[T2] where to inject the water

[Chris Dreike]

Robert,
Thanks for the additional information. I have yet to try drilling a hole in
the appropriate spot on my 34 carb. I do know that the vacuum advance port
does not provide the correct vacuum for your famous water injection. That
port provides max 5" of vacuum at mid throttle and none at max throttle.
As for my fuel injection, I'lll need to remove my throttle body and find a
spot just above the butterfly to drill a small hole. Maybe in the next few
weeks I can give it a try.

Chris,
64DD Kamper Kit
71 sunroof



On Tue, Jul 30, 2019 at 7:06 PM Robert Mann <robtmann7 at gmail.com> wrote:

>       For the tiny fraction of ICE users who realise water-injection is
> highly cost-effective, I point out some recent clarifications about where
> to inject the water.
>       For carbs with a throttle butterfly, the general rule which emerged 3
> decades ago persists: a tiny hole just outside the butterfly is the water
> injection site.  As summarised in my article, on the over-run or at idle
> the vacuum here is negligible (just when no water is wanted).  As the
> butterfly opens, vacuum builds to 1/3 atm, and at fast cruising is 1/6 atm,
> suctions so strong that the water feed to that hole must be choked by a
> needle in the range used for blood sampling (c. 0.5 – 0.7mm).
>       The tiny hole in the venturi connects to the nozzle providing vacuum
> for retarding the distributor.  The medical needle is stabbed into the
> rubber connector just outside this nozzle, so as to position the needle
> point inside the nozzle.
>       For carbs with a throttle slide instead of a butterfly, the water is
> injected downstream of the main fuel jet but still inside the throttle
> slide.  I have done this in Amal carbs (on Norton & Jawa motors).
>       Slapping the water needle in *after* the carb, for convenience in the
> carb/intake flange joint, works OK for motors which are flat-out most of
> the time e.g my Jawa 50.  The suction is presumably maximal on the
> over-run, which is not desirable (tho' if some trace of oil can be
> emulsified into the water, it may then help to prevent the piston seizure
> so notorious when hot strokers go onto the over-run at the end of a
> straight).  One racing stroker trying this position for the needle sucked
> up the whole contents of the 150ml water bottle *fast *!  So I fear you do
> have to drill into your Amal  ...
>       The different vacuum connections on VW carbs remain somewhat
> mysterious, to me at least.  My carb happens to be the excellent Brosol
> 'Brasilian Weber' 30.  The vac connection for distributor retard is OK for
> water.  I had to get rebuilt the diaphragm can on my distribr, and suspect
> corrosion may have been caused in that can by water coming down that vac
> tube from the carb.  This potential is a good reason to slap the needle in
> so near the carb that the needle point is actually well inside the metal
> nozzle.
>       For other carbs, the strict way to identify where to slap in the
> needle is to read the vacuum regime at any given takeoff spot by an
> ordinary vac guage on the dash.  Cheap 4mm ID flexible tubing is fine for
> this approx 11' connection to the dash guage.  After you've identified the
> carb nozzle which has the right vac regime, transfer the tube to the intake
> horn so that the guage becomes a conventional intake manifold vac guage, an
> estimable asset.  At worst, you'll have to drill a small hole into the
> intake horn below the carb.
>
>      I have far less experience with the newfangled systems termed *fuel
> injection*, but the general idea is to slap in at least 1, perhaps 2 large
> stainless needles (used to drain c. 1 pint from a vein) in the narrowest
> accessible part of the air intake *after* the filter.
>
> Robt Mann
> '73 1600dp Devon camper
> various Jawa strokers
> <http://www.kuratrading.com/HTMLArticles/writings.htm>
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