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VNT-15 Mk1 Rabbit laggy boost
by
Rising
on 27 Sep, 2014 10:04
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Hello all!! I'm pleased to report I have finally joined the league of turbodiesel owners! Going to do a more official build thread soon and detail out problems we ran into etc for future visitors but I have a few questions about what I should expect out of this new setup and how to tune it properly.
Here is what I'm running:
Vnt15 no shaft play- (vane stop screwed up against lever to lock vanes in "open" position)
2" downpipe- (modified stock alh downpipe exits underneath car for tests until I get an exhaust welded up Monday)
2" intercooler piping
Big bar and plate style eBay intercooler (the one theman53 was selling but sold before I could buy it from him.. 2.5")
Mk1 gasser intake with a custom by to 2" adapter.
GovMod N/A Pump with slightly turned up fuel screw
Dinky little horrible 2" cone filter that is going in the trash soon
Cheap eBay mechanical boost gauge
Okay so who knows the accuracy of my guage. But the car seems to not make much boost at all under normal driving. Even up hills and stuff the egts start to climb (quicker than n/a) but I only get like 1-2 psi unless I mash it. I hear the turbo spooling but don't see much on my gauge even a bit of vacuum it seems sometimes at first press of the fuel pedal.
Now I haven't really been hammering it out of fear I've only been getting braver over the past few days. But it seems like if I get on it pretty good egts climb fast and then around 1100 or so start coming back down as boost comes up to around 8 psi or so but still stay around 1000-1050 until I let off. But no more boost than about 8. And that's almost pedal to the metal. And it seems even then only to really take off in the upper ROMs like above 2200 or so (I'm guessing... I don't have a tach)
Now I know the vanes are open but I thought i had read a few people running open vanes with still fast spool and more like 15 psi even without an LDA. Also 0 boost on the highway seems weird. I've gone back over almost all the intercooler clamps.. But am I correct in assuming this is a boost leak? Or is this just normal behavior for a 1.6td vnt with open vanes?
My Buddy's Volvo c30 can make about 4 psi revving up the engine and I can't even get my gauge to move positive at all.. Seems weird since I thought diesel engines needed more spool and my turbo sounds like a jet aircraft and his is barely noticible.
Anyway is there anything else to check? Timing? More fuel? Less fuel? Close the vanes some? Just be happy?
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#1
by
libbydiesel
on 27 Sep, 2014 12:31
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In my experience (I've installed several VNT-15s on 1.6 engines) you will get very little boost with the vanes fully open. I have also seen posts from other people (mostly R.O.R.) saying that they got lots of boost and fast spool with the vanes fully open. My only explanation is that there was significant over-fueling involved and lots of smoke. If you don't wantto make a vane control at this time, I would suggest using a piece of M6 allthread and a couple washers in order to be able to adjust the vane angle until you get good response.
It's good to take a little care with that type of setup, though, as you will not have any wastegate or vane control limiting boost at higher rpms.
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#2
by
Rising
on 27 Sep, 2014 13:54
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Libby this is actually brilliant. A load off my mind. Good to know that nothing is actually broke.. Most likely.
It makes so much sense too. I always questioned how you would control boost ever with a vnt if wide open vanes yielded 17 psi. So now it seems vane control is in my future. Though perhaps if I ran your setup you just posted with just slightly more closed vanes I could see some better response until I could build something to control them. Then I could just control max boost by max fuel..
I love your version of the vane control. I've read over your threads on it several times. I still don't fully understand how I would go about building one though. I wish I could come up with a clever vacuum operated system.
This forum is awesome.
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#3
by
libbydiesel
on 27 Sep, 2014 15:35
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The picture I posted is of my '91 ALH Vanagon. I've been running it like that for more than a year. The vanes are about midway. My long-term plan is to install an 1852v that I have along with making the vanes functional but I've had other priorities. As is, the performance is excellent anyway.
One vane control concept I have suggested before is to use a a GM or Merz auto trans vacuum control valve on the injection pump and then run vac and intake manifold pressure to the two sides of a dual acting air cylinder to control the vanes. In that situation, vac or boost would open the vanes. When the accelerator opened, vac would drop and without boost present, the vanes would close. Once boost rose vanes would open.
