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Old 02-07-2016, 10:47 PM
  #881  
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Lift alone isnt the magic passport to big power gains. All the lift in world isnt going to help if the valves arent opening and closing at the right times.

Not all cam designers are concerned with a peak power number on the dyno. Some understand the concept of valvetrain longevity, and will go with a gentler lobe, at the expense of a few horsepower.

Sometimes theres very very little to be gained with more lift, especially if your head flow isnt there.

Imo, theres two ways to validate your cam selection. First, a dyno test. Second, run it in the field for a while. If it makes the power you want, and the combo lives up to your expections without component failure, then its a win.

My biggest concern with excessive valve spring pressures, is the extended idle times we have with boats. Contrary to what some think, high spring pressures, coupled to long idle times, is hard on the lifters.

I do believe the ultimate setup is the least amount of spring necessary to control the valvetrain. Finding that setup, is the hard part. Find me an oem gasengine that will go 300k miles with 500 plus pounds of spring pressure. Chit, i think the gm trucks had sub 100lb seat pressure and would easy go 200k miles without a valve cover off. But of course, they had minimal lift, and never saw north of 5k rpm.
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Old 02-07-2016, 10:52 PM
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Originally Posted by mmb View Post
If you run that much pressure and the springs are staying consistent and not losing pressure you're fine. The next thing I worry about is the roller shaft breaking in the lifter. They always look good until they break.

The valves, retainers, rocker arms do not break very often.
And when that roller shaft breaks, or wheel comes apart, it gets ugly in a hurry.
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Old 02-07-2016, 10:58 PM
  #883  
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Heres a good read on lobes from kip fabre. Even though its ls based talk, its good stuff. Kind of shows how two cams can be very close iin specs, but one can be hardee on the valvetrain

http://ls1tech.com/forums/generation...cam-lobes.html
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Old 02-07-2016, 11:00 PM
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From kip


Someone came up with this statement and it stuck, “THE MORE AGGRESSIVE THE RAMP RATE, THE MORE OVERALL AND UNDER THE CURVE POWER”. It was probably some cam lobe designer trying to BS people. Ramp rate? What is that? Velocity? Acceleration? Degrees from .006” to .050”? You must have high acceleration and jerk to have a lobe that has a low .006” to .050” number like 49 degrees, and that will beat the snot out of the lifters and be noisy. We use a smoother ramp of about 55 degrees. The .050” to .200” can be pushed if you want a high duration @.200”, but you will have higher accelerations before and at the nose which will float sooner. If you have two cams, both having [email protected]”, one with .340” lobe lift, one with .360” lobe lift, the lobe with the higher lobe lift (.360”) will always have a higher .200” duration.*
Why does everyone want to know the .200 number? because some said the higher the .200 number the better the lobe? Or is it more power it will make?
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Old 02-07-2016, 11:03 PM
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All this cam talk... would somebody please perfect an electronically controlled camera shutter type setup to replace the cam and valvetrain all together... the technology has to be out there...
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Old 02-07-2016, 11:24 PM
  #886  
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Originally Posted by MILD THUNDER View Post
So, by following your logic, if i was to take a 502 magnum 224 duration, .480 lift camshaft, and switch to a 224 deg , .680 lift camshaft, my valvetrian would last longer?

Try selling that one to general motors lol. Hence why a 502 mag will go 900 hours without a valve cover off, and a hp500 wont go 350 hours with similar cam and .600ish lift.

The turbo guys tend to run short duration cams, to help build low rpm power off boost, with lots of lift. Those setups kill valvetrains, until they back the lift down.

Rather than argue theories, i'll look at what crane , comp, lunati, howards, mercury, and others offer in a cam application. Once I start seeing a trend in their patterns, i start believing. You can look at all their lobes, and when duration goes way up, so does lift. When duration goes way down, so does lift, with all things being fairly equal.
We are talking about .050 lift not a 1/4" - 224/.480 and 224/.530 is splitting hairs. Yes lift goes up with duration because a 250/.480 cam is hard on the valve train where a 250/.650 cam is going to be nicer to the springs.
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Old 02-07-2016, 11:39 PM
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Originally Posted by mmb View Post
We are talking about .050 lift not a 1/4" - 224/.480 and 224/.530 is splitting hairs. Yes lift goes up with duration because a 250/.480 cam is hard on the valve train where a 250/.650 cam is going to be nicer to the springs.
If you were to go to say comps master lobe catalog, and look at their "endurance" or "marine" profiles, vs their bracket , strip, drag race style lobes, you will see that if .050 durations are the same, say something like 260, the endurance cams will have less lift, and the drag race cams, will have more lift. If your theory is correct, wouldnt the endurance cams, have bigger lobes if that was true ? Why are they limiting lobe size then ?
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Old 02-08-2016, 12:03 AM
  #888  
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Going excessive in either direction is bad & Race engines max everything out. But basing all your decisions off of comp lobes designs doesn't mean anything either. Telling someone to change a cam because it needs .050" less lift is crazy, .600 range lift is going to be needed to make decent power and if it only lives 300 hours vrs 900 then it is what it is. .050" lift isn't going to make a whole hell of a lot of difference.

You just said a 224/.600 lobe goes 300 hours - a 243/680 is a lot smoother than that!
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Old 02-08-2016, 06:53 AM
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Originally Posted by MILD THUNDER View Post
And when that roller shaft breaks, or wheel comes apart, it gets ugly in a hurry.
I know how that feels and gos. And when it happens it looks somthing like this[IMG] [/IMG]
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Old 02-08-2016, 07:16 AM
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Originally Posted by mmb View Post
Going excessive in either direction is bad & Race engines max everything out. But basing all your decisions off of comp lobes designs doesn't mean anything either. Telling someone to change a cam because it needs .050" less lift is crazy, .600 range lift is going to be needed to make decent power and if it only lives 300 hours vrs 900 then it is what it is. .050" lift isn't going to make a whole hell of a lot of difference.

You just said a 224/.600 lobe goes 300 hours - a 243/680 is a lot smoother than that!
I surely dont feel comfortable telling him to keep it, based solely off .050 numbers and lift number. Besides the fact i have seen the carnage from those cams like his, as well as thier power number be down compared to a shelf cam with less lift.

It will be interesting to see how the dyno session goes. A crane 630 lift hyd roller like the 741, 651, call for 150 closed, 450 open, with valve float at 6800, and a max recommened rpm of 6400 with that combo. But, they arent very intense lobes.

An engine builder recently got an invite to do some spintron testing on some marine bbc packages. Might be some interesting data to be found . Maybe tims package can be tried out.

Tim, what was the recommmended spring pressure from bob on your cam ?
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