Restrictor reduces mass flow.

Mike Halloran
Pembroke Pines, FL, USA

But increase flow speed?

I have the impression that English is not your first language, and that what you are calling a "restrictor" is really something else. Please post a photo or diagram of the device that you are talking about, so that we can identify what it really is.

A "restrictor" serves the function of reducing flow, and nothing else.

Putting a "restrictor" in front of a turbo compressor with the sole function of being a pressure-drop device, so that the turbo has to work harder, at a higher pressure ratio which means it has to spin faster to achieve a given boost pressure, is never going to be a good thing to do. NEVER.

Yes, English is not my first language, sorry for my mistakes :)I'm talking about "restrictors", which is used in WRC cars. Like this http://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/iE8AAMXQW...

That is NOT for increasing power.

That is required by the rulebook for LIMITING the power. The rulebook somewhere will require that all of the engine's intake air has to be drawn through something with either X mm diameter or X square millimeters in area (I don't know what X is, it is "a number").

It's a rounded venturi shape because that minimizes the restriction. It's right at the turbo inlet because that's where the effect of that restriction is "least bad".

But make no mistake, that engine would make more power and be capable of higher boost and would be less prone to blowing up the turbo if that thing were removed and the diameter of the turbo intake duct were no smaller than the diameter of the turbo inlet itself.

It only exists because the rulebook requires it to be there. It's a nice, rounded, aerodynamic shape because minimizing the "bad" effects of what the rulebook says they have to do, is what race engineers do.

i didn't say that it increases power :) i found one article which says that it increase torque at low-med rpm's, because it "accelerates the gases flowing through it and directs the air flow to the center of the turbocharger's compressor wheel" (link http://www.rallycars.com/Cars/turbo_restrictors.ht...'s posible, yes?. Thank You Brian and Mike for Your answers, and i want to ask another question about turbo's, but i don't want create new thread, maybe someone can explain to me, why on some turbochargers around inlet wheel are circular or other shape holes? like this http://image.eurotuner.com/f/news/eurp_1202_turbon...
http://www.sonicperformance.com.au/productimages/8...

article link don't work in my previous post, there's new http://www.rallycars.com/Cars/turbo_restrictors.ht...

Consumer products often contain arrays of features in attractive patterns, included for the sole purpose of helping the product fly. ... off the shelves.

I.e., there may be some actual technical function associated with the features pictured, or they may be a marketing function.

Mike Halloran
Pembroke Pines, FL, USA

I find it very difficult to believe a restrictor can increase torque. I do know the engines will be tuned for peak power to occur at lower engine speeds (reduced friction). This will result in higher torque at these speeds, but that is a tuner decision, not a benefit provided by the restrictor.

The restrictor "caps" air massflow at the choked flow value and essentially makes these "constant power" engines ie very flat power curve - falling gradually with rpm as friction and airflow (VE) losses increase.

je suis charlie

The restrictor may well increase power at flows short of choking but will reduce maximum power relative to an unrestricted engine. I believe –but will defer to actual expertise- that the turbo impeller is velocity sensitive and will do a bit better with higher velocity (lower pressure) intake flow. This assumes all the variables are optimized. An unrestricted engine would be optimized for higher flows and probably compromise the flow at restrictor levels.

Quote (Overrun)

I believe –but will defer to actual expertise- that the turbo impeller is velocity sensitive and will do a bit better with higher velocity (lower pressure) intake flow

Since the compressor's job is to increase the density of the air above ambient, I'm finding it hard to imagine a situation where it would be able to achieve a better outcome when starting at a deficit. It could be that for a specific compressor, in a very narrow range of specific conditions, your hypothesis may prove to be true, but I think generally, it is false.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

"The presence of the restrictor, which actually accelerates the gases flowing through it and directs the air flow to the center of the turbocharger's compressor wheel, essentially increases the engine torque. We can roughly estimate the drop in engine power to be as high as 40% whereas the engine torque can be increased, through appropriate engine management, by around 20%"

That is a load of crap. Unless the car is operating at high speed and has a functional aerodynamic intake scoop, the only driving force causing air to flow through the restrictor is the pressure difference created by the turbo. Engine torque is proportional to mass flow, and for a given mass flow, a larger pressure difference will be required with the restrictor present. This means the turbo will be operating at a higher pressure ratio, and using more energy, creating backpressure and limiting output. Velocity of the airflow through the restrictor is irrelevant.

I think what this article is missing is this:

For a given engine, with a given maximum intake pressure limitation, there exists a certain size of turbocharger that will produce maximum peak horsepower. This configuration will have reduced low end torque due to the inefficiency of the large turbocharger at low mass flows. Let's say for argument sake on a given car that this 'optimal' turbo has a 67mm inducer.
If we then make a rule that this engine must be fitted with a 50mm restrictor near the turbocharger inlet, the 67mm turbo will go in the trash and we will fit something with a 50mm inducer, or maybe slightly larger. Now we have a smaller, faster spooling turbo which will make much more low end torque but run out of steam at high mass flow rates. We will make more low end torque, but much less peak power. For a high revving engine, this could in fact mean that peak torque is increased but peak power decreased.

In other words, the increased torque is not due to the restrictor, it is because the restrictor forces the team to fit the engine with a smaller turbo.

Yes, turbo matching for lower rpm is typical for restrictor engines.

No, the inducer will not be smaller, in fact for a given power output (same massflow), the restricted engine will need a larger inducer since the compressor intake air density is lower.

je suis charlie

Who said anything about given power output?
The reference being discussed clearly states 40% drop in peak power.

"The reference being discussed clearly states 40% drop in peak power."

. . . and in that context I would assume they are referring to a given engine and turbo combination with restrictor added. Funny (I just did the calculation) a choked adiabatic restrictor produces a 40% drop in air density.

je suis charlie

Quote:

maybe someone can explain to me, why on some turbochargers around inlet wheel are circular or other shape holes? like this: http://image.superstreetonline.com/f/news/eurp_120...
http://www.sonicperformance.com.au/productimages/8...

Hi, i find out for what reason this holes are in turbo's, it's "anti-surge" or "ported-shroud" housing.
"A Ported Shroud compressor is a feature that is incorporated into the compressor housing. It functions to move the surge line further to the left by allowing some airflow to exit the wheel through the port to keep surge from occurring. This provides additional useable range and allows a larger compressor to be used for higher flow requirements without risking running the compressor into a dangerous surge condition. The presence of the ported shroud usually has a minor negative impact on compressor efficiency."
http://www.turbobygarrett.com/turbobygarrett/surge...