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#4
by
Alcaid
on 28 Sep, 2014 03:49
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Vacuum on one side and boost on the other would both act the same direction on the cylinder and there is no vacuum on a diesel that drops. Vacuum from vacuum pump is constant and there is no vacuum ever in the intake manifold like on gassers. Got a sketch to describe what you are trying to suggest?
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#5
by
libbydiesel
on 28 Sep, 2014 08:40
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The Merz or GM vac control valves were created in order to be able to run the same auto trans in both gasoline and diesel equipped vehicles. The vacuum control valves receive full vacuum to their inlet and drop vacuum output based on their position in order to simulate the vacuum conditions that exist in the intake manifold of gasoline engines. Therefore, at no pedal the output is full vacuum. Vac ouput gradually drops as the accelerator is depressed until full pedal, or close to it, results in no vacuum.
Yes, vacuum and boost on the two sides of a dual acting cylinder will both pull the same direction. A spring would need to be added to the cylinder so that its normal state with no vac or boost applied would result in vanes closed. The result would be that at no pedal, the vac side would pull the vanes to open. As the pedal is depressed and vac drops off (still no boost), the vanes would close. As boost rose, with pedal still applied, the vanes would open back up to regulate max boost.
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#6
by
BlueMule
on 30 Sep, 2014 03:45
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Really old scool yo. Here is the unicorn in question. Hope the image shows up.
BlauMuli
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#7
by
libbydiesel
on 30 Sep, 2014 06:50
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Yup, that's it. I'd probably pull a used one off an old Mercedes injection pump rather than pay the money, but the GM ones are still available new and might more easily adapt to be right on top of the accelerator lever pivot point on the injection pump.
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#8
by
theman53
on 30 Sep, 2014 07:19
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#9
by
libbydiesel
on 11 Oct, 2014 09:15
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I believe that part would work, but the electronic portion would be superfluous. There is a version of that part that does not have the electronics and is typically less expensive.
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#10
by
Rising
on 08 Nov, 2014 16:32
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Libby,
How much boost is your vanagon running max/at cruise on your vanagon? (I know this won't be too directly relatable to my rabbit but looking for some ideas)
My rabbit right now is peaking out at about 16-18 psi with the vanes set about half way. Max egts gets up close to around 1150-1200 at the top of 3rd. It was a bit higher (I had to let off before 60) before the temperatures dropped outside. (I also replaced the leaky head gasket. That could be it too)
On the highway I make about 2 lbs of boost on up to maybe 6 on a hill.
Boost never gets up over 10 without really getting onto it. Does this sound like fairly normal operation?
I'd like to see more boost with less fuel(lower egts) on the highway.
I'm also wondering how im reading threads of people with stock turbos turning their n/a pumps all the way up and people getting Giles pumps and spinning tires in third.. My car doesn't have the fuel turned up very far and seems much more tame than those. I've never even really had trouble with the tires spinning in first. Is this just lag? It seems that my egts are already maxed out and more fuel would just raise them further. I figured with an intercooler and a more modern turbo I'd have lower egts and more room to play with I guess.
Anyway I guess I'm asking if this seems normal for the vnt15/if I should open/close the vanes to see more of the results I'm looking for. Or is vane control going to help these issues with faster spool and wider vanes up top?
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#11
by
vanbcguy
on 09 Nov, 2014 08:46
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Vane control is what it's all about. The vanes need to be fully closed until the turbo has spun up to get any sort of low RPM boost. If you don't have any sort of vane control then there isn't a lot of point or benefit to having a VNT turbo.
The VNT15 can be spooled by around 1500 RPM and producing peak boost before 2k, that's really the only reason to use a turbo as small as it. The major benefit is low RPM boost capabilities.
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#12
by
Rising
on 14 Nov, 2014 18:27
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Vane control is what it's all about. The vanes need to be fully closed until the turbo has spun up to get any sort of low RPM boost. If you don't have any sort of vane control then there isn't a lot of point or benefit to having a VNT turbo.
The VNT15 can be spooled by around 1500 RPM and producing peak boost before 2k, that's really the only reason to use a turbo as small as it. The major benefit is low RPM boost capabilities.
Roger that. So what I'm seeing is typical of non controlled vnt. Excellent then. Now to devise simple vane control...
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#13
by
theman53
on 31 Mar, 2015 07:25
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Bump for me.
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#14
by
theman53
on 21 Apr, 2015 18:01
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