Ever wonder how your engine’s cylinders fire in sequence? It’s an easy detail to overlook, but firing order has a big impact on the performance and “smoothness” of an engine. Recently, automotive historian and engine guru David Freiburger broke down this often-overlooked aspect of engine design, focusing on the popular “4/7 swap.”
The video begins when Freiburger defines what it means by firing order through the well-known sequence: 1-8-4-3-6-5-7-2 as an example. He comments, however, that this firing sequence was indeed common for several classic American V8s: Chevys, Mopars, Buicks, and Olds. Subsequently, Freiburger introduces a very interesting topic: “companion cylinders” or “bibs,” which describe pairs of cylinders reaching TDC together because of a design trait of the crankshaft.
Freiburger even shows viewers two different camshafts to point out the difference in lobe placement that allows for this swap.
The focus of the video is how the aftermarket can alter this firing order. By changing the order and position of specific lobes on the camshaft, you can change which companion cylinder fires first. A common modification, especially in older Chevy engines, is the 4/7 swap, where the firing order of cylinders 4 and 7 is reversed.
It’s also pointed out that swapping both cylinders 4 and 7 and cylinders 3 and 2 results in the firing order used in modern LS engines. Those of you who cross brand lines might know that small-block Chevrolets and Fords have different firing orders. That’s due in large part to the fact that they have different cylinder-numbering methods, and the camshaft designs are more similar than you might think. “If you take an FE or an early [Ford] 302 and you number the cylinders as if it was a Chevrolet, you know what the firing order is? 1-8-4-3-6-5-7-2!”
Freiburger has certainly been around the block a time or two, and not that we don’t trust him but it was a good opportunity to reach out to Luke Bandt at Howards Cams to get his take on the old 4/7 swap, and see if this was just academic or if they are still selling these cams.
“We offer small-block Chevy, big-block Chevy, hydraulic to flat tappet and solid roller in 4/7 swaps. We even do Pontiac and Olds. If we make a standard cam for it, we can do it,” stated Howards’ Sales Manager. “The biggest thing is that if we put a 4/7 swap in an engine that makes a lot of…
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