HEY GRUMPYVETTE?
I'm building a mild performance, 9:1 static CR, 350 for my 55 and looking into camshaft choices...I understand the intake closing point (degrees) will affect the dynamic compression ratio (DCR)....My question is what DCR should I be shooting for?
That answer depends on the fuel octane, cylinder head temp. and several other variables but generally 8.0-8.5:1 dynamic works out well if your going to run mid grade pump gas
READ THIS THREAD!
http://www.chevytalk.org/fusionbb/showt ... tid/92966/
heres some differant calculators
http://www.kb-silvolite.com/calc.php?action=comp2
http://www.wallaceracing.com/dynamic-cr.php
http://www.smokemup.com/auto_math/compression_ratio.php
http://www.miata.net/garage/tirecalc.html
http://not2fast.wryday.com/turbo/compre ... sure.shtml
average the results
IDEALLY you would sellect the horsepower goal, and the displacement,youll work with too reach that goal. then the cylinder heads, intake and exhaust are sellected that supply the necessary flow rates,in that rpm band, you pick the cam too match the intended rpm band,and flow rates and power range for the application, you then match the compression ratio, to the cam timing too maintain the correct dynamic compression ratio, and you sellect the matching drive train and gearing to keep the engine IN the matched rpm band the vast majority of the time.
naturally if your limited to a set displacement or compression ratio the other factors must be sellected with those limits in mind
[color]IM reasonably sure this charts based on a 350-383 chevy or similar size engine, but its a good rought guide on most engines under 400cid displacement on matching the durration to the intended operational rpm band[/color]
In most cases the upper rpm band limit is either limited by valve float with the more comon hydralic lifters, or the auto transmissions shift rpm point,(yes there adjustable in some cases but rarely shift higher than 5500rpm-6000rpm even with a shift kit installed) theres not much point in designing a combo that runs into potentially higher rpms if youll seldom reach, or can,t reach them., the lower rpm limits set by the necessary minimum lower rpm band the cam and compression ratio , and engine displacement will allow the engine to smoothly produce power from.
most performance cams list a MINIMUM converter rpm or cruise rpm
heres your trans gears
2.74 1.57 1.00 0.67
rear gear 3.55:1
tires 27" tall
all the info you need is here
http://www.geocities.com/z_design_studi ... zx_tt.html
viewtopic.php?f=71&t=555
lets look at your particular
plug in your specs to the calculator and links, and look nup your cam specs for the suggested cruise or operational rpm band
heres free cam sellection software
http://www.compcams.com/Camquest/default.asp
btw once you use it to find that approximate lift ,durration and lca, you can buy any companies cams with similar specs.
BTW HINT, with that rear gear and compression ratio , ID STRONGLY SUGGEST YOU stay UNDER 218-220 durration at .050 lift and with a 108-112 LCA
Most auto transmissions are either adjustable,OR PROGRAMABLE in some cases, or there are aftermarket shift kits available too alter the shift points or convert to manual operation, but in most cases youll still find 5500rpm-6000rpm about the max possiable shift point, and frequently you can,t get quite that high with the less expensive kits.
for a street car the shift points are lower so the cam sellected should be milder to match the realistic rpm band thats actually in use!
http://store.summitracing.com/egnsearch ... &y=13&x=26
http://www.jegs.com/webapp/wcs/stores/s ... 9_-1_10529
I'm building a mild performance, 9:1 static CR, 350 for my 55 and looking into camshaft choices...I understand the intake closing point (degrees) will affect the dynamic compression ratio (DCR)....My question is what DCR should I be shooting for?
That answer depends on the fuel octane, cylinder head temp. and several other variables but generally 8.0-8.5:1 dynamic works out well if your going to run mid grade pump gas
READ THIS THREAD!
http://www.chevytalk.org/fusionbb/showt ... tid/92966/
heres some differant calculators
http://www.kb-silvolite.com/calc.php?action=comp2
http://www.wallaceracing.com/dynamic-cr.php
http://www.smokemup.com/auto_math/compression_ratio.php
http://www.miata.net/garage/tirecalc.html
http://not2fast.wryday.com/turbo/compre ... sure.shtml
average the results
IDEALLY you would sellect the horsepower goal, and the displacement,youll work with too reach that goal. then the cylinder heads, intake and exhaust are sellected that supply the necessary flow rates,in that rpm band, you pick the cam too match the intended rpm band,and flow rates and power range for the application, you then match the compression ratio, to the cam timing too maintain the correct dynamic compression ratio, and you sellect the matching drive train and gearing to keep the engine IN the matched rpm band the vast majority of the time.
naturally if your limited to a set displacement or compression ratio the other factors must be sellected with those limits in mind
[color]IM reasonably sure this charts based on a 350-383 chevy or similar size engine, but its a good rought guide on most engines under 400cid displacement on matching the durration to the intended operational rpm band[/color]
In most cases the upper rpm band limit is either limited by valve float with the more comon hydralic lifters, or the auto transmissions shift rpm point,(yes there adjustable in some cases but rarely shift higher than 5500rpm-6000rpm even with a shift kit installed) theres not much point in designing a combo that runs into potentially higher rpms if youll seldom reach, or can,t reach them., the lower rpm limits set by the necessary minimum lower rpm band the cam and compression ratio , and engine displacement will allow the engine to smoothly produce power from.
most performance cams list a MINIMUM converter rpm or cruise rpm
heres your trans gears
2.74 1.57 1.00 0.67
rear gear 3.55:1
tires 27" tall
all the info you need is here
http://www.geocities.com/z_design_studi ... zx_tt.html
viewtopic.php?f=71&t=555
lets look at your particular
plug in your specs to the calculator and links, and look nup your cam specs for the suggested cruise or operational rpm band
heres free cam sellection software
http://www.compcams.com/Camquest/default.asp
btw once you use it to find that approximate lift ,durration and lca, you can buy any companies cams with similar specs.
BTW HINT, with that rear gear and compression ratio , ID STRONGLY SUGGEST YOU stay UNDER 218-220 durration at .050 lift and with a 108-112 LCA
Most auto transmissions are either adjustable,OR PROGRAMABLE in some cases, or there are aftermarket shift kits available too alter the shift points or convert to manual operation, but in most cases youll still find 5500rpm-6000rpm about the max possiable shift point, and frequently you can,t get quite that high with the less expensive kits.
for a street car the shift points are lower so the cam sellected should be milder to match the realistic rpm band thats actually in use!
http://store.summitracing.com/egnsearch ... &y=13&x=26
http://www.jegs.com/webapp/wcs/stores/s ... 9_-1_10529
