| Intake porting guide |
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| Overview The D0VE / D3 series cylinder head castings are blessed with good intake port layout and design. The work required to see 300 cfm with a stock valve is minimal. One of the issues that plagues these castings is an intake versus exhaust flow imbalance. As cast the heads have a miserable I/E ratio of about 50%, which chokes the engine plain and simple. Current theory holds that 70% is a good target ratio for a high performance cylinder head. Some racing castings are near 80%. I have found that 60% to 70% is a good target and that a 200 cfm exhaust port will support 700 hp with no issues at all. If your I/E ratio is near 60% or a bit higher use a dual pattern cam favoring the exhaust side by about 6 to 10 degrees at .050" lift. If near 70% it is not as great an issue and 6 degrees will help high rpm power. Single pattern cams will make more midrange torque with less peak HP.. Some of the better exhaust ports I have seen are in the neighborhood of 200 to 220 cfm. This would suggest an intake flow of 300 cfm to achieve this 70% target. As I have researched the intake ports I have found it too easy to get good intake flow while having to fight for every cfm of exhaust flow. Bear this in mind when porting the intake side of the head. With a large CJ valve I have seen 340 cfm intake ports that are surprisingly stock in cross section and appearance. When this is done the flow ratios go down in the low 60% range which will require a split duration cam favoring the exhaust side. A 300 cfm intake port will support 600+ hp in a max effort application. It isn't necessary to go overboard on the intake side of these heads. Don't fall prey to the bigger is better mentality and hog out these ports. The latest revision on page 5 gives ported cross sectional information and measurements. Keeping the port as small as possible with maximum flow is the goal. The old tried and true basics of blending the seat and shaping the short turn give the most bang for your time investment. Port matching to your intake gasket and streamlining the valve guide will help also. Installing the large 2.19" or 2.24" valves will help move the max flow figures down into the .5" to .6" lift range as the smaller valve is the major obstacle to flow in this lift range. The installation of the larger valve with out doing the necessary bowl work and chamber work will do little to increase flow and in some cases will hurt flow. DO NOT overlook the importance of working the intake side of your castings. Many don't and then assign blame for low HP to the bad exhaust port. This is not the case. Choose your casting based on RPM level and port cross section. The CJ, the PI and the D0VE are large to small in descending order. The more inches or RPM you are running the more important the bigger runner volume becomes. |
| All casting numbers starting with C8VE-A and ending with D8VE share almost identical port architecture. The entry roof height is slightly lower in the newer castings. After proper porting mods they ALL flow very well |
| For ALL passanger car iron castings |
