wastegating facts

I usually start of by setting the secondary gate on the bench at around 26-28psi. I try to shoot for a max of 65psi at the manifold with around 32-35 in the cold pipe. This works out to a very low pr on the secondary.( somewhere around 15psi + ambient)
 
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JWT,

In generalities.

What is "drive pressure" and at what point (or level) does it begin costing horsepower?

More specificly......Given the same fuel input how much horsepower is lost between a full drag race turbo setup and a more streetable application?

Most of the common rail guys that are making big power (800hp plus on #2) are running huge (HUGE) turbos. Is it possible to spin smaller (more streetable) turbos "faster" and still make the big Hp numbers?
 
What does the turbo and wastegate do when you whack it with 500 hp of nitorus? Is this bad? Can compressor wheels be welded back together?

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Well I was thinking about adding an external wastegate due to the dual internal gates not flowing enough. But if adding gates increases BP, I better weld up all my gates!:hehe:
 
Sorry I sold you that wastegate Adam.....I'll take it back with a modest restocking fee of course...lol
 
I have a question. Why is it when i set my top gate to 25,28,35,45,50 or even close it off do i still have a high primary pressure? I am running a s300 62/65.70 secondary and a gt4202-74.5/83/1.15 as a primary with a extrernal gate. When i have 45 psi in valet i see 32 psi off the primary. When i am at 75 psi in full fuel i see 45 off the primary. I have tried many different secondary combo and have also tried a standard s400/1.32 as a primary all with the same pressures. When i lower my primary boost the truck seems to lay over early in the rpm under full power. Before i installed a gate for the primary i would hit 50 psi no matter what charger i ran gt4202 or a s400. Any thought would be appreciated.
 
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JWT said:
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.
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Couple things to note. On the majority of systems that use internal wastegates, a spacer is used between the turbine housing and the exhaust manifold.

Some just get a hole saw and drill out the center devider in the housing to allow gases from the front three cylinders to escape into the wastgate
 
Bponci said:
I have a question. Why is it when i set my top gate to 25,28,35,45,50 or even close it off do i still have a high primary pressure? I am running a s300 62/65.70 secondary and a gt4202-74.5/83/1.15 as a primary with a extrernal gate. When i have 45 psi in valet i see 32 psi off the primary. When i am at 75 psi in full fuel i see 45 off the primary. I have tried many different secondary combo and have also tried a standard s400/1.32 as a primary all with the same pressures. When i lower my primary boost the truck seems to lay over early in the rpm under full power. Before i installed a gate for the primary i would hit 50 psi no matter what charger i ran gt4202 or a s400. Any thought would be appreciated.
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Hard to say brad. I dont have any problems at all keeping my GT42 under control. I usually hit 45 psi total with the Blue Chip turned off, and have about 17 off the primary. After that they start to close in on eachother. WOT it's 27 on the primary with 57 total.

Cruising at 70 MPH, it's 10 total with 3 off the primary.

At 24 psi,there is 9 off the primary.

A 62mm wheel and a 74mm wheel are a little too close in size to get a good rippin compounded set. I have a 60mm wheel in my top turbo, if the whole thing were perfectly compounded, I would have used something closer to 80-82mm,but design constraints changes the end result.
 
FYI, I have a thread over on NWB graphically illustrating some of the concepts discussed here, but I need to rebuild it after the server migration.
 
ok, here is some bait.

Say I have a turbo with this compressor wheel in it. The turbine section is a HX40. On a 300 HP Cummins 24 valve running from 1500 to 3000 RPM would this be able to keep EGT safe?
 

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Thanks a lot DF, I was trying to just lurk and learn LOL

My turbo knowledge is not at the level you guys are obviously at so I was flying low and trying to keep up, like most probably reading this I have learned a lot from both you and JWT!

What an interesting thread though, JWT comes out of the gate with a first post like that, naturally gets his integrity and knowledge questioned, answers back which some very knowledgeable information and is now being respected and looked to for information.

