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Re: Cam Guys
[Re: emarine01]
#895044
01/02/11 11:14 PM
01/02/11 11:14 PM
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Joined: Feb 2009
Posts: 1,532
off the grid
340B5
pro stock
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pro stock
Joined: Feb 2009
Posts: 1,532
off the grid
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I did the math,(trig) on it and a .509 smallblock cam goes from 248@.050 to 251@ .050 lift.
Yeah, it's got a smallblock.
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Re: Cam Guys
[Re: emarine01]
#895046
01/03/11 12:33 AM
01/03/11 12:33 AM
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Joined: Feb 2009
Posts: 1,532
off the grid
340B5
pro stock
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pro stock
Joined: Feb 2009
Posts: 1,532
off the grid
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Yup, still comes off the base circle at the same point, but from there on, it's 1.6 times lobe lift instead of 1.5, so that gets to .050 lift sooner thus increasing @ .050 duration. As far as advertised duration goes you have to remember that different manufacturers rate adv. dur. at .006, .020 and who knows where else.
Yeah, it's got a smallblock.
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Re: Cam Guys
[Re: 340B5]
#895047
01/03/11 12:51 AM
01/03/11 12:51 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Yup, still comes off the base circle at the same point, but from there on, it's 1.6 times lobe lift instead of 1.5, so that gets to .050 lift sooner thus increasing @ .050 duration. As far as advertised duration goes you have to remember that different manufacturers rate adv. dur. at .006, .020 and who knows where else.
BUT in reality its still opens and closes at the same
duration points... and thats what REALLY counts....
sure you have the increase of area under the full
curve but it doesnt make cyl pressure till it closes
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Re: Cam Guys
[Re: 340B5]
#895048
01/03/11 02:34 AM
01/03/11 02:34 AM
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Joined: Jul 2010
Posts: 2,091
Delray beach, Florida
Performance Only
top fuel
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top fuel
Joined: Jul 2010
Posts: 2,091
Delray beach, Florida
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Quote:
Yup, still comes off the base circle at the same point, but from there on, it's 1.6 times lobe lift instead of 1.5, so that gets to .050 lift sooner thus increasing @ .050 duration. As far as advertised duration goes you have to remember that different manufacturers rate adv. dur. at .006, .020 and who knows where else.
it doesn't get to .050 tappet lift any sooner regardless of rocker ratio. the valve will open slightly more at .050 with a 1.6 vs. a 1.5, and likewise on the closing. pretty simple math to find the increase for your camshafts particular lobe. bottom line is you get a little more lift and area under the curve. the actual camshaft duration does not change.
machine shop owner and engine builder
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Re: Cam Guys
[Re: Performance Only]
#895051
01/03/11 10:10 AM
01/03/11 10:10 AM
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Joined: Feb 2009
Posts: 1,532
off the grid
340B5
pro stock
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pro stock
Joined: Feb 2009
Posts: 1,532
off the grid
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Sorry, not buying it. OK.. after re-reading you said lift @ tappet. I hope no one here would think that. The quicker ratio does get the valve to .050 lift sooner and therefore increases @.050 duration. CAMSHAFT GEOGRAPHY AND LOBE FUNCTION 1) Max Lift or Nose 2) Flank 3) Opening Clearance Ramp 4) Closing Clearance Ramp 5) Base Circle 6) Exhaust Opening Timing Figure 7) Exhaust Closing Timing Figure 8) Intake Opening Timing Figure 9) Intake Closing Timing Figure 10) Intake to Exhaust Lobe Separation 
Last edited by 340B5; 01/03/11 01:40 PM.
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Re: Cam Guys
[Re: emarine01]
#895053
01/03/11 03:18 PM
01/03/11 03:18 PM
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Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar
master
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master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
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Quote:
Seems that people say that changing to a higher rocker ratio increases cam duration with the lift, like 4 degrees from 1.5 to 1.6, I am not too sure I buy this, I can see where area under the curve will change but not duration, I'm I missing something 
It's just a comparison thing. The cams duration will remain the same, but the duration and lift at the valve will change with rocker ratio. If the rocker ratio was 1:1 (and assuming zero lash) the valve duration and lift would be the same as the cam. The normal 1.5:1 rocker ratio is what most comparisons are based from. Changing to a higher ratio rocker arm, results in higher lifts at all points, so if you compare valve durations at the same lift, the higher ratio rocker arm will reach the same lifts sooner/later making the valves see "comparably" more duration at the valves.
