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Discussion Starter · #1 ·
I have a basic understanding of duration, overlap, lsa, etc and the fact that changing them affects the resultant engine performance. Yesterday, out of the blue I started wondering about something and would like to have input from some of the knowledgeable people here.

The basic idea of changing a camshaft is almost always to get not only more power, but the most power for a given combination of specifications. When you change say the LSA, you affect other specs even if they remained unchanged.

My question is..........Why do cam manufacturers not determine the maximum lift thats usable and use it on all their cams no matter what the other specs are? Now I realize that they can't make every cam end up with .700 lift because springs won't handle that. So what I'm saying is, if a certain reasonable spring (daily driver /some racing typical) pressure and coil bind height will work with anything from a mild engine to a semi-race engine, and you don't have piston/valve issues........why don't all these milder cams employ the max lift possible. Opening the valve further can only help (or no change) any lobe profile.......so why use less lift than what is possible? Doesn't seem to me that it would have any detrimental affect on how the cam behaves.
 

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The laws of physics prevent excessive rates of lifter acceleration on the cam lobe with excessive non tangential loads of force. These forces can excessively wear or destroy the cam/lifters.

Do some reading on the subject. You will find rates of cam rise @.050” lift is a standard measure. The amount of degrees between zero lift and amount of degrees at .050” (lesser is faster) will pretty much determine the character of the cam. A street profile is generally around 220 degrees at .050” lift. A greater number of degrees (overall profile) between 0 (base circle) and .050” lift is a gentler cam and most likely last longer in street driving. Faster rates are harder on valve train.

Plenty of very detailed information is available on this topic. Cam producers have spent years and piles of money producing profiles to achieve the most that laws of physics allows the hardware in quest for more power.
 

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Race it, Don't rice it!
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What he said, you can only open and close that valve so fast. Lift is determined by the 'steepness" of the ramp and the length of the ramp.

Like the ramp you used to jump on a bicycle as a kid, If you make it too steep, you run into it, not go up it. Then you got an idea to make it longer and even add a but of concave curve to the ramp to make sure you go over it, not into it.
Lift is determined by the 'steepness" of the ramp and the length of the ramp.

A roller cam/lifter has a wheel to roll up the ramp, tolerating more lift then say, the snow sled on the jump at the bottom of the big hill.

You on the right track though, Mike Jones once said he plots the ideal lift per degree for your engine specifics, then works backwards to make it live.
 

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Depends on the engine right down to cam lobe and lifter wear factors. As lift goes up so does spring pressure, this is more determinant than duration. In the case of the SBC Gen I and II this quickly gets into severe wear issues at this point. This arises from the design of relatively small diameter cam shaft teamed with small diameter lifters, this being a design decision made in the early 50’s where life was just crawling out from under the flat head Ford so the times and the thinking was a lot different. The downside of design decisions on big investment items is your stuck with them into a future you can’t see. Here you need to realize that the design of an engine is likely to start 3 to 5 years before the first one is cradled into a production vehicle coming down the assembly line. You not only have to have the idea of a new engine you have to study several design and manufacturing options, you have to get management buy in to go to finance to fund the project. Once agreements are in place serious design work on the engine starts and with design of a production facility which likely needs to include a new investment in land and structures as you can’t interrupt current production. Tooling from manufactures like Cincinnati and many others in business back then have to be brought into the engineering design process for both the engine itself and the factory manufacturing process layout. Prototype engines need to be built and tested results of the testing bring design changes and more prototype testing. Once the engine design is stable and a test production line is in place you can actually start testing the line on preproduction engines to test them against spec to see if the line actually produces the needed quality product. Then you have to scale that up to meet production rate which always brings another flood of problems that are likely to fall back to product design and likely factory design changes. That was the way things were done till the midish to late 1980’s. That manual cut and try process eventually became computer simulations we use today, but in the 1950’s being able to do that in simulation on a lap top was the stuff of Buck Rogers.

Bogie
 

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the future
In March 2020, Koenigsegg Automotive AB announced its first four-seater car, the Gemera, which is powered by a sequentially turbocharged 2.0l inline-three engine in conjunction with three electric motors. Working with the motor to propel the front wheels is what Koenigsegg calls the Tiny Friendly Giant (TFG) engine. It is rated at 600 bhp and uses the camless Freevalve technology.
 

