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Discussion Starter #1
I need to know from a wise man among you about compound turbo charging.

I would like to maximize the RPM range of the 4BT from idle to full power. One of the ways in doing this is compound turbocharging.

1.) In a compound turbo set up for a diesel engine, are both turbos the same size or does a larger feed a smaller turbo?

2.)Where is the best website or even book to explain turbo selection? I read through the post's here and gathered some information but need a "Jedi Knight who knows the way of the force" on this matter.

3.) Will the primary turbo have to have a waste gate?

I'm really entertaining the ideal of a compound turbo set up.

Ford is doing it with their 6.4 powerstroke. Even though that engine is computerized I'm know there is a formula map for what kind a turbo set up to use along with boost levels.
 

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Go over to powerstrokenation.com and post your questions on compound turbos in general. There are some informed persons there.
Bob B.
 

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Try the book "Turbochargers" by Hugh Macinnes.
Don't have it yet, but it's on my Christmas list.
Have heard from several people that it is a very helpful book...

May also try asking some of the turbo shops and places who advertise in Diesel Power Magazine. Might ask the different places if they already have compounds for a 4BT, and/or if they could build a setup for you. You can probably learn some just by telling them what you want your engine to do, asking a few questions about how and/or why they think whatever turbo combo they have or want to sell you will work. Although you may not learn a whole lot without spending money either, but it's worth a try.

Grigg
 

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Try the book "Turbochargers" by Hugh Macinnes.
Don't have it yet, but it's on my Christmas list.
Have heard from several people that it is a very helpful book...
I didn't find it that good. There were also some blatant errors in the one I read. Like the rotation arrow drawn the wrong way on the compressor wheel.

The basics of compound turbocharging is the small turbo is similar in size to the standard turbo on your engine. Slightly smaller if you want earlier spool.

The bigger turbo sizing depends on your goals. For maximum power you can split the pressure ratio between them, essentially making each one work as hard. For lower boost levels you can use a wastegate to bypass some of the small turbos exhaust, making the bigger turbo take more of the load.
But either way, the big turbo has to be capable of flowing the maximum air that your engine will draw with two turbos blowing into it.

There are some people here who've done just that on a 4BT, but mostly for max performance with a lot of supporting engine work.
I have a plan much like yours of a big flat boost curve. But it hasn't happened yet.
 

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Discussion Starter #5
The basics of compound turbocharging is the small turbo is similar in size to the standard turbo on your engine. Slightly smaller if you want earlier spool.

The bigger turbo sizing depends on your goals. For maximum power you can split the pressure ratio between them, essentially making each one work as hard. For lower boost levels you can use a wastegate to bypass some of the small turbos exhaust, making the bigger turbo take more of the load.
But either way, the big turbo has to be capable of flowing the maximum air that your engine will draw with two turbos blowing into it.

There are some people here who've done just that on a 4BT, but mostly for max performance with a lot of supporting engine work.
I have a plan much like yours of a big flat boost curve. But it hasn't happened yet.
I'm looking for a flat torque curve to maximize the RPM range, not looking for alot of power. If I push 140-150 HP I would be perfectly satisfied. Having that horsepower it won't need large turbos. So if I can get away with using small turbos to get 150 horsepower, that's all what I'm looking for.

For a compound set up, does the larger turbo feed boost into a smaller turbo?

Which turbo would be the primary, the one bolted to the exhaust manifold? I'm sure it would have to have a wastgate because of the larger turbo feeding it boost??
 

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Flow on the exhaust side will go from the small turbo to the large. Flow on the intake side will go from the large to the small.

For 150HP there is no need for twins. An HY35 should work great. It will spool very quickly with a 9cm turbine, but is wastegated so it will hold steady boost once peak is reached.
 

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The small turbo is bolted to the exhaust manifold, the big one blows air through it and gets fed exhaust from it.

I suspect your biggest hassle is going to be fitting everything in. That's what keeps holding me up. I also think I need a heavier flywheel to be able to enjoy the power down really low without rumbling. 1400rpm is where my (Isuzu) engines sweetspot starts.
 

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For 150HP there is no need for twins. An HY35 should work great. It will spool very quickly with a 9cm turbine, but is wastegated so it will hold steady boost once peak is reached.
X2 Compounds would be wasted if you only aiming for 150HP.

