Compound turbo 3B (1 Viewer)

[gerg]

The large turbo can still utilize its stock internal wastegate, but I would recomend clamping it and let it free bost unless it boosts more than you want. Undersizing the small turbo's turbine, as dougal said, is one way to take advantage of a compound set up. you dont necessarily have to go for huge amounts of boost, although if done well you can have you cake and eat it too.

 

[Dougal]

The large turbo can still utilize its stock internal wastegate, but I would recomend clamping it and let it free bost unless it boosts more than you want. Undersizing the small turbo's turbine, as dougal said, is one way to take advantage of a compound set up. you dont necessarily have to go for huge amounts of boost, although if done well you can have you cake and eat it too.

The problem with clamping a wastegate, is you've just limited your whole engine system to the choke flow of the turbine. Which can be less than half of what the compressor is capable of.
Once you hit choke flow, the exhaust pressures climb and your flow-rate remains.
Power is choked off and feels like it hits a wall at a certain rpm.

With my clamped wastegate on my T2560 I was hitting this wall at around 2,500rpm where the engine would cease to deliver any more power or rpm under load (at lower loads it would rev out).
I fitted a 22psi wastegate actuator with about 4mm more preload than normal and I now have far more power across the board. Hills which I used to think were good at 100km/h with the foot flat and 24psi boost can now be climbed at the same speed with 18-20psi boost and lower EGT.

Turns out I was generating more power with the wastegate clamped. But I was using it to fight exhaust drive pressure, not turn the crank.

I'm now a big proponent of working wastegates.

 

[gerg]

I guess I should qualify what I was saying about clamping the large turbos wastegate. Clamping a wastegate to prevent leakage on an otherwise over sized turbo so that it produces its maximum boost, but would never reach its housings choke point. For example, ill be swappng a hy35 as the large and am just a tad worried it wount spool at all in the lower rpms, so clamping the wastegate is to help get the most boost out of it possible. I dont think id be choking it until perhaps 3500rpm, and even then I think it would do fine.

 

[Dougal]

This will have you questioning your sanity.
I reach maximum boost after the wastegate has cracked open.

 

[gerg]

I must admit, it sounds like a bit of an oxymoron... how is that exactly? Large or small turbo? I could see small turbo clamped and choking the VE of the engine and not spooling due to less energy I guess. Large turbo not soo much unless your talking large turbo on large motor.
Hmm interesting.

 

[Dougal]

I must admit, it sounds like a bit of an oxymoron... how is that exactly? Large or small turbo? I could see small turbo clamped and choking the VE of the engine and not spooling due to less energy I guess. Large turbo not soo much unless your talking large turbo on large motor.
Hmm interesting.

I only run small turbos.
GT1549 on my work car. T25 on my 4BD1T.

The turbine only needs a certain pressure ratio to work and deliver the required power. Any more than that is just strangling the engine.
For my T25 the turbine chokes somewhere around 15 lb/min of flow. The compressor is capable of 25 lb/min of flow. I can actually hit the 15 lb/min choke point before I hit max boost. Ideally I think you want to start bypassing just before the turbine chokes which is often before max boost. This is so the wastegate can progressively open and bypass more and more flow around the turbine once it has reached choke flow, allowing the turbine and wastegate together to pass more and more exhaust as rpm (and sometimes also boost) builds.
If you try to open the wastegate too late, the turbine can choke off the engine and kill power before it's been able to generate enough boost and flow to start bypassing and allow higher flow.

 

[Wheelingnoob]

My head hurts, think I'm going try the 19T compressor on the TD04HL first lol.

 

[gerg]

Yeah im gonna upgrade my teo4h-13c to a 19t as well and do a rebuild on it. It was ancient when I got it and the compressor is on the small side. Not the greatest idea to run a larger tubine with a smaller compressor as your small turbo and expect it to boost soon. I think the housing chokes before it gets going. Much like what we are talking about.

