Cam School
Thread Starter
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Road Master
Joined: Aug 2008
Posts: 936
Likes: 3
From: Massachusetts
Cam School
Hey guys, I need some schoolin'. Thanks to this forum and you guys, I'm going forward to install a gear drive cam in my 05 EGS. I think I know what cam I want but I'm comparing brands and specs. In a previous thread Harleypingman (Carl) was nice enough to provide this awesome link to the Big Boyz Cam Comparator. Here it is:
http://www.bigboyzcycles.com/tccams.htm
Here's my questions,
What role does "Duration" play in HP/TQ performance..or does it?
And what exactly is Overlap?...Is more or less better?
http://www.bigboyzcycles.com/tccams.htm
Here's my questions,
What role does "Duration" play in HP/TQ performance..or does it?
And what exactly is Overlap?...Is more or less better?
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
All of the above questions about cams and more are answered at nightrider.com.
Duration is the amount of time computed in crankshaft degrees that the cam holds the valve off of the seat. The greater the duration the longer the valve is off of the seat. Up to a point, this allows the engine to breath better. In general engine displacement and desired RPM's dictate what duration will work best. Increasing duration of a cam will move the power higher up the RPM.
Overlap is the time measured in crankshaft degrees that the intake and exhaust vales are open simultaneously. This happens near TDC when the exhaust is closing and the intake is starting to open. The amount and where the overlap has a major effect on power. As duration increases overlap increases all other things being equal. As overlap increases you should increase mechanical C/R . In general for a given engine the shorter the overlap the lower the RPM will be for maximum torque. Overlap changes may require exhaust changes to take advantage of the change in the inertia of the exhaust and intake pulses.
Hope this helps.
P.S. If you have a bagger or heavier bike try any of the Woods "6" series of cams, or give Bob Woods a call. If you use one of his cams you won't be sorry.
Duration is the amount of time computed in crankshaft degrees that the cam holds the valve off of the seat. The greater the duration the longer the valve is off of the seat. Up to a point, this allows the engine to breath better. In general engine displacement and desired RPM's dictate what duration will work best. Increasing duration of a cam will move the power higher up the RPM.
Overlap is the time measured in crankshaft degrees that the intake and exhaust vales are open simultaneously. This happens near TDC when the exhaust is closing and the intake is starting to open. The amount and where the overlap has a major effect on power. As duration increases overlap increases all other things being equal. As overlap increases you should increase mechanical C/R . In general for a given engine the shorter the overlap the lower the RPM will be for maximum torque. Overlap changes may require exhaust changes to take advantage of the change in the inertia of the exhaust and intake pulses.
Hope this helps.
P.S. If you have a bagger or heavier bike try any of the Woods "6" series of cams, or give Bob Woods a call. If you use one of his cams you won't be sorry.
Thread Starter
|
Road Master
Joined: Aug 2008
Posts: 936
Likes: 3
From: Massachusetts
All of the above questions about cams and more are answered at nightrider.com.
Duration is the amount of time computed in crankshaft degrees that the cam holds the valve off of the seat. The greater the duration the longer the valve is off of the seat. Up to a point, this allows the engine to breath better. In general engine displacement and desired RPM's dictate what duration will work best. Increasing duration of a cam will move the power higher up the RPM.
Overlap is the time measured in crankshaft degrees that the intake and exhaust vales are open simultaneously. This happens near TDC when the exhaust is closing and the intake is starting to open. The amount and where the overlap has a major effect on power. As duration increases overlap increases all other things being equal. As overlap increases you should increase mechanical C/R . In general for a given engine the shorter the overlap the lower the RPM will be for maximum torque. Overlap changes may require exhaust changes to take advantage of the change in the inertia of the exhaust and intake pulses.
Hope this helps.
P.S. If you have a bagger or heavier bike try any of the Woods "6" series of cams, or give Bob Woods a call. If you use one of his cams you won't be sorry.
Duration is the amount of time computed in crankshaft degrees that the cam holds the valve off of the seat. The greater the duration the longer the valve is off of the seat. Up to a point, this allows the engine to breath better. In general engine displacement and desired RPM's dictate what duration will work best. Increasing duration of a cam will move the power higher up the RPM.
Overlap is the time measured in crankshaft degrees that the intake and exhaust vales are open simultaneously. This happens near TDC when the exhaust is closing and the intake is starting to open. The amount and where the overlap has a major effect on power. As duration increases overlap increases all other things being equal. As overlap increases you should increase mechanical C/R . In general for a given engine the shorter the overlap the lower the RPM will be for maximum torque. Overlap changes may require exhaust changes to take advantage of the change in the inertia of the exhaust and intake pulses.
Hope this helps.
P.S. If you have a bagger or heavier bike try any of the Woods "6" series of cams, or give Bob Woods a call. If you use one of his cams you won't be sorry.
Again, thanks for the schoolin" teach!!
Extreme HDF Member
Joined: Apr 2006
Posts: 10,449
Likes: 46
From: Roswell, GA
Glad to help. I used Head-Quarters HQ-0034 cams and highly recommend them--many happy users on HDF.
The 34's have an intake close of 36* which provides earlier torque than a later closing 40* intake.
Good luck with your choice.
The 34's have an intake close of 36* which provides earlier torque than a later closing 40* intake.
Good luck with your choice.
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
Wow I didn't even cover LSA, so I will add it now. Cams with short duration, high lift and a narrow LSA give you more low and mid-range power. For more top end power longer duration and more LSA are better. As I believe it is PhilM has in his signature "All parts need to enhance/balance each other".
Thread Starter
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Road Master
Joined: Aug 2008
Posts: 936
Likes: 3
From: Massachusetts
Wow I didn't even cover LSA, so I will add it now. Cams with short duration, high lift and a narrow LSA give you more low and mid-range power. For more top end power longer duration and more LSA are better. As I believe it is PhilM has in his signature "All parts need to enhance/balance each other".
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Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
LSA is Lobe Seperation Angle. It is the angle of seperation in camshaft degrees between the centerlines of the intake and exhaust lobes.LSA determines the valve timing and overlap period for a given duration, therefore it has a major effect on the power characteristics of a given cam. Mild V-Twin cams usually range from 100-104 degrees. While the hotter cams are between 103-110 degrees.
Hope this helps.
Hope this helps.
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Thread Starter
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Road Master
Joined: Aug 2008
Posts: 936
Likes: 3
From: Massachusetts
LSA is Lobe Seperation Angle. It is the angle of seperation in camshaft degrees between the centerlines of the intake and exhaust lobes.LSA determines the valve timing and overlap period for a given duration, therefore it has a major effect on the power characteristics of a given cam. Mild V-Twin cams usually range from 100-104 degrees. While the hotter cams are between 103-110 degrees.
Hope this helps.
Hope this helps.
(oh yeah sorry I called you Carl in the last post..got mixed up)
Thx