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Discussion Starter · #6 ·
I appreciate the replys. Still though, the question remains. Let me rephrase what I am asking. First I understand that steeper ramp rates can cause more wear. What I'm saying is that there are existing cams available that already have more aggressive ramp rates and they are proven to work. Generally when these aggressive ramp rates are employed, the manufacturer also has incorporated more lift as well. So why don't they use that same amount of lift that the aggressive cam has ...........in their milder cams. Its proven that the valve can travel the increased lift distance without hitting a piston, and without suffering coil bind. Why not use that same increased lift on all the cams that are milder. The ramp isn't going to be as bad as the one with more duration. Mechanically I see no reason to limit lift on milder cams.

You can move the lobe separation angle and it has a major effect on how the engine behaves.
You can change the duration and it has a major effect on how the engine behaves.
You can make the ramp more aggresive to open further more quickly and it has a major effect.
You can increase lift and it doesn't affect the personality of the cam, it just provides the possibilty for more flow.


Maybe thats a better explanation.:)
 

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You must not be an engineer. So I‘ll try again. The ramp rate would have to be greater than the race cam profile in a shorter duration. The pressure angle goes thru the roof and a lifter no matter if flat or roller could not possibly last. So much unit of rotation per unit of rise can not exceed physical possible limits. Convince your self by trying to draw out to scale say 10:1 to see the pressure angles created. You may not understand pressure angle. It is the resulting force vector thru the point of contact. Which gets even worse with a flat tapped As it becomes even greater off center. I’m pretty sure this is not clear as one needs experience in force and vectors. Sorry I tried but maybe not good enough.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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Another part of valve lift is the rocker arm ratio. When the companies list the valve lift, they calculate that based on the ratio of the rocker arm the production engine had. The small block Chevrolet cam with a 1.5 ratio rocker arm. The big block Chevrolet had 1.7 ratio rocker arms. I think the LS stuff also has a 1.7 ratio rocker arm.

If the cam advertised a .450 valve lift for a small block using a 1.5 ratio rocker, it would be .480 with a 1.6 ratio rocker arm and .510 with a 1.7 ratio rocker arm. The rocker arm multiplies the lobe lift on the camshaft to translate into greater lift at the valve.

If you're comparing valve lift figures from different engines it's not always generated purely at the camshaft lobe. The same goes for how they are advertised.
 

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So why don't they use that same amount of lift that the aggressive cam has ...........
Make the ramp too steep for the lifter to live.

You can increase lift and it doesn't affect the personality of the cam, it just provides the possibilty for more flow.
Increasing lift without changing the duration increases lift speed. Too steep, the lifter won't survive.


Also look at the lifter bores, they hold the lifter in place, increase ramp speed, increases the side loading of the lifter into the bore. Too much side loading, breaks things.
It's always better to have LESS cam lift, and more rocker duration.


Maybe thats a better explanation.:)
Duration largely determines the rpm range, Once the duration is set, the limits are the lift so it'll live a while.
People would be very angry if they bought cams that didn't last a while because the lift/degree in duration caused the ramp to be too steep.

A couple or 5 years ago, I was using a FT cam with near .400 lobe lift and .600 at the valve. It got replaced every 20 races, 900 laps or 300 miles because of the wear or breakage. That got expensive at $420 each so I had it changed up to .350 lobe lift and 1.8 rockers for a .630 lift, same duration. It has 75 nights or 3500 miles and looking good. The differnce is the ramp speed for the duration.
 

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To add

Build a ramp about 50' long and give it a 10' angle uphill. Now drive up it at 10 mph. Think about what happens when you increase that speed to 100mph.
Now increase the ramp to 45 degree, drive up it at 10mph, then again at 100mph.
Picture it now?
 

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The Comp XE series in flat tappet and roller. Without me having to reread everything you wrote exactly what are you trying to get to. For circle track racing, drag racing, street performance all have differing requirements from a cam this includes multiple things that include lift as one perimeter among others.

