HALLZ

iTrader: (1)

i ran across this from a MAJOR cam company. Are they talking about reverse split cams????




Inverse Radius Cams: Just Say No!

These days everybody wants more: Bigger, "Fatter Intake Profiles, yielding more "Area Under the Lift Curve" and Higher V.E. (Volumetric Efficiency). Some Racers mistakenly believe that a more aggressive roller camshaft requires a visit to one of the cam companies struggling for recognition, who push alternative cams with cute names like "Inverted Radius" (Actually a Re-entrant, Concave or Hollow-Flank profile Cam). Unfortunately these cams are not a wise choice considering their major drawback: the undesirable hidden side effect of reduced valve train life expectancy! Subsequently, many who purchase these cams learn to live with problems like broken or prematurely worn-out valve springs, "dropped" valves, bent pushrods, etc., unaware their valve train has been "Jerked" around by a camshaft of reduced stability at higher RPM!

These cam grinders are not however solely responsible for promoting misinformation about these so called "Inverse Radius" Cams. With the aid of the computer and the addition of new tools of the last decade or so such as the "Cam Doctor" "Audi Cam Pro" etc., Cam Profile Dynamics which were once the privy of cam designers alone can now be viewed by many others. With this new technology, there has been a new crop of "experts" who love to talk Cam Profile/Valve "Dynamics". <--- (anyone around here like this????)

I am often amused by the cavalier attitude of some of these neophytes who seem to have this view when it comes to Valve Acceleration & Jerk Curves: "The more radical looking they are the better". Well, pardon me for saying so but to paraphrase conservative columnist William F. Buckley, "Ignorance Is Not A Virtue". The only time you should want your 2nd & 3rd differential curves (Acceleration & Jerk) to have greater amplitude or to have the "look and feel" of "Radical" is when you're dealing with limited RPM levels.

It is no coincidence that industrial engine production cams such as those manufactured by John Deere, Caterpillar Tractor, Allis Chalmers etc. are designed in this manner. They are low speed engines! (Have you ever heard of anyone running one to five or six thousand RPM?) They are the cams with the familiar hollow or concave flank and whenever you see one of these cams, remember: Their physical appearance is the result of their High Acceleration & Jerk Peaks and such characteristics are always associated with more moderate (not higher) RPM levels! These inverted looking cams will give you a slight torque increase because they will usually have 2-4 degrees less seat duration for a given duration at .050" lift. The problem occurs when you try to run such cams at up to 8000 plus RPM where they do not belong. It is simply a case of "Nada Por Nada" as they say in old Mexico. You don't get something for nothing. Those who can limit such cams to say 7000 or so maximum RPM and have appropriate valve train components won't fair too badly, but those who insist on consistently running cams like these at Higher RPM levels is "Rolling the dice" every time they does so. They should therefore not be too surprised when the dice on occasion roll "Craps".

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cracker

iTrader: (1)

That all makes sense.

Plus, My reverse split picked up 37 with a cam swap. My standard split RPM2 cam picked up 60 with just a cam swap.

The specs are similar with the Reverse having quite a bit more lift.
RS- 234/230 .598/.591 112+2 = 358 rwhp/349 rwtq
RPM2- 232/236 .571/.577 112 = 381 rwhp/354 rwtq

So my experience (without you underlying details) have been anything but a success.

FDLS6

iTrader: (4)

That excerpt has nothing to do with reverse split cams, traditional split cams, etc.. it is specifically adressing the shape of the cam lobe, intake or exhaust. The "inverse radius" is a term for a lobe shape. Each manufacturer has different contours for their lobes, and many offer differrent contours or lobe shapes with different designs.. compare the comp xe to the comp xe-r.. the xe-r is a more agressive lobe.. The article points out that they feel the "inverse radius" lobe is too agressive because of the very rapid changes/acceleration of valvetrain movement.. hope that helps.
Bryan

Noyzee

iTrader: (37)

I run a rev split. they say it is the way to go with turbos, i hope it is, it seems to make good power!
it is mild cam tho.
222/216 563/563 116lsa.

93PONY

Like FDLS6 said, it has nothing to do with reverse-split/standard split profiles. It's ONLY refering to the actual curve of the lobe itself.

Comp has LOTS of these type of lobes....MANY of you run them.

Camshaft core size also plays a role. The smaller the core, the more stress on the valvetrain with these types of lobes. Luckily the LS1 uses a very large core. (unlike the LT1)

With the proper valvetrain these lobe profiles are NOT a problem on LS1's turning 7K rpm.

