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#1
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Asymmetrical lobes
I measured a UD hyd flat 288 lobe today. I tried to measure for asymmetry. I was expecting less duration to lift the lobe on the opening then closing ramps. It took 83* for the lifter to rise from .010 to .250 on the opening ramp and 84* for the lifter to drop from .250 to .010. Surprised by the lack of difference I measured at a lower lift. The lifter took 11* on the opening between .002 and .010 and 15* on the closing between .010 and .002. So the total difference between .002 and .250 was that the closing ramp took 5* extra and 4* of that was at .010 or under
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#2
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So it's setting the valve down softly, if I'm reading your post correctly. That's a good thing.
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#3
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pmd400 you've got too much time on your hands
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#4
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X2!Tom
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#5
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That’s correct. I was just surprised that the only difference between the opening and closing was at .010 lift and under. I thought most of the ramp would be different. Would it matter much if it was symmetrical? As in slower opening, not faster closing
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#6
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Probably at a cost of some HP.
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#7
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For sure. Although I could search the net a lot longer and still be none the wiser
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#8
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Drill down further,
Lets say keeping a intake valve open at low lift just a bit longer provides more of a charge and increases combustion pressure by 5 lbs remember that force is acting on a crank arm which is converting linear force into rotational force that is more torque And if i did my math right your getting that 5lbs a power stroke 41.6 times a second at 5000rpms. = more HP. Little things can add up
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A man who falls for everything stands for nothing. |
#9
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Harolds comments from another thread....
Both Harvey and I design Unsymmetrical cams, where the opening side and the closing side are different everywhere except at the nose, where we match both sides through the 3rd derivative, at least. We both use different off-sets, the difference between the opening and closing sides, even at .050". My old 288R that I designed in April, 1980, thought it was a 282 at .020 when it opened, a 252 at .050. Then it knew it was a 258 at .050 when it closed, and 294 at .020, still closing. The 288R was notorious for bottom-end torque, and good power everywhere. It had 176 at .200, one degree more than the Crane R260/4167. What I use now is the R255416H. This rascal thinks it is a 279 at .020 when it opens, still a 252 at .050, still a 258 when closing, and now a 288 at .020. At .200, 180 degrees. I've lost 5 degrees at .020, kept the same duration at .050, and gained 4 at.200. It has gained power everywhere. Remember, it is not WHAT the duration is, but WHERE the duration is, that counts in camshafts. Remember, the engine sees WHERE the duration occurs, not WHAT the duration is. Harold Brookshire UltraDyne Cams .
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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE |
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