wastegating facts

last i checked the purpose of a wastegate was to control the boost while on the go pedal a blow off valve is used to reduce pressure on decel on th intake side.
 
This is a correction I wrote decelerating instead of accelerating referring to my first post.

If you read my first post I said that (during acceleration)
You have to be accelerating when the wastegate opens. Therefore the boost is rising as the wastegate opens to stabilize the pressure not the wheel speed; the wheel speed will still increase to supply engine demand during acceleration.
As I said before if you look at a compressor map you will see that the wheel speed must increase to maintain at constant pressure as flow demand increases, (follow the speed line on the map) and you will see that it drops off.
 
ford69557ci said:
I looked at a few of my runs on my logger this is a thumper tnetics 102mm with a 60mm gate on a small chevy. tps 100% boost 42psi gate set at 45psi 8000rpm drive pressure 38psi. tps 100% boost 45psi 8400rpm drive pressure 43psi. tps 100% boost 46psi 8600rpm w/g open drive pressure 30psi. That tell me that if your drive pressure is increasing with the gate open maybe you need a bigger gate? I run an external on my 12v also just because they are higher flowing
Click to expand...


I don't want to de-rail this not so informative thread, but wow to this post! 46 psi on a sbc from a 102mm :rockwoot: What kind of hp?!
 
wow. this really took off.

Lets make it SIMPLE!!!

Since you are supposedly talking to an engineer with garrett, then this person should know that pressures dont mean diddly when calculating turbine power...it all about mass flow and temp....or more specificly the combination of mass flow and the change in enthalpy across the stage.

Enthalpy changes with temp more than it varies with pressure.


Constant RPM, Increasing load.

as load increases, to keep RPM constant, fuel and air consumption go up. (resulting from higher boost pressure and fueling rate).

This higher fuel and air consumption result in an increasing mass flow through the turbine.

Turbine power= (Turbine efficiency) x (exhaust gas mass flow) x (change in exhaust gas enthalpy)

when the gate opens, the mass flow across the turbine changes.....

the only reason drive pressure goes up as engine rpm goes up is because more turbine power is needed to run the compressor at a higher engine speed. i.e, more mass must go through the turbine.


yeah, I know..blah blah blah....

now, I need some popcorn.
 
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That would be slightly over 1700 at the wheels with the little chevy. Gas or diesel the same theory still applies on turbocharging. I need the pop corn too this is kinda entertaining. I think I might give turbonetics a call on this subject they are the ones that setup my race combination so I am sure they will have some good input on this.
 
yeah, there is nothing all that special about a wastgate...it's nothing more than a valve.


True, gas or diesel....it's all the same when it comes to turbocharging...just the pressures, temps and air/fuel ratios are different.


I dont even know why devided scroll housings with internal gates which only vent half the cylinders were even brought up....they SUCK in a performance application.

There is a learning curve....but it is not very steep...putting the theory to practice is the fun part
 
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this is true i have destroyed several turbos and engines on my quest for the mid 7's but i have learned alot and have had fun doin it i just need sponsors it gets kinda pricey:tree:
 
Diesel Freak,
You talk very complacently about turbochargers. The dual passage turbocharger is very efficient when used in conjunction with a pulse manifold it utilizes the pumping exhaust pulses from the engine much more effectively than a single volute turbo.

As far as your other statement (it’s all about mass flow and temp.)

In engineering terms we refer to it as density ratio. For that discussion we would need to get into compressor efficiencies and intercooler effectiveness, that is not what I was trying to discuss.

The point I was trying to make was that increasing waste gate size on any turbocharger
Should not be necessary, it is much more efficient on a high pressure system during acceleration to open the wastegate at the max required boost level, to prevent a high back pressure developing on the three front cylinders when using a dual passage Turbo with a single wastegated port. Or higher pressure on all ports when using a duel port wastegating.
This would be even more critical when using a compounding system as the pressures entering the second stage could be as high as 35+ lbs at times, after this passes through the second stage wheel the compressor pressure may be 55=lbs and this is the pressure signal that is sent to the wastegate; so tell me why some of you set the wastegate to 24lbs?
This would be like setting the wastegate 6lbs if it were possible on a single turbo application.

In engineering terms we refer to it as density ratio. For that discussion we would need to get into compressor efficiencies and intercooler effectiveness, that is not what I was trying to discuss.
 
JWT said:
Diesel Freak,
You talk very complacently about turbochargers. The dual passage turbocharger is very efficient when used in conjunction with a pulse manifold it utilizes the pumping exhaust pulses from the engine much more effectively than a single volute turbo.

As far as your other statement (it’s all about mass flow and temp.)

In engineering terms we refer to it as density ratio. For that discussion we would need to get into compressor efficiencies and intercooler effectiveness, that is not what I was trying to discuss.

The point I was trying to make was that increasing waste gate size on any turbocharger
Should not be necessary, it is much more efficient on a high pressure system during acceleration to open the wastegate at the max required boost level, to prevent a high back pressure developing on the three front cylinders when using a dual passage Turbo with a single wastegated port. Or higher pressure on all ports when using a duel port wastegating.
This would be even more critical when using a compounding system as the pressures entering the second stage could be as high as 35+ lbs at times, after this passes through the second stage wheel the compressor pressure may be 55=lbs and this is the pressure signal that is sent to the wastegate; so tell me why some of you set the wastegate to 24lbs?
This would be like setting the wastegate 6lbs if it were possible on a single turbo application.

In engineering terms we refer to it as density ratio. For that discussion we would need to get into compressor efficiencies and intercooler effectiveness, that is not what I was trying to discuss.
Click to expand...

