digifant head conversion to CIS?

[peterh40]

Hi,

I tried this out on the Cabriolet thread to no avail ("getting my head straight")...I have a 78 rabbit with '87 JH engine based on block number and a head I can't identify that had the original CIS system bodged in with loose fitting plastic injector ports. It's a P/N 025 103 373 AA [space] 3ME with hydraulic lifters and clearly digifant injector ports. It was badly installed in my bunny so I'm bringing it up to the 85-87 era that the block number says it is. So now I have the CIS-Lamda system from an 85 cabby with air shrouded injectors and new inserts to put in...so here are the questions.

1) This one is a little theoretical. The Digifant head doesn't appear to have any port or hole near the injector seat vent holes to allow air to blow down the lower insert...will this affect the spray pattern enough to matter?

2) Is the injector hole bored to the same depth, or would I need to bore it a little lower to accept the lower insert and get the spray to the right place.

3) in order to install the CIS injectors I can: a) put in only the upper inserts b) drill out the head to accept the lower inserts too. c) bore it deeper AND open the hole up. What's best. (I know what's easiest!)

4) I know I could just find another head but I'd rather spend that on other things that need fixing!

The mods so far include installing a Jetronic freq valve control box, a CARB compliant CAT with an O2 port, adding an O2 sensor and control box relay, ditching all the EGR stuff, adding the hall effect based distributor, and changing the intake, fuel distributor and emission stuff to match the engine year... California smog is challenging!

Thanks in advance for any help!

-Peter-

[nairmac]

I run a digi hydro head with CIS. I just used non shrouded injectors and the upper inserts with new CIS green o rings. I have a wideband installed and see steady constant air/fuel numbers. This has been my daily driver for nearly 4 years now, passes NV smog. Works fine.

[peterh40]

So after some more googly study, I realize there is little value to drilling out the head for the lower air shroud inserts since there is no porting to get air from in front of the throttle body, to around the shrouds. It also seems many people have just closed off that port on the head without ill effect.

It seems all the shroud does is help atomization at idle. I guess the small reduction in idle air by blocking that port is made up for by adjusting the idle speed. So that is basically where I'll be to just install the upper inserts and the injectors (maybe with the hats off).

Any thoughts on the idle air loss or on the effect of potentially poorer atomization on smog at idle?

-Peter-

[nairmac]

I run a digi hydro head with CIS. I just used non shrouded injectors and the upper inserts with new CIS green o rings. I have a wideband installed and see steady constant air/fuel numbers. This has been my daily driver for nearly 4 years now, passes NV smog. Works fine.

My engine idles nicely @ 1100-1200 rpm. I believe this is more due to the ported cylinder head and intake manifold and the large single-plate throttle body than any other reason.

[peterh40]

Thanks I really appreciate the reference to real life experience. I guess I'll perform the actual experiment and see how the idle emissions compare with the CA smog limits.

I guess worst case is I have to get another head.