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- Nov 26, 2009
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Some people are afraid to use the Sifton 480 cam. Those who do use it have to pay very close attention to the lifter overlap in the tappet block. A few go so far as to silver soldering a spacer to the underside of the lifter shoe to give it more overlap.
But if you allow only .030" clearance between the cam lobes and the tappet blocks at full lift you end up with about .050 to .060" overlap at the bottom of the lifter block tangs at 0 lift and that's enough.
This way you don't have to add more weight (a spacer) to the lifter.
For all out racers using this high acceleration cam its a good idea to use light weight Harley Titanium valves with the 5/16" stems to guard against valve bounce. The Harley flat trackers manage this with over 8000 RPM and their ML cam has about the same ramp acceleration as the 480. The Harley ML cam has much gentler closing ramps than the 480 (to avoid valve bounce) and that is why the asymmetrical JS 480 cam is redesigned with more gentle closing ramps than the commonly available 480.
Note - I recently communicated with a guy who used to drag race in the 1970s. His stock looking 850 Commando used a 480 cam and he turned 1/4 miles in the 11s and pissed off a lot of multi owners. This guy knew what he was doing and actually made his own BSA type lifters.
But if you allow only .030" clearance between the cam lobes and the tappet blocks at full lift you end up with about .050 to .060" overlap at the bottom of the lifter block tangs at 0 lift and that's enough.
This way you don't have to add more weight (a spacer) to the lifter.
For all out racers using this high acceleration cam its a good idea to use light weight Harley Titanium valves with the 5/16" stems to guard against valve bounce. The Harley flat trackers manage this with over 8000 RPM and their ML cam has about the same ramp acceleration as the 480. The Harley ML cam has much gentler closing ramps than the 480 (to avoid valve bounce) and that is why the asymmetrical JS 480 cam is redesigned with more gentle closing ramps than the commonly available 480.
Note - I recently communicated with a guy who used to drag race in the 1970s. His stock looking 850 Commando used a 480 cam and he turned 1/4 miles in the 11s and pissed off a lot of multi owners. This guy knew what he was doing and actually made his own BSA type lifters.
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