two stage actuator
Turbo Mini Forums

i got the turbo from dan now, ( cheers dan by the way!)
it has a two stage actuator, it has tow outlets on it rather than one,
does this mean it has two stages of boost like high / low
how does it work and does anyone know what boost you get from it?
cheers
DAN :)

Hi
I think you might find it's not a 2 stag actuator, but there are actuators out there with 2 inlets on. this is meant for finer boost control and not 2 stage.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

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I have also seen actuators with 2 inlets before, think it was off a subaru with 2 banks of cylinders, hence it took the boost reading to the actuator from 2 places rather than just using one side and assuming the other was the same

Anyway, how could you have a 2 stage actuator? As soon as the 1st stage opens then the wastegate dumps exhaust gas so you won't ever be able to make any more boost pressure to get to a 'second stage'

that was it sorry, i was being dumb. still learning all this turbo stuff, it has two inlets.
DAN :)

In fact I have just seen the picture of said actuator in your other posting.
What it looks like to me is that it has 2 inlets, one to open the wastegate, and one to keep it shut, rather than the usual type which use pressure to overcome a spring.
I am guessing this is off a sequential twin-turbo set up where a small turbo produces boost from a relatively low rev range, and then over a higher rev threshold, the big turbo kicks in, and then the small one is "switched out" using a valve.

PS Do you know what this turbo came off? As it may be that even though it is a T2 it may be nearly as big as a T3 in terms of compressors and housings.....

Edited by Tom Fenton on 30th Sep, 2004.

its off of a r5 gtt

Here are some thoughts - I've never got to the bottom of the real use myself - and i've asked a few people!

I know WRC cars use two inlets as they can be more accurately controlled over a larger boost variation than a single pipe. It does need clever electronics however - your normal aftermarket ECU won't do this!

As an extreme, Imagine you wanted a min boost of 5 psi, and a max of 20. This wouldn't be achievable with a single pipe system, you just wouldn't be able to bleed off 15psi ACCURATELY.
With a twin entry actuator, we can have a 'soft' spring in the dashpot that opens the wastegate at just 5psi, and we can bleed off say 5psi very accurately by pulsing a solenoid valve (as in the original metro). Hence we are now at 10psi.
To bleed off more air becomes more difficult however, due to the duty cycle of the solenoid, so the other side of the diaphram is connected to the plenum chamber, via another solenoid valve (with an exhaust - again, just like the metro). By operating the valve, boost presssure pushes the diaphram back, hence increasing the pressure that the wastegate will open. By varying the dutycycle of two solenoids, you'll get a high boost capability...

As regards the R5GT.....
As i recall, if you unscrew the brass twin-entry union off the T3 compressor, there is a tiny pilot hole the signal has to pass through.
In the T2, this is much larger. I know i've had to fit a reducer into my signal line to avoid wastegate flutter, but all it does in reality is slow down the response of the actuator (not ideal really). by introducing a 'proportion' of the boost pressure (from the plenum for example) onto the rear face of the diaphram will cause a damping effect - but will need an ECU to control the amount of 'damping' air relative to boost pressure...

Of course, i could be totally wrong, but i'm guesing it's (at least on the R5GT) to achieve a fast acting wastegate, with some form of damping to avoid overboosting...

no worries on the turbo dan, glad it came through safe and sound!

the twin port actuator on the five has been a contenshish (spelling??) issue, i had a five for a while and numerous people played with the actuator port piping.

I can remember one of the feeds comes from the carb elbow, but can't remember exactly where the other comes from. I remember alot of people used to modify the arrangement to what was called the 'cup mod'. This basically reduced the actuator to a single line set-up, and involved capping off the open end of the actuator and the open end of whatever you have taken off!

It was supposedly to improve lag, as it reduced the amount of volume of air which required boosting. Some people did the mod, and then swapped back after having problems, while others swore by it.

The five also had an overboosting sensor in the main boost pipe from the intercooler to the carb, i think this went to the ignition module.

Check out www.rtoc.org and look at the turbo wizard section. There used to be some useful info in there.