someone should try it

[Erikclaw]

How would you control the amount of pressure the atmospheric make to keep it in the happy PR? WG? or adjusting the housings etc?

 

[Powerstroke Cowboy]

Thanks Charels!!!!! But with a 12 psi per turbo I came out with a 65-67psi at the manifold?????


Now sombody needs to put one together and try it!!!!


Imagine the boost you could make withthis type of set up!!!

 

[Powerstroke Cowboy]

How would you control the amount of pressure the atmospheric make to keep it in the happy PR? WG? or adjusting the housings etc?

Wastegate it. If you tried to control it by the housing you would need a realy BIG housing, And then you would loose the quick response.

thince you would not be running it much higher the 20psi, You could run a tight housing then just waste gate around it after you hit 20 psi of boost.

You could set it up so all it would take is 20 psi backpressure to make 20psi of boost. Then let the waste gate dothe rest..

 

[Erikclaw]

Thanks Cowboy, now put this set up with tow powers and boost to the moon. LOL Very intriguing to say the least.

 

[Charles]

How would you control the amount of pressure the atmospheric make to keep it in the happy PR? WG? or adjusting the housings etc?

Gate the factory setup and then gate the first stage you add on. I would use a 60+mm gate ahead of the stockers and a 44 at the first stage.

The only issue with respect to boost would be keeping it in check.

Just for an eye opener..... if you had the first stage running 25lbs and the signal line to the gate for the stock chargers blew or something and they jumped up to say 45lbs and the first stage wastegate tightened down to maintain that 25lbs and didn't drop any boost..... you would then have just over 146lbs of boost on the manifold....

So needless to say....on a truck with ample fuel delivery, a VERY robust wastegate plumbing system should be employed, and whenever possible the gate signal lines should be plumbed failsafe so that if lines blow the gates will come open.

With three stages the ability to hit astronomical manifold pressures on accident gets pretty damn easy.

 

[Erikclaw]

Gate the factory setup and then gate the first stage you add on. I would use a 60+mm gate ahead of the stockers and a 44 at the first stage.

The only issue with respect to boost would be keeping it in check.

Just for an eye opener..... if you had the first stage running 25lbs and the signal line to the gate for the stock chargers blew or something and they jumped up to say 45lbs and the first stage wastegate tightened down to maintain that 25lbs and didn't drop any boost..... you would then have just over 146lbs of boost on the manifold....

So needless to say....on a truck with ample fuel delivery, a VERY robust wastegate plumbing system should be employed, and whenever possible the gate signal lines should be plumbed failsafe so that if lines blow the gates will come open.

With three stages the ability to hit astronomical manifold pressures on accident gets pretty damn easy.

That would be a BAD thing. 150psi!? POP!!

Since you would have to gate the crap out of the atmospheric, would you need something as big as an 88mm? Would seem you could go smaller and still maintain the same psi.

 

[Charles]

Thanks Charels!!!!! But with a 12 psi per turbo I came out with a 65-67psi at the manifold?????


Now sombody needs to put one together and try it!!!!


Imagine the boost you could make withthis type of set up!!!

If they're all running 12psig then the manifold would see 73.38psig.

12psig at sea level is a PR of 1.81632:1.

1.81632^3 is a final PR of 5.99213:1

A PR of 5.99213 at sea level results in a gauge pressure of 73.384.

At a manifold pressure of 70psig each charger would have to be between 11 and 12lbs.

Your noted disparity was simply the result of rounding.

 

[Charles]

That would be a BAD thing. 150psi!? POP!!

Since you would have to gate the crap out of the atmospheric, would you need something as big as an 88mm? Would seem you could go smaller and still maintain the same psi.

In reality, you may actually need a charger bigger than an 88 depending on how low you want the overall boost. Remember, with 3 stages the PR for each stage is very low. Compressors have to be very large to move a lot of air at relatively low pressure. It may prove difficult, or nearly impossible to restrain the stock chargers to low values, forcing the first stage to make relatively little pressure else blow the heads into the hood with too much manifold pressure.

In this case the required size for the first stage keeps getting bigger and bigger.

Contrary to intuition here.... the lower the pressure from the first stage the BIGGER that charger must be. Compressors like to make more pressure as they move more air. To move a lot of air at very low pressure requires a bigger wheel.