To some extent lift can be traded for duration an example is using 1.6 rockers instead of 1.5’s on an SBC. The 6 percent gain in lift and rate of lift creates a reaction not unlike adding 6 percent more duration. There are other things that affect this but without changing the duration or the lobe centers the faster lift rate and greater total amount does not affect the LSA which in the lobe centers are held increasing durations increases overlap and creates later valve closing times compared to crank rotation. This has as effect on the needs of compression being raised to compensate for reverse pumping on the intake side. Obviously the lift rate is involved as well as this affects how much off seat exposure is available primarily in the overlap period and that of intake closing.

Another consideration is port flow where a weak port is better served with longer duration than it is with greater lift. A strong port can take advantage of greater lift as well as more duration. But the end use can’t be ignored. There except for drag racing, circle and road courses need some balance of torque to horsepower across an operating range. A decent example was the old SCCA Trans-Am where Chevy used a small port head on the DZ302 with a lot of cam while Ford’s Boss 302 used huge port head’s and a milder cam. These two approaches on paper and the dyno look wildly different but on the track were very close in performance. Given the need to win you can consider that the designers had good reason not to mix Chevy’s wild cam with Ford’s wild head’s at least not on a carbureted engine for this application.

Which brings us to modern port or direct in cylinder fuel injection which totally changes both the port volume and cam timing dynamic.

For the street unless your point building for a stop light to stop light drag racer your requirement is going to look more like a road course racer. A closed course oval racer is another cam problem again. That will vary by whether the course is dirt or paved and how big it is. All out racing like dirt late model with a built Gen I SBC you see lifts into and above .7 inch with purpose build head’s. For lesser classes that require stock production head’s lifts are much less simply because the rules on head’s limit port volume thus breaking capacity.

When you get to Gen III SBC’s with EFI you see big lifts but the whole engine is designed in that direction where Gen I and II you have to do a lot of work to go in that direction which includes improving cam stiffness. Here these cams since they can’t be made huge in base diameter like the Gen III up cam, these are made with the lobe heel becoming the base circle diameter.

Bogie
 

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look from this perspective
duration needs to be longer for higher rpm as that gives the cylinder more "time" to fill.
I have a 283 that I want to rev to 7500 rpm
so I opt for duration of 250º
my 2.02 heads with a valve lift of .750 inches might be to big of a door to open and air flow velocity might be weak
compared to .585"
Your 393 cube engine might want that .750"?
If the cams are all the same then heads need to be changed to match cams/engines
 

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Generally when these aggressive ramp rates are employed, the manufacturer also has incorporated more lift as well. So why don't they use that same amount of lift that the aggressive cam has ...........in their milder cams. Its proven that the valve can travel the increased lift distance without hitting a piston, and without suffering coil bind. Why not use that same increased lift on all the cams that are milder. The ramp isn't going to be as bad as the one with more duration. Mechanically I see no reason to limit lift on milder cams.
This is one area you are looking at from the wrong end.
The increased lift is a an attribute that was the result of the aggressive lobe rate of lift.....it was unavoidable in order to keep valvetrain part velocities in a range that the valve spring can control. More lift wasn't incorprated "as well"
You have to accelerate the lobe off the base circle and up the ramp, but then decelerate the lifter as you get near the nose of the cam, peak lift, etc or you just throw the lifter off the cam nose like a pole vaulter. Part velocities all need to stay in a range that everything can stay in contact and not get thrown apart, nor a hard crash when coming back down to zero lift.

It is easily possible to design a cam and lifters that will run together just fine.....but destroys lifters, pushrods, valvesprings, valve seats in the head in very short order....not just bad cam lobe and lifter life.

It's a whole system that has to be taken into account. Not just max lift that clears the piston.

You can't do, for a SBC example, a milde near stock 200° [email protected]" and whopping .700" lift......the side of the lobe would be so steep a flat tappet lifter just digs in and shears off, or a roller wheel just gets smashed off from being hit broadside from the short duration high lift lobe..

"Why not use that same increased lift on all the cams that are milder. The ramp isn't going to be as bad as the one with more duration."
No, it is going to be a lot worse.....shorter the duration, the steeper the ramp is for high lift.
 

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Discussion Starter · #15 ·
Again, not an engineer but have a decent grasp of the dynamics everyone is talking about. Quite possibly I am viewing it incorrectly but the picture in my mind is of a sweeping curve on a highway that makes a 180 degree turn. If I increase the radius of the turn so that the vehicle travels further (but faster), it would seem that its a gentler curve rather than a more aggressive one. Watch a Nascar race and you see the guys who are driving up by the wall. They increase tire wear because they are traveling further each lap than the guys running the bottom line.
The guys running the bottom line are traveling a shorter distance at a slower speed but the frictional losses are much greater and they suffer more tire wear than the guys traveling further. Possibly this isn't a good example, and I don't mean to be argumentative. What I'm picturing (thinking) is that the lobe profile really wouldn't change, it really would only extend maybe .050 further. I think essentially the same progressive ramp rate could be used and the change incorporated near the upper end of the lobe where the transition is smoother. The transition from the lobes heel to the beginning of its upward travel would seem to be the place most likely to produce lifter trama rather than the continued path upward. Also spring pressure is usually greater for aggressive cams. I'm more interested in just somewhat high performance street variations. I admit that I'm hardheaded (dense), but I do appreciate the help from you guys.:)
 

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Your analogy with race track is, pardon the expression, totally out to lunch. There is nothing similar. Try to draw out with paper and pencil what the cam profile is. Use a graph and plot points for lifter rise thru the rotation. Be sure to take out for rocker arm ratio.

Or better yet in a bare block with cam shaft and a lifter, watch the movement as you turn the camshaft. Now build up some epoxy on the cam lobe (let dry and sand smooth) to the lift you describe. See how lifter bites into lobe (epoxy).

Unless your going to prove it to your self with some type demonstration, not being technical, you will not comprehend what we have been trying to explain.
 

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there used to be special lifters for SBC that had no radius on the foot so they could theoretically run the lifter that much closer to failure. We started putting Ford or Chrysler lifters in them which makes Iife easier and most race tracks don't check for that
 

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What I'm picturing (thinking) is that the lobe profile really wouldn't change, it really would only extend maybe .050 further.
And that is what you absolutely cannot do, because the lifter intersects with the cam lobe on an angle.

I think 57Nomad is right, until you grasp what is happening with the cam lobe and lifter interface at every degree of rotation you aren't going to understand why you can't just "add .050" up the side of the lobe.
 

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Discussion Starter · #20 · (Edited)
I think the thing that sticks in my craw is that everyone is apparently telling me that a more aggressive cam with higher lift works without problems but the same lift won't work in a less aggressive cam. Different cam manufacturers derive different ideas on what works for each level of performance. On top of that there are individuals who want custom cams for their engines and they also vary from the cam manufacturers recommendations. There is no one formula for cam manufacture. All specs are variable. What I mean is that there is no law of physics that says all cams with a certain duration can only lift a certain amount and they will fail if someone alters that amount. That said, the design of the interacting components do have a point where they will always fail.........but a lot of these cams fail even when the builder has followed the manufacturers recommendation. Different oils and different quality lifters and even different spring pressures all contribute.

I'm going to attach a compilation of some cam specs. They are for a roller as that is what I'm going to buy if anyone ever gets some cam blanks in stock. Anyway I wanted to buy the Comp 285XR-10 but it hasn't been available for over a year. Notice that all 4 cams have 110 degree LSAs, which the only significance is that its mild street performance similarity.

The main concern is lift and duration. If you look at the two Comp cams at the bottom, it appears that they are doing exactly what I was alluding to. The two Comp cams have virtually the same lift (.003 difference is negligible). One has 230 degrees duration while the other has only 218 degrees. This seems to say that Comp realizes the benefit of keeping the higher lift on the milder cam.

Now look at the two Howards cams. Still 110 degree cams. Their solution for 521125-10 cam has less lift (Howards .539 vs .555 Comp) but more duration
( H- 227 vs C-218) .

Comparing the slightly higher performance versions, we get Howards at .583 vs .558 Comp.
Duration is Howards at 233 vs 230 Comp.

This simply demonstrates that different manufacturers are able to incