The quench area is designed to squeeze the trapped air and fuel in this area and squish it into the combustion chamber, creating turbulence. This area is called the quench space or sometimes called squish–which is a really good descriptor of its purpose. When the piston achieves top dead center (TDC), this creates a very tight clearance between the flat portion of the piston and the flat portion of the head. The quench area is that flat portion of the piston that matches the flat portion of the combustion chamber on a wedge type cylinder head. It’s interesting that many enthusiasts tend to overlook the combustion space as a place to improve engine power. Adding the 0.020-inch deck height to the 0.041-inch head gasket creates a distance of 0.061-inch between the top of the piston and the flat portion of the cylinder head. These are quality head gaskets but are generally 0.041-inch thick. We’ll assume that your engine is currently using a composition head gasket. Of course, this means removing the cylinder heads to make this improvement and that’s where many guys don’t want to make the effort. With a 0.020-inch negative deck height, this means we can use a thinner head gasket to improve the compression. If the pistons are closer to the deck (0.005-inch below for example), this improves the compression ratio but also limits the thickness of the head gasket since we are limited to roughly 0.040-inch for piston-to-head clearance. In my compression ratio equation, I assumed the piston is 0.020-inch below the block deck surface, which is excessive, but we can use that to our advantage. One of the dimensions that is not easily changed is the distance from the piston top to the deck. This engine uses a dished piston with 13 cc’s of volume that reduces the compression. Chevy’s literature states this is an 8:1 compression engine, and that’s what we found when we measured one of these engines a couple of years ago. The standard Chevy 290-horsepower 350 Chevy crate engine you can buy isn’t even that good. With a composition head gasket, the piston 0.020-inch below deck, and a 76cc combustion chamber, and with a composition head gasket this puts the static compression at 8.5:1. Since we don’t know much about your 350 small block, we’ll assume it employs the typical flat top, four eyebrow production pistons. Internal combustion engineering has come a long way to achieve these higher static compression ratios and still operate on 91-93 octane fuel. We won’t get into all the details as to why but suffice to say that those older combustion chambers were not designed to accommodate that kind of compression. Having said that, you can’t run that much compression on a small block Chevy using older, ‘70s vintage iron heads. The LT1is designed to operate with premium fuel but comes from the factory with a true 11:1 static compression ratio. There’s a reason that all the latest generation LS engines and especially the new gasoline direct injection (GDI) LT1 Corvette engine have higher compression ratios. Assuming that the added compression is not excessive, adding compression is the best way to improve power while also improving efficiency. Jeff Smith: Raising the compression ratio is an excellent idea for several reasons. I’m thinking a little extra compression wouldn’t’ hurt but I can’t afford a set of aluminum heads. The engine runs fine on the cheap 87-octane stuff and doesn’t ping at all. The other parts are an Edelbrock Performer intake, a 600 cfm Holley carb, and cast iron exhaust manifolds. The previous owner said it was rebuilt and has a cam but he couldn’t remember the specs. I don’t know much about the engine because it came in the car. Is there a cheap way to increase compression on my small block Chevy? I have a 350 small block with iron heads.
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