Just supposing I decide that a 32mm restrictor is the way to go with my car, where do I get one, or does it have to be custom made?

I found this:
linky

I'm guessing that it's specific to a Subaru Group N turbo. I use a T28 or could use a T25 if this would be better?

My line of thinking is I jamb a restrictor in there with everything else stock, for Perce-Neige... it won't matter _much_ if we loose 25% power on a snow/ice rally... maybe it will even be better. Then I have until the summer to figure out what to do long term.

Commenst/suggestions?

Thanks...Martin.

This was for my Subaru, and for 40 mm (the original spec way back, not much smaller than the bore of the turbo itself). What we did was take a 40 mm bore Weber carb part and adapt it to the turbo. Seemed to work well and should have been designed efficiently. YMMV.

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Don Kennedy

Thanks for the idea Don! I don't believe I have any 32mm webbers though... I do have some 40's... maybe no one will notice :-)

-Martin.

Martin,

Do you have a spare turbo on the bench that you can take good photos of, and accurate measurements?

If you do, i'd be happy to model something for you, and give you 2d drawings. You'll need to find someone to lathe up the piece for you tho.

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Chris

40mm Webers may be taking around a 32mm choke, if you're trying to go that route.

Hi Chris,

Thanks, that would be really helpful!

Yes I have an old junk one (T28) that I could measure/photo. I'll dig it out tonight...

I guess that means I can't just buy a restrictor and make it fit :-)

-Martin

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mekilljoydammit
40mm Webers may be taking around a 32mm choke, if you're trying to go that route.

I'll have to dig those out too and see... not sure if I'll go that route, but might be a good "plan B"

I think you need to build a restrictor recepticle somewhere in the flow path. That way when someone in charge gets their undies in a knot and changes the rules, you take out what you had in and pop in the proper sized restrictor de jour. I'm only half kidding.

Do they specify a location for the restrictor? The farther away from the turbo, the better flow you should have. Also, aim for a 2-5deg taper on the diverging side, and up to 15 on the converging side. I think these are the values for a standard nozzle for max flow without choking.... I think.

Here's the rule:

12.6.3 Turbocharger/Supercharger Restrictions.

Forced induction engines must have an air inlet orifice of 32mm diameter or less. If the forced induction is equipped with a larger inlet, the use of a restrictor is required. It must have a minimum width (parallel to the direction of the airflow) of three (3) mm and be placed within 50 mm of the compressor blades.

If a car is fitted with multiple induction systems, then the total area of the two restrictors cannot exceed the area of the restrictor listed above. Competitors must have in place a mechanism to allow the induction system to be sealed by the use of wire and CARS seals. With the wire and seal in place, it must be impossible to access the restrictor without removing the wire and seal. The wire and seal cannot be installed without a detailed examination of the restrictor and without the seal being in place. Competitors must be prepared to dismantle the induction system to allow for verification of compliance with the rule above.

Not mine, but exactly what I'm working with....

Quote
MRWmotorsports
Here's the rule:

12.6.3 Turbocharger/Supercharger Restrictions.

Competitors must be prepared to dismantle the induction system to allow for verification of compliance with the rule above.

I imagine CARS must have a tool (like RA and NRS have) to insert in the intake system to check the restrictor without disassembling? I don't remember what they did for me at Pines?

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Don Kennedy

I imagne they do, but don't know. It's not a big deal, it's easy to get at.... they need to inspect, and lockwire/seal it somehow so I imagne they would need it disassembled at least for the initial inspection.

In a brainstorming sense, I betcha someone could come up with a plate thingie with a machined hole in the middle that would accept a 40 or 45 DCOE choke; they're retained with set screws, have decentish diverging angles (not perfectly ideal for the application, but not a flat plate either) and for the ones sized for a 40 DCOE, are available off the shelf in 2mm increments from 28 to 36mm bore for like, thirty bucks US. With a lathe, you could even have the adaptor plate thingie taper to open from the 40/45mm the carb choke would open up to, to whatever the inducer of the turbo is... again, not a perfectly ideal contour, but quick and easy to swap different restrictors for different events. And probably pretty cheap, comparatively.

May not be legal for some of the more anal restrictor rules (some rules specify a maximum outside diameter around the throat area to make sure nobody's doing anything clever) but quick and dirty. I'm tempted to ebay a T28 and try to make one for grins.

You know, I think a certain person who makes a lot of green parts and frequents this board may have made a turbo restrictor or two. Just a hint...