 

[Erikclaw]

In reality, you may actually need a charger bigger than an 88 depending on how low you want the overall boost. Remember, with 3 stages the PR for each stage is very low. Compressors have to be very large to move a lot of air at relatively low pressure. It may prove difficult, or nearly impossible to restrain the stock chargers to low values, forcing the first stage to make relatively little pressure else blow the heads into the hood with too much manifold pressure.

In this case the required size for the first stage keeps getting bigger and bigger.

Contrary to intuition here.... the lower the pressure from the first stage the BIGGER that charger must be. Compressors like to make more pressure as they move more air. To move a lot of air at very low pressure requires a bigger wheel.

I get it, a bigger wheel moves more air without changing the density as much. So a bigger charger is better to keep the stockers at a more happy pr level.

 

[Charles]

I get it, a bigger wheel moves more air without changing the density as much. So a bigger charger is better to keep the stockers at a more happy pr level.

Pretty much.

Since the stock chargers are only going to be able to be held at a given PR with any practical amount of wastegating, the resultant room between that PR and the target manifold pressure is all that's left for the first stage to make up. If that value is low, then the first stage must be bigger to move the same volume of air with equal efficiency than if it were able to spin up higher and run more pressure.

For instance, on a 7.3 a GT47-88 first stage charger will make similar power to a 70 some odd mm single charger because the single is much higher in the map, where it can move to the right without exceeding the choke point of the wheel, whereas the 47 is just loafing along near the bottom of the map in comparison. Seeing as the maps lean to the right, you can move the same air at a higher pressure with a smaller charger as you can with a bigger charger running less pressure.

However, once you start exceeding the pressure ratios where the single stage can maintain equivalent efficiency, the multistage setup starts to pull away. And even when they are equal in full power efficiency, the multistage system will have a much broader powerband and much better driveability.

 

[TyCorr]

Good god! This setup would be pure domination. Especially if there was to be the ability for lots of fuel. I would bet it'd be harder than easy to keep boost in check.
For driveability sake wouldnt it be essential for the stock setup to make more than 20lbs? Or am I underestimating the big charger? The end result is clear to me but a couple of processes in the middle Im hazy on

 

[Powerstroke Cowboy]

If they're all running 12psig then the manifold would see 73.38psig.

12psig at sea level is a PR of 1.81632:1.

1.81632^3 is a final PR of 5.99213:1

A PR of 5.99213 at sea level results in a gauge pressure of 73.384.

At a manifold pressure of 70psig each charger would have to be between 11 and 12lbs.

Your noted disparity was simply the result of rounding.

Charles.

Could you explian this step you used, to get the minifold pressure to me a little more clearer??? Every time I ask sombody that seems to know how to do it. They never share the information. If no one whant to share it then how can I learn it??

Any help you can give me would be great Charels..

This somthing I would love to learn. It would come in handy alot, AND I think I am missing somthing.

 

[TyCorr]

Pretty much.

Since the stock chargers are only going to be able to be held at a given PR with any practical amount of wastegating, the resultant room between that PR and the target manifold pressure is all that's left for the first stage to make up.

Is this all done on paper? The wastegating of the stock chargers that is? Or do you actually have to hook boost gauges up in various points to get everything setup?

 

[Charles]

Charles.

Could you explian this step you used, to get the minifold pressure to me a little more clearer??? Every time I ask sombody that seems to know how to do it. They never share the information. If no one whant to share it then how can I learn it??

Any help you can give me would be great Charels..

This somthing I would love to learn. It would come in handy alot, AND I think I am missing somthing.

Since I obviously cannot know exactly where you might be getting hung up, I'll try to explain everything in detail, simply ignore the parts you have a firm grasp on.


12psig (psi gauge) is 26.7psia (psi absolute), 12psi + 14.7psi of atmosphere. Since the gauge is set to zero at 14.7psi, a reading of 12 tells us we actually have 26.7psi.

This represents a pressure ratio across that compressor of 1.8163:1, 26.7psia / 14.7psia. The meaning of this is that the compressor is taking in air at 14.7psia and compressing it 1.8163 times such that it is discharging air at a pressure of 26.7psia. That is the pressure ratio. It is technically described as P2/P1 where P2 is the outgoing and P1 the incoming pressure.


From here the easiest way to see this might be to simply take a ride through the system.

The first stage takes in air at 14.7psia at sea level. If it's producing a pressure ratio of 1.8163, then it is compressing that air from 14.7psia to 26.7psia on it's outlet.

