The idea behind this effort was to use one flow bench to test as many small-block and big-block Chevy cylinder heads as possible. By using one flow bench and the same test procedure, we eliminated many of the variables that exist between different benches and operators. All the tests were performed at Westech Performance Group by John Baechtel and Steve Brule using a SuperFlow 600 computerized flow bench. We tested each head not only for intake and exhaust flow at 28 inches of water, but also measured each combustion chamber and intake port for actual volume.
There are a couple of important notes worth remembering when using this data. The cylinder heads are broken down into two main areas :small-block and big-block heads. Within each of these areas are three categories. We found the easiest way to categorize these heads was by intake port volume. For the small-blocks, Category 1 encompasses all heads with intake ports smaller than 180cc's. Category 2 includes heads from 180cc to 199cc while Category 3 lists all small-block heads larger than 200cc. For the Rat motors, the port volumes are larger but also split up into three categories. Category 1 for Rat motors lists all heads under 220cc while Category 2 includes 220cc to 299cc intake port heads. Category 3 lists all Rat heads with ports from 300cc to 370cc.
Most of the heads were tested both with an open exhaust port and with an exhaust pipe. This way, if you are more comfortable with one type of test, we have data in either form. Another line on each chart calls out the E/I, the exhaust-to-intake relationship at 0.400-inch valve lift. This gives you an idea of how well the exhaust flows in relation to the intake. Most cylinder head experts will tell you that a number above 70 to 75 percent is considered good, especially if the intake port flow is also a good number.
While the temptation is great to concentrate on the peak lift flow numbers, we suggest concentrating on the mid-lift flow numbers and how they compare. For street engines with valve lifts that do not exceed 0.500-inch, it makes little sense to choose a head with great flow numbers at 0.600-inch valve lift since the valves never open that far. The valve lift curve hits the mid-lift numbers such as 0.300- to 0.400-inch twice in each valve lift curve while peak lift is only achieved once per cycle. Judging a cylinder head by its mid-lift flow potential can be beneficial in choosing the right cylinder head for a street engine.
This will be an on-going project. As new cylinder heads are created and produced, we will continue to test these heads and report on what we find. So if you want to know the latest information on the state of art in street-oriented cylinder heads, it would be wise to check our site on a semi-regular basis.
We designed this web site so that you can call up each cylinder head individually and look at the flow numbers. We did this so that it would be easy to create your own personal cylinder head reference manual by merely calling up each category and printing out the information. Then those pages can be placed in a notebook where you can use them for instant reference whenever you need it.
We have tested well in excess of 65 cylinder heads and the list is constantly growing. This represents a tremendous amount of work both by the CHP staff and also by our friends at Westech Performance Group. We hope you find this information helpful in your high performance Chevrolet education. We've sure had fun putting it together and will continue to update this file with every new test that we perform. Now that the database is also on carcraft.com and in Car Craft magazine as is the former Chevy High Performance editor Jeff Smith, we will be adding Ford, Chrysler, and BOP heads. If you have any suggestions please use the email link on the home page.
Each head is carefully placed on the SuperFlow 600 flow bench and tested from 0.050-inch to 0.0700-inch valve lift. In most cases, the heads were tested twice to ensure the accuracy of the flow numbers. In addition, the computerized data is more accurate since it displays the actual flow numbers instead of percentage of flow.
Each head was also tested for valve diameters, combustion chamber volume and intake port volume to maximum accuracy.
Almost all the heads were flowed with a flow pipe on the exhaust. Data is delivered on the exhaust side with and without the flow pipe.
Combustion chambers were also checked to establish combustion-chamber size. The trend with later heads is certainly a movement toward smaller, tighter combustion chambers that enhance combustion efficiency.