Re: Roller cams and max open degree's
[Re: mopar dave]
#3005406
01/14/22 11:20 PM
01/14/22 11:20 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
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New York
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The lobe's peak is then (briefly) a perfect radius concentric and equal to the base circle plus lobe height
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Re: Roller cams and max open degree's
[Re: polyspheric]
#3005408
01/14/22 11:39 PM
01/14/22 11:39 PM
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Joined: Jan 2003
Posts: 1,760 Windsor, ON, Canada
Diplomat360
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Windsor, ON, Canada
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The lobe's peak is then (briefly) a perfect radius concentric and equal to the base circle plus lobe height Yup...and plugging in a little math here could literally convert the length of that perfect radius and it's proportion to the size of the roller lifter's roller wheel diameter to crankshaft degrees duration. Effectively at the very peak (nose) of the lobe you have a phase where the roller wheel begins traversing that radius and eventually "comes around" to the other side of the nose, while all along the lobe nose hasn't really moved away all that far. I think this is the "hang" time you're seeing. Math should prove out this perception and for my purposes I literally took a measurement of the lobe lift every 5 deg and as you can tell that "hang" time is there. Disclaimer: that math I referenced above is a bit beyond my feeble know-how as it took me a couple of hours to build a spreadsheet calculation to show and compare the piston bore movement per each crank deg rotation of a stock 3.58" vs stroker 4" crank. Interesting results though, especially as you try to compare that to the lobe open and closing events and try to understand how the combustion pressure dissipates on the piston's downward push on the power stroke. (sorry, tangent thought right there...)
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Re: Roller cams and max open degree's
[Re: mopar dave]
#3005429
01/15/22 01:14 AM
01/15/22 01:14 AM
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Joined: Jan 2003
Posts: 31,041 Oregon
AndyF
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I Win
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Oregon
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I'm sure it's not flat on the nose, but i have never noticed this before with any other cam i had. May not be flat, but pretty close to it as the indicator stays right on 0 for atleast 10* as i stated. Just curious if this was normal and i never noticed before. Thanks That is just what you are seeing, it isn't what is actually happening. The tappet is moving up and then back down but you can't see it because the tools you are using aren't good enough. If you used a yard stick to measure bearing clearance you would say the clearance is zero because you wouldn't be able to see it with the yard stick.
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Re: Roller cams and max open degree's
[Re: Stanton]
#3005486
01/15/22 10:43 AM
01/15/22 10:43 AM
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Joined: Jan 2003
Posts: 1,760 Windsor, ON, Canada
Diplomat360
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Rough math ...
cam bore of approx. 2.5" (I think I'm overestimating big time here) assume max lobe size so radius from cam center to tip of lobe = 1.25" pi x R squared = 5" dia. 5" / 360 degrees = .014" per degree cam turns at 1/2 crank speed so 10 crank degrees = 5 cam degrees 5 x .014 = .070"
I don't think you would see much movement on the dial indicator for less than .070" of rotation at max lift - particularly on a roller cam. Nice, that's what I'm talking about! To get the real nose measurement you could take the cam lobe base circle diameter, divide by 2 and add the lobe lift, this would give actual R value I think. Once plugged into the remainder of the calculation you provided that would give you a precise measurement of the distance covered at the nose for each crank degree rotation.
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Re: Roller cams and max open degree's
[Re: mopar dave]
#3005493
01/15/22 10:58 AM
01/15/22 10:58 AM
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Joined: Jan 2003
Posts: 31,041 Oregon
AndyF
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I Win
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Oregon
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I understand Andy, but the tools i'm using are the same tools i used to install about a dozen or so other cams and i have not ever notice the indicator stall on the nose of the cam for this long of a duration of time. Not a big deal, just thought i might have a better ground lobe than what was on my other roller cams in the past. Adding duration on the nose of the cam, allowing the valve to stay open a bit longer at max lift would be cool or am i wrong in thinking that. You aren't wrong about the duration. I always measure the duration at 050 and then at 200 and sometimes at even higher lift. The more aggressive lobes will have more duration at higher lift. Measure the duration at 300 or 400 sometimes and compare that between lobes and you'll see. Of course the downside is that lobes with lots of duration at higher lifts are usually much harder on the valvetrain since everything is just getting beat to heck.
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Re: Roller cams and max open degree's
[Re: mopar dave]
#3005517
01/15/22 12:14 PM
01/15/22 12:14 PM
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Joined: Oct 2005
Posts: 8,873 Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 8,873
Ontario, Canada
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To get the real nose measurement you could take the cam lobe base circle diameter, divide by 2 and add the lobe lift, this would give actual R value I think. Once plugged into the remainder of the calculation you provided that would give you a precise measurement of the distance covered at the nose for each crank degree rotation. You could do all that but I overestimated so much on the numbers that the end result would be significantly less than .070. Just not worth the hassle IMHO. i.e. if you have a 1" dia. base circle and a .750 lift cam (1/2" lobe height) you end up with .043" travel for 5 degrees of cam travel. You won't see any movement on a dial indicator at max lift. And the smaller the cam the less travel.
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Re: Roller cams and max open degree's
[Re: Stanton]
#3005525
01/15/22 12:32 PM
01/15/22 12:32 PM
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Joined: Jan 2007
Posts: 8,041 Mt Morris Michigan
mopar dave
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No problem. I have a half dozen dial indicators, i'll try my best one and see if there is any difference, in fact, i will see if i can find a new digital one and compare. Thanks guys. What is a good brand name digital to look for? A bunch over on ebay from $26-$299.
Last edited by mopar dave; 01/15/22 12:38 PM.
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Re: Roller cams and max open degree's
[Re: mopar dave]
#3005529
01/15/22 12:44 PM
01/15/22 12:44 PM
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Joined: Dec 2013
Posts: 403 Romulus, MI
GTS340
mopar
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mopar
Joined: Dec 2013
Posts: 403
Romulus, MI
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No problem. I have a half dozen dial indicators, i'll try my best one and see if there is any difference, in fact, i will see if i can find a new digital one and compare. Thanks guys. What is a good brand name digital to look for? A bunch over on ebay from $26-$299. Mahr or Mitutoyo
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Re: Roller cams and max open degree's
[Re: mopar dave]
#3005574
01/15/22 02:22 PM
01/15/22 02:22 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
Joined: Oct 2007
Posts: 4,206
New York
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For some of the lobe contour, roller diameter is very important, but of course not at all for max lift and base circle. If the roller diameter changes, the effects are not continuous or linear. Harley-Davidson, running out of money 50 years ago, used Chet Herbert V8 roller lobe profiles in their Sportster-based race engine. Dick O'Brien (the boss) said "I know there are weird vibrations and loss of control, but it's all we could do for this season". Reason: Herbert SBC .750" roller, H-D .855" roller.
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