URGENT: Help to Select the RIGHT CAMSHAFT
03-23-2007, 06:57 AM
#17
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Join Date: Sep 1998
Location: US 1 Mile Marker 52 in the Florida Keys
Posts: 8,321
a lopy idle (which is describing a sound) is a side effect of variations in the cam design. i want to say it's due to increased overlap.
typically the lower the lobe (not lope) separation angle the more lope you get...ie...choppier idle.
now in general cams that are designed to pass emissions are ground on a higher lobe separation angle to make the idle smoother.
off the top of my head i only know specs on the LSx style cams. but most aftermarket cams average 112 to 114 deg of lobe separation. while the cam that cam stock in the ZO6 corvette was a 117.5 deg angle. this was done to allow for a bigger cam, but still pass emissions.
also, in general, the lower the lobe angle, the lower in the rpm band that the power will peak.
typically the lower the lobe (not lope) separation angle the more lope you get...ie...choppier idle.
now in general cams that are designed to pass emissions are ground on a higher lobe separation angle to make the idle smoother.
off the top of my head i only know specs on the LSx style cams. but most aftermarket cams average 112 to 114 deg of lobe separation. while the cam that cam stock in the ZO6 corvette was a 117.5 deg angle. this was done to allow for a bigger cam, but still pass emissions.
also, in general, the lower the lobe angle, the lower in the rpm band that the power will peak.
03-23-2007, 07:46 AM
#18
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Join Date: Dec 1998
Location: Haslett, Michigan
Posts: 2,161
Lope is the sound of exhaust gases blowing back into the intake tract due to both valves being open at the same time. This also makes it harder to maintain emissions compliance.
Lope does not equate to power. It's the sound of inert exhaust gases mixing with your fresh air. Generally as you increase the speed of the engine, the less mixing takes place. Lobe duration on a cam, as it's increased, pushes the engine's powerband upwards. The sacrifice is loss of low-RPM torque for high-RPM horsepower. Everything's a balancing act, and in order to use that high-RPM power, you have to match the rest of the engine: The intake has to be tuned for the high RPM power, the cylinder heads have to be able to flow the proper amount of air, the exhaust system has to be big enough, the torque converter and gearset has to be appropriate for the RPM band of the engine.
Since you have determined that you want to retain most of the stock powertrain, your cam selection is very limited in terms of how wild you can go before your cam profile's operating characteristic falls outside of the remaining powertrain's ability to make power. You'll want to maximize torque from idle to 5000 RPM.
Lope does not equate to power. It's the sound of inert exhaust gases mixing with your fresh air. Generally as you increase the speed of the engine, the less mixing takes place. Lobe duration on a cam, as it's increased, pushes the engine's powerband upwards. The sacrifice is loss of low-RPM torque for high-RPM horsepower. Everything's a balancing act, and in order to use that high-RPM power, you have to match the rest of the engine: The intake has to be tuned for the high RPM power, the cylinder heads have to be able to flow the proper amount of air, the exhaust system has to be big enough, the torque converter and gearset has to be appropriate for the RPM band of the engine.
Since you have determined that you want to retain most of the stock powertrain, your cam selection is very limited in terms of how wild you can go before your cam profile's operating characteristic falls outside of the remaining powertrain's ability to make power. You'll want to maximize torque from idle to 5000 RPM.
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