I like your explanation Doug. It sort of halts a positive feedback loop. I just have to sell off some stuff to get the project funds going as we just finished our rennos and were 10 grand over budget. Happy with how it went, just too much money. Then ours and our renters washing machine broke, had to replace our gas stove and bought my wife a mazda 5. Has been an expensive year.

 

[cody c]

I only run small turbos.
GT1549 on my work car. T25 on my 4BD1T.

The turbine only needs a certain pressure ratio to work and deliver the required power. Any more than that is just strangling the engine.
For my T25 the turbine chokes somewhere around 15 lb/min of flow. The compressor is capable of 25 lb/min of flow. I can actually hit the 15 lb/min choke point before I hit max boost. Ideally I think you want to start bypassing just before the turbine chokes which is often before max boost. This is so the wastegate can progressively open and bypass more and more flow around the turbine once it has reached choke flow, allowing the turbine and wastegate together to pass more and more exhaust as rpm (and sometimes also boost) builds.
If you try to open the wastegate too late, the turbine can choke off the engine and kill power before it's been able to generate enough boost and flow to start bypassing and allow higher flow.

Interesting, I guess you define the actual "choke" point by feel, like when the engine seems to run out of power and according to the tach, then adjust your wastegate(s) to push power past that rpm.

Its too bad running a cruiser on a dyno is costly, otherwise it would be more appealing to play with wastegates and actually see what differences it makes adjusting wastegate springs and compare your horsepower/torque on a graph.

I suppose you could adjust your fuel a few times around the wastegate adjustment as well.

 

[Dougal]

Interesting, I guess you define the actual "choke" point by feel, like when the engine seems to run out of power and according to the tach, then adjust your wastegate(s) to push power past that rpm.

In the absence of a drive-pressure guage. Yes. With a drive pressure gauge you can avoid the guesswork and see when the drive pressures start to spike.

 

[cody c]

In the absence of a drive-pressure guage. Yes. With a drive pressure gauge you can avoid the guesswork and see when the drive pressures start to spike.

Not familiar with drive pressure gauges, it sounds like a psi gauge which your comparing to your boost gauge, perhaps it wouldn't hurt to throw another bung in the exhaust manifold and plug it when I weld it up so I have the option if i want to play with wastegate settings at some point.

Ill have to read up on them.

 

[Dougal]

Not familiar with drive pressure gauges, it sounds like a psi gauge which your comparing to your boost gauge, perhaps it wouldn't hurt to throw another bung in the exhaust manifold and plug it when I weld it up so I have the option if i want to play with wastegate settings at some point.

Ill have to read up on them.

On the gauge end, it's simply a boost gauge. You need a scale that will double the boost you expect to see.
On the hot end, you need metal fittings into the manifold and a long enough section of metal tubing to get away from the manifold heat. Then plastic/rubber to the gauge.

I used an industrial pressure gauge originally and put shots of grease up the line from the gauge end to dampen out needle flutter. Worked great.

 

[cody c]

alright, I had a look around and there are a few but not a lot of manifold pressure gauges out there, and it looks like most of them are a bit on the lower side of the range i.e. 0-50 or 0-35 which may not be suited to a turbo or compound setup, I get the impression that a 0-80 psi range would be better, or maybe even 0-100.

I think the cooling line from an air compressor or similar with the rings around the line to increase surface area may help, as well as a restrictor orfice and maybe a small collector/volume bottle of some sort to even out the pulses.

Oh yeah, I picked up the flanges today from MSO, they look alright, but I will have to oblong the holes a pinch on the last flange from the manifold.

edit: its too bad they dont make these in a larger range, the price seems alright:

http://www.gbinstruments.com/electr...ectronic-manifold-gauges-electric-gauges.html

 

[Dougal]

alright, I had a look around and there are a few but not a lot of manifold pressure gauges out there, and it looks like most of them are a bit on the lower side of the range i.e. 0-50 or 0-35 which may not be suited to a turbo or compound setup, I get the impression that a 0-80 psi range would be better, or maybe even 0-100.

I think the cooling line from an air compressor or similar with the rings around the line to increase surface area may help, as well as a restrictor orfice and maybe a small collector/volume bottle of some sort to even out the pulses.

