Like a "square" lobe. There are no angles,just straight down.

 

The whole combination determines the shape of the torque an hp curves as well as the peak points. The cam I used as a reference was far from a ProStock cam. The 267/277 were seat durations. The .050 was more like 215/225.


If you drove at 60 mph/2500 rpm the engine would turn 2500 revs per mile. 10,000 miles then is 25 million revs, and 100,000 is 250 million. If you spend much time in the lower gears it's a LOT more revs than that.

It's not just overlap degrees that count, it's the area of the overlap triangle that really counts. FWIW in my cam example there was -3 degrees of overlap @.050 lift and only about 6 deg*sq-in of total overlap area.

With some really good heads I would expect that cam to peak torque around 5000 and power in the low-mid 6s on a 350-370 cube engine. With the small overlap area it should idle like a pussycat, and have no trouble with low speed driveways. Yes, it is an aggressive inverted flank cam as you might suspect. Hey, there is no free lunch!

 

The one thing that most people miss is where the LSA or more importantly the ICL places the max lift of the valve relative to the crank angles. If you look at it basically like most guys who get to that point do that the airstream in the port is connected to the top of the piston then it gives you a better look at to what is going on. What really happens is a movement of pressure from low to high and where the valve is relative to that, at certain points you want the valve to be open more, and that's what ICL does for you.

In this Vizard quote:

"There is much said about LCAs that needs to be thrown out with the garbage. First let me make one major point quite clear. For a given spec of engine there is only one LCA that will give optimum torque and horsepower. It is not, as many cam company techs would have you believe, a variable parameter."

For the most part I agree with him, FOR THE MOST PART. The thing that I will say is that for a given duration there is a set centerline for that lobe, intake and exhaust. If you change the durations of the cam than the centerlines will change. You can keep one lobe the same, change the other lobe so therefore the centerlines will change, with that change comes a change in LSA. The centerlines are not going to change a ton though, 114LSA's are not optimal for most if any street NA motors that run below 7000rpm. (2 valve motors only)

The other article which is a test that Mike Petralia did before he went over to RTM to work on TV stuff is a very good article as well just to SHOW people what the differences are in LSA for a particular cam. I don't think he kept the ICL the same in that test so it's more of a test on how overlap changes the power curves but it still shows some good things.

dude,

The only reason those inverted flanks are hard on parts is that you have to get the acceleration curves right AND control the spring coils. If you do that they will not have a problem.

Bret

 

dude,

The only reason those inverted flanks are hard on parts is that you have to get the acceleration curves right AND control the spring coils. If you do that they will not have a problem

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The ones I run look like a mushroom and the acceleration is almost instant. Don't believe there is any salvation but to run another style of lobe or rebuild often.

 

The more I fool with different combo's the more I believe the statement That there is but one duration AND ICL to make max power in a particular combo. If that combo happens to be a 383 then that duration and ICL will probably not work on another 383 combo unless the heads,intake tract and exhaust and compression are EXACTLY the same and the RPM limits are the same.

 

Gary,

You flatter yourself if you think I read all of your posts above. I learned the lesson of reading most of your stuff, it's about as usefull as **** on a bull for me. After saying that, WTF are you even talking about in reference to the B and F body cams. They are different cams for different vehicles doing different things, and if they end up with the same overlap and different centerlines it's due to that overlap being what is acceptable for 100,000 mile emissions on that motor. Boy that's a ****ing hard one.

The funny thing is that as odd as it may seem and as much as we want to think we can make a motor do what we want, we really can't. We can just give mother nature what she wants and that in the end makes the most power. Even though I get the valve events inside and out, along with what else makes a cam and valvetrain work, you can still use a basic LSA for a combination and tweak from there to get the best results. Meaning..... if you start with lets say a 110LSA and that's optimum I could add a bunch of duration and widen the LSA out and make less power, but if I threw that added duration on the same 110LSA it would make more power and that would basically change every opening and closing point but keep the peak valve lift at the same spot.

Sometimes it's more important to figure out why something does what it does, rather than think your opinion on the matter works. The old man and I have been thru this in terms of the piston speed thing, and I guess this can be another thing. Valve events are the key but they should not be set in stone, but to get to the perfect ones you have to start someplace and usually I start with a set LSA, lift and duration and tweak from there, since it's a much faster way to get to the optimum cam.

Bret

 

As useful as wits on a bull!!!!!
That's like ***** on a priest,wits on a nun and them damn pisants!!!!!! That's the three most useless things in the world.
I agree I am lost with A/G's discussion. Can't make heads or tails out of it.

 

Gary,



If you want to talk numbers, put out some cam specs. I don't care or keep the stock cam numbers on hand, no need too. Remember I don't read all of your posts, or even any of them.

Well considering that I have my father too talk to about this stuff on a daily basis face to face we get a lot of the same "quotes", still doesn't mean that it doesn't apply.

IF you want the attitude, keep up with the comments that we just repost the same dribble you say. (Far from it) You rubbed me the wrong way and so your just one of those combative *******s with a chip on your shoulder that wants to nit pick at bs, time and time again, so YEAH the attitude for YOU is here to stay.

Bret