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Re: Cam Guys
[Re: emarine01]
#895055
01/03/11 09:53 PM
01/03/11 09:53 PM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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The change in valve duration is variable from .050 to max lift between the 1.5 vs the 1.6 ratio. At .050 its around 2* more difference with the 1.6,s and pretty much stays there duration wise on the lift ramp to near the top of the lobe. As the lobe peaks things change, the valve duration increases more then 2*, actually a bunch 10*, 15* or more vs the 1.5,s. But its effects arent as great as the extra duration would suggest. The cams effective duration is still only around 2* bigger at the base. Lets face it, if its a 250* duration cam, its still around a 250* duration cam. Its not no 260* or 270* cam. A .600 lift cam may have about 5* of duration or less at the nose. With the 1.6,s youd have .640 lift at the nose. To scrub off that extra lift it could take a extra 10* on either side of the lobe before the lift see,s .600 again. You got the Ramp up and the Ramp down, things at the very peak lift wise are moving slow. So it takes longer to move the valve thus creating the extra valve duration over the nose vs at the seat. E Marine, see if your buddies know this. mike 
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Re: Cam Guys
[Re: Sport440]
#895056
01/03/11 11:02 PM
01/03/11 11:02 PM
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Joined: Jan 2007
Posts: 3,695
nc
emarine01
OP
master
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OP
master
Joined: Jan 2007
Posts: 3,695
nc
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Hum.... This is not lookin as good as it did last night, Well the exact argument was.... going from a 1.5 ratio to 1.6 is the same as changing to a cam with 4* more duration, I said: That is not true, its like going to a more aggressive lobe, Now after reading the new posts I am not too sure of my position, well anyhow I don't know how they came up with exactly 4* more duration  The way I see it is cams are measured by tappet lift, seems .050 is common, so no rocker change is going to effect this....But the end result @ the valve will see the change.... May have to go to a vote to see who is buying here Oh one more point... its a bunch of Chevy guys I am debating with, but don't let that influence your opinion 
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Re: Cam Guys
[Re: emarine01]
#895057
01/03/11 11:44 PM
01/03/11 11:44 PM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Here's a real world example of showing 1.6 and 1.5 rockers w/ the same cam, same pushrods, and same brand of rockers. The measurements were taken at the valve w/ the lash at .020" for 1.5 and .022" for 1.6. Valve -- 1.6 --- 1.5 .006 -- 302.5 - 302.5 (SAE duration) .020 -- 291.5 - 290.5 .050 -- 273.5 - 271.0 .100 -- 251.5 - 248.5 .200 -- 216.0 - 211.0 .300 -- 184.0 - 177.0 .400 -- 152.0 - 140.0 .500 -- 113.5 -- 95.0 .550 --- 90.0 -- 63.0 .600 --- 58.5 Peak Lift - .637 - .589 NOTE 1: The "net" effective change to the "duration at .050 thou" # measured at the lobe can be approximated by the increase in duration at the valve measured at .075". I didn't measure that lift value, but you can average the increases seen at .050" and .100" valve lift and come up w/ an estimate of about 3 degrees. NOTE 2: If the lash hadn't been adjusted for the higher ratio, the duration would have increased from .006" on up because the lifter would have contacted the lobe farther down the ramp at the point when the lash was taken up. NOTE 3: This is the cam I was using in the Challenger since having switched to the Stage VI heads. My cam, my measurements, my data, my analysis, (blah, blah, blah). So, there's your answer. I'm just not sure what the question was...
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Re: Cam Guys
[Re: emarine01]
#895060
01/04/11 02:33 PM
01/04/11 02:33 PM
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Joined: Dec 2008
Posts: 1,200
UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Quote:
Hum.... This is not lookin as good as it did last night, Well the exact argument was.... going from a 1.5 ratio to 1.6 is the same as changing to a cam with 4* more duration,
All is not lost to those Chevy guys ................just tell em duration will not increase if lash clearance is corrected , you still can win that argument. 
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Re: Cam Guys
[Re: 340B5]
#895062
01/04/11 10:07 PM
01/04/11 10:07 PM
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Joined: Jan 2007
Posts: 3,695
nc
emarine01
OP
master
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OP
master
Joined: Jan 2007
Posts: 3,695
nc
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I will play a little catch up here, Nahhhh.... the Chevy guys are not that smart, they live by the hot rod mag gods  If its in print its gota be right, It was a Comp cam guy with the 4* thing but it was not @ .050, They just thought it was cause they just don't get it, I was thinking of splitting some hairs but I don't write for hot rod... so anything I say cant be right, plus I own a Mopar so what would I know anyway, funny thing is my 414 runs right with their 632s or I would not fit in the club to debate with these knuckle heads in the first place...Man that was long... I was thinking of throwing in the towel cause after reading some of the posts I can see that The comp cam guy is correct to a point even though I have solid ground to stand on, after reviewing some of the exact changes in lift points to duration I thought it was valid enough to give the 4* cause it could get close to .050 just need a little more rocker ratio or mess with the lash.... Plus if I don't loose every now and then they wont let me play  then you guys will be stuck with me
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