Gaza
 

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For 150HP there is no need for twins. An HY35 should work great. It will spool very quickly with a 9cm turbine
Ditto that, I can't imagine you not being happy with it. Try it and see first, then think about compounds later if you think it might help.
 

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Try the book "Turbochargers" by Hugh Macinnes.
Don't have it yet, but it's on my Christmas list.
Have heard from several people that it is a very helpful book...
I didn't find it that good. There were also some blatant errors in the one I read. Like the rotation arrow drawn the wrong way on the compressor wheel.
Well, I did get the book for Christmas, and I just finished reading it a few minutes ago.
I thought it was very informative, written by a turbocharger engineer with a few patents to his name.
I think it is a book worth buying if you have any interest in turbochargers. It answered a number of questions i had about turbos, and explained a few things I didn't even know I didn't know :eek:

On th other side is it's an old book now so what was the latest and greatest then is not so much now. The book was also mostly for gas engines, although much of the info applies to diesels, and he has a few sections on diesels. For a basic understanding of turbocharging it's still a good book.

I would like to find a newer book about turbos with diesels being the primary focus, any one have any recommendations?

Grigg
 

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I run an HY35 and it is awsome. Comes on strong and flows quit a bit of air. The 9cm is a good size for the 4bt and egts are very controlable. I bet you can make 200 to 250 hp with one on a 4bt purdy easy. Well see what I'm puttin down whenever I get a chance to hit the dyno.

Just my $.02
 

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For 150HP there is no need for twins.
What about for efficiency? EMP is supposed to be reduced closer to 1:1 or lower and you're converting more of the exhaust's energy to work (like a compound steam engine).

Altitude as well. I live at 5200' elevation and many highway passes are over 10,000'. High altitudes drive up the pressure ratio and reduce the airflow. A single turbo, especially a VNT as in my case, is right on the surge line most of the time and its maximum boost is limited by that surge line. My turbo is capable of 28psi as a single, but that dang surge line forces me to limit boost to 15psi.

I need a low pressure compound (3-5psi) to reduce the pressure ratio which will allow me to keep well clear of that line and reach my desired 20-25psi boost range.

I need help figuring out which LP turbo would be best for my needs.
 

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OM617, there is a local turbo shop called Majestic Turbo http://majesticturbo.com/ that has a really knowledgeable staff that may be able to help you out. It has been a few years since I have dealt with them, but I have never heard anything bad about people's experiences there.
 

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What about for efficiency? EMP is supposed to be reduced closer to 1:1 or lower and you're converting more of the exhaust's energy to work (like a compound steam engine).
I also think for both efficiency and drivability there are still benefits to compound turbos at well below the power levels where they're strictly necessary.

Hopefully I'll still think this when I get my compound setup working, it's been two years of procrastination already.:rasta:
 

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OM617, there is a local turbo shop called Majestic Turbo http://majesticturbo.com/ that has a really knowledgeable staff that may be able to help you out. It has been a few years since I have dealt with them, but I have never heard anything bad about people's experiences there.
My only bad experience is their lack of knowledge. They went to great lengths to explain to me why I could not run a diesel turbo on a gasoline engine....I have to gasoline engines powered with turbos oe to diesel engines, and I was just trying to buy a turbo. So far as rebuilding I think they are fine, but I would not ask them anything on sizing or application without making sure the info you recieve is correct.
 

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What about for efficiency? EMP is supposed to be reduced closer to 1:1 or lower and you're converting more of the exhaust's energy to work (like a compound steam engine).

Altitude as well. I live at 5200' elevation and many highway passes are over 10,000'. High altitudes drive up the pressure ratio and reduce the airflow. A single turbo, especially a VNT as in my case, is right on the surge line most of the time and its maximum boost is limited by that surge line. My turbo is capable of 28psi as a single, but that dang surge line forces me to limit boost to 15psi.

I need a low pressure compound (3-5psi) to reduce the pressure ratio which will allow me to keep well clear of that line and reach my desired 20-25psi boost range.

I need help figuring out which LP turbo would be best for my needs.
The surge issue you are experiencing could most likely be solved with sizing on a single....seems easier to me than fabricating twins. I guess you could recover a little more out of the exhaust energy, and it would be interesting to see if you could quantify reliably if there is any fuel or power efficiency to the crank shaft.

