Thread: VNT Turbo Setup??

[QUOTE=Dougal;1881695]In my experience swaged pipes just make everything awkward to get on and off. Bolt on straps (tig a threaded stub onto each pipe, also serves as a locator for the joiners/boots) are so nice and easy to get on/off and positively locate the pipes too.

Even with good clamps and no straps it's marginal enough that a bit of oil on the sleeve and it'll never stay. If you ever need to do a repair in the dark of night somewhere, there will be oil all over the joints and they won't stay.

With straps the BS stops, forever. Consider putting them on in the future.


I don't mean a simple flare on the end
I proper swage 20mm from the end would look like an olive was slid up the pipe
Only needs to be 2mm or so high
It held my oil soaked pipes at 30psi and the boost flares were probably almost double that
Most sheet metal places would have a hand machine I guess

Dc

Pull the stainless pipes out and put a spot of weld every inch or so around the pipe inside of where the clamps sit. This will stop the bends slipping off when you are boosting. Using this method standard hose clamps will do the job adequately.

Originally Posted by mike_ie

As mentioned in my earlier thread, I've bolted a GT2260v variable geometry turbo from a 3.0l Iveco Daily van to my Isuzu engine. To control it I'm running a dawes valve setup as shown - nothing complicated - the alternator vacuum pump applies vacuum to the actuator, and boost from the turbo cancels out that vacuum pressure proportionally, as shown.



snip...

Mike, for others that might follow you and use a similar system with a VNT turbo, what size orifice (the damper shown in the diagram above) did you use in the line from the vacuum pump?

I would expect 0.8 to 1.0 mm would be about right.

The orifice prevents loss of vacuum for the brake booster and its size combined with the adjustment of the needle valve controls the vacuum pressure at the actuator before boost pressure increases enough to crack open the Dawes valve.

Edit: this is probably as good a thread as any to add a link to a good page for DIY overhaul of a Garrett VNT turbo

Originally Posted by Bush65

Mike, for others that might follow you and use a similar system with a VNT turbo, what size orifice (the damper shown in the diagram above) did you use in the line from the vacuum pump?

Still in the process of getting it right, but I'll post a full write-up in the next couple of days with measurements etc.

Originally Posted by mike_ie

My understanding is this:

At slow engine speeds, the vanes are in the closed position narrowing the gap between them which effectively accelerates the exhaust gas onto the turbine wheel. At high engine speed the vanes open up slowing the exhaust gases, which stops the turbocharger from over-boosting.

...

Or am I wrong??

I have just been looking at some Garrett literature and from that it is not surprising you reached this conclusion. However their explanations are very simplistic. Logic would lead most people to assume this because reducing area increases gas velocity, and vice versa.

Originally Posted by Bush65

This part is not strictly correct, but has no relevance to your problem, I'm just a pedantic old basket.

Think of the turbine converting energy/enthalpy in the exhaust gas to mechanical energy (torque and rpm in this case).

The enthalpy is mass of gas, its temperature and pressure. Increase any or all 3 to increase enthalpy.

Now the intent of the variable nozzle into the turbine is primarily to change the nozzle area, smaller to increase pressure, and vice versa, and thus change the available enthalpy.

The vanes also have an affect on the torque produced by changing the angle of gas flow into the inducer.

Edit: more energy is required to get a 60 mm compressor wheel spinning faster, to produce boost, compared to a smaller wheel.

Gas velocity is not a parameter that determines the work done by turbo machinery e.g. pumps, compressors, turbines.

Specific Work, (or work / mass of fluid) is used for turbo machinery calculations the 1st pic below is a part copy from here gives the specific work for compressors and gas turbines (compressible fluids).

The other pics are 2 pages from Turbocharging the ICEng by Watson and Janota. The section of the book these pages came from, was on Constant Pressure Turbocharging i.e. the exhaust manifold evens out pressure pulses (pulse turbocharging is in a different section of the book).

The only variables used are Absolute Temperature and Pressure.

John, that makes perfect sense when you think about it. You could have a massive amount of air and a small fan/turbine, but if all the air is at atmosphere pressure it will have no force behind it to spin the turbine. A small amount of air at high pressure (think air compressor nozzle) on a small turbine would easily spin.

Another way to put it is a planes wing. You can still fly a plane in thin air. Lift from the wing is gained by a difference in pressure top and bottom of the wing. Nothing to do with absolute volumes of air.

Mike, you can now change your location

Originally Posted by Judo

Another way to put it is a planes wing. You can still fly a plane in thin air. Lift from the wing is gained by a difference in pressure top and bottom of the wing. Nothing to do with absolute volumes of air.

true but not quite.

to maintain the same amount of lift in thiner air as thicker air you must increase speed. IE the same MASS of air must pass over the wing.

It is the same with every thing else, what differs is mechanical efficancy