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Project Twin VNT - Twin Turbo TD42 Patrol - Episode 1-2-3-4-5-6-7-8-9-10-11-12-13-14

40K views 205 replies 62 participants last post by  james008 
#1 ·
#74 ·
Excellent stuff mate - enjoying the build - noticed your off sider was missing?


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#79 ·
Folks,

Sorry for the radio silence. This has been due somewhat to me going on holidays, but mainly due to my computer giving up the fight after 6 long years. Frustrating as this project saw me buy 16gb DDR3 for it, which is now incompatible with my new AM4 mb.

Episode 5 is ready, only it's trapped on my harddrive. A new Ryzen is on its way to me now, as soon as I've installed it I will upload episode 5 (should be later this week)(assuming hd is not corrupt).

Spoiler alert... it contains fuel pump tuning - and graphs.

Thanks for your patience,
 
#90 ·
Given the amount of thought that has gone into this project, I am sure you have considered carefully what turbo's to use.

It has recently been explained to me that the problem with variable vane turbo's in a performance application, is that when the pitch of the blades changes, they effectively close off your intake, and minimise the amount of airflow. This we do not want when trying to make torque.

So, my question is - why are you using variable vane turbo's???
 
#91 ·
It has recently been explained to me that the problem with variable vane turbo's in a performance application, is that when the pitch of the blades changes, they effectively close off your intake, and minimise the amount of airflow.
You'll have to explain that one to me mate, considering the vane blades are in the exhaust housing, how do they close off your intake?
 
#94 ·
At low rpm the vanes are closed but there is still a small opening and direct the exhaust flow near 90 degrees to the turbine blades. Having the vanes closed changes the a/r ratio of the turbine housing. Effectively makes a smaller area for the exhaust flow. This smaller area increases the pressure in the turbine housing, so you have high velocity exhaust flow across the vanes at around 90 degrees to the turbine blades. This is what makes the turbine spool the compressor quickly and reduces lag.
On a car with a vnt from factory the ecu controls the boost by opening the vnt vanes which makes the a/r ratio bigger which decreases the exhaust gas pressure.The angle that the exhaust gasses hit the turbine blades is changed as well so you get less drive but more mass flow through the turbine as the a/r gets larger. The compressor slows down and boost pressure is reduced. That's my take on vnt turbos.
 
#97 ·
Not gibberish at all.

One thing I do know, is that pressure is only one factor in how a turbo functions. Volume is also important. This is on the compressor side of course, where one turbo can provide a larger volume of air than another at the same pressure rating. So higher pressure is not necessarily better.

So on the exhaust side of a VNT, you will be increasing the pressure on the vanes when they are closed off, but also the maximum volume of air will be reduced. But of course at lower RPM, the exhaust volume will be less.

Interesting. I cannot offer anything else at this point, as this is not my theory. I am just passing on info from a recent discussion with another member. Perhaps he will post up some info if he sees this, and wishes to contribute.

All of us are interested in the results from this.
 
#98 ·
pressure is only one factor in how a turbo functions.
True.
Volume is also important...one turbo can provide a larger volume of air than another at the same pressure rating
On a test bench, yes. But plumbed into an engine extra air flow is converted into pressure (because the piston "blocks" the air's path). On any engine at any given RPM, you cannot have one turbo flow more than another without also increasing pressure... they are linked.
So on the exhaust side of a VNT, you will be increasing the pressure on the vanes when they are closed off, but also the maximum volume of air will be reduced.
You will be increasing the pressure in the exhaust manifold when the vanes close. This will in turn increase the velocity of the exhaust gas hitting the turbine wheel, creating an increase in shaft speed and therefore volume of air flow at the compressor... not a reduction.
Pressure in your exhaust manifold is a good thing... sort of... it's "how hard" your turbine is working. Too low and it can't do anything... not very efficient. Too high and it can't cope... also inefficient. VNTs modulate to keep it in the best range (as much as possible).
 
#100 ·
Over the last few days i have had the opportunity to play with vnt turbos on a turbo test machine or more percisely a turbo dyno test machine. Very interesting stuff and i have learnt quite a few things i really had not thought about with vnt and turbos in general. Shyane is correct just not quite explained correctly. He said or was trying to say is vnt tech turbos generally develop a lot of backpressure or emp during spool or near transion point of shaft rpm. Usually it is a spike in pressure. This emp pressure is usually in the area of 1.5 to 2.5 ratio emp:imp this pressure adds to the blocking effect of cylinder filling hence more load against the compressor wheel which in turns slows down the turbo shaft speed or spool. So as shayne pointed out it reduces comp air flow. On the turbo dyno this condition is very evident in the kg/min or lbs/min graph which increases comp air heat hence a lot less volume with a fugged higher pressure due to a higher than expected PR for the shaft rpm.

I am not saying a well adjusted and sized vnt is not a good thing but i am saying there is a lot more going on in a vnt turbo that is determentrial to flow values than a open volute and gate. Having just tested and dynoed some 20+ vnt turbos over the last few day here in poland i can tell you even brand new bw and garrett oem vnt's are not adjusted correctly for closed vane position. One turbo we tested for a merc diesel brand new wouldnt spin the shaft until 8 psi of exhaust pressure was reached in closed vain position. The spec states .5 psi 20c air for 10000 shaft speed.

As said i have learnt a lot more about turbo's in the last few days.
 
#104 ·
vnt tech turbos generally develop a lot of backpressure or emp during spool or near transion point of shaft rpm. Usually it is a spike in pressure... adds to the blocking effect of cylinder filling
Interesting. Sorry I didn't understand what you were saying Shayne.
I have my vane limit screw backed right off to make the vanes close up as much as possible, the idea being faster spool. But if I understand correctly, you are saying the enormous EMP spike created by this will actually slow my spool. I should open it up a bit for optimal response. Correct?
 
#113 ·
That clutch bleeder that comes back up the firewall that you mention will be in the way of the airbox can be removed, and the three way block plugged. Makes it easier to bleed the clutch anyway. Some models don't have it, and many of us have removed it.
 
#118 ·
Your garage floor must be spotless or your feet like leather.
My garage floor is pretty clean.
My feet are somewhat like leather.
I still get swarf in my feet all the time. I ask not for a lighter burden, but for broader shoulders!

(End up in my hands on a regular basis)
Are... are you walking around on your hands?
 
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