You'd think those ugly old OEM cast Iron heads would be better placed at the bottom of the scrap heap than on top of Performance Unlimited's Pro-Porting© bench… but that's not the case. Many iron cylinder heads possess the performance of the gods within them, just lying in wait for their prince to awaken their eternal sleep...

Of course not all iron heads are worthy of this process, but those that are, can release hundreds of horsepower to it's lucky owner. First, the ports are opened up… but not just for the sake of making them bigger. Here we see an intake port being scribed (yellow) to be opened up on the port roof of this upside down head. This provides a 'straighter' path for air to enter the intake, thus less being restrictive, with less of a bend under the valve.

Next is to contour the port shape to specific dimensions for maximum flow, derived from our prior flow bench testing. Every aspect is addressed, and every detail is considered for the absolute maximum performance. A surprise to many, that cast iron can be polished to a much higher degree than aluminum due to the density of the material. Our pre-heat-treatment process results in a much harder surface, as well as intentionally hardening the valve seats for better wear with unleaded fuels and higher spring pressures. Since cast iron cuts much harder than aluminum, the same procedure takes quite a bit longer, and more aggressive tools must be used. This is where many home enthusiasts go wrong, by taking too much off after pushing on the grinder for hours on end. Unlike alloy heads, welding up an Iron head is a very costly and time consuming process. On rare occasions a port will need to be cut into the water jacket and welded to be raised for increased flow. However, we reserve this kind of modification as a last resort only on cast Iron, and for only the highest output applications.

The  primary concern is usually paid to the exhaust port, since it typically needs the most help. After careful and meticulous grinding, this particular application revealed the highest area of resistance was the bend around the bump where the header bolt seated deep into the head.By removing this obstruction, grinding thru to the threaded hole (yellow) was inevitable. Rather than very expensive and risky welding in this relatively thin area, a special plug was machined (blue) and inserted and epoxied into the blind hole. When fully seated, the protruding plug was ground and blended into the port wall (orange), resulting in a perfect and very secure and reliable option to gain an additional 4% flow on top of all the other gains we would get. On the dyno, it proved to be worth another 21 horsepower alone!

Extra special attention to
detail is necessary to
extract the absolute
maximum potential from
iron heads, as you can see
by this fabulously
contoured and polished
exhaust port. All
obstructions, bumps,
humps and knobs have
been removed and blended
to form on fluidic high
flowing port. Note the
gentle transition from the
bowl, past the valve guide
and out the runner itself!

Imagine water running through this port… there would be no ripples at all. Over 30-40% in flow was gained by our Pro-Port Exhaust modifications, even exceeding that of the alloy racing head's flow. 

After the
porting
work is
finished,
and a
perfect
valve job is
laid down,
there is still
more work
to be done.
VERY
Carefully,

the freshly cut relief below the three angle valve job needs to be re-blended back into the newly contoured shape of the port. Without even touching the pristine valve seat even a little bit, the sharp chamfer is transformed into a flowing, gradual radius. This important aspect is worth 15-19% in additional gains… very significant!

Finally, the
combustion
chambers
get
completely
worked
over,
ground,
contoured
and polished
to provide
the absolute
maximum

flow potential and significantly reduce the chance for pre-ignition or detonation with higher compressions and lower octane fuels. The heat reflection capacity of the micro-polished chamber dramatically aids in this performance advantage, and keeps the chamber clean long after other heads will have already carboned up.

The finished Pro-Port© product is quite awesome, indeed. Visually, structurally and mechanically. Set up with the same meticulous attention as the Alloy head package, each valve spring, height and pressure is measured and assembled in exacting tolerances in accordance to the individual valve locations..

This particular head as an example, is a 1970 Ford 429 head. Below we compared the OEM specs to the Pro-Port© specs. The incredible gains over an already legendary flowing head are obvious, and the Pro-Port© heads exceed that of the aftermarket, Race only Cobra Jet aluminum head with it's monstrous ports!