How To Size A Turbocharger For A Compound Setup?

[KTRON]

I just finished rebuilding my Detroit Diesel 6V53T military engine. In the process of rebuilding, I changed some parts to turn the engine into a truck engine.

Unfortunately that process made mounting my turbocharger impossible with stock parts. (unless I bought a different blower/turbo - not going to happen)

Because of this I need to design custom intake/exhaust manifolds to even mount the turbo

Since I have to go through all of that trouble, I was thinking of running a compound turbocharger setup to increase low end torque, and create more boost at lower rpm's.

The stock turbocharger I have is an AiResearch TV8104 (Detroit Diesel Part Number: 5101431)

Because the turbocharger wheels are so big, I would expect that it doesnt make any boost until the engine is revved up considerably. This engine will be used in a truck one day, so it will be optimal to have some boost at lower rpm's

How do I figure out what turbocharger I need to buy in order to get maximum efficiency out of the engine?

The engine is governed to 2800rpm loaded, 3025rpm unloaded.

Displacement wise, its 318 cubic inches, 335-350 horsepower

Peak rpm is met at 1600rpm, which is 770lb/ft

Below is a horsepower/torque curve for my engine series

(Mine doesnt have an aftercooler, otherwise, its the same engine. Both are rated with N70 injectors)

These are the only compressor maps I was able to find for the turbocharger series I have(TV81XX):

364TV81:

408TV81:

I am not sure what the difference between 364TV81 and 408TV81 is...

Here are some specifics in terms of 53 Series Turbochargers:

(Published December 1984)

I think that my best choice for now is to still find a smaller turbo to work with the bigger TV8104 that I have.

At a later time, I could sell my TV8104, and buy a more modern turbocharger. There must be something better, its been 26years since that publication.

In terms of the smaller turbocharger, I have heard that "too small" of a turbocharger can restrict the exhaust flow of the engine, so whatever it is, it should probably be bigger than a T04B98, and smaller than a TV6000 series

I would like to stick with Garrett/Ai Research

I am not necessarily looking to make horsepower, only boost to keep the dedicated supercharger from sucking power from the engine. (I need about 8PSI boost at lower rpm's to equalize pressure on both sides of the blower)

Here are some pictures of my engine during my rebuild process:

Any turbocharger guru's out there...

Any recommendations would be greatly appreciated,

Thanks,

Chris

Edited September 22, 2010 by KTRON

[ThaddeusW]

I am not a turbo expert but you ask a very interesting question. I once thought about the math involved but the simplest idea is to split the difference. Go a few sizes down from the factory standard for your power setting and then spec a smaller turbo that can make up the difference. In theory the smaller one should spool up fast and build boost on the low end and then the larger turbo spins up as the RPM's climb giving you full boost.

I don't have the time to analyze the graphs at the moment but I must say you are doing your homework quite well. I would like to know what you come up with and if I get the chance I might try to crunch some numbers as well.

Good luck!

[theakerstwo]

Think about this. Unless you have a by/pass blower your turbo is limited on the boost that can go pass the blower. Turboed DD engines did go to a by.pass blower in the later years of production to use the extra boost.Some hot rods plumb the turbo boost direct into the air box covers to use the boost. But all of this takes many hours of playing with turbos not speaking of the money to get there.

[KTRON]

My engine is not a silver engine. It does not have a bypass blower.

My engine has a turbocharged block and a naturally aspirated blower.

I have seen dyno charts for both turbocharged 6V53T engines running natural and turbo blowers, and the natural blower fed turbo engines make significantly more low end torque (~50-75 lb/ft more between 800-1400rpm) because of the excess air flow. (Natural blowers have ~2" longer rotors)

I am not planning to run a "factory" Bypass Blower on my engine. I have literature on it, and because of its 7/8" - 1" diameter bore through the blower end plate, it will only yield a 7 horsepower boost. (purely makes power because of pressure equalization) A $1500 end plate for 7hp gains is not a very wise use of money.

Because I am young (21yrs old), and I love to experiment, I thought up a way to build my own bypass blower.

I am going to get my hands on 4 reed valves, (mainly used for carbureation in large 2 stroke gasoline engines), and mount them onto each of the 4 air box covers. Reed valves are essentially one way valves, so air flow wont be disturbed when the engine is in operation.

At low rpm, there will be low turbo boost, so the reed valves would be closed. The blower fixed atop the engine is a positive displacement roots blower. (Detroit Diesel 2 cycles require air pressure in the air box to run - air needs to be forced into the liner openings for efficient combustion)

When turbo boost builds, the blower is still positive displacement, however the reed valves will open, allowing undisturbed air from the turbocharger directly into the airbox.

