Camshaft/Compression Ratio relationships
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*OK, now with that disclaimer in place, I will attempt to help you see how the SCR (static compression ratio) plays out with the cam timing. There may be a mathematical *formula, but I'm not aware of it, so I just use what information I have available to me and try to figure it out from there. We will not get into DCR (dynamic compression ratio) here. That's a whole other subject for another time. | *OK, now with that disclaimer in place, I will attempt to help you see how the SCR (static compression ratio) plays out with the cam timing. There may be a mathematical *formula, but I'm not aware of it, so I just use what information I have available to me and try to figure it out from there. We will not get into DCR (dynamic compression ratio) here. That's a whole other subject for another time. | ||
| − | *The main point to consider is the intake closing point after bottom dead center. That's what controls the amount of cylinder pressure the *motor will make. | + | *The main point to consider is the intake closing point after bottom dead center. That's what controls the amount of cylinder pressure the *motor will make. You don't make any compression at all until the intake valve closes. |
*Here is a list of camshafts taken from the Crane catalog that I refer to when I'm trying to get in the ballpark for matching the SCR to the *IC point, taking into consideration the lobe separation angle and useful range of the camshaft. Again, this will only put you in the *ballpark and you should always lean on the manufacturer for a final decision. | *Here is a list of camshafts taken from the Crane catalog that I refer to when I'm trying to get in the ballpark for matching the SCR to the *IC point, taking into consideration the lobe separation angle and useful range of the camshaft. Again, this will only put you in the *ballpark and you should always lean on the manufacturer for a final decision. | ||
| − | *First is the SCR range of the motor, then the intake and exhaust duration @0.050" tappet lift, then the lobe separation angle, then the *intake closing point and finally the operating range. Now please, don't anyone take this as the final word on camshaft choice. I only posted *it to help the OP understand the relationships and this is a very short list of the thousands and thousands of cam grinds that are available *to you. | + | *First is the SCR range of the motor, then the intake and exhaust duration @0.050" tappet lift, then the lobe separation angle, then the *intake closing point and finally the operating range. Now please, don't anyone take this as the final word on camshaft choice. I only posted *it to help the OP understand the relationships and this is a very short list of the thousands and thousands of cam grinds that are available *to you. This chart was taken from the catalog of small block Chevy grinds with emphasis on the 350 cubic inch motor. Be aware that larger *displacement motors will tolerate more camshaft and smaller displacement motors will be less tolerant or more camshaft. In other words, with *the proper choice of cam for a given set of conditions in a 350, the same cam will be milder in a 406 and wilder in a 302. |
*7.50-8.50........184/194....104....16....500-4000 | *7.50-8.50........184/194....104....16....500-4000 | ||
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