The second stage compressor then takes in this air at 26.7psia and compresses it another 1.8163 times such that it takes the air from 26.7psia and compresses it to 48.5psia.

The third stage compressor then takes in this air at 48.5psia and compresses it yet another 1.8163 times, such that it takes in the air at 48.5psia and compresses it to 88.08psia.


And with 3 total stages, each running a pressure ratio of 1.8163:1 and starting at 14.7psi, 88.08psi is exactly what you will end up with.

Converting back to gauge pressure, our boost gauge would read out 73.38psi (88.08psia - 14.7psia worth of atmosphere).



I hope that does it.

 

[Dzchey21]

Gate the factory setup and then gate the first stage you add on. I would use a 60+mm gate ahead of the stockers and a 44 at the first stage.

The only issue with respect to boost would be keeping it in check.

Just for an eye opener..... if you had the first stage running 25lbs and the signal line to the gate for the stock chargers blew or something and they jumped up to say 45lbs and the first stage wastegate tightened down to maintain that 25lbs and didn't drop any boost..... you would then have just over 146lbs of boost on the manifold....

So needless to say....on a truck with ample fuel delivery, a VERY robust wastegate plumbing system should be employed, and whenever possible the gate signal lines should be plumbed failsafe so that if lines blow the gates will come open.

With three stages the ability to hit astronomical manifold pressures on accident gets pretty damn easy.

I suggested two 44mm gates because you could put one on each uppipe pretty easy but i suppose a 60mm gate would be ok too, just have to modify the uppipes to make that happen.

I didnt really think it would be neccessare to gate the primary turbo but your right it probably a good idea to do so, just so everything can be in check.

As far s the fail safe on the gates, light springs would probably do the trick, that way if you loose a reference line the gates will just blow open instantly. might be tricky to set the gates initially but damn, i think this set up would be fun, and relativly cost effective, you could spend alot of money on wastegates and still be pretty cheap in perspective


So whos gunna try it? Im half tempted to not get that 71mm vgt and give it a shot LOL

 

[Charles]

Is this all done on paper? The wastegating of the stock chargers that is? Or do you actually have to hook boost gauges up in various points to get everything setup?

At minimum in this case you would need a boost gauge reading manifold pressure and another reading the first stage boost pressure. You could then set the pressure ratios to optimize the compressor efficiency based on your expected flow rates.

The next level of tuning would involve pressure readings being taken in the exhaust system before the stock chargers and between them and the turbine of the first stage compressor. This will allow you to dial in the boost:drive ratios for each stage, and for the system as a whole. This will allow you to see areas where one stage can be pushed harder while another can be relaxed a bit with the same manifold pressure being achieved with less total system drive pressure by making use of the sweet spots of turbine flow and shaft speed.

The third level of tuning would be to either implement a shaft speed sensor on one or all compressors such that with the collected pressure ratio data the shaft speed data allows you to plot exact points on the compressor maps and place each stage at its most efficient point with surgical precision. This level can also make use of a simple temperature probe placed in the intake air stream at the manifold to verify the lowest intake air temp for a given boost, substantiating efficiency calculations. Even further still a person could place such a probe behind each stage to further fine tune them while also continuing the balancing act between drive pressure and compressor efficiency.

At any point housings, wheels and bearing types can be altered and tested.

Depending on practicality, it can be very simple or very complex. The more in-depth you go the less likely that you are wasting anything with improper housings or selected pressure ratios, but the higher the cost of attaining that data and making those changes. For instance, each housing is usually on the order of a few hundred dollars...

 

[TyCorr]

At minimum in this case you would need a boost gauge reading manifold pressure and another reading the first stage boost pressure. You could then set the pressure ratios to optimize the compressor efficiency based on your expected flow rates.

The next level of tuning would involve pressure readings being taken in the exhaust system before the stock chargers and between them and the turbine of the first stage compressor. This will allow you to dial in the boost:drive ratios for each stage, and for the system as a whole. This will allow you to see areas where one stage can be pushed harder while another can be relaxed a bit with the same manifold pressure being achieved with less total system drive pressure by making use of the sweet spots of turbine flow and shaft speed.

The third level of tuning would be to either implement a shaft speed sensor on one or all compressors such that with the collected pressure ratio data the shaft speed data allows you to plot exact points on the compressor maps and place each stage at its most efficient point with surgical precision. This level can also make use of a simple temperature probe placed in the intake air stream at the manifold to verify the lowest intake air temp for a given boost, substantiating efficiency calculations. Even further still a person could place such a probe behind each stage to further fine tune them while also continuing the balancing act between drive pressure and compressor efficiency.