Now the key point is this:

The homemade bypass will be more efficient than the stock detroit diesel bypass as long as the tubing going into the reed valve is more than the 1" diameter that the bypass blower from detroit is.

The more flow you can run the better. The goal is to equalize pressure on both side of the blower, ultimately unloading the blower.

In order to do this, I propose building custom turbocharger(s) to blower intake, where 50% of the turbo boost is allowed to enter into the dedicated roots blown supercharger, and the other 50% will be diverted (into probably a 2.5" or 3" diameter tube), and then split equally into 4 zones, where it will be fed into reed valves and into the engine.

The 50-50 goal is to maintain pressure on both sides of the blower.

So once 8PSI is made, the engine can operate essentially without the blower.

Normally, compound turbocharging is ineffective on a 2 cycle because of the dedicated blower, but because I am routing air around the blower, it "should" make more boost at a lower rpm, thus increasing lower end torque.

That is a big concern on a two cycle detroit. They are really weak in the 500rpm-1200rpm range. They really only come alive at higher rpms >1600.

The actual horsepower and torque required to run the blower (I have heard that the blower takes 40-70horsepower on the 6V53T engine) would essentially be brought back into the usable horsepower range of the engine, increasing overall efficiency

Fabrication will be a challenge, but reed valves and tubing aren't all that expensive. A second turbocharger will be expensive, but as long as its sized properly, the engine should make significantly more power between 600-1200rpm

My next big concern is finding the best small turbocharger (which works with the bigger turbo, makes 8psi boost at low engine rpm (800-1200), and something that doesn't restrict exhaust flow too much) I have heard bad things about too much back-pressure on the old two strokes

Thanks for hearing me out,

I do not know how to read compressor maps just yet.

I heard the "Turbochargers" book by Hugh MacInnes, is great. I have to see about getting a copy to learn.

Chris

[theakerstwo]

Keep reading cause your on the right road.The other thing is i think the cam timing needs some rethinking.

[Stian1979]

I got a 6V53T on my hand and I'm walking around with the same thoughts as you.

I have some practical experience with turbos building a 2L gasoline with turbo, but for diesels I have only done maintenance, but I had a heavy interest in the subject and have read some turbo theory and had to do some calculations on it while I was studying for becoming a marine chief engineer.

Because of my background in marine I have taken a different approach than you and instead looked at the large B&W and sulzer diesels where the construction is quile similar to the detroit, but the root's blower is gone.

Instead they have a electrical blower that supply the engine on low load and at startups.

I have also looked at man diesels jet assist system where compressed air from 30bar bottles are injected to help spin the compressor wheel.

I think that trowing off the blower would benefit the whole construction since it would save some weight and some hp.

My last idea(it's all in my head at this stage) was to use twin turbos merging into one collector supporting the larger turbo with exhaust.

Doing this would allow me to use a crossover from the bank to the other so that one turbo could be sealed off using throttle bodies using only one turbo witch would give a good low end response. Once at a certain rpm and boost level the second turbo could be engaged by opening the throttles so it would become a sequential compound setup using 3 turbos.

This could be combined with a low budget electrical supercharger (I know they are piss, but they could be used for this) to start the circulations of air at startup and a 12V compressor could provide compressed air to spool the turbo.

Advantages would be good fuel economy.

Less parts that could break.

Less maintenance.

More power with same mechanical load.

Disadvantages would hight cost of buying the turbos.

Much tuning time to make it work,

Probably require some programing skills if a sequential should work without too much trouble.

You would become the freak for thinking out of the box.

[ThaddeusW]

"You would become the freak for thinking out of the box."

F*** that. Do what you want to do! Who gives a rats ass what anyone thinks? I like how you are thinking, have you ever considered a degree in engineering? You are on the right path, we need more engineers in this country, the Asians are taking over in that field.

The idea of removing the blower is an interesting one as it will remove the mechanical drag but there has to be a positive pressure in the air galley at all times. You could substitute an electric blower or even use compressed air but they all cost energy too. So it boils down to efficiency.

Given a Detroit winds up to over 2000+ RPM the exhaust valves in the cylinder are opening and closing at the same rate, 2000+ times per minute. So if we say the engine is running at 2000 RPM, the valves open a little over 33 times a second. And given out of a possible 360 degrees of rotation the valves will be only open for what 10-15 degrees of that cycle (I don't actually know, just give an example)? So for the 30 something milliseconds per revolution, the valves might only be open for about 1.25 milliseconds (given 15 degrees of exhaust valve open timing.)