Yes, you are correct...I talk about them like they are nothing more than a machine. It's just a turbo!!!!

As for density ratio...I was speaking about the exhaust side (not the air side)...density ratio is meaningless on the exhaust side.


now on a compound system...say for instance the one I built for my truck. The little gate on the top turbo has a 22 psi TiAl spring set (this is NOT it setpoint)...shimmed 3/16". The gate operates on a pressure differential. Primary boost holds it closed, while secondary boost opens it.

Nothing new here.

The whole system is regulatged by boost pressure from the Primary stage. Which is limited by a 50mm gate with a 1.0 bar spring. It has a simple ball and spring boost controller...it's about as simple as it can get. It's tuneable from 38 psi all the way to over 60 with the turn of a knob.

works great, lasts a long time!!!

so, what exactly are you trying to educate us about? There is a LOT of knowlege here in this board. Some know more than you and I combined...
 
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I think some guys open the secondary=top turbo's wastegate at 26psi because they want more exhaust energy doing work on the more efficient Primary bottom turbo. Once the top turbo is spooled and making boost in the center of it's efficiency island, center of it's compressor and turbine map, why would one wastefully push it further out into the less efficient part of the map when you could instead open a wastegate and divert some enthalpy to that big bottom turbo that is barely starting to make boost.

In fact, why not let the motor breathe easy and get that big turbo spinning, why choke it down forcing all of the exhaust flow through the small top turbine.

Diesel guys tend to size their twins farther apart, or with more of a mismatch. eg. Sourceautomotive twins with stock HX 35 on top and a big ole S-400 on bottom.
 
ford69557ci said:
I looked at a few of my runs on my logger this is a thumper tnetics 102mm with a 60mm gate on a small chevy. tps 100% boost 42psi gate set at 45psi 8000rpm drive pressure 38psi. tps 100% boost 45psi 8400rpm drive pressure 43psi. tps 100% boost 46psi 8600rpm w/g open drive pressure 30psi. That tell me that if your drive pressure is increasing with the gate open maybe you need a bigger gate? I run an external on my 12v also just because they are higher flowing
Click to expand...

See, this is a most excellent post, because:

a) it's not from a book, it's real-world; and
b) it contains DATA.

JWT, you've got some of your theory right, but some of it is most definitely wrong. The data above illustrates this pretty well if you ask me (max boost at a nicely reduced drive pressure). If you want to convince any of us, go put some probes on your truck (if you even have one) and bring back the data. Then we can discuss the findings.

Lacking real data, this thread is pointless wandering argument.

You also need to remember that many modern chargers are double wastegated, and not all of us drive an I6, so thing one thing you are arguing somewhat effectively is actually a rather narrowly defined circumstance.
 
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Ok Diesel Freak what you described there is not a bad idea and I wouldn’t try to criticize your system, on your system you know that you have at least 20 lbs to compound the primary turbo pressure. What I was referring to was the systems that use internal wastegates and open the top one at 24lbs. they are obviously not taking into account the primary turbo pressure that is feeding into the upper turbo and being compounded. In a perfect world if you only had 10 lbs of pressure on the lower turbocharger the total pressure entering the upper turbo would be over 24lbs. 10lbs+ambient pressure 14.7 at sea level = 24.7 lbs and that is before it has been compounded. The pressure that is opening the wastegate as you know is the compounded pressure so on the systems with a single wastegate on a dual passage system are virtually running the top turbo on the 3 front cylinders of the engine.
The upper turbocharger should be the stock turbo or similar size (a larger one can be used for extreme horse power; like dragsters that don’t have the best street drivability), the lower turbo should be selected for max flow requirements. If the top turbocharger does not have a restrictive exhaust housing when running on the engine as a single unit it will not be restrictive on a compounding system.
You are also better of to run the bottom turbocharger at lower pressure, I try to keep the lower turbo around 25 – 30lbs of boost this allows it to run at a lower temperature and pass though choke if necessary without overspending the compressor wheel. On some of the systems I have built for racing or hill climb events. Correct selection of the turbochargers and piping size is critical for best compounding
If you have 28lbs on the lower turbo that is a little lower than 3 bar. +14.7 = 42.7lbs total pressure going into the second stage; if the top turbo is running at the equivalent of 2.5 pressure ratio, the total pressure on an efficient system would be 106.7lbs; less ambient pressure; would be about 92 lbs of boost. Give or take a few lbs.
This is approximately what we achieved on 60 series Detroit at 1600 hp and over 3000ft lbs of torque. We use an external wastegate on the upper turbo only, but for lower boost systems an internal wastegate can be used with custom actuator.
 
JWT.

Mr. Todd.
I enjoyed the TDR Magazine article. I am one of those guys that opens my secondary at around 26psi. After reading the article I am a bit confused as my results on the dyno have been favorable set like this. I admit to being somewhat of a turbo slut and enjoy reading all I can about compounds. If you are ever going to be down in Northern California, I'd enjoy meeting and listening to your thoughts on the matter. A better setup is always my goal.

RonA
 
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I think your missing the point about the 24psi thing. People are setting their actuators with shop air to open the gate at 24psi. That doesn't mean the secondary is making 24psi on it's own because the drive pressure also acts upon the wastegate pucks. In reality when calculated it's more like 10-12psi (unless the primary is slow to spool then the numbers will be higher). Making the larger primary do most of the work after it is spooled is a much more efficient system. Essentially the secondary jump starts the primary and then get's out of the way.
 
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