Turbo J Pipe on Stock Manifold

[crushers]

some of the 2Fs in the past used a similar aproach to turboing.
pipe up, turbo, pipe back to exhaust ... seemed to work from what i read.

remember you are not building a race car, you have an old beast that wants to breath better.

 

[canucksafari]

Those were my thoughts Wayne. All I really want is a little more air for climbing mountain passes with a max boost of 8-9 psi. High speed is not my objective; keeping the EGTs down is the main thing. I have been driving NA diesels for the last 6 years, so I think I am use to the speed now.

I think I can shield it and brace it well enough. I am going to give it a try as soon as i can get the bits for my mig gun ordered in.

Do you have any recommendations on a ubrew turbo for a 4.2L?

 

[amaurer]

2. The extra length damps out the exhaust pulses and exhaust pulses are also turbo food.

I've heard this about this "exhaust pulse" theory before and it strikes me as bull****... but you tend to know your s***, so can you educate me?

 

[cody c]

I've heard this about this "exhaust pulse" theory before and it strikes me as bull****... but you tend to know your s***, so can you educate me?

I'd be curious to hear the physics on this as well.

 

[Wheelingnoob]

I've heard this about this "exhaust pulse" theory before and it strikes me as bull****... but you tend to know your s***, so can you educate me?

Its not BS at all I have seen it used and work in the performance car world. If you can get the exhaust pulses in line and not bouncing off each other (waisted energy) then the increase in turbo response and power can be impressive.

Canuck if you need a hand I can help, can you get an exhaust manifold flange made? If you can the extra work to make a manifold for the turbo would be worth it.

 

[canucksafari]

Its not BS at all I have seen it used and work in the performance car world. If you can get the exhaust pulses in line and not bouncing off each other (waisted energy) then the increase in turbo response and power can be impressive.

Canuck if you need a hand I can help, can you get an exhaust manifold flange made? If you can the extra work to make a manifold for the turbo would be worth it.

I think I have some sort of cad file for the manifold flange somewhere. Not that it is the main issue. If I go with the turbo manifold, I will need a new manifold gasket which could also serve as a template. I would just need to find a place that will cut it out for me at a reasonable price.

But before all of that, i need to decide which turbo is best for a Ubrew.

 

[amaurer]

Its not BS at all I have seen it used and work in the performance car world. If you can get the exhaust pulses in line and not bouncing off each other (waisted energy) then the increase in turbo response and power can be impressive.

I know people say things like that all the time, I'm wondering physically how the phenomenon works. People also say that fuel line magnets and HHO generators are impressive, for example.

EDIT: This page makes some convincing arguments about scavenging http://www.modified.com/tech/modp-0906-twin-scroll-turbo-system-design/viewall.html

However that doesn't seem like a turbo-specific concern and doesN'T seem to have much bearing on a 4 cylinder engine.. I'm still confused on why exhaust pulses are considered something that helps a turbo extract energy from the exhaust stream.

 

[Wheelingnoob]

I know people say things like that all the time, I'm wondering physically how the phenomenon works. People also say that fuel line magnets and HHO generators are impressive, for example.

EDIT: This page makes some convincing arguments about scavenging Twin Scroll Turbo System Design - Modified Magazine

However that doesn't seem like a turbo-specific concern and does seem to have much bearing on a 4 cylinder engine.. I'm still confused on why exhaust pulses are considered something that helps a turbo extract energy from the exhaust stream.

Sorry cant explain it any better, I'm not an engineer.

I have seen the benefits of it first hand on my Supra in its varying stages of development. It ended up with a BW turbo running divided entry turbine housing and a waste gate on each side. It was made to keep the runners the same length and keep the exhaust pulses septate from side to side (front 3cyl vs rear 3 cyl) the exhaust sides came into contact right at the turbine wheel.

I ran the same turbo and turbine on a standard manifold with one waste-gate and none equal length as well. The cost of remaking the manifold and adding a 2nd gate was well worth the performance increase. It hit full boost faster (same boost setting) made more power (fuel was tuned to account for the faster boost and power) the exhaust had a very different smooth bark to it as well.

Again I'm not an engineer just some one that has played with turbo cars for 12 years and tried everything from twin turbo to compound turbo to single turbo.

Canuck, if you are interested in getting a flange made I know of a few local places that can do it. Usually about $100.

I would let Dongle weigh in on the turbo best for it. On Gavin's HJ60 (4.0L 6cyl) we did a T3 supper 60 with a .48 exhaust and its spools very fast and makes good power. Not sure how that would equate to the 4.2 but should be close.

 

[cody c]

I know people say things like that all the time, I'm wondering physically how the phenomenon works. People also say that fuel line magnets and HHO generators are impressive, for example.

EDIT: This page makes some convincing arguments about scavenging Twin Scroll Turbo System Design - Modified Magazine

However that doesn't seem like a turbo-specific concern and doesN'T seem to have much bearing on a 4 cylinder engine.. I'm still confused on why exhaust pulses are considered something that helps a turbo extract energy from the exhaust stream.

Ohhh... It sounds like it is more of a harmonic effect, and directing the energy towards the turbo than back along the manifold.

So in a single rail the pulse from each cylinder provides pressure back along the rail and towards the turbo, where as a header style exhaust with specific length runners could direct the pulses towards the turbo more efficiently than back along a manifold.

Still, seems a little like putting perfume on a pig when building parts for an old diesel cruiser, but gotta try and make the best out of what you got

 

[Dougal]

I've heard this about this "exhaust pulse" theory before and it strikes me as bull****... but you tend to know your ****, so can you educate me?

It's pretty simple. The exhaust gas comes out the cylinder as high energy pulses. If you have a long enough pipe these pulses will smooth out into a steady flow, but the steady flow has a lot less energy in it than the pulses do.
If you can keep the pulses as strong as possible into the exhaust wheel then a large chunk of that pulse energy can be used to drive the turbine. Giving you earlier spool up and better boost/backpressure ratios.

Hence all engine manufacturers using low volume exhaust manifolds to keep the pulse energy right into the turbine.

Pulse tuned manifolds, like my Isuzu 4-2 one and most 6 cylinder manifolds split to deliver 3 cylinders to each turbo port are an attempt to spread or combine the pulses to enhance the effect. But they are all history now, all modern automotive engines are using minimum volume turbo manifolds.

 

[amaurer]

It's pretty simple. The exhaust gas comes out the cylinder as high energy pulses. If you have a long enough pipe these pulses will smooth out into a steady flow, but the steady flow has a lot less energy in it than the pulses do.
If you can keep the pulses as strong as possible into the exhaust wheel then a large chunk of that pulse energy can be used to drive the turbine. Giving you earlier spool up and better boost/backpressure ratios.

(emphasis mine) I'm not trying to be obtuse, but I still don't follow; where does the energy go? Are we making a second law argument based on the lowered turbine efficiency due to the lowered average temperature?

Edit: Or maybe we're assuming a temperature drop due to adiabatic expansion in the pipe?

 

[Dougal]

(emphasis mine) I'm not trying to be obtuse, but I still don't follow; where does the energy go? Are we making a second law argument based on the lowered turbine efficiency due to the lowered average temperature?

The energy is dissipated as heat, that heat and more is lost from the pipe through radiation, conduction and convection. Engine bays are windy places.

The losses are two-fold.
Lost pulse energy and lost heat.

Turbos feed on pulses and on heat. The more of both you give them, the less drive pressure they require to produce the same boost. The result is your boost/backpressure ratios improve along with engine efficiency.

The energy in an exhaust stream is made up of the heat, the velocity and the pulse energy. A longer pipe loses the heat energy, loses most of the pulse energy and this cooling also reduces the velocity. It's a lose, lose, lose situation.

 

[amaurer]

The energy is dissipated as heat, that heat and more is lost from the pipe through radiation, conduction and convection. Engine bays are windy places.

The losses are two-fold.
Lost pulse energy and lost heat.

Turbos feed on pulses and on heat. The more of both you give them, the less drive pressure they require to produce the same boost. The result is your boost/backpressure ratios improve along with engine efficiency.

The energy in an exhaust stream is made up of the heat, the velocity and the pulse energy. A longer pipe loses the heat energy, loses most of the pulse energy and this cooling also reduces the velocity. It's a lose, lose, lose situation.

I'm on board with you that a longer pipe causes energy loss, both thermally from the pipe itself, and kinetically from viscous forces inside the pipe.

However for a pipe of a given length, why is a pulsed exhaust flow better than a steady state flow with the same average velocity, pressure, and temperature? THAT is the assertion that I assume is being made by the "maximize your pulses" logic, and that is the bit I don't understand - if the wisdom was simply "keep manifold volume to a minimum" then I think I'd grasp the concept better... but thats not what I thought was being said here (as a log-style manifold would seem to suffice).

 

[Dougal]

However for a pipe of a given length, why is a pulsed exhaust flow better than a steady state flow with the same average velocity, pressure, and temperature? THAT is the assertion that I assume is being made by the "maximize your pulses" logic, and that is the bit I don't understand - if the wisdom was simply "keep manifold volume to a minimum" then I think I'd grasp the concept better... but thats not what I thought was being said here (as a log-style manifold would seem to suffice).

Because I don't think you can do that. You can't dissipate pulses perfectly down to the same averages and the same total energy. The pulses get lost in turbulent mixing, which helps nothing.

 

[amaurer]

Because I don't think you can do that. You can't dissipate pulses perfectly down to the same averages and the same total energy. The pulses get lost in turbulent mixing, which helps nothing.

I may be able to accept that... would you agree with me if I said that its not pulsed nature of the flow thats actually important, but rather that maximizing the pulses goes hand in hand with minimizing losses?

 

[Dougal]

I may be able to accept that... would you agree with me if I said that its not pulsed nature of the flow thats actually important, but rather that maximizing the pulses goes hand in hand with minimizing losses?

Yes. The goal is maximum energy from the exhuast ports into the turbine.

 

[amaurer]

Thanks for the tutorial.

 

[canucksafari]

Yes. The goal is maximum energy from the exhuast ports into the turbine.

So in lay terms then the best is a a cast log manifold, followed by headers or manifold/J pipe? I can't see a J pipe being worse for heat loss than a J pipe off a log manifold.

 

[crushers]

the amount of heat loss you will see in that short pipe will have little effect on your tank of an engine ...

 

[BC40]

So in lay terms then the best is a a cast log manifold, followed by headers or manifold/J pipe? I can't see a J pipe being worse for heat loss than a J pipe off a log manifold.

Hmm, my understanding from naturally aspirated applications: the pulse pressurizing the log manifold when one cylinder is on exhaust stroke 'interferes' with the flow of a subsequently openning exhaust valve. So you lose efficiency and any scavenging effects. Position of the port and firing order affect this diferentially. That is why a equal length headers keeping the flow divided are effective. Though in this case feeding a turbo, the longer header tubes radiate a lot of heat, so there would be a point where losses outweigh gains.