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454 Chevy Big Block Build - Ask Anything

Compression is a great way to make more power with the rule-of-thumb improvement of a 3 to 4 percent increase in power for every point of compression-let's say from 9:1 to 10:1. The limiting factor here is the 91-octane fuel. With the compression already at 9:1, any increase will improve power, but you're running on the ragged edge of detonation. You might be better off to leave the compression as it is and be more aggressive with the ignition timing. Any attempt at reverse cooling is a waste of effort as well. When GM started with a clean sheet of paper on the new generation of LS engines, the company went back to conventional coolant routing and just moved the thermostat to the inlet side.

One way to improve combustion efficiency (which equates to both power and fuel efficiency) is to pay particular attention to piston-to-head clearance. This will most often require mocking up the engine with at least the four corners of the engine (cylinders 1, 8, 2, and 7) to measure the distance between the piston tops and the block. The ideal way is to also ensure that the block deck is not just flat but square to the crank. We've seen blocks (especially Rat motors) that are tilted in relationship to the crank. The relationship of the piston to the head includes not just the deck (a 0.005-inch-or-less distance is good) but also the head gasket thickness. If you don't want to go through the expense of this machine work, it's still good to measure so you know how thin a gasket you can get away with. For example, if the pistons average around 0.024 inch down in the hole, you could add a thin Fel-Pro rubber-lined head gasket (PN 1094) that is only 0.015 inch thick. Adding the two dimensions, you end up with a piston-to-head clearance of 0.039 inch, which is about as tight as you'd want to go. The thinner head gasket also reduces the total combustion space volume, which increases compression. The beauty of this approach is that decreasing the piston-to-head also increases what is often called squish or quench. As the piston approaches TDC, the tight portion of the wedge chamber and the piston squish or push the air/fuel mixture out into the deep portion of the chamber, increasing mixture motion, which generally reduces the combustion chamber's tendency toward detonation. This also can mean that the engine needs less timing to make the same power. Less total timing requirements (especially at peak torque where the engine is running at peak volumetric efficiency) means less negative work where the engine has to squeeze against combustion activity and also means less chance of detonation. All this tight quench work creates a situation in which the engine is making more power with less ignition timing-power and efficiency go up with no negatives! This is the reason we go through the effort to blueprint engines rather than just assemble them with whatever clearances are created. So to wrap this up, it appears that with a mild cam and valvespring swap along with maybe a little bump in the static compression ratio you can come very close to achieving your major torque goal. But what would really help is if you can figure out a way to add a set of long-tube headers.

More Info Federal-Mogul (Fel-Pro) Southfield, MI 248/354-7700

GM Performance Parts Warren, MI 800/577-6888

Summit Racing Akron, OH 800/230-3030

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