1.9 Head Porting for Street Applications

[RallyBob]

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.

[RallyBob]

Starting with the exhaust port, the bowl area is blended from just off the valve seat to about 1/2" into the bowl. Try not to make this area too big, the idea is simply to get rid of the sharp edge/transition from the cutting of the new seat by the machine shop. When grinding the short side radius, I begin by grinding straight 90 degrees perpendicular to the exhaust seat, and then rounding the radius over and smoothing it out. This method helps to provide a reference point rather than just randomly grinding and not knowing how much material you've removed.

So far, the only tools I've been utilizing are my air powered die grinder and a 1/2" diameter oval-shaped double cut carbide burr. The shank I'm using is 4" long, which has plenty of length for access to any parts of the ports.

[RallyBob]

Moving onto the bowl area of the intake port, these first two pics depict the worst part of the intake port. Note the significant 'lip' that upsets the airflow past the seat and into the combustion chamber. And this is with a valve that's .150" larger than stock! This is one reason that I prefer the larger intake valves (1.85") because it eliminates that lip.

On the opposite side of the intake bowl, you can see there is a lot of 'meat' adjacent to the valve guide boss which also impedes flow. I basically 'hog' this area out with the 1/2" carbide until the radius between the guide and the side of the bowl matches the carbide's radius. From this point, the seat-to-guide area is blended in smoothly, but making sure I don't make the transition to the seat a sharp angle, but rather radius it slightly so there is a smooth transition from the 60/45/15 degree seat into the bowl. Note: this will be difficult to do at the 'lip' area I described, since by nature the bowl already undercuts the seat area by a little. So minimal removal of material below the 'lip' helps to ease this radius a bit. It won't be as good as the opposite side of the bowl no matter what, so do what you can and don't worry too much about it!

[RallyBob]

This first pic shows the' lip' area after grinding. Certainly not perfect, but you just gotta deal with it! going to the larger 1.85" valves would completely eliminate this lip, but with 1.72" valves some will always remain.

By now the intake throat area has started to show a lot of improvement compared to earlier photos, you can see how the transition is smoother and the bowl width has increased substantially.

I then jumped to the intake guide area, not removing it completely, but rather smoothing it into a shape reminiscent of an Opel GT's hood bubble. This flows better than leaving the entire guide intact, but will last longer than a full competition prep where most of the guide is ground away.

[RallyBob]

The first pic in this series shows the bowl area complete, but the roof of the port has yet to be touched. The second pic shows the finished roof...this was not excessively ported, maybe 1/16" of material has been removed.

Next is the intake port side at the center divider. There is a slight bump here that coincides with the head bolt hole between the intake ports. Some material can be removed here, but being overzealous with the grinder can break through to the head bolt hole. I started by grinding about 1/16" of material away at the 'peak' of this protrusion, shown in the photo. Once this is done, then the entire side wall is lightly ported....basically the carbide is simply floated over the surface to remove the surface roughness and to blend it into the protrusion that was just ground down.

[RallyBob]

The opposite or 'outer' intake port wall show here begins with a straightening of the port entrance...perhaps for the first 3/8" to 1/2" of the outer port wall. Once this is done, again the port wall is lightly 'floated' with the carbide to removed the rough casting and blend the port opening to the rest of the port wall and all the way to the bowl area.

At this time I also straightened the short radius of the intake port, and rounded it into the intake port floor.

[RallyBob]

In this next sequence, the exhaust valve guide is slightly streamlined. I begin by removing some material from both sides of the guide, not grinding into the roof area or the sides of the port, only removing the material around the guide itself. The top edge of the guide is ground down until it it roughly parallel with the roof of the port.

To give an idea of how effective just blending the bowl and trimming the guide is on a 1.9 exhaust port, these two simple mods improve the exhaust flow by almost 40%!

[RallyBob]

Nothing special as far as finishing up the exhaust port....just a matter of blending the port opening to the rest of the port, and to the bowl area itself. No significant material needs to be removed, again just 'floating' the carbide over the port surfaces to smooth any irregularities out prior to polishing.

[RallyBob]

The last step in the porting process is the unshrouding of the combustion chamber. This is a very critical step for improved airflow, especially for the intake side of things. The first photo shows the intake unshrouding half done...this sort of indicates just how much material is removed from here to let the intake valve breathe, especially at low valve lifts. Comparing the unshrouded chamber next to the stock chamber, there's a noticeable radius to the unshrouded chamber.

The final steps to finish the porting would be to polish the ports and combustion chambers. While I didn't show these final steps here, my preference is to polish the intake ports with 36 grit sanding rolls. The course finish helps to keep the incoming air/fuel atomized. I've noticed a big difference in low rpm and cold-start driveability compared to an 80 grit finish.
For the exhaust ports and the combustion chambers, I like to start with 80 grit and finish off with 180 grit. Carbon buildup is less noticeable with the smoother exhaust ports although the airflow gain is neglible.

That about covers it for basic Opel head porting, it's not rocket science, just common sense stuff and the knowledge of a few small details that can make or break the hp potential.

Bob