CIS Cylinder head question

[Peter Jones]

We had some fun and games vacuum testing this head when I had it reco'd.

It took a little while to figure out that there is a gallery that runs across the back of the head that connects the injectors together. I think this is what is refered to as the "AIR SHROUDING" system.

I'm replacing the injectors, seals, insulators and their o rings.

The head had the fitting that connect to this gallery blocked off.

My question is How does this sysytem acually work and what is the gallery connected to? Vacuum?

In this photo you can just make out the gallery between the injector holders.



Here's a picture of the fitting (its the black plastic piece bolted to the head) I could do with a new one of these if anyone has one lying about.
I'm getting all the injector holder parts from germanautoparts.com



Any info would be much appreciated.

Pete

[VR6 STORM]

Hi,
You are right, that is an air shrouded injector head, with an air gallery that runs across the back of the injectors.

I rebuilt an early Mark 2 Golf engine to go in my MK1 GTI many years ago, and the MK2 engine had this drilling and the assocaited plastic part. My earlier DX code engine didnt have this drilling or air rail.

I still have the Golf and bought it with me when we emigrated last year.
This engine is an EV code i.e. solid lifter 1800 MK2 Golf.

I believe that the plastic stub was connected into the pipework upstream of the vaccum booster in the MK2.

I am not sure what VW were trying to do with this system as there is little data that I have found on it, but I think it was to aid in the fuel atomisation from the injector.
It only seems to be found on early CIS 1800cc motors with solid lifters. I dont think the hydraulic 8V CIS heads had them. Dont quote me on that though.

The early motors that dont have this drilling have different injectors. The later motors with this air shroud system have an injector with a little silver cap on the end and an oring.
You can fit early injectors in an air shrouded head, but if I remember correctly you cant fit later air shroud injectors in the earlier head unless you take off the silver cap (it does come off wit a bit of prying)

I ran mine with this plastic fitting both connected to the inlet system and disconnected and capped and never really noticed any difference.

On a lot of 8V heads you see in scrap yards, this feature on the casting isnt drilled out.

I have actually tapped mine out and fitted a blanking plug now as the car has a turbo techncis turbo kit fitted and G60 injectors with aftermarket EFI (an Emerald system). I had to mess about with machining brass injector inserts to get the G60 ones to fit.

I probably have not answered your question for you, but maybe some of this will help? I can scan some piccies of an air shroud injector etc from a UK manual if it helps?

Regards

VR6 Storm

[VR6 STORM]

Ha ha,
have just looked at you cylinder head picture and noticed that it is a hydraulic one! So ignore that comment about hydro heads not having this drilling... duuuh!!

[Peter Jones]

Thnks for that any info helps.

This motor is a GX prefix, the worst of the 1800s It's in my Mk1 hence the plumbing mystery.

K-Jet, Hyd, low compression etc etc. 85 Hp from memory.

When I pulled it down it had one unshrouded and three shrouded injectors like this.



I'm replacing all the seals so I may as well hook it up. I'll make up a new fitting to replace the plastic thingy and see how it goes.

Pete

[VR6 STORM]

Hi, am pretty sure that that air injector in the picture should have an o-ring on the sliver steel part at the bottom. Are you replacing those too?
I dont think you will go too far wrong fitting it up with the air pipe connected to the intake system. Its just not clear from the books wether it goes upstram or downstream of the throttle body.
Why was that GX motor so detuned? The euro motor was good for 112-115 HP in stock trim.

[Peter Jones]

I'm not sure why the GX is so low spec, it's CR is something like 8.5:1 and the cam is only 250 degrees duration.

Yep there should be o rings at both ends of the injector, I've got all of them new ready to go. There's another o ring in the head under each of the plastic insulators.

Pete

[VR6 STORM]

Funny why they did that as the emissions spec on the early 80's MK1's in the UK was good, never mind
Good luck with the rebuild and if you think I might have any info that can help then just email me.

Cheers

[Peter Jones]

I guess what I'm still after then is a definitive answer on where does this connect? Do an MK 2 owners have an engine bay pic of this item? I'm guessing there was one of those booster valves with the extra small diameter lines coming off the side.

On the face of it, if it were connected after the butterfly it would effectively be connected to itself and there would be no pressure differential to cause air to flow.

In any case I can't see air flowing anyway because every thing else should be sealed.

If it's connected before the butterfly isn't that just atmospheric pressure (minus the drop across the aircleaner) in which case I'd just vent it to atmosphere?

So if it is a vacuum connection and the area around the shank of the injectors is sealed, how does this work? Is the logic to apply a partial vacuum around the injector to act as an insulator? Perhaps the connection is simply a breather to prevent this sealed off area of the injector blowing the o rings as heat causes the air surrounding the injector to expand?

Pete

[Peter Jones]

Here's a quick drawing of how it works.

Each injector is surrounded by a sealed chamber of air.

Each chamber is connected to all the others by a gallery drilled right across the back of the head.

There is a single connection to this galery at the back of the head which connects to ....?????



Pete

[roccodingo]

Hey pete,

Have modified my 1600 injection system to run with the 1800 air shrouded injector head.

From what i have read and heard, the air shrouding helps to insulate and cool the injector from the heat present in the head ( the earlier unshrouded injectors use to suffer from hot start problems, heat build up after turning the engine off would boil the fuel in the injector and lines, making hot starts difficult at times, usually on days with high ambient temps, would require bleeding the injectors of vapour till they started squirting juice again )

The head i am using has a metal pipe pressed into the head *( as opposed to your bolt on plastic fitting) I ran a hose from here to a tube silver soldered onto the metal air pipe that goes from the throttle body rubber bellows to the auxillaury air valve, this way the injectors always recieve air around them ( air supply after the fuel distributor plate, but before the throttle butterflies) and doesnt upset the idle speed or the mixture setting of the fuel distributor.

Good to hear your changing all the seals ( inc the insulator seat seals and insulators) I used these buggers...

http://www.techtonicstuning.com/show...artnum=133.341

HTH..