# Air Shrouding injectors



## chickenfriend (Jan 31, 2005)

I was wondering if the reason VW dropped the air-shrouded injector was because EFI made it obsolete?
I would expect the Air S. would have made some contribution to fuel economy and power. Were there any published facts on that, and would a comparision or fuel economy or hp ratings between 1983 and 1984 GTI's be a valid to evaluate that?
Where is the tap on the intake system for the air shrouded vacuum?


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## polskipolak (Aug 22, 2003)

*Re: Air Shrouding injectors (chickenfriend)*

I have seen threads that explain what the air shrouding was for. I think it was for better atomization of fuel (??) you should be able to find something in the search. 
As for where it hooks up: It is attached to the backside of the cylinder head between cylinders 3 and 4. From there it goes to a connector on the bottom side of the intake boot thats attached to the throttle body.


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## chickenfriend (Jan 31, 2005)

*Re: Air Shrouding injectors (polskipolak)*

Thanks a ton for drawing that.


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## wclark (Mar 28, 2001)

*Re: Air Shrouding injectors (chickenfriend)*

Air shrouding was introduced to improve fuel atomization at idle, when the periods between intake air pulses past the injector are long. During this idle period the injector is still spraying fuel and with little air movement it does not remain atomized well. The air in the shroud comes from upstream of the throttle body where the air pressure is higher than in the intake, at the injector location, during idle. The air is directed behind the metal cap on the injector where it mixes with the fuel spray at a fairly high velocity to atomize the fuel and help it remain suspended in the intake until it is drawn into the combustion chamber.
Pulsed injection systems do not deliver fuel to the intake during the period between combustion chamber intake strokes so do not need to worry about the fuel remaining atomized for a relatively long time.


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## chickenfriend (Jan 31, 2005)

*Re: Air Shrouding injectors (wclark)*

So, can you notice a difference in the smoothness of the engine at idle with air shrouding vs non-shrouding? That should be easy to test.
And, how if any is fuel economy improved, mpg numbers? That should be fairly easy to test averaged out over a few tanks. I expect more idle time the better the benefit.
If there are not any noticeable, significant benefits to air shrouding, is it then just for better emissions?
Thanks for the theory.


_Modified by chickenfriend at 11:43 AM 4-30-2007_


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## ABA Scirocco (May 30, 2001)

*Re: Air Shrouding injectors (chickenfriend)*

FWIW, I've never noticed any significant difference in performance either at idle or off idle between the two, nor do I know of anyone that has. From Walter's description, to sounds to me like this might be, primarily, a means of reducing curb idle emissions.


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## wclark (Mar 28, 2001)

Emissions primarily. If there were an idle quality issue with the non-shrouded system, Bosch would have done something before 1984 when they began using on some CIS-E (or KE-Jetronic) systems. VW, Audi, BMW, Volvo, Mercedes, Porsche, Peugot, Ferrari, DeLorean, Lotus, Saab, Rolls, all used some form of the Bosch K and/or KE-Jet systems (continuous type = CIS) and most started before Bosch introduced air shrouding.


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## chickenfriend (Jan 31, 2005)

*Re: Air Shrouding injectors (wclark)*

Thanks for the comments.
I Googled for more info on air shrouded injectors but nothing came up as far as any proven effect on fuel economy or power.
The most specific information was about how they effectively reduce hydrocarbon emissions at idle.
There probably were studies on it back in the day, but those are not on the web.
The most interesting question I had answered by the search was why the one-piece intake gaskets have that wierd looking arch-to clear the air nozzle on the head.
True that the air shrouded injectors returned on mk4's?


_Modified by chickenfriend at 7:26 PM 5-1-2007_


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