Reply With QuoteIt sounds like you need a gruntier actuator.
FTTAI
I have been running my VNT for a while now with a simple ON/OFF switch to open or close the vanes.
Some of it may be useful in setting up a system that is using a Dawes system.
Observations;
Planting the right foot - if I allow the boost up to say 15psi before I open the vanes, I get smoke until the vanes fully open up due to the lag in vanes openning although the boost continues to rise.
ie. it would appear that the back pressure caused by the Vanes being closed prevents enough air entering the cylinder to burn the fuel cleanly. Makes sense.
So if I flip the switch at around 5psi while the right foot is down, the boost continues to rise as the vanes begin to open and all the fuel is cleanly burnt with no smoke.
In both cases the full boost is the same once in a steady state (ie. vanes completely open).
Now I have found that as long as there is a certain amount of boost (due to what ever previous load and right foot application) then with the vanes fully open the boost will still rise. For example on flat highway, 5th gear as long as there is about 7psi boost, I can have the vanes fully open and when I plant the right foot the boost will rise. Now if there were only 6psi boost, if I open the vanes and plant the foot the boost drops and therefore doesn't get enough air flow to burn the fuel and hence increase boost and boost falls. This minimum amount of boost varies with load etc.
Another observation is that say boost was at 6psi (in the above scenerio), vanes were openned and the boost falls away (with right foot planted again), then if I flick the switch to close the vanes to try to get that boost back - there can be too much air flow in certain situation which holds the Vanes open and therefore boost never rises. In such circumstances if I lift my right foot for long enough to reduce the fuel burnt and hence pressure on the inlet of the turbine then the vanes will close, boost will rise and I can plant my foot again. This lifting of the foot is less than a second. If I don't lift, then boost doesn't go anywhere or even drops.
How does this relate to a Dawes setup??
Well say you are aiming for max 15psi boost on your dawes setup and therefore set the valve to suit 15psi.
Effectively your aren't opening that switch until you hit that 15psi. Where in a right foot planted situation it should be begining to open at 5psi.
Now if you set it at 5psi, with right foot planted the vanes would open at this pressure and you would get maximum performance - just like in my example above where boost continues to rise with less back pressure. In a steady state, part load situation (cruising down the highway) then you wouldn't be pumping 15psi that you didn't need into your engine and hence zapping power through inefficient pumping losses of back pressure. You would be sitting on ~5psi.
Now depending on the specific vehicle set up, that 5psi may be too low to then build boost if the right foot is planted and may need to be tweaked a little higher. Although if the Vanes are bouncing between open/close at 5psi it may be OK. Only testing would tell. Or a little higher anyway for your cruise condition may suit anyway.
What I am saying in a nut shell is: It may be better to set a dawes valve up at a lower opening pressure than what ever the maximum you want to achieve is.
People may of already found this thru trial and error, I thought I just share my observations.
ForumSage
It sounds like you need a gruntier actuator.
I have been doing some research on this subject over the last few days seeing i have a IHI VGT turbo on route to me .
Im not keen on any sort of electrical control and i have been looking for other alternatives to the dawes valve set up also .
I found this old thread started by Steve and it never was completed as a win or fail any more comments on this Steve http://www.aulro.com/afvb/technical-...o-control.html
As far as i can work out a vac actuator to pull the vanes shut from the fully open position once the motor has started will work good then to feed boost pressure into the other side of the actuator to over come the vac to open the vanes as boost builds seem to me like it can work .
I may even have to run 2 actuators to get this set up to work as im yet to find an actuator for a turbo which has a line input on either side of the diaphram .
Any input from you guys would be great
Master
There was a garrett turbo on ebay a month back that has an actuator with twin feeds like you describe, I was looking at and was not sure so contacted the seller. It seems it was used as you describe to control the turbo vanes.Originally Posted by lokka
Garry do you still have any info about this turbo ? If you sent the guy a message id say you would have a item no with the message as it would be good to look it up and see if the pic or any info was still available .
TopicToaster
SubscriberSorry Lokka. The VNT project died shortly after that thread when I sheared the end off the turbo shaft (Lefty loosy - righty tighty no worky for turbos)
Still like to fit one at some stage (and have collected a few goodies to try), but really need another vehicle to play around with as the boss gets crinkly when I break the County to do "unnecessary" mods.
I'm waiting for the 120 and bottle of rockinghorse farts I requested to arrive so I can get started
Steve
1985 County - Isuzu 4bd1 with HX30W turbo, LT95, 255/85-16 KM2's
1988 120 with rust and potential
1999 300tdi 130 single cab - "stock as bro"
2003 D2a Td5 - the boss's daily drive
Master
For dummies like me it's difficult to visualise what's going on without pictures and drawings............
So a vacuum-actuated VNT will have the vanes closed at low vacuum and then the vanes will open as you plant your foot?
A pressure-actuated VNT works the other way: it will start opening the vanes as the boost increases?
Or am I off the track and in the bushes?
Close but no cigarFor dummies like me it's difficult to visualise what's going on without pictures and drawings............
So a vacuum-actuated VNT will have the vanes closed at low vacuum and then the vanes will open as you plant your foot?
A pressure-actuated VNT works the other way: it will start opening the vanes as the boost increases?
Or am I off the track and in the bushes?
Using vac from the vac pump on the alt which is only realy there to assist the breaks by means of the vac assist booster i plan to tap into this line so once i fire up the motor the vac actuator pulls the vanes closed (so smallest setting fast spool up) as the spring loaded actuator with no vac will hold the vanes at maximum opening (largest setting same as when turbo reaches full boost at full noise) Once motor is running at idle it will have potential to gain boost at very low revs which im hoping is just off idle then once boost builds the boost signal IE positive inlet pressure can be fed to either a boost actuator linked to the same arm as the vac actuator or fed into the other side of the vac actuator diaphram to over come the vac and slowly pull the vanes open as the revs rise power increases and boost rises
It all sound good in theory but i bet there will be some teething issues
Master
Told you so!
OK I think I understand what you're doing.
What are you going to use to modulate both the vac and the positive pressure?
TopicToaster
Vacuum is negative pressure, it sucks the diaphragm of the actuator towards the side the vacuum is applied to. Boost pressure will push the diaphragm away from the side the pressure is applied. Sticking vacuum to one side and pressure to the other side of a diaphragm is only going to assist the vacuum in drawing the actuator harder towards the side the vacuum is applied to.
I think what you are trying to do is what the Dawes valve is used for, once a certain boost pressure is reached to overcome the spring in the Dawes valve an amount of boost leaks through to overcome the vacuum. I think Bush65 put up a diagram of how that needs to be configured.
I searched and found the diagram I was thinking of, it was in a thread by mike_ie
Last edited by slug_burner; 22nd April 2013 at 11:13 PM. Reason: added image
........
Maybe we're expecting too much out of what really is a smallish motor allready pushing 2 tonnes. Just because it's a v8 doesn't mean it's powerfull.
One answer REV IT BABY REV IT!!!
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