Cam, carb, and compression! That is what the local street racing heroes always told me when I was in my teens.
In my opinion, the biggest hurdle that SoCalJetBoaters face with building more power, particularly in a Chevy is compression. Even those peanut-port heads have decent flow for the power levels that most are running; comparable to an entry-level race head for a small block and by today’s standards, a 454 is a tiny big block.
Most of the threads that I read here typically involve the large chamber heads combined with flat-top pistons or even a slight dish. That will typically result in a static compression ratio in the range of 7.8:1 to 8.2:1. A larger camshaft will aggravate the situation even further as the dynamic compression ratio will drop with every change. As a cam gets bigger, the duration has to increase as well. It is this increase in duration that kills the performance of a low-compression engine.
As the duration increases, the intake valve is opened sooner and held open longer relative to the crankshaft. The longer the intake valves are held open after bottom dead center (ABDC), the less dynamic compression the engine will develop. Air can not be compressed while the valves are open. Increased duration holds the valves open until the piston is further up the cylinder during the compression stroke. So, instead of the compression ratio being from BDC, it will be calculated from when the valve actually closes. The intake valves closing will be in the neighborhood of 60 to 100 ABDC. That will equate to a stroke of 3.250 (at 60 degrees ABDC) to 1.977 (at 100 degrees ABDC). In a 12.75:1 static compression ratio engine will have a theoretical dynamic compression ratio closer to 10.54 to 6.81 respectively. The actual dynamic compression ratio is a lot more complicated, but you can see how intake valve closure affects actual compression.
Compression is important to the performance of the engine because power output is directly proportional to the expansion ratio of the air/fuel during the combustion process. More air/fuel compressed into a smaller area will expand more, applying more pressure against the surface of the piston and therefore more force against the crankshaft through the connecting rod resulting in more torque.
Bottom line, when you are working with an engine that is already compression limited, there is not a whole lot you can do to improve performance before you need to change pistons. Yes, the heads can be milled and the block decked, but that will only yield marginal results and not be worth a half point in compression. Switching to closed chamber heads could net you about 8.66:1 compression with a stock flat top piston. Milling closed chamber heads will get you close to 9:1 but IMHO, not worth the reduced rigidity and risk of warping. Without a piston change, you are really leaving a lot of performance on the table.
If it was me, and my engine was mechanically sound, I would spend my money on a centrifugal supercharger, a CSI blow-through carb and a good ignition system. Even a cast crank and a 2-bolt block should easily handle moderate boost around 6#.
To make the same power naturally aspirated, you will really have to step up your compression, camshaft, head flow, and induction. Bolt-ons just won’t get you where you want to be.
Good luck,
Joe
