Theoretical underpinnings
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Elite HDF Member
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From: Seattle, WA
Theoretical underpinnings
... of the design of certain Headquarters and Kuryakyn cams ...?
Subject: discuss the theoretical underpinnings of a few of the cam designs which produce intake valve lift of a greater value than exhaust valve lift ...
... not sure which cams off the top of my head; but, there are several cam grinds with higher intake lift than exhaust lift ... always kind of wondered about that--especially since the intake valves are larger than the exhaust to begin with ....
Also, there are a handful of guys I've seen who have installed 1.725 rocker arms on the intake side while leaving the exhaust at 1.625 ...
... I am about to get on that band wagon ....
I am sporting the Andrews TW37B cams in my 95" with SE flat-top pistons ... using the SE Performance MCR heads putting CR at 10:1 ....
My bike is running really well, but I got a half-set of 1.725 rockers off another forum member ... I had been toying with the idea of doing the intake-side only rockers for a while, and jumped on an opportunity that presented itself ....
With the greater air flow (presumably?) I am also toying with the idea of adding a 50mm throttle body ... I have an '05, so have the 43mm (??) t/b vice the later 46mm t/b ....
Any thoughts ...? THX in advance ....
R/
'Chop
Subject: discuss the theoretical underpinnings of a few of the cam designs which produce intake valve lift of a greater value than exhaust valve lift ...
... not sure which cams off the top of my head; but, there are several cam grinds with higher intake lift than exhaust lift ... always kind of wondered about that--especially since the intake valves are larger than the exhaust to begin with ....
Also, there are a handful of guys I've seen who have installed 1.725 rocker arms on the intake side while leaving the exhaust at 1.625 ...
... I am about to get on that band wagon ....
I am sporting the Andrews TW37B cams in my 95" with SE flat-top pistons ... using the SE Performance MCR heads putting CR at 10:1 ....
My bike is running really well, but I got a half-set of 1.725 rockers off another forum member ... I had been toying with the idea of doing the intake-side only rockers for a while, and jumped on an opportunity that presented itself ....
With the greater air flow (presumably?) I am also toying with the idea of adding a 50mm throttle body ... I have an '05, so have the 43mm (??) t/b vice the later 46mm t/b ....
Any thoughts ...? THX in advance ....
R/
'Chop
Road Master
Joined: May 2007
Posts: 851
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From: Mitchellville, Ia.
You need to know the percent of exhaust to intake air flow your heads supply to determine how the engine will respond best. Some engines need more exhaust flow, some less. Some can reach the magic number by kicking up the intake. We recently installed a stage 3 R&R package with 58mm TB, 107" pistons, and Andrews 54 cam. Best results cam from 1.72 intake rockers only.
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Elite HDF Member
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From: Seattle, WA
(i) you did not address theoretical underpinnings ...
(ii) above, I conceded that at the 'top' of the cam cycle (i.e., the point of highest lift) there is no advantage to the higher leverage of the rocker arm ... however, at all points between the base circle and 0.5 lift, there would exist an improvement in CFM flow rates ... the 1.725 additional leverage applies to all points off the base circle--not just the highest lift point.
So, my conclusion is that there still may be some benefit to utilizing the rockers ...
* * *
Does anyone have a response to my previous question ... what is the 'optimal' ratio of intake to exhaust port flow ...? In Kingofcubes' words "the percent of exhaust to intake air flow" ...? THX!
R/
'Chop
Road Master
Joined: May 2007
Posts: 851
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From: Mitchellville, Ia.
That is the magic question, the next question that is significant is at what degrees of crank rotation (which involves the valve lift @ crank degrees and piston location) to set the percent of flow at. This is propriatory info for most porters/designers.
Last edited by Kingofcubes; Sep 22, 2011 at 12:15 PM.
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Could you please explain more on this? Thanks...
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Joined: Nov 2007
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Sometime thinking about the HD engine there seems to me to be two separate engines connected as one.
Using the TTS tuner. For whatever reason, my front cylinder has about 7-10 % less flow than the rear. I think the crank rotation and the almost universal front exhaust exit--hard 90 degree almost---as to do with this.
I don't think it is the intake or intake valves. I have all the engine could ask for there.
These higher lift rockers make me wonder how they would work for the front leaving the rear stock. Somebody bound to have tried thes.
Just thinking.
Using the TTS tuner. For whatever reason, my front cylinder has about 7-10 % less flow than the rear. I think the crank rotation and the almost universal front exhaust exit--hard 90 degree almost---as to do with this.
I don't think it is the intake or intake valves. I have all the engine could ask for there.
These higher lift rockers make me wonder how they would work for the front leaving the rear stock. Somebody bound to have tried thes.
Just thinking.
Last edited by Old Gunny; Sep 22, 2011 at 05:53 PM.