16V K headed turbo, race engine, need for restrictor
Turbo Mini Forums

The onset of failure of the compressor due to insufficient inlet pressure will feel like a stone wall.

The flow will get to a point where vacuum pockets start to ocurr at the compressor inlet. Then it just wont go any futher.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

But to what extent ?

R5 GT Turbo use a 32 mm carb and can be made to deliver impressive bananas.

So what power limit are we talking about ?

Rusty by nature

addy ,having the restrictor after the turbo ,eg r5,makes a totally different set of rules come into play.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Sorry, I understood "close to the inlet" the wrong way ...

Rusty by nature

I will ramble on a bit here, as I am midway designing the restrictor.

As the rules do not state anything about orifice distance from the compressor wheel I want to place it far out from the wheel, and have a diffusor angle of between 7 and 10 degrees to help the flow recover before hitting the compressor inlet. I have also planned to taper the diffusor all the way out to the ID of the throat of the compressor housing, and not just to the compressor wheel. This throat is 68 mm, while the compressor wheel is 50. The restrictor is 32 mm.

I am planing on making the restrictor something like this:


The inlet is on top.

I have then using equation 4-50 in the following http://www.chem.mtu.edu/~crowl/cm4310/Chapter4b.pdf calculated the choke mass flow of air to be 0.27 kg/s, which at this non elevated pressure is about 0.23 m3/s. This is more than I would ever need, and is enough for 340+ hp the way I understand it. Would this then mean, that if I have a turbo that can manage to leave with 0.528 bara at the inlet while still giving me the desired boost pressure I would have no real loss due to the restrictor. Any of you maths people (Paul? :) ) please advice!

Many thanks in advance!

also, do you think that the floXpress in Solidworks would have any meaningful usage in this exercise? I have tried (as you can probably see from the lids)...

I did some work trying to analyise maximum compressor air flow based on the inducer diameter here:

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=390242

Your use of equation 4-50 assumes that you have a pressure ratio of at least 1.67. So if you have 15 psia at the inlet of the restrictor, then you will have 9 psia at the compressor inlet.

9 psia is a bit low and my guess is that the compressor will be limited well before then.

What will actually happen is that you will reach a point of equilibrium where the maximum air flow will create a pressure drop across the restrictor which will be at the limit of the performance of the compressor inlet. i.e its "sucking" ability.

My only experience with Solidworks was with the simple built in CFD. That would not do anything other than show the amount of diffussion was optimal.

How have you derived the venturo profile? It looks good to me, but there are some published optimum profiles somewhere.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

The venturi profile is purely based on readin some info around and drawing in Solidworks. I have had troubles finding anything scientific about optimum profiles.

Why do you think 9 psi at the inlet is a bit low? it will only increase the pressure ratio for the compressor no? or would it also hurt it in other ways?

As the absolute pressure at the compressor inlet drops towards zero, there is a point where it will start to deliver less flow than shown on the compressor map due to separation (vacuum pockets) in the inlet stream.

This will depend very much on the inlet design of the compressor wheel and the speed of rotation.

Google "venturi flow meters" for optimum profiles.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I've only skim read so forgive me if this has been mentioned, but the WRC cars due to the restrictor are tuned for massive torque. They "only" make 300bhp but they do so at relatively low revs, so make huge torque. They make use of this with the 7 speed boxes, you only have to hear one flying through the forests pulling gear after gear using the torque to work out how they are fast and still have the restrictor.

I know Tom. They wont make any more HP after around 5000 rpm. but this is in a 2 litre engine. I am only using a 1.343 liter engine.

Just get some long intake runners on it Andre.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

:) the intake runners from the o ring face will approximately be 180 mm. and then there is some centimeters from the end of the trumpet to the wall in the plenum

this is a close to optimum restrictor according to the following source: http://nepis.epa.gov/Exe/ZyNET.exe/500013Z...s=10&ZyEntry=13

it ends up being 33 cm! :)

My understanding is that if you limit the angle of the tapers to 10 degrees (5 degrees each side), then the pressure loss is minimised.

I would just make your original design a bit longer.

On the intake runners, 280mm from head face to trumpet would be the ideal for a race engine with limited maximum air flow, based on my simulations.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

thats on a 5 port right Paul? This is a Bmw 16valve head. 280 mm would be well outside the grille even on a Clubbie like mine...

That's on a 7 or 8 port.

Marcel has it sorted:



Thats 18", 450mm to get peak torque down at 3000rpm.

Edited by Paul S on 19th Aug, 2011.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I guess this also depends on cams, cam timing, valve sizes and other things like that though?

Yes, everything needs to be working in harmony.

If you are using the 285 cams, then you may not see as much benefit from the longer runners.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I am using the SC sprint cams. One of the reasons we get away with 12:1 cr

In that case, use the revs and limit the boost to what can be efficiently delivered by the turbo and restrictor.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Thats the plan! We are planning to keep the powerband where it is, just raising it. The restrictor should not be to much of a hinderance according to the guy I have seeked help with for this build. I thrust him, but gind it rewarding to figure it out myself as well.

He is very experienced with e85 fueling and is the general agent for comp turbos in europe. He supplies turbos to a lot of the european rallycross guys, including sverre isachsen, which is current european champion, and they also run restrictors.