For such a short duration, the exhaust gasses explode out of the valves and the scavenger ports open pushing the rest out. So the key point here is to maintain a high enough pressure and flow to push against any back pressure and be able to properly scavenge the cylinder and fill it with fresh air. So a good starting point would be to put a pressure gauge on the air galley and use a graphing type recorder (data acquisition is the technical term that would apply here). And on top of that a mass flow meter to determine the actual quantity of air needed at a given RPM and load. Yes it will get a bit hairy going that route.

Using an electric blower for low speed scavenging could work in tandem with a flapper or some type of "check valve" that would close cutting the electric blower off and letting a turbo system take over. The electric blower could then be shut off to save energy. A second check valve could be used to prevent the electric air charge from bleeding back out of the turbo charger. Then, as the turbo boost drops off as the RPM's / load drops off, the electric blower will restart providing the boost necessary for low RPM's. That would be an interesting system as it would eliminate the parasitic draw of the roots blower at high RPM's. A regenerative or centrifical blower would work in your application. But finding one with a 12 volt motor is going to be a huge challenge (12V brushed motors suck).

If you really want to go crazy, the blower should be driven by a brush-less high speed DC motor. Something custom would be in order of you plan to do-it-yourself. BLDC motors are becoming popular for HVAC systems. So you might be able to source an HVAC blower driven by a BLDC motor that could provide the flow and pressure for low speed scavenging.

Fun topic eh?

[Stian1979]

I like how you are thinking, have you ever considered a degree in engineering? You are on the right path, we need more engineers in this country, the Asians are taking over in that field.

The idea of removing the blower is an interesting one as it will remove the mechanical drag but there has to be a positive pressure in the air galley at all times. You could substitute an electric blower or even use compressed air but they all cost energy too. So it boils down to efficiency.

I have all the schools needed for sailing chief engineer and spent my time in school calculating termal efficensy of diesels with variations in operational conditions. It's a nice understanding that helped me understanding alot, but I have no interest in ending up behind a desk(again)

The idea to remove the blower is quite old. It's been done on sulzer and B&w engines for 50years++.

To be honest I'm disapointed that detroit stoped the development on two strokers since both the tiny twostrokes from bombardier and the large ones from sulzer can compete both on emisions and efficensy.

[Stian1979]

How do I figure out what turbocharger I need to buy in order to get maximum efficiency out of the engine?

I think the general advice is to pick a turbo that is half the size of the LP unit(low pressure unit) so you will have about half the increase ower each turbo.

If the turbo you pick is too small I would worry about it overspeeding.

I deffently think you need to go for wastgates to make this work.

EDIT: I found something interesting here

and here

Just imagine the possebiletys here.

You could inject fuel two times per cycle.

You could inject at tdc and inject a second time once the exhaust valve was about to open creating lots of power to spool a turbo.

Edited November 24, 2010 by Stian1979

[ThaddeusW]

I have all the schools needed for sailing chief engineer and spent my time in school calculating termal efficensy of diesels with variations in operational conditions. It's a nice understanding that helped me understanding alot, but I have no interest in ending up behind a desk(again)

A simple engineering degree doesn't mean you are desk bound but it gives you some options and a possible fallback. A two year associates degree might not sound like much but its a good thing to have under your belt regardless. College education always has a nice ring to it, especially for prospective employers.

The idea to remove the blower is quite old. It's been done on sulzer and B&w engines for 50years++.

To be honest I'm disapointed that detroit stoped the development on two strokers since both the tiny twostrokes from bombardier and the large ones from sulzer can compete both on emisions and efficensy.

I figured the idea of using an electric blower is quite old. Detroit stopped the 2 stroke development simply because they gave up on the emissions problem. And I also bet it was around that time that the demand for 2 cycle detroits for Marine and industrial use began to drop off. Maybe they saw the writing on the wall.

[Stian1979]

Detroit stopped the 2 stroke development simply because they gave up on the emissions problem. And I also bet it was around that time that the demand for 2 cycle detroits for Marine and industrial use began to drop off. Maybe they saw the writing on the wall.

Well it would have helped if they stoped working on a 70yo design.

It's greatly improved, but still a 70yo base.

Catterpillar 4 strokes would also be poluting pices of iron had they continued there design on a 70yo base.

A 2 stroke has a advantage off 50% less mecanical friction since it's producing power on each revelution. The large B&W and sulzers use less fuel per kW than any other engine and emmisions are not a problem, but the fuel they often use is nasty stuff. It resembels asphalt and need to be heated to 80C for pumping and 120C if you want to inject it.

But this engines has seperate lubeoil forcylinders and crank so engine lube oil don't get into the combustion. Am I getting off topic?