SB Cam Specs.
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Re: SB Cam Specs. (clearrun)
3896929 (300HP) 195/202 .050" dur., 108 ICL, 116 LCA, .390"/.410"
3863151(350HP) 221/221 .050" dur., 110 ICL, 114 LCA, .447"/.447"
The above info is from the Chevrolet Power Manual, and will allow you to characterized these cams in DeskTop Dyno.
Duke
3863151(350HP) 221/221 .050" dur., 110 ICL, 114 LCA, .447"/.447"
The above info is from the Chevrolet Power Manual, and will allow you to characterized these cams in DeskTop Dyno.
Duke
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Re: SB Cam Specs. (SWCDuke)
Duke,
Thanks for the info but; I am not familiar with ICL and LCA #s. I am used to lobe separation being specified as one number in degrees from peak of EX lobe to peak of IN lobe. From the numbers it looks like LCA is the number I am used to seeing advertised. Could you please explain ICL / LCA.
Thanks for the info but; I am not familiar with ICL and LCA #s. I am used to lobe separation being specified as one number in degrees from peak of EX lobe to peak of IN lobe. From the numbers it looks like LCA is the number I am used to seeing advertised. Could you please explain ICL / LCA.
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From: delmont pa
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Re: SB Cam Specs. (clearrun)
ICL = Inlet centerline (crank degrees)
LCA, LSA = Lobe center angle, lobe separation angle (both are the same parameter measured in cam degrees)
Desktop Dyno has a "cam math" section. If you plug in duration - either at .050" lifter lift, or .006" valve lift, which is the "seat to seat" timing - along with ICL and LCA the program can compute the actual open/close timing points.
Also if you have any two of the three parameters - ICL, ECL (exhaust centerline), and LCA, you can compute the third from the following formula,
LCA = (ICL+ECL)/2
by suitably rearranging it for the unknown parameter.
Knowing the ICL and ECL can give you some insight into the cam design. OEM cams have relatively early exhaust phasing, which is expressed as a rather high ECL in the range of 116 to 122 degrees BTC. This is because the SB has a relatively restrictive exhaust port, so early exhaust phasing is best, especially with the OEM exhaust manifolds. OEM cam ICLs range from 108 to 114 degrees ATC and a later (larger number) ICL indicates a later closing inlet valve, which will tend to move the torque curve to the right, which would shift the 80 percent bandwidth to a slighly higher range.
That's one of the points I don't like about aftermarket cams. They are typically ground with both ICL and ECL of 110 degrees (which yields 110 LCA). This phasing results in too much overlap for a street engine, especially if the .050" duration is more than about 220 degrees. Headers will help, but you typically loose significant low end torque. With headers and open exhaust, or a very low restriction exhaust, the overlap will gain some top end power, but little if any with the OEM type manifolds.
Overlap works with the wave dynamics generated by a proper length header to aid exhaust scavenging and initiate inlet flow when the piston is near TDC, but overlap kills low end torque due to exhaust gas dilution of the fresh charge, especially at part throttle when exhaust port pressure is much higher than inlet port pressure, and without headers the extra overlap doesn't improve top end power, so with OEM manifolds you get to a point where overlap just kills the low end without a giving anything back anywhere in the rev range.
Duke
[Modified by SWCDuke, 9:03 AM 7/12/2002]
LCA, LSA = Lobe center angle, lobe separation angle (both are the same parameter measured in cam degrees)
Desktop Dyno has a "cam math" section. If you plug in duration - either at .050" lifter lift, or .006" valve lift, which is the "seat to seat" timing - along with ICL and LCA the program can compute the actual open/close timing points.
Also if you have any two of the three parameters - ICL, ECL (exhaust centerline), and LCA, you can compute the third from the following formula,
LCA = (ICL+ECL)/2
by suitably rearranging it for the unknown parameter.
Knowing the ICL and ECL can give you some insight into the cam design. OEM cams have relatively early exhaust phasing, which is expressed as a rather high ECL in the range of 116 to 122 degrees BTC. This is because the SB has a relatively restrictive exhaust port, so early exhaust phasing is best, especially with the OEM exhaust manifolds. OEM cam ICLs range from 108 to 114 degrees ATC and a later (larger number) ICL indicates a later closing inlet valve, which will tend to move the torque curve to the right, which would shift the 80 percent bandwidth to a slighly higher range.
That's one of the points I don't like about aftermarket cams. They are typically ground with both ICL and ECL of 110 degrees (which yields 110 LCA). This phasing results in too much overlap for a street engine, especially if the .050" duration is more than about 220 degrees. Headers will help, but you typically loose significant low end torque. With headers and open exhaust, or a very low restriction exhaust, the overlap will gain some top end power, but little if any with the OEM type manifolds.
Overlap works with the wave dynamics generated by a proper length header to aid exhaust scavenging and initiate inlet flow when the piston is near TDC, but overlap kills low end torque due to exhaust gas dilution of the fresh charge, especially at part throttle when exhaust port pressure is much higher than inlet port pressure, and without headers the extra overlap doesn't improve top end power, so with OEM manifolds you get to a point where overlap just kills the low end without a giving anything back anywhere in the rev range.
Duke
[Modified by SWCDuke, 9:03 AM 7/12/2002]
