The deck clearance is measured as part of the compression ratio calculation. Figure the ga
We were straying fairly far from the way Chrysler originally assembled the 440, so we had to perform a wide range of critical measurements to ensure that it would all work. Piston-to-head clearance, valve-to-piston clearance, pushrod length, and valvetrain geometry are some critical checks to be made. A mistake in these areas can mean disaster.
Another measurement that should not be overlooked is the actual compression ratio. A wide range of possible chamber volumes, block-deck heights, gasket thickness, possible piston modifications, and a host of other variables will affect the compression ratio. Piston manufacturers will toss a number out there, based on their own assumptions of values for those variables. This generally can serve as a ballpark guide, but will not necessarily give the ratio for your own combination. Throw in various widely published chamber-size specs, usually not production based, but theoretical drag racing NHRA minimum volumes, and it's easy to be totally off when estimating the ratio.
The only real way to figure the ratio is to measure it. The accompanying photo captions detail the setups we used for the various measurements, but how do you get the ratio? You've gotta do the math. If the word "pi" makes you wince, find a buddy who paid attention in high school math class. The basic formula for compression ratio is:
Total volume above the piston at BDC
Total volume above the piston at TDC
With the piston's flat area down exactly .500-inch from the block's deck, we can calculate
Total volume above the piston at TDC includes the chamber volume, gasket volume, piston deck clearance volume (which can be positive or negative depending on the compression height), minus any piston dome, or plus any dish. Some of these volumes (regular shapes) can be calculated from measurement, while others (irregular shapes) are best measured by displacement (CCing). We cover the procedures we used in the accompanying photo captions.
To get the total volume at BDC, add the swept volume (volume created by the area of your bore times the stroke) to the volume figured at TDC. Divide the number at BDC by your TDC figure, and you've got your ratio. Ours worked out to 12.66:1.
Rather than making a mess when pulling up the Plexiglas, and spilling checking fluid every
Cam Do It
Wouldn't it be great if we had an expert engine builder on hand each time we built an engine, carefully considering our individual parts combination, and coming up with an appropriate cam to get the job done? Unfortunately for most of us do-it-yourselfers, hiring a top pro to select our cam is virtually a pipe dream-until now.
Thanks to Cam Masters-which has developed a program based on sophisticated computer modeling-for less than $30, custom-tailored cam selection now is within easy reach of the average enthusiast.
The heads were bolted onto the block with Milodon's dead-soft, solid copper head gaskets.
Taking into account individual variables for your specific engine, such as compression ratio, bore, stroke, valve sizes, rod length, cylinder head flow curve (if available), rocker ratio, and planned fuel octane, you select the application of how radical you want to go, and the Cam Master program will deliver custom specs for your engine. The selection of performance level is overlap-driven, since after all, overlap is the biggest factor in how radical the combination will idle. We chose a hot street/strip grind (70-90 degrees of overlap in the Cam Masters model), and the Cam Master program worked out the optimal duration for the intake and exhaust lobes, lift, overlap, and the all-important lobe separation and installed centerline angles.
Cam Masters does not grind cams, but based on the specs the company calculates, it will find the closest match in an off-the-shelf grind from its extensive database of the leading manufacturer's cams, or point you to the correct lobes if a custom grind is desired. The program also will provide the part numbers for a matched set of components to complete the valvetrain. Cam Masters is a Warehouse Distributor for many of the major cam manufactures, so you can have the cam ordered with a single phone call, or take the numbers and go shopping yourself.