![]() ![]() The reason for this is that a large cross-sectional area requires high engine speeds to create a sufficient inlet air speed. Using a very large cylinder head with a long duration cam in our lightweight street rod produces a very sluggish engine with poor throttle response, and probably won’t make decent power until the engine is spinning at very high engine speeds, just like the Ford Boss 302. This creates a combination that allows this engine to make excellent low-speed torque. But on the other hand, if our small-block is going to be used in a 1932 roadster with a stock torque converter and tall gears, we should be looking for a cylinder head with smaller ports to create good torque and excellent throttle response. This means the engine operates in a very narrow power band at high RPM, which means that a cylinder head with a larger port cross-sectional area would probably work well. Let’s say that our engine is to be used in a lightweight dragrace car using a deep gear and a 5-speed transmission. Just as with choosing a camshaft, we need to know how this engine is to be used to best approach the cylinder head selection process. However, engine power production is also affected by several other considerations. All other considerations being equal, the larger head flows the most air if all we’re concerned with is airflow on a flow bench. The bigger-is-better theorists suggest that given the choice of several heads, take the biggest, in other words, the one with the largest cross-sectional area. This is defined as the height times the width of a port at its tightest point. The plan is that once you understand the theory behind why some heads work better than others, it makes future engine configurations and concepts easier to generate since you don’t have to go through the trial and error process each time. Here comes that theory stuff again, but we try to make it easier on you this time. If that’s the case, then why haven’t the Ford Boss 302 or the Ford Tunnel Port 429 engines been more successful and longer lasting? Let’s look into this a little deeper. That tends to fly in the face of suggestions from other sources claiming that size matters-pushing instead bigger ports with the max flow. His suggestion is to create the most flow you can get from the smallest port. The best line we’ve ever heard was from Pro Stock racer “The Professor” Warren Johnson. ![]() The simplistic approach is to generate as much flow as you can squeeze in between the head bolt and pushrod holes. The number of theories on cylinder head port configuration, valve layout, and flow potential are probably equivalent to the number of small-block Chevy cylinder head manufacturers-a bunch. Now that we’ve got our requisite politician-bashing out of the way, we can get to the guts of this chapter. You can copy and paste this link to share: SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE This Tech Tip is From the Full Book, HIGH PERFORMANCE CHEVY SMALL BLOCK CAMS & VALVETRAINS. The classic, “Oh yeah, this motor makes 575 at the crank,” sounds an awful lot like, “Read my lips-no new taxes!” It’s incredibly easy to lean against the fender of your Camaro at a local car show and throw out horsepower numbers with the same genuine enthusiasm that politicians use when promising tax reductions. ![]() This may seem like flogging the obvious, but plenty of performance enthusiasts are only interested in the appearance of power, rather than achieving a given power level. This deserves no more emphasis than in this chapter on matching camshafts and cylinder heads, since the integration of camshaft valve timing with the cylinder head is critical if your goal is optimal power. Several times throughout this book we have mentioned the concept of using the systems approach when planning and building a performance street engine and/or race engine.
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