Before we begin, let me apologize for the wonky color balance in this update’s photos. I had the white balance set wrong on the camera, and although I corrected it to some extent they still look a little weird.

Drunk with success from porting the turbocharger housing, I decided to match-port the exhaust manifolds too. Although the real-world benefits will probably be slight, I figured that since I was going to refinish the manifolds anyway, I might as well work them over internally as well. Here’s how I did it:

Unlike the manifold-to-turbocharger junction, I can’t simply use the carbon marks on the manifolds as a guide. That’s because they won’t be going back onto the same heads they came off of in the first place. Here, we can see that McCoy has done a little work on cleaning up the ports, and even if they were as-cast, they might be different from my old heads due to production tolerances and core shift.

In order to match the manifolds to the heads, I need to make a template. The cardstock that Airborne Express uses for their overnight envelopes is perfect for this. Step one is to cut a piece to fit over the ports and secure it to the head with some tape so that it doesn’t move around while I work on it.

With the cardstock in place, I use a ball-peen hammer to gently tap where the first manifold bolt hole is. I’ll use this as a registration mark to make sure that my template isn’t moving while I mark the other holes.

By gently tapping around the edges of the port, the cardstock gets "die cut" into a perfect image of the port. Now that the first one is complete, I’m locating the next bolt hole by feel so I can punch it out as well.

Next, I move on to the far port, marking its outboard bolt hole first as well. You can see by the way I’m holding the hammer exactly how little force it takes to cut the cardstock against the sharp edge of the port.

Just one more to go… To make sure I was getting an accurate template, as I started each new cutout I made sure that the previous holes were still in alignment and the cardstock was flush with the surface of the heads.

With all the holes punched, a quick once-over with the hammer makes sure that everything is completely punched out.

The finished product, labeled to show what side and orientation is correct. The same process is repeated on the other side, obviously…

Now, time to prep the manifolds. Because there’s no gasket installed between the head and the manifold, the machining of the mating surfaces is critical for good sealing. Rather than risk screwing this up with abrasives, I elected to simply clean the flanges as best I could with some carb cleaner and a rag. I still may end up retrofitting gaskets just in case, though.

Sorry for the terrible production values in this picture… The manifolds are located on the head by the two center port bolts. The other four bolt holes are intentionally oversized to allow for production tolerances and the expansion and contraction of the headers. Here, I’ve dropped a couple of bolts into the center port holes in order to properly center the template, then taped it in place. You can see that there’s a slight mismatch on the outside edge of this port, and the same is true on the other end. The center port is actually a pretty good match.

The template is used to mark the manifold for porting. An expert would use machinist’s dye here, but a magic marker works OK, too.

With the manifold secured in the bench vise, porting begins with a carbide bit to do the rough shaping.

Here’s what it looks like after the basic cutting is done. With the mismatch corrected, all the ports get treated to some grinding to increase their size by about 1-2 mm to make them larger than the openings in the head. By creating a "step", in theory a barrier to return flow is created. While this is now a well-established practice for normally-aspirated and supercharged engines, it’s anyone’s guess what it will do in a turbocharged application. I couldn’t find anyone who thought it might be detrimental, so I figured  it was worth a shot.

Finish work continued with 40 and 80 grit rolls, and was completed with a 120 grit flap wheel. Considering all the bumps and intrusions into the flow path created to clear the mounting bolts for the manifold, I didn’t bother to put a final buff on the runners. Instead, I tried to smooth out the transitions and the short-side radius in the first inch or so of the passages. I know that most of this effort is probably wasted compared to simply switching to tubular headers, but I want to stick with the stock manifolds. Besides, right now I have more time than money, and the novelty of porting hasn’t worn off yet.

Now that the manifolds have been taken care of internally, the next step will be to clean them up in the
blast cabinet and coat them on the outside, then strap them to the new motor.