This is a 026 103 373 aa I believe: looks like a hydro tappet kjet head with the air shroud tube (lower emissions at idle through better fuel atomisation). If so, can not drill. (Pictures pinched from vwcaddy.com) What carb are you using? As Danster said, the coolant preheats the manifold for better fuel atomisation. For the carb it's only necessary to have coolant flow through the manifold if you're using it as originally fitted, as the coolant controls various temperature-dependant warm-up valves in the carb. If you were using a manual choke with cable, it's not really needed, as the manifold also has an electric hedgehog heater inside iirc.
I have just double checked the part numbers on several heads, 1987 digi head pn 037 103 373 (no air shroud) 1988 digi head pn 026 103 373 AA (no air shroud) 1987 kjet head pn 026 103 373 AA (air shroud drilling present) Your head looks like it would be ok to open up the water way, but it really is not that important to do this. It looks like it has been quite nicely ported so presumably you are after power gains. Keeping the inlet manifold cooler will help slightly with reducing intake charge temperatures. As Alex mentions, the coolant heated manifold is more to do with emissions and carb icing on a std engine.
danster thanks for the info i will be drilling the hole as even tho i am putting a webber on it i don't want to have any carb icing issues. and yes you are right this is a ported head courtesy of vagabonds (aka martyn) over in wales, he did me an intake manifold to match it so should see good power gains from it. cheers john
rich can you measure the angle of the hole or stick a drill bit in the hole and take a picture from the end of the head so i can see the angle. thanks john
Personally, I wouldn't think coolant flow through the manifold will make any difference to carb-icing. There's a rubber gasket/flange that effectively reduces heat conduction into the carb body from the manifold to a minimum, to avoid boiling the fuel in the float chamber. Little or no heat will rise by convection up towards the vulnerable bits of the carb, because whenever the engine is running, there's airflow the opposite way, down through carb into manifold. The mechanism that does most of the carb-icing-prevention is the thermostatic control of air entering the carb at a nice mild 20C. Factory airbox, when working/maintained with non-leaky vac hoses, non-stuck mixer flap, intact warm-air hose and non-gummed-up thermostat does a good job of this.
hells bells that is a steep angle oh yes and thanks for the pic! off to work out the exact angle i need to drill hole at now cheers john
rich can you measure the angle of the hole and see what you get? as me and jerry(bristolfish) look at it the other day and are abit unsure of the actual angle we made it between 42 and 50 deg from the head, can you check yours and let me know? cheers john
My eldest is asleep and he has a protactor/compass so my maths are failing and can't figure another way to measure and accurate angle, unless theres another clever way?? Failing that can do it in the morning.
do it in the morning bud just stick an 8mm drill in hole place piece of card of paper against head and draw a line on piece of paper along edge of drill bit then take paper indoors and measure angle with protractor, simples cheers john
