Thread: Waste Gate

What is your expected drive pressure upstream of the bigger turbo's turbine?

Originally Posted by Dougal

Reducing exhaust backpressure has minimal effect on EGT's. I've fitted *tiny* turbines to my engine, backpressure went through the roof but EGT's only increased as much as you'd expect with the ideal gas law.



You don't need to bypass the little turbo unless the big turbo is massively oversized or you're controlling boost levels.
The little turbo can flow a certain volume, but we can increase the mass flow through it easily by compressing the air and exhaust it processes.
The big turbo does this already, when it spools up it'll compress the air and exhaust through the little turbine, letting it flow a bigger amount of air than it could alone, but still only passing the same volume (because it's compressed).

Remember, your engine which sits in the middle faces exactly the same volume flow as always, just it's compressed more. Your little turbo faces exactly the same prospect.

It's like you've taken a standard single turbo engine and put it in a room with double the air pressure. It processes more air mass and it generates more power. But the volumes remain the same.
It's a b'stard to get your head around.

But anyway, 4BD1T or other engine?
There's a guy called "carcrafter" on 4btswaps.com who's plumbing up his 4BD1T for compounded holsets right now.
My original plan of being the first to fit a variable vane turbo, then compounds to a 4BD1T has evaporated through procrastination.

Mate we are both thumping keybords at the same time. posts missed and a bit out of order.

we are on the same wave length but i will add incresse pressur is to incresse temp ( same volume of energy)

as pressure is the difrence between inside and out. or the big turbo the difrence is beween the manifold and the inlett of the small turbo. as it is for the small turbo the difrence being the diffrence between the outlet of the big turbo and the tail pipe BP

you are correct but look at the energy wasted buy the gas fighting past the small turbo, and we doint need to completly bypass, just bleed of a bit. but more than the std waste gate will handle.

any way i think we are trying to teach eac`h othere to suck eggs, but all good, its good to be questiond makes you re think things

Originally Posted by Dougal

What is your expected drive pressure upstream of the bigger turbo's turbine?

ill email my spread sheat though, cast your eyes over it and let me know what you think

Originally Posted by Dougal

Do you know the wheel sizes in your BW compound setup? The wheel radius and the housing A/R ratio gives you an equivalent area at the wheel tips which seems as close to a universal turbo sizing number as I've found.

Is the wastegate on the smaller turbo sensing total boost or the boost from the larger turbo?

There are some setups which start to bypass the small turbo as the larger one picks up. A wastegated little turbo gets part way there but they're bypassing the compressor too.
This one bears the same name (R2S) as yours, but the function varies.
.

The only dimensions I can easily check are the compressor inducer and turbine exducer for the LP turbo. Below is some info I have found. My measurement agree for the LP turbine exducer, but I make the LP compressor inducer approx 52mm vs 53mm given.

K16
Compressor wheel OD 2.39" (60.7mm), inducer 1.60" (40.64mm)
Turbine wheel OD 2.17" (55.12mm), exducer 1.81" (45.97mm)
Turbine A/R 1.1
Mass flow 0.19 kg/s

K27
Compressor wheel OD 3.19" (81.03mm), inducer 2.09" (53.09mm)
Turbine wheel OD 2.16" (must be a typo), exducer 2.47" (62.74mm)
Turbine A/R 1.1
Mass flow 0.38 kg/s

From a BorgWarner article on this particular turbo and its original application;

The high pressure turbine has a bypass valve which is opened by a pneumatic actuator. The engine management system commands the bypass to maintain valve closure up to approximately 2,000 rpm for maximum use of the small turbo’s low inertia and quick response. As the rpm increases, it then opens the valve to regulate system boost pressure and to keep exhaust manifold pressures within limits.

My intention is to use boost pressure to regulate the wastegate. It will involve some trial and error.

Originally Posted by clean32

ill email my spread sheat though, cast your eyes over it and let me know what you think

Look forward to it.