PI Non PI Specs.
- Thread starter blown90
- Start date
CobraRed_96_GT
Active Member
Non-PI Cams - 1996-1998
Advertised Duration @ Lobe: 233*/242*
Advertised Duration @ Valve: 242*/254*
Duration @ .050" @ Lobe: 186*/191*
Duration @ .050" @ Valve: 202*/207*
Lobe Lift: .256"/.259"
Gross Lift: .461"/.466"
PI Cams - 1999-2004
Advertised Duration @ Lobe: 233*/239*
Advertised Duration @ Valve: 242*/252*
Duration @ .050" @ Lobe: 184*/191*
Duration @ .050" @ Valve: 200*/209*
Lobe Lift: .280"/.295"
Gross Lift: .504"/.531"
Centerline: 112*/116*
Advertised Duration @ Lobe: 233*/242*
Advertised Duration @ Valve: 242*/254*
Duration @ .050" @ Lobe: 186*/191*
Duration @ .050" @ Valve: 202*/207*
Lobe Lift: .256"/.259"
Gross Lift: .461"/.466"
PI Cams - 1999-2004
Advertised Duration @ Lobe: 233*/239*
Advertised Duration @ Valve: 242*/252*
Duration @ .050" @ Lobe: 184*/191*
Duration @ .050" @ Valve: 200*/209*
Lobe Lift: .280"/.295"
Gross Lift: .504"/.531"
Centerline: 112*/116*
CobraRed_96_GT
Active Member
i dont know if your talking about advertised duration, or duration at a certain lift, but for high rpms the PI cams dominates for sure. You see only changes in exhaust duration that are 3 and 2 degrees longer with the npi cams, but that's not a good indicator alone.
With the pi cams you have a peak lift of .504/.531 so since the exhaust lift is a GOOD deal more than the npi cams you dont need to keep the exhaust valve open as long to push out the gases since it's open more. Therefore you have have less duration and still be more effcient, plus less duration means less overlap - so the exhaust valve is better seated before the intake opens to let air in. You'll notice that the intake durations a very close, yet the PI cam has .43 more lift, that means the lobe is steeper and is opening the valve faster to get to the .504 - so it will see gains in flow across the lift cycle - not just at peak lift over the npi cam.
Think of it this way, lift is the size of your garden hose in diameter - duration is how long you turn it on. (also the larger the diameter the more you can turn the facet cuz it has a larger capacity)
to fill up something as fast as possible, you can either use a comparatively small hose and turn it on longer for a fraction of a second or you can use a larger hose and turn up the faucet more due (it's capacity to flow) but use it a fraction of a second less as long
ALSO (lol) if you look at performance cams like compcam's xe262ah vs the xe268H (which is for npi heads) the 262 has a good amount less duration than the 268, but opens to .550 while the 268H opens to .500 - no only can you expect more gains on a comparatively less "stage" cam - you can bet you'll see them at a higher rpm than the 268's. This is also why you see people being limited in their rpm power band by their springs - since good springs are needed for high lift because high lift cams open much faster since they need to get to a further distance in relatively the same amount of time - while duration on the other hand doesn't as much require a good spring.
With the pi cams you have a peak lift of .504/.531 so since the exhaust lift is a GOOD deal more than the npi cams you dont need to keep the exhaust valve open as long to push out the gases since it's open more. Therefore you have have less duration and still be more effcient, plus less duration means less overlap - so the exhaust valve is better seated before the intake opens to let air in. You'll notice that the intake durations a very close, yet the PI cam has .43 more lift, that means the lobe is steeper and is opening the valve faster to get to the .504 - so it will see gains in flow across the lift cycle - not just at peak lift over the npi cam.
Think of it this way, lift is the size of your garden hose in diameter - duration is how long you turn it on. (also the larger the diameter the more you can turn the facet cuz it has a larger capacity)
to fill up something as fast as possible, you can either use a comparatively small hose and turn it on longer for a fraction of a second or you can use a larger hose and turn up the faucet more due (it's capacity to flow) but use it a fraction of a second less as long
ALSO (lol) if you look at performance cams like compcam's xe262ah vs the xe268H (which is for npi heads) the 262 has a good amount less duration than the 268, but opens to .550 while the 268H opens to .500 - no only can you expect more gains on a comparatively less "stage" cam - you can bet you'll see them at a higher rpm than the 268's. This is also why you see people being limited in their rpm power band by their springs - since good springs are needed for high lift because high lift cams open much faster since they need to get to a further distance in relatively the same amount of time - while duration on the other hand doesn't as much require a good spring.
Similar threads