Hitman#1

iTrader: (1)

The simplest way to explain an "inverted flank" cam is a simple picture. Imagine looking at a cam lobe from the side. A typical standard cam lobe looks like this: (_). An inverted flank cam lobe looks like this: )_(. It is basically a way to get a much faster opening and closing rate, with out having to lift the valve any higher or add any additional duration.

Ed Curtis

Well,

The comments by this "major camshaft" company sounds like "someone" is trying to discredit the likes of Comp Cams and the now defunct Ultradyne (Harold is now with Lunati) with their fast ramp or inverted flank camshaft profiles. I guess this may be some sour grapes from the deal where Comp handed Cxrxaxnxe their *** with a dyno test "correction" of full page ads last month. But hey, what do I know....

Inverted flank roller camshafts HAVE THEIR PLACE in the realm of high performance. They just need to be applied correctly and this is not always the case. The potential HP goals and rpm range are important, as are the peripheral equipment used in the valvetrain. A designer has to have all the factors considered before you can design the profile using thes faster lobes. Some people know what to do with all these lobe options whereas others just "play the role"...

I totally agree with the intent of the "letter" and that some "neophytes" DO NOT have an idea of what each factor "is" when designing a camshaft and hence, do more copy cat designing rather than originating profiles. However, to state the cam lobes are "no good" is too much of a blanket statement and, in this guy's opinion, misleading..

Bottomline... Do your research before buying a camshaft.. There's a lot of mis-information and hype out there just to make a few extra bucks, though totally confusing consumers at the same time! Give the people who do this best a shot at explaining why a "box" cam that was used in a buddy's car may not be the right choice for your particular application. Or maybe why a "box" cam IS a better choice... Don't guess.... Get the data....

Ed

J-Rod

I can't really expand much on what Ed and otheres have already said. Inverse Flank and the like as stated relate to the shape of the lobe, and not whether your cam is reverse, conventional, or symetrical. Its all about what the shape of the lobe is.

Think about it this way. If you have ever rode a bike before, think about the difference between say a mound of dirt in your yard, and a say a half pipe. You can usually ride up both, but one will accelerate you up much quicker than the other. I know this is a huge oversimplification, but it helps give you an idea of what we're talking about.

Although Ed doesn't care for them, there are cams out there that have such an agressive lobe on them that they literally "launch" or basically throw the lifter right over the top of the cam when you reach a certain RPM and it lands on the closing side of the cam. Its hard on parts, but they make mad power in lift limtied classes.

Thats all about the lobe shape. In that case you are intentionally introducing valve float...

Old SStroker

What J-Rod said.

Also:

Non-inverted (convex) cam lobes are ground with a large diameter grinding wheel, say 20 to 24 inches in diameter. Inverted flank (concave) lobes need to be ground with a wheel with a radius somewhat less than the inverse radius on the flank. Something like 6 to 8 inches in diameter would not be unusual. Not every cam manufacturer has a high end cam grinder which will use wheels this small. True, a 20 inch wheel could possibly grind an inverted radius just over 10 inches, but accuracy would be difficult to control as grinding wheel diameter changed as it was trued or "dressed" during the grinding operation. Smaller wheels, and CNC give more control of the lobe profile and the resulting valvetrain motions.

Comment on the original post: If a cam designer isn't looking past the jerk curve to the next derivatives (rate of change of jerk, etc.) he/she may not be using the most sophisticated design software. I've heard the next 3 derivatives of Jerk called Snap, Crackle and Pop. Those whimsical names are like some of those which particle physisists call the elusive quarks: Up, Down, Charm, Strange, Top, Bottom. There is probably a connection. My take is that you'd probably like the minimum Jerk, S, C & P you could get and still achieve the lift curve you want. I suppose a cam designer could specify say maximum jerk values and then work backward thru acceleration velocity and lift. In precomputer days (1960s), that's how some cams were designed. It took lots of manual calculations to come up with a new lobe.

FWIW, jerk, or rate of change of acceleration is what you feel when your transmission shifts during acceleration of your car. Increasing shift firmness in an automatic increases the jerk you feel. It's an aptly named derivative, IMO. You can imagine what large values of jerk do to your valvetrain.

Just for grins try a Google search on "Fatter Intake Profiles" from the first post. I only got one match.

HALLZ

iTrader: (1)

Good Info guys thanks!!!