its obvious some of the guys on this site need to understand the differance between static and dynamic compression ratios, and thats understandable as its a difficult concept to grasp at first
but you need to understand it before selecting a combos components
the differance between STATIC COMPRESSION RATIO AND DYNAMIC COMPRESSION RATIO is where the piston is in the cylinder when the valves close and the piston can accually start compressing the REMAINING VOLUUM IN THE CYLINDER VS the STATIC COMPRESSION THAT ASSUMES THE PISTON STARTS COMPRESSING THE INSTANT IT LEAVES BOTTOM DEAD CENTER AND STARTS UPWARD ON THE COMPRESSION STROKE!
let me try and explain, the short version is that the PISTON COMPRESSES NOTHING untill BOTH VALVES ARE CLOSED, .......thats the only compression ratio that matters,.... since its the only compression ratio the engine ever sees.
static compression is simply the differance between the cylinder volume at BOTTOM DEAD CENTER(BDC) and its compressed volume at TOP DEAD CENTER (TDC), into the combustion chambers,... dynamic compression takes into account that on the pistons upward compression stroke the valves have not yet closed and nothing gets compressed by the piston untill they do, that of course depends on the cam and rockers, pistons and connecting rods, the cylinder voluum, the rod/stroke ratio, ETC.,used, in the combo, and the rpm levels to some extent BTW, ALUMINUM HEADS can usually operate at a higher dynamic compression simply because ALUMINUM releases heat to the coolant much faster than iron, its the lower heat levels that remain in the cylinder that help prevent detonation..when you increase the dynamic compression the heat levels in the heads combustion chamber rise , the differance in the RATE heat leaves the cylinder allows a slightly higher dynamic compression level from aluminum before the same HEAT levels are REACHED & MAINTAINED in the combustion chambers
heres a calculator for static cpr, which you need to figure first
http://www.rbracing-rsr.com/compstaticcalc.html
http://users.erols.com/srweiss/calccr.htm
heres some differant calculators
http://www.kb-silvolite.com/calc.php?action=comp2
http://www.wallaceracing.com/dynamic-cr.php
http://www.kennedysdynotune.com/Dynamic ... 20Tech.htm
http://www.empirenet.com/pkelley2/DynamicCR.html
average the results
your engines torque curve is more the result of displacement, compression,ratio,selected cam timing and both header design (scavenging) and intake design (SINGLE vs DUAL PLANE ETC.)than just port cross sectional area alone, and if your wearing valve guides the valve train geometry and clearances, and lubrication system, and the oil used in it, and your valve spring rates and seals need to be carefully checked and a rocker stud girdle and roller rockers used
and port cross sectional area and flow numbers have a larger effect than port shape alone
naturally youll need to match the port cross sectional area, length, and plenum to the intended displacement and rpm band, and cam timing, but just assuming a swap from rectangular port to oval will always result in more torque will not always be true over the whole power band, especially if the rest of the combos designed for a totally different rpm band than the heads you've selected.
tweaks like tuned merge collectors, and slightly different cam timing and intake swaps can get a great deal more of the torque potential from a slightly different port size,and there are calculators you can use to find a limited selection of choices,in header length, diam., collector, intake port length and cross section and runner length, plenum size, cam timing and valve size to look thru.. too narrow your search for the best match to your application vs just guessing and swapping parts till you think youve got it correct
http://forum.grumpysperformance.com/viewtopic.php?f=52&t=333
but you need to understand it before selecting a combos components
the differance between STATIC COMPRESSION RATIO AND DYNAMIC COMPRESSION RATIO is where the piston is in the cylinder when the valves close and the piston can accually start compressing the REMAINING VOLUUM IN THE CYLINDER VS the STATIC COMPRESSION THAT ASSUMES THE PISTON STARTS COMPRESSING THE INSTANT IT LEAVES BOTTOM DEAD CENTER AND STARTS UPWARD ON THE COMPRESSION STROKE!
let me try and explain, the short version is that the PISTON COMPRESSES NOTHING untill BOTH VALVES ARE CLOSED, .......thats the only compression ratio that matters,.... since its the only compression ratio the engine ever sees.
static compression is simply the differance between the cylinder volume at BOTTOM DEAD CENTER(BDC) and its compressed volume at TOP DEAD CENTER (TDC), into the combustion chambers,... dynamic compression takes into account that on the pistons upward compression stroke the valves have not yet closed and nothing gets compressed by the piston untill they do, that of course depends on the cam and rockers, pistons and connecting rods, the cylinder voluum, the rod/stroke ratio, ETC.,used, in the combo, and the rpm levels to some extent BTW, ALUMINUM HEADS can usually operate at a higher dynamic compression simply because ALUMINUM releases heat to the coolant much faster than iron, its the lower heat levels that remain in the cylinder that help prevent detonation..when you increase the dynamic compression the heat levels in the heads combustion chamber rise , the differance in the RATE heat leaves the cylinder allows a slightly higher dynamic compression level from aluminum before the same HEAT levels are REACHED & MAINTAINED in the combustion chambers
heres a calculator for static cpr, which you need to figure first
http://www.rbracing-rsr.com/compstaticcalc.html
http://users.erols.com/srweiss/calccr.htm
heres some differant calculators
http://www.kb-silvolite.com/calc.php?action=comp2
http://www.wallaceracing.com/dynamic-cr.php
http://www.kennedysdynotune.com/Dynamic ... 20Tech.htm
http://www.empirenet.com/pkelley2/DynamicCR.html
average the results
your engines torque curve is more the result of displacement, compression,ratio,selected cam timing and both header design (scavenging) and intake design (SINGLE vs DUAL PLANE ETC.)than just port cross sectional area alone, and if your wearing valve guides the valve train geometry and clearances, and lubrication system, and the oil used in it, and your valve spring rates and seals need to be carefully checked and a rocker stud girdle and roller rockers used
and port cross sectional area and flow numbers have a larger effect than port shape alone
naturally youll need to match the port cross sectional area, length, and plenum to the intended displacement and rpm band, and cam timing, but just assuming a swap from rectangular port to oval will always result in more torque will not always be true over the whole power band, especially if the rest of the combos designed for a totally different rpm band than the heads you've selected.
tweaks like tuned merge collectors, and slightly different cam timing and intake swaps can get a great deal more of the torque potential from a slightly different port size,and there are calculators you can use to find a limited selection of choices,in header length, diam., collector, intake port length and cross section and runner length, plenum size, cam timing and valve size to look thru.. too narrow your search for the best match to your application vs just guessing and swapping parts till you think youve got it correct
http://forum.grumpysperformance.com/viewtopic.php?f=52&t=333