Holler: Cylinder Head Porting, Part 1
Allpar’s own Bob O’Neill is assembling a 2.2 Turbo engine for his ’86 Daytona C/S with the goal of hitting over 200 HP at no more than 12 psi of boost. In addition, he expects to maintain mid-30s mileage while tooling down the highways and byways of this great nation. Of greatest importance is attention to detail on the cylinder head. The head with its ports, valves, and combustion chamber has probably as much effect on performance and economy as practically all other aspects of the engine. For Bob to meet his somewhat lofty goals, the cylinder head most certainly has to be a major player.
Figure 1 Inspect all of the cylinders for cracks, even around coolant passages.
The head used will be a garden variety 782 Swirl Port casting. For starters, the head is completely disassembled. The sensors, studs, fittings, valves, and everything else is removed. This leaves us with a bare casting. If you missed it, we covered preparing the valves in a separate article.
Many of these heads have been known to crack. Before spending 20+ hours porting this one, it will be sent off to a competent machine shop to get a generic cleaning and pressure testing. Cracks between the valve seats are common on these heads and as long as they pass the pressure test, these cracks can be ignored.
Figure 2 Heating allows the guides to be pressed without damage to either the head or the guide.
Once back from the machine shop, the head goes in the oven and gets roasted to about 325 degrees. This will allow the guides to be pushed up into the head, where they will be out of the way for porting. A special tool I made up is used to push the guides without damaging them. A few taps with the hammer, and we have lots of grinding room below. It should go without saying that the hot head should only be handled with heavy leather gloves, and after pushing the guides, allow to cool.
|The guides are pressed up into the head and out of the way of porting.||Sometimes called gasket matching, port sizes are established.|
I like to start by opening the port inlet to gasket size. The intakes should be opened out to the exact size of the gasket on the sides and top, while leaving the floor alone. The exhaust ports get opened up within 1mm of the gasket size. I try to leave about a 1mm border on the exhaust ports of the head and the intake ports of the intake manifold. The exhaust manifold gets opened up to the full gasket size and the intake ports in the head get opened up to the full gasket size. This leaves a very small step from the intake manifold to the head, and from the head to the exhaust manifold.
Figure 5 After opening size is established, the walls are opened up back into the port.
As I rough out the shape of the port openings, I try to somewhat blend the walls back into the throat of the ports. After the port openings are roughed to shape, I mark around the perimeter with a magic marker. As I open the rest of the port, the magic marker will tell me when to stop so I don’t make the port inlet even larger by accident.
Figure 6 Magic marker prevents opening the mouth up more than wanted.
This port opening size should taper every so slightly into the port, converging at the short side radius. This taper serves us 2-fold; first accelerates the air and fuel as it enters the turn into the bowl, and secondly it accentuates the Powre Lynz we will be adding after we achieve the shape we want.
Figure 7 I use a gauge to keep the port widths the same.
Speaking of shape, more material is removed from the tangent side of the port to bias the flow along that side. By biasing the flow toward the tangent of the cylinder, it enters the cylinder in a natural spiraling swirl. This swirl helps to better homogenize the air and fuel. The overall size of the port width is checked with a gauge (or inside calipers). With the width equalized to the proper size, the ceiling of the port is hogged out to improve flow, and keep it riding somewhat high in the port. Looking down a finished port, it appears that the guide is in crooked. This is due to the angled roof. Keeping the cylinders equal is important.
|Figure 8 The port bias can be seen here.||Figure 9 Biased and cleaned up with a sanding roll.|
The exhaust side gets the same biasing treatment. By inducing a bias on the exhaust stroke, velocities can be enhanced while jump-starting the swirling process. During valve overlap this exhaust swirl will start the directional flow on the intake charge. Again, port width is checked and equalized.
After the ports are shaped as carefully as possible, a sanding roll is installed on the die grinder and small irregularities are worked out. The exhaust port will be called finished after this part, but the intake ports get a couple of more steps.
|Home-made insert greased, ready to install.||Greased inserts installed.|
|Add epoxy to fill in unwanted voids.||Looks nasty, but after a little reshaping it will clean up nicely.|
There is a large canyon around the guide in the bowl of the intake port. Most porters simply grind away the sharp edges and call it good. I prefer to fill this are in with epoxy and reshape it to my liking. I made up some special tools that fit in the guides, but have a shoulder. They will create a small gap between the valve and head so there is no friction. The area is roughed up and sand blasted to ensure a proper bond with the epoxy. The inserts are greased and installed in the guides. The epoxy is then worked into place. Allow about ½ day for the epoxy to set. Grab the inserts with pliers, twist, and pull.
Figure 14 The set epoxy is reshaped to induce even more swirl going into the cylinder.
After the epoxy has had at least 2 days to fully set, the area gets reshaped.
|Mike Holler, known on Allpar forums as mpgmike, also contributes to mpgResearch.com. He has contributed many columns to Allpar:|
|Interiors||Budget interior restoration: making the inside of your car look like new again
Red carpet treatment: Installing new carpet in an old car
|Porting||Porting heads for performance: step by step
Head porting example, part 1 | part 2
Intake manifold porting
Exhaust manifold porting (turbo)
Poly Quad heads: porting revisited
|Turbochargers||Turbochargers - all you need to know (interview)
Turbocharging the slant six for power and economy • Revisiting the turbocharged slant six
Budget turbocharger rebuilding (and Turbo Rebirth)
Installing a boost gauge
|Other||Powder-coating for a brilliant, durable finish
Custom pistons: roll your own!
Prepping valves for performance: grinding and polishing
Old cars: an opinion
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