Dual cooling lines on A Factory Dry Pipe ???

[dlsderoo]

So I have an original factory drypipe for a blaster and it only has one inlet fitting for cooling. there is a 1/4" brass plug next to it but that goes directly into the exhaust probably for water injection. On top of the manifold there is another protruding boss that looks like i could drill and tap a cooling fitting there. But, I started drilling and i'm 5/8" deep and I haven't hit the cooling chamber yet. Has anyone else ever done dual cooling on this pipe?? I'm baffled

 

[dlsderoo]

Maybe I drill and tap it out to 1/2" threads and put a 3/8 x 3/8 x 1/2 tee

 

[dlsderoo]

The Buzzard you were correct I needed to drill a little deeper and I hit the water jacket. Thanks for the support !