor spools up after re-opening the throttle, but dont understand otherwise.

Can someone more experienced than I (most of the regulars on here) please point out the flaws in my logic ?.

I have just machined a nice block of alloy with six take offs to bolt to the inlet manifold with the big banjo bolt and feed the servo, my anti run-on valve,boost guage, actuator ,dump valve and MJ from there - did I waste my time ?.

Wouldn't your wastegate snap shut when you close the throttle if you are taking your actuator feed from the manifold?

Also you would be exposing the actuator diaphragm to a vacuum when closing the throttle, I can't imagine this will do the diaphragm inside it much good.

Every non VNT turbo I have seen has a take off for the actuator on it. I can only assume that it is here for a good reason.

Edited by John on 6th Jan, 2010.

If something is worth doing, it's worth doing half of.

Is the actuator diaphram up to the job of dealing with fuel contamination?

Boost is measured post throttle. The wastgate maintains the pre throttle pressure, therefore only somewhere at full throttle should you see full boost at the manifold. at part throttle the pre throttle pressure may still be at set level, but the engine is running 'throttled' with a lower pressure. Also, as the throttle is snapped shut from full throttle full boost, the pre throttle pressure spikes and opens the wastegate to help stall the compressor/ turbine.

Thanks for the comments. I understand and will act upon the suggestions,particularly with reference to possible fuel contamination. Im not sure the vacuum issue is as important.

Sprocket, with all due respect to your much greater experience, I agree that the pre throttle pressure rises abruptly when the throttle is snapped shut and that this would open the wastegate if the take off was measuring pre throttle, but its not going to do the compressor any good if it stalled it - I thought that was why we had dump valves ?.

Looks like I have a spare manifold tapping available and that I need to re-plumb the wastegate.As I have removed the brass two way connector from the compressor housing and blanked it off, and I dont want to take all the manifolds off again I guess I can just take the feed from the plenum ?.

id agree tadge

the spike of pressure should not really happen with a good blow off valve anyway .

and id prefer to keep the rpm of the turbo wheels as high as possible to get good response on the next gear .

i have run a wastegate on either side of the blade , and if i had the choice, without a bit of hassle , i would run it engine side every time ,especially with an su that makes a bit of resistance to flow .
this would ,in theory ,stabilize boost at the valve in the head which is where i want to measure it .

you do theoretically want to find a stable area to take off the signal in the manifold... and this may not be so easy as before the carb.

re fuel affecting the wastegate diaphragm , it could be true but i have not found it so on my bike or on the tvr .

Edited by robert on 7th Jan, 2010.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Dave.

Like you, I was concerned about wastegate control but in my case my doubts were in the context of the wastegate being controlled by my Boost Controller (which bleeds off actuator signal to achieve valve conrol). If I am feeding my boost controller with a post throttle manifold pressure why would I not want to use the same pressure to control the actuator ?

I spoke to a few on TM a while ago on this, most notably Robert, when I was having fuelling problems.

I've just moved my actuator take-off from the brass two-way on the compressor snail up to the manifold via a new drilling alongside the banjo, similar to what you've been doing yourself no doubt.

I've found that in this position, the stability of the boost has increased and that lag has reduced, but some of this could be down to the combined effect of the controller which I have now well and trully got sussed out.

I'm looking for some better weather to take the van out for a spirited drive and a RR session back up to Northampton Motorsport to find some missing nanas but the indications so far are that the move of signal take-off position to after the throttle butterfly has improved my setup.

I take the point about the susceptability of the diaphragm to fuel/air mixture but will keep an eye out for anything untoward at regular actuator pressure checks.

Richard.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

Apart from possible fuel contamination, as the OEM position is the compressor outlet (as it's role in life is to control compressor pressure, not manifold pressure) it will never see vacuum in the OEM configuation..... the diapragm may only have a backing/reinforcing plate on one side.

Schrödinger's cat - so which one am I ???

Some differences in opinion here, as so often is the case. Thank you Rod for clarifying for me why vacuum on the actuator diaphragm is not a good idea.

I think that I will persist with my present set up at least until the engine is run in -which may be some time with the present weather.

I may then experiment with snail take off and plenum take off and then see if it matters.No one has suggested that the plenum idea is not a good idea.

As Robert has said, this may be the more pressure stable area that is desirable, but will still be subject to spike pressures until the dump valve opens .

All good info for future consideration -thanks everyone.

Manifold pressure at part throttle will be lower than compressor discharge pressure, so if the wastegate actuator is controlled with manifold pressure the compressor pressure will be higher to maintain the desired manifold pressure, and at part throttle, that could potentialy be bad, pushing the compressor into surge (high pressure, low flow) which is why OEMs all take the actuator pressure feed from the compressor discharge.

This is interesting. I have used a tapping on the plenum (after the throttle body) to control the actuator.

Now the actuator is the Renault 5 jobbie with a connection each side of the diaphragm, so I assume that it will cope with boost and vacuum on either side. I stand to be corrected.

Now I have found that at a high speed cruise, the turbo is spooled up, but the throttle is still holding a vacuum. What I don't know is if the pressure after the compressor would be enough to open the actuator, I doubt it though.

Whether the compressor is going into surge is debatable. I never noticed any surge type noise.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

i have my take off from the manifold,
should this be moved back to the turbo,
i just tgought everything should read the same psi

Paul,s experience matches my own in that the car is highly responsive when opening the throttle from a cruise speed of, say, 3000rpm, with negative boost showing until the throttle is opened.Very satisfying when overtaking on the motorway in a 50 year old car.Clearly the turbo is well spooled up, but providing very little boost until asked to do so.Dont really understand how.

Couldn't you just run a one way valve inline so it never sees a vacuum?

