Compound help, 12 to 1400HP

Smokem said:
It doesn't work like that, high drive pressure will create rearward thrust loads, compressor surge and abrupt shaft speed reduction will create forward thrust loads.
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Then I am confused.:doh:

So your telling me that the exhaust flow that is being forced OUT of the turbine housing, is pulling the turbine wheel out with it?

I would have thought that the turbine wheel is pushing the rotating assembly towards the front compressor cover.
And the shape of the compressor wheel...looking somewhat like a drill bit, for example, is pulling the entire rotating assembly "forward".

And when you throw a big ol charger in front of that turbo, and force 35 psi into the face of the compressor wheel, it's pushing the rotating assembly in the opposite direction?

Again...70psi in one direction, minus the 35psi in the other direction...equals 35 psi of "Thrust"...not 70 psi, like it would be as in a single turbo situation.

Not trying to start a pissing match, I'm just trying to understand what your saying...as I may have read it incorrectly...or I'm totally misinformed about what the heck is happening in my compound setup.
 
khaoskustoms said:
What do you see for primary boost?


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My secondary is an s475/87/1.0, and I see 42 psi from the 98mm and 83psi overall. That's on my 1115whp tune. That's at 4300' elevation and an average of 7500' DA
 
Pressure differential is just one part of the equation. The difference is that when a small charger is compounded, it is forced to flow a much greater air mass. The larger mass flow has a significant effect on thrust load.
 
mike diesel said:
My secondary is an s475/87/1.0, and I see 42 psi from the 98mm and 83psi overall. That's on my 1115whp tune. That's at 4300' elevation and an average of 7500' DA
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Damn you have **** air! Currently I've only ran my old 11.90 tune and I got 30psi out of the 95 and 65psi overall with my 61.5/68/.90 secondary. Which is about the same as my old setup.


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Extended Power said:
Then I am confused.:doh:

So your telling me that the exhaust flow that is being forced OUT of the turbine housing, is pulling the turbine wheel out with it?

I would have thought that the turbine wheel is pushing the rotating assembly towards the front compressor cover.
And the shape of the compressor wheel...looking somewhat like a drill bit, for example, is pulling the entire rotating assembly "forward".

And when you throw a big ol charger in front of that turbo, and force 35 psi into the face of the compressor wheel, it's pushing the rotating assembly in the opposite direction?

Again...70psi in one direction, minus the 35psi in the other direction...equals 35 psi of "Thrust"...not 70 psi, like it would be as in a single turbo situation.

Not trying to start a pissing match, I'm just trying to understand what your saying...as I may have read it incorrectly...or I'm totally misinformed about what the heck is happening in my compound setup.
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On a compressor, the discharge pressure will be felt on the rear side of the wheel on that effective surface area. Considering a 62mm wheel could be in the 85-95mm range on the OD, that is a lot of area at a high pressure. Even if its being fed half pressure in as a secondary charger, its only acting on about half that surface area. The same is true on the turbine, but it would be the front side, or the bearing side if it make it more clear. The thrust loads are going to oppose each other to make it a bit more balanced.

I don't think its the steady state of high boost that is hard on the thrust, its going to be the quick changes from the active to inactive side of the thrust that is going to wear it out quickly. I had a S366 that was worn out on the thrust from being in and out of boost so much, hammering back and forth on the thrust bearing.
 
^^I like to think of it as a "tug of war" between the turbine and compressor wheels. The compressor is trying to pull itself forward as it's grabbing the incoming air. Exhaust pressure pushes the turbine wheel towards the exhaust outlet as it tries to push through it.
Ideally, the closer they are to a "tie", the less thrust load there will be.
A lot can affect that balance though, like compound pressure as mentioned (although if the primary has a 1:1 boost/DP ratio, then it may not affect secondary thrust...?), on/off boost as mentioned, changing wheels...ie putting on a large compressor wheel can create more "pull" towards the front, not to mention running closer to the surge line.
 
Like Tate said, it is the pressure between wheel and backplate that is pushing against thrust bearing. Same on both sides but less on the turbine side because it is smaller and back of the turbine wheel is usually cut open between blades so much less surface area.
 
Leiffi said:
Like Tate said, it is the pressure between wheel and backplate that is pushing against thrust bearing. Same on both sides but less on the turbine side because it is smaller and back of the turbine wheel is usually cut open between blades so much less surface area.
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Unless something fundamental in turbocharging has changed the net thrust is almost always positive. This being the sum of the turbine and compressor and positive being in the direction of the compressor to the turbine. As to operating point near choke producing the highest axial load in the positive direction and near surge more neutral.

With that it's easy to see where a charger in a secondary position is exposed to even more positive thrust as inlet pressure increases.
 
Here are some thrusts out of secondaries on the C13 (right) and C15 (left).

GT40 based secondary on the C13 supposedly. Some oddball internal things like with many of the CAT products. GT47 based primary.

GT42 based secondary on the C15. The primary is GT55 based.

Front:

BBB7B35E-2F12-4412-ADB0-42CB7F188124_zpsfi8clvrg.jpg


Back:

30E6CA81-31E1-49F7-B7DD-9274C74C4700_zps0trrzr5i.jpg



Take those for what they are worth. Not much wear at all on either on the front (compressor) side of the GT42. Heavy wear on the GT42 thrust on the back side.

Minimal wear on the front of the GT40 thrust on the left most pad. Hard to see in the picture. No wear on the rear of the GT40 thrust.


Not sure if those are of much value but that is typical of these turbos. I can get sizes on all four turbochargers in those setups if they are of value for the discussion.
 
What sort of boost numbers are being run on trucks like that? I'm willing to wager that a TT OTR truck will be driven less like a race car than a TT pickup truck that people think are race cars.
 
Tate said:
What sort of boost numbers are being run on trucks like that? I'm willing to wager that a TT OTR truck will be driven less like a race car than a TT pickup truck that people think are race cars.
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40+psi. The thing these see more than a pickup truck is cycling. Imagine the number of times those compounds spool up in a day at full load. They take more of a beating than one might realize.
 
smoke machine said:
Why has no one suggested the 468/87 1.1 over 484/96 1.32 or 1.56?
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I'm with you. I'm not even sure you'd need the 87mm secondary turbine... I think a box FMW 467 over a billet 484 ought to get the job done, and would lite if you so much as looked at the skinny pedal.
 
Joesixpack said:
Unless something fundamental in turbocharging has changed the net thrust is almost always positive. This being the sum of the turbine and compressor and positive being in the direction of the compressor to the turbine. As to operating point near choke producing the highest axial load in the positive direction and near surge more neutral.

With that it's easy to see where a charger in a secondary position is exposed to even more positive thrust as inlet pressure increases.
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Compounding doesnt change much because exhaust pressure is also increased.
 
smoke machine said:
Why has no one suggested the 468/87 1.1 over 484/96 1.32 or 1.56?
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Not to stir the pot, but your hp in your signature with that setup isn't close to what the original 12-1400hp target is. Just Sayin.

Then again your injectors are only 45%......
 
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Those numbers where on a stick bottom end 6.7 with 190k miles. Will have new numbers very soon with built bottom end, p&p head, cam, and 225% overs. I run a 68/83 1.1 over 484/96 1.32 on the 5.9 single cab as well. Makes 100psi @125 drive on fuel on a 10.0 pass at 6300 lbs. again limited on fuel with 160% overs That's why I would step up to the 87 turbine.
 
smoke machine said:
Those numbers where on a stick bottom end 6.7 with 190k miles. Will have new numbers very soon with built bottom end, p&p head, cam, and 225% overs. I run a 68/83 1.1 over 484/96 1.32 on the 5.9 single cab as well. Makes 100psi @125 drive on fuel on a 10.0 pass at 6300 lbs. again limited on fuel with 160% overs That's why I would step up to the 87 turbine.
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Big change. Hope you get close to the numbers you want with them!
 
smoke machine said:
Those numbers where on a stick bottom end 6.7 with 190k miles. Will have new numbers very soon with built bottom end, p&p head, cam, and 225% overs. I run a 68/83 1.1 over 484/96 1.32 on the 5.9 single cab as well. Makes 100psi @125 drive on fuel on a 10.0 pass at 6300 lbs. again limited on fuel with 160% overs That's why I would step up to the 87 turbine.
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How well does that spool and what converter ?
 
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