Dont get me wrong.... I love the idea of twins and my truck is a weekend of fabbing and a fuel plate away from twins for the same reasons as well as a little more power. I even have a turbo on the shelf(have the dumb idea an HX40 over a 35 would work well for this arguement) that would work for the effciency boost and a little more power. However, with said mods it would get ugly in the transmission department as I think more upgrades would soon be needed.
 

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What about for efficiency? EMP is supposed to be reduced closer to 1:1 or lower and you're converting more of the exhaust's energy to work (like a compound steam engine).

Altitude as well. I live at 5200' elevation and many highway passes are over 10,000'. High altitudes drive up the pressure ratio and reduce the airflow. A single turbo, especially a VNT as in my case, is right on the surge line most of the time and its maximum boost is limited by that surge line. My turbo is capable of 28psi as a single, but that dang surge line forces me to limit boost to 15psi.

I need a low pressure compound (3-5psi) to reduce the pressure ratio which will allow me to keep well clear of that line and reach my desired 20-25psi boost range.

I need help figuring out which LP turbo would be best for my needs.
The turbine needs pressure across it to work, at 1:1 pressure ratio (turbine inlet/turbine exhaust) there's no 'blow' to spin the turbine! The prob with compounding, as your thinking, is automotive sized turbocharger turbines need a pressure ratio of 2:1 to do any work at all, and 2.5 or 3:1 to peak efficiency. Drive pressure is compounded (multiplied) just as boost pressure is; so you'd have higher exhaust pressure (EMP) with compounded turbos, to get the same boost (28 psi), than you'd have with the proper sized single turbo (about any single turbo can do 28 psi easily, in the appropriate situation/installation). Small sized automotive turbocharger compressors will do 2.5 to 2.8:1 pressure ratio at max efficiency, and large automotive turbo compressors will work at 4:1 with good efficiency (aircraft jet engine sized centrifugal compressors can do more than 8:1). Compounding is necessary, and efficient, when you want/need an intake(boost) pressure ratio that is higher than can be achieved with a single compressor stage. (To do a set-up that compounds two low compression ratio compressor stages to make a single-stage-level pressure ratio (28 psi), but has two turbines driven at regular, 2:1, turbine pressure ratios (about the min that will work), is prob off-design conditions for most typical automotive application/size turbos)

Turbochargers are (for all practical purposes) altitude independent; turbocharged piston/recip aircraft engines demonstrate that, to very high altitudes. Turbine efficiency increases with increased altitude, and compressor characteristics (maps) stay the same, except that compressor speed increases as intake density decreases (altitude increases).

If you have a compressor surge problem, certainly that's a wrong sized turbocharger. Turbos are designed with well matched turbines and compressors; more or less, the mass flow into an engine is the same as the mass flow out of it. VGT, VNT etc doesn't change the compressor, or turbine; the variable turbine inlet geometry is only a means of keeping the turbine pressure ratio high (or higher than it would other wise be) at low mass flows (low engine rpm).

Sequencial turbo charging is what you need! About any automotive sized turbo can make 28psi efficiently; you just need a very small primary, and a way to by-pass it so the secondary turbo won't choke at high flows.

There's efficiency ... and there's efficiency. Reducing compressor PRs across two compressor stages could increase compressor efficency, compounding the exhaust back pressure with two turbines prob doesn't increase the engine's efficiency, viscious losses with the extra flow paths prob doesn't help, either... FWIW, any charge air cooling just throws away some part of the energy that was recovered from the exhaust by the turobcharger...
 

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Jim, I may have read his post wrong, but I thought he was speaking of 1:1 comparing the exhast drive pressure to the boost pressure achieved, not the pressure ratio across the turbine. (but I may be :confused:)
Ah ha... my mistake! I was confused by the steam compound expansion idea... my appologies offered to OM617!

Looking at the exhaust manifold pressure to intake manifold pressure ratio, compounding turbos for relatively low boost/manifold pressures is prob a step backward in that respect; compounded turbines would have higher EMP for the same IMP. Turbines can typic do much more work across stages than compressors can do; increasing the number of turbine stages is usually a detriment to efficency, more are worse when fewer will do...

doing the simplest inexact example; a single turbo might have a 2.5:1 turbine press ratio (2.5:1 EMP to atmospheric pressure ratio) at a 3:1 compressor ratio design condition. A low boost compound might have two 2:1 turbine PR's compounded for a 4:1 (overall) EMP to atmo ratio for the same 3:1 comp PR...
 
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