![]() ![]() Everybody here said it wasn't a good idea. If you use the DCR calculator, you can theoretically get away with 12:1 compression with this cam. I was thinking about running a similar type of cam (poston 112- same as 107 on 112 center). 4 becomes 8, or -3 becomes -6).I've been trying to get a straight answer to this question too. If you have a value in camshaft degrees, double it to get the right crankshaft degrees (ie. Remember to use crankshaft degrees, and not camshaft degrees. If you don't know what this is, don't worry about it and leave it as-is. A value of +4 degrees is most common for built-in advance in aftermarket cams. Some manufacturers build advance or retard into the cam, and some installers purposely advance or retard the cam. Use a negative number (-4) for retarded cams, and a positive number (4 or +4) for advanced cams. If your cam is advanced or retarded, include the amount of advance or retard here in crankshaft degrees. Only people with dual-pattern cams should need to do this, or those that have precisely measured the intake valve closing angle themselves on their engine. You'll need to place a checkmark in the box beside the field to make sure the calculator ignores the cam duration and intake lobe centerline fields above. If you'd rather enter the intake valve closing angle directly yourself, you can do so with the field on the left. ** The factory stamp code can be found on the nose of the camshaft We're still working on a way to accomodate dual-pattern cams.Įnter your own custom numbers manually, or click on the "Stamp" code in the chart below to have those numbers automatically loaded into the fields on the left These numbers assume a single-pattern cam (most common). The ADVERTISED duration is the number that should be used, not the duration at 0.050" since compression doesn't begin until the valve is fully seated. The most common cam's numbers are pre-entered here (cam grind "N"). Below is a chart of common stock Pontiac cams. Your cam manufacturer provides these figures. Only change this if you're using a different length. Stock Pontiac connecting rods were always 6.625" long. An accurate value here has very little effect on the final result.ĭata Needed to Compute Dynamic Compression If in doubt, check with your piston manufacturer. ![]() This number can vary depending on the type of aftermarket piston you use. It has very little effect on the result anyways.Īccepted values for this on stock engines were 0.0025" to 0.0033". If you don't know this value, just leave it as is. The number pre-entered here was measured from my own stock pistons. This is the distance between the top of the first compression ring and the top of the piston. Valve reliefs on stock-type pistons are typically 6cc in volume. A negative number (-6) indicates a protrusion like a domed piston top. Here a positive number (6 or +6) indicates a depression in the piston like valve reliefs or a dished piston top. A typical value of 0.042" has been entered based on most common experience. This varies depending on the gasket material, manufacturer, etc. One of the more common changes to a Pontiac block is to have a 0.00" deck height. This only needs to be changed if your engine differs from factory spec in this respect. Stock piston to deck clearance has always been right around 0.023" throughout the production of the Pontiac engine. Where do I find the combustion chamber volume? ** the 350 actually displaces 354 cubic inches Data Needed to Compute Static Compression and DisplacementĮnter your own custom numbers manually, or click on any of the numbers in this chart to automatically load them into the fields on the left Please note, this calculator requires that JavaScript be turned on in your browser. The numbers pre-entered correspond to a stock '77/'78 Pontiac 400 W72. If you can't find some of the numbers, just leave them as is. While intended mostly for Pontiac engines, it'll work just as well for any other OHV V8 engine too as long as you can provide all the necessary specifications. Here's a displacement and static/dynamic compression ratio calculator. Static/Dynamic Compression Ratio Calculator ![]()
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