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Street porting a 1.9 big valve head
I've had a lot of requests to share information about porting a 1.9 head for street use. Here's a pictoral on doing it yourself. This is not an end-all method by any means, it is simply a safe way to port a 1.9 head to improve performance rather than hurt it. This particular head is a 1971 1.9 head that has had bronze valve guides installed, hardened exhaust seats, and has had the seats cut for 1.72" and 1.50" Chevrolet valves.
The first thing I will usually do it scribe out the port locations. I don't recommend using the stock gasket as a layout tool, as it's not necessarily ideally sized for street performance. So for reference I've shown some dimensions which I've found work well for street use. Note the port sizes are barely bigger than stock, and are basically just squared off.
I use a head gasket to scribe the bore locations onto the head surface. This is done to show how far the combustion chamber can be unshrouded for improved flow. This step is often overlooked, but it very critical to improved flow with larger valves.
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