At any point housings, wheels and bearing types can be altered and tested.

Depending on practicality, it can be very simple or very complex. The more in-depth you go the less likely that you are wasting anything with improper housings or selected pressure ratios, but the higher the cost of attaining that data and making those changes. For instance, each housing is usually on the order of a few hundred dollars...

I kinda pictured it this way minus the shaft speed sensors. Ive never even seen anything like that but I havent looked for them either. I like how you detailed each step and explained the steps neccesary to achieve peak efficiency with each charger. It seems as though building the setup is only about half the work, with collecting data and fine tuning it all taking as much time/money as the cold, hard parts.

I still have hope that'll Ill be putting a second charger on mine when the injectors get swapped in. I like the idea of having steady, plentiful air from idle to 3k rpms.

 

[Charles]

I suggested two 44mm gates because you could put one on each uppipe pretty easy but i suppose a 60mm gate would be ok too, just have to modify the uppipes to make that happen.

Whatever's easiest. Two 44's would probably work well.

I didnt really think it would be neccessare to gate the primary turbo but your right it probably a good idea to do so, just so everything can be in check.

With only minor changes to the wastegate duty cycle my 55 will sing right to the pin on my 30lb first stage boost gauge in an instant, with no sign of slowing down. A gate will be mandatory unless you run an obnoxiously large housing, and even then I doubt it will control it. I had a 1.39 housing on the 47 and it wasn't even close to being controllable. It would snap the pin on that gauge at even less change to the gate duty cycle. Even if you managed to control the first stage without a gate, it would be a vicious monster coming onto boost IMO. With no gate to soften the hit by opening as it lit, it might light off like a semi just rear-ended your truck.

As far s the fail safe on the gates, light springs would probably do the trick, that way if you loose a reference line the gates will just blow open instantly. might be tricky to set the gates initially but damn, i think this set up would be fun, and relativly cost effective, you could spend alot of money on wastegates and still be pretty cheap in perspective

For example, sometimes people will set the gate so that it will run ____psi on spring, which is higher than their intended boost, and then they will have a controller that sends ____psi to the bottom of the gate to oppose the spring and allow the gate to open as boost is reached. In this system, when/if the signal line ruptures the boost will jump up to that governed by the spring. Which for a second stage, can be a monsterous jump, and when compounded, can wrap a boost needle around the pin in a hurry.

On the contrary, if instead a person used a spring that was a bit lighter than what would hold the boost they desired, as you suggested, and then ran boost to the top port to supplement the spring pressure so that the desired boost was achieved, if/when the signal line ruptured the boost would simply fall off and the driver would notice smoke and a sluggish truck. No biggie.

The ultimate plumbing circuit from a performance standpoint is to have the spring set as above, so that on spring it will hold boost below what you desire, and then have a 4 port solenoid that will feed manifold boost directly to the top port when off boost, and then start to switch to the bottom port as boost rises. In this way the gate valve can be made to stay perfectly shut until just before the desired boost is achieved and then all the pressure can be diverted to the bottom port to snap the gate open. Once the ramp rate and steady-state values are dialed in well overshooting and valve bounce can be all but eliminated and you get a system that pins the values you want very quickly and very accurately. It's still relatively failsafe in that in the event of the bottom port line blowing off the solenoid will still cycle to 100% duty cycle as the controller attempts to quell the rising boost pressure and the additional pressure added to the spring via the top port will be vented through the solenoid exhaust port and you will be running on spring only. The boost will be higher than it should be, in that the bottom port wouldn't be receiving any signal to oppose the spring and open the gate further, but it wouldn't get as out of hand as if you were running on full spring with a bottom port only setup.

The most failsafe is obviously the top port controlled setup where the spring alone will not support the desired boost.

So whos gunna try it? Im half tempted to not get that 71mm vgt and give it a shot LOL

Do it. You know you want to tell people you're running triples...

 

[lubeowner]

Would the bearings and the shaft in the little turbo be able to handle the stress of that high boost and for how long?

 

[cfdeng7]

If I understand it correctly all of the turbos will be on the low side of their maps keeping pressure ratios low. With low pressure ratios even though its high boost it should be low stress. Charles will be able to correct me if I'm wrong but that is how I understand it.