http://www.competitiondiesel.com/forums/showthread.php?t=126189&page=4
Claiming 20psi of turbine pressure will build 40psi of boost pressure?
Its a diesel but why does this seem to defy physics ?
OR is it the effects of a huge turbine vs. a small compressor wheel? Still doesn't make sense IMO its like inflow is smaller than out flow

 

My setup runs at a .90:1 exhbp to intbp ratio at 28 psi boost pressure.
It is possible.

 

Agree that it is possible to have more boost pressure vs exhaust pressure (some people call that "cross-over").

Still I would like to see a fairly closely sized Turbine and compressor wheel make 40 psi of boost at 20 psi of exhaust pressure IF everything on the intake tract was sized properly. If the intake trace was restricted some Ford Supercharger guys would make 28 psi of boost and be slower than another Ford racer making 20 psi of boost with the same supercharger. The engines were both 347 cid Ford engines.

JMO

Tom Vaught

 

I think somebody's turbine pressure gauge is broken or not actual turbine pressure. There has to be something to drive the turbo.
I could by near 1:1, but 2:1 and its only a 700ish HP diesel idk.

 

Was it a compund turbo setup?

 

Idk , doesn't sound like it.

 

I have a video on youtube showing the backpressure test I did with the S510.
The ratio was 1.5-1.6:1 with an old Turbonetics T76 Q trim I was running before I started the big experiment of throwing the B/W S510 on a small V6.
The combination with the 91mm certainly would not work without the nitrous assist, though.

http://youtu.be/WwEYZkKCQOM

The reduction in backpressure, along with achieving crossover, which my combination was configured to take advantage of (cam specs and manifolding), meant a difference of 25% BHP between running the T76 and the S510/91mm.

They say achieving crossover is the holy grail of turbocharging. I agree. For the heads I'm running on my car, I am getting exceptional performance.

 

LOL the sky isn't falling any more , the truth comes out

 

There are quite a few modern wheel combinations that will yeild higher boost than drive pressure when sized properly. Pressure ration doesn't explicity define energy availalble to be extracted, you also have higher temps and mass flow (remember, we are adding fuel).

 

What I feel the favorable tp to bp ratio allows is more interesting tuning possibilities that would result in much improved VE.

 

Hey lance,
It's true, exhaust Bp can be lower than boost
I see it on the Dyno regularly with large cat diesels
But, not all the way through rpm range

 

Scearch some of boost engineers posts too..
Tom has a fellow engineer with a twin 91 mm 481 wedge engine, he refers to sometimes...similar results as talked about here...

 

All very interesting... If there really is 2:1 ratios out there we shouldn't need much for a wastegate spring... just feed boost to the control port and it'll never open.

 

Lance. I get the impression that you don't believe a ratio less than 1:1 is possible?

 

No, I understand it can be achieved. Just dealing with wastegating various turbo setups every day I'd have to say on the whole its not terribly common. Truely when dealing with street sized setups. I'm constantly recommending ways to keep the gate shut to combat turbine pressure vs the available boost pressure. Air flow won't open a wastegate valve, its position is strictly effected by pressure. And if there isn't any positive turbine pressure to deal with it should be a simple as using bp in the control port to enhance the spring to achieve whatever pressure is required for desired tp.
But it hardly ever seems to be that simple.

IMHO It takes a Truely Large turbosystem to achieve those numbers (vs total post compressor / pre turbine system air flow).

 

You're right about that, Lance.
Have you ever seen a B/W S510?

 

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I have done a few low boost setups with BW's EFR line (like 10 psi with a 6258 on a 1.6l), and drive/boost never exeeds .7, peak boost at 3500 rpm, spinning to 7k. The 6758 on my 2.3 is .8-ish at 4000 rpm, and 1.2 @ 7,000 rpm (this is running 20 psi).

The most modern wheel combinations absolutely slaughter the old rules of thumb regarding boost/drive pressure. The only negative consequence is much more wastgate is needed than previous experience tells you, as the pressure ratio is no longer available to drive flow through it.

 

Could be why we're using larger and larger WGs and smaller and smaller actuators on top. Soon we'll be using actuators smaller than the valve and 60mm valves on everything LOL. Good thing all my actuators are interchangeable and they support pressure over the top.

 

Yup, truly a B.F.T. when you look at the engine

Turbine size/flow is definitely on climb with the engine truly becoming the biggest restriction. Lighter turbines and bearing drag are really whats making this possible.

 

I'm not an expert, but the B/W S510 is using standard journal sleeve bearings, a large diameter shaft compared to other racing turbos, and the wheel isn't what I would call light. Maybe just a more efficient overall turbine side design?