Oh yeah, I picked up the flanges today from MSO, they look alright, but I will have to oblong the holes a pinch on the last flange from the manifold.

edit: its too bad they dont make these in a larger range, the price seems alright:

http://www.gbinstruments.com/electr...ectronic-manifold-gauges-electric-gauges.html

You are massively over-thinking this. Oil pressure gauges have the requried scale and are available anywhere.

There is no flow through the pressure line, only heat conduction along it. Any metal line just needs to be long enough to get away from the heat. A couple of feet is heaps, put a coil into the line to let it flex and absorb vibration.

A needle valve (adjustable) or a shot of grease up the line stops the needle chatter.

 

[slowandsteady BJ]

Cooling the drive pressure gauge tube is important, but keep in mind you have soot to deal with as well. That's why Dougal suggested the grease (i believe). Ive seen guys run a half dozen loops of copper line in about a 3" dia. loop to help with the soot and heat. This Install on a Cummins is a bit ghetto but you get the idea.

 

[cody c]

You are massively over-thinking this. Oil pressure gauges have the requried scale and are available anywhere.

There is no flow through the pressure line, only heat conduction along it. Any metal line just needs to be long enough to get away from the heat. A couple of feet is heaps, put a coil into the line to let it flex and absorb vibration.

A needle valve (adjustable) or a shot of grease up the line stops the needle chatter.

Well... Im not sure if I just want the gauge in permanently and have it match the other gauges and mostly use while I play with the wastegate springs when I get around to that, or if I want to install something temporarily and then remove it later when I feel Ive got the most out of the two turbo's.

Cooling the drive pressure gauge tube is important, but keep in mind you have soot to deal with as well. That's why Dougal suggested the grease (i believe). Ive seen guys run a half dozen loops of copper line in about a 3" dia. loop to help with the soot and heat. This Install on a Cummins is a bit ghetto but you get the idea.

Yup, I get the cooling part, the reason I brought up alternatives (air compressor line) for cooling is that I was looking at permanent installation ideas, that coil of copper works great Id bet, but it doesnt look great (no offense Im sure it was just used for tuning) and I see that you have a "collector" bottle midway which I assume is to balance out needle flutter.

I see online there is some filter systems which are used for manifold pressure systems to keep the soot away from the gauge, after the air is cooled enough Id think something similar to a fuel filter would maybe be better for capacity to smooth out the needle and keep the soot back, or at least for a more permanent gauge, something ike this after the air is cooled:


http://www.siliconeintakes.com/prod...d=267&osCsid=2604539da0491e81475cf16a9bf17a49

 

[slowandsteady BJ]

that coil of copper works great Id bet, but it doesnt look great (no offense Im sure it was just used for tuning) and I see that you have a "collector" bottle midway which I assume is to balance out needle flutter.

No offence taken..... I just got that pic off Google! Not my handy work. LOL.

When you get this all done Cody, you have to take some videos and send them to me. I think this is going to be great.

 

[Dougal]

There is no need for a filter because there is no flow through the tube.

 

[cody c]

There is no need for a filter because there is no flow through the tube.

mmmmmmm... maybe.


Everytime you increase the pressure from the manifold to the gauge you are pressurizing the air and it is moving towards and back from the gauge between startup and turning it off... just a little.

I suspect it wouldnt be an issue for testing or probably even short to mid term, but like anything connected to the exhaust system, I think it will eventually get soot through it.



Ill post a video of it all when Im done, how does 2015 sound?

 

[Dougal]

mmmmmmm... maybe.


Everytime you increase the pressure from the manifold to the gauge you are pressurizing the air and it is moving towards and back from the gauge between startup and turning it off... just a little.

I suspect it wouldnt be an issue for testing or probably even short to mid term, but like anything connected to the exhaust system, I think it will eventually get soot through it.



Ill post a video of it all when Im done, how does 2015 sound?

I ran it for a year. The only soot is in the line connecting to the manifold. The other 2.5m or so of line have fittings still clear of soot.
The grease shot is at the gauge end, so that's not it.