I run mine after the butterfly, I don't have the fuel contmination issue with my setup, but with regards to vacuum it seems ok...only time will tell I suppose.

Edited by matty on 7th Jan, 2010.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

First, my comment about the actuator seeing vacuum was "may" be a problem :)

I've not pulled one apart to see how they are constructed inside but the T3 version only has the one connection which will never see vacuum in the OEM configuration, so I'm guessing it isn't designed specifically to handle vacuum..... normal operating pressure 7psi positive, vacuum is 15psi negative.

Re. the increased repsonsiveness from cruise with the connection after the throttle plate, it's probably not surprising but "may" not be good.

The actuator is there to open the wastegate to limit the turbine power once the compressor has reached the set pressure. If you are measuring the pressure somewhere where it is potentially lower than the actual outlet pressure, the turbine will be driven harder so the actual compressor outlet "may" be higher.... hence potential for surge etc...

However, the reallity is probably that at cruise there simply isn't enough exhaust gas to significantly over-drive the turbine even though the wastegate has been disabled by the signal being taken from the wrong place.

But probably enough exhaust gas to keep the turbine at a higher speed than the designer intended so giving you the quicker response when the throttle is openned.

It would be interesting to monitor the actual compressor outlet pressure at cruise with the wastgate actuator being fed the "wrong" signal.
:)

Schrödinger's cat - so which one am I ???

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

There are two ways to use a BOV

One is to dump the boost on large sharp throttle changes, as most use them

The other is to control boost by bleading off excess pressure

Just to be clear i wasnt sure if the diaphrams where fuel resistant or not, it was more of a possibility type question/statement that i thought i would put forward.

IMO i think it would be more responsive if taken from the compressor housing, I.E the wastegate should react faster to presure changes as its closer to the source, especially when the turbo spools. This and gear changes is the only time i can think that you would see any kind of boost spike if the take off was on the vacuum side. But then the delay is most probably to short for any boost spike to be noticed unless you have silly charge piping runs.

When i get a new boost guage for the S-Body i will plumb the old one up to the pressure only side and see what the difference between the guages is at cruise.

If there is negligable difference then i think it would be safe to say that surge isnt one of the problems to be looking at.

James, if I understand your post correctly you are talking about wastegate response - I was talking about engine response.

It does seem that unless someone is prepared to run tests with all the variations we have mentioned, there will always be anecdotal evidence to show that each persons way is best.

BTW, just in case,what are the symptoms of compressor surge and will it total the turbo in one instance or does it need repeated abuse ?.

There are two phenomenon that kill centrifugal compressors, and how well the compressor survives depends on the design of the compressor bearings and thrusts.

Surge batters the thrusts while rotating stall batters the bearing. Rotating stall is a precursor to surge; the compressor becomes noisey and the discharge pressure will fluctuate rapidly by about 10%; full gas flow reversal is not yet occuring. Surge is full gas flow reversal with relatively slow and large pressure fluctuations. Surge gernerates thrust and counter thrust loads, while rotating stall generates torsional vibration in frequencies that reach critical limits.

Think of surge as, all the air that was discharged under pressure suddenly changing direction, flowing backwards through the compressor while the compressor is still rotating at high speed.

Rotating stall is small areas of high pressure that have seperated from the majority of the gas that is discharged from the tips of the compressor wheel in the direction of rotation. These 'stalled' areas of high pressure impact the tips of the compressor wheel causing high frequency vibration

Turbochargers are relatively small and the bearings are relatively large for their size. some turbos may last indefinately, others may last for a considerable time before the show signs of stress.

If you are happy that running the wastegate off the manifold, improves engine response, are you also happy that the turbo may last 30k miles before it really starts to show signs of stress. It might live indefinately but its a comprimise you would have to put up with. While I understand the physics, I am not clever enough to work out the math. I get the gut feeling that running the actuator off the maifold is bad, but other than understanding the physics of why it is bad, I cannot prove why it is such.

I like to think that if it was such a good idea, that it improved the engine response without detrimental effect to the mechanical components, why do OEMs not do it this way?

as for whether turbos will experience surge at part throttle when the wastegate is controlled off the manifold pressure, I dont know, but there is always the possability that at some point the engine will be in a condition that it will.

The boost you run at the manifold is all that you care about. So regardless if you run the control from the manifold or the snail the turbo will do the same. For example if you tune for 10psi (using whatever control, bleed valve, etc) then you are tuning on your boost gauge, which is connected to the manifold. The losses between the compressor and the carb are constant so regardless of where you control the actuator from it will open at the same time and boost to give you what you want at the manifold. It is really only the coming on and off boost you will alter, if at all, I don't believe it will effect the surge.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I don't think you are taking into account the throttle? Part throttle will casue a pressure drop in the manifold compared to the comressor discharge? cruse is rougly around 25 - 50 % throttle, part throttle is roughly 50 - 75% and full throttle is 75 -100%

Running at part throttle will see a drop in pressure across the throttle, which means that if the actuator is controlled off the manifold, the compresor discharge would need to be at a higher pressure, but lower flow, and that is where you could potentialy enter the surge region.

That is how I understand it, I could be well be wrong. It just doesnt 'feel' right, thats all :)

Yes, but part throttle creates very little boost, but what it does create can be seen on the boost gauge, which is connected to the manifold, so where is the problem going to come from? At part throttle I doubt that you even trigger the actuator, especially if you have a boost controller or MBC.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I think that the potential problem that Colin is describing is shown in this log:



In the middle of the chart I'm getting full boost at part throttle. At that air flow the throttle must be adding a few psi to the pressure at the compressor.

I'm not sure that it is doing any damage though.

EDIT: Full boost at 50% throttle in top on this one:

Edited by Paul S on 8th Jan, 2010.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."