It takes confidence in ones personal knowledge to come on THIS forum and post like that, most engineers will not take the time and for that I give him kudos!
 
However, he came across like a rino. My educational and professional focus is not narrowed into one aspect of Mechanical Engineering...well, this is not entirely true...Cogeneration and Nuclear Powerplants make it slightly skewed, but the nice thing, a turbine is a turbine...regardless of the fluid that passes through it.

Turbos are not a voo doo device. They have to abide by all the thermodymanic principles.

Wastgates are simpler yet...it's an air operated diaphragm valve.
 
Dude, fluid mechanics, and thermodynamics....MY bread and butter!!

I was hoping JWT would really dig into the theory and make me get out some old text books.

But, I am ok with discussing application and practice.
 
Diesel Freak said:
Dude, fluid mechanics, and thermodynamics....MY bread and butter!!

Hey ha maybe you can answer my question...okay i can hit close to 45psi on my stock charger. I have a boost elbow and wondering if i should put it on or not cuz i can't exactly afford another one :(....and like you said or someone did your just blowin hot air pretty much after 35psi (right?). Also i want to know if this elbow will help my turbo bark. I can bark it around and above 25psi like when i shift and if i don't drive it right you know, so will that help it?
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If you are building a compounding system you should select a bottom turbocharger with sufficient flow to produce your targeted HP, at pressure ratio of 2.5 to 3.5.
The bottom turbo is essentially raising what is normally ambient pressure into the top turbocharger. The top turbocharger will operate as normal and raise that pressure by a similar pressure ratio.
The wastegate should not be opened until the targeted pressure or near to it is reached. This will give you the most efficient compounding. You will probably have to use a custom wastegate or an external gate that is capable of higher pressure. Opening the wastegate early will slow down the upper turbo and speedup the lower one. The high velocity air from the bottom turbo can pass through the slower moving top compressor wheel with very little compounding and poor efficiency. If a compounding system has 45lbs of boost on the lower turbo that is almost 60lbs total pressure including 14.7 ambient pressure, if the top turbo has 70 lbs boost that’s not good compounding. Also 45 lbs of boost is at a high wheel speed and does not produce a favorable temp or density into the second stage.
The same boost pressure could be obtained with lower turbo boost levels in the 22-26lb range, on a well balanced system with better density ratios into the engine.

Having said all this I do think though a lot of you people out there have done an amazing job in achieving some incredible horse power with the systems you have built.
I am not trying to criticize any of you or suggest that I am smarter. I am just trying to pass on some of my knowledge that I have obtained in 47 years working with Turbochargers, and with some of the leading turbocharger companies.
I am getting a little older now and it gives me a great deal of pleasure to see how popular the turbocharger has become, at my age I am as enthusiastic about turbo charging as I was in my twenties. Keep up the good work guys.

John Todd
 
Ok so if we are asking questions, I have a S362 and a S480, the 62 has a dual internal = to 40mm, I have an external 50mm gate bypassing both chargers. I will tune the 40mm for street driving with no drugs, then use the 50mm external for the drugs. I have 13mm worth of fuel and over 500hp of nitrous for the Dyno. For the street I am expecting 75 total PSI total with 35 to 40 psi from the 480. For the dyno I am going to gate fast with the 50mm to save the chargers. I am shooting for over 1300 hp.

What am I missing? Comments?
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I would tell the guy in the background that smoking is bad for his health.
 
Joey89 said:
Hey ha maybe you can answer my question...okay i can hit close to 45psi on my stock charger. I have a boost elbow and wondering if i should put it on or not cuz i can't exactly afford another one :(....and like you said or someone did your just blowin hot air pretty much after 35psi (right?). Also i want to know if this elbow will help my turbo bark. I can bark it around and above 25psi like when i shift and if i don't drive it right you know, so will that help it?
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De-tune the engine!!
 
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Cant do that......he decides who stays and who goes.....plus he may not share his beer any more.
 
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