Heads Up

With the bottom half completed, it was time to decide on the “top half” aka the heads. Now, stock Corvette Heads are made from cast iron, which makes them quite heavy. They also require some special inserts placed in the valve seats to cope with today’s unleaded petrol. (The theory here is that the lead provided a cushioning effect when the valve hit the cast iron valve seat as the valve closes. That lead is now gone, so the cast iron head has to have a special hardened valve seat inserted.)

There are many aftermarket heads available for Chevy’s these days, with many suppliers offering cast aluminum versions as an option. Of course, one of the great advantages here is the reduction of weight over the front suspension.

Again, there are many styles of aluminum heads out there. The first choice is small or large combustion chambers, which affect the compression ratio. Higher compression generally ends up in better performance, but can mean that premium fuel has to be used. A high compression engine fed on normal fuel can result in the fuel being ignited prematurely, commonly called pinging. Another choice is the size of the port or tube that delivers the air / fuel mix to the engine. A head with a large port might get more air / fuel by volume at high revs, but there might be a reduced “pull” of air/fuel through the carburetor at low revs, causing a “flat spot”.
I diligently reviewed all of the viable options out there and had a particular brand/style in mind. I was going for Edelbrocks, with 72 cc chambers and 170 cc Inlet Ports. I figured that these heads, combined with the other engine elements (particularly the camshaft) would give me a good package for doing what I want to do….. Cruizin.

One day I dropped into Eagle Auto Parts at Revesby to pick up a few parts. Out of curiosity I asked Dave what they had in the way of Chevy Aluminum Heads. Dave produced a pair of Patriot Performance Heads. They looked great, there were right there in front of me, no more looking around, no more decisions to be made, go on, just buy them and go home and bolt them on. So I bought them.

Bad move...... I strayed from my criteria after all that due diligence. Now, I must say that the Patriot Heads are probably great heads (I haven’t started the engine yet) but let’s say there are some compatibility issues.

Dave & Tony at Eagles cautioned that my existing Inlet Manifold may not be compatible with these tall port heads. I decided to take my chances. Guess what, my manifold was not suitable so I had to buy another one.

I didn’t realize at the time, the Patriot heads are true performance heads, they don’t incorporate passages that allow the exhaust gases to heat up, and hence turn off, the choke on the carburetor. Guess what, I have to buy another carburetor now, one with an electric choke. I’ll also have to add some wiring to the car so that the electric choke will work.

There were a few other compatibility issues with this choice of heads. We’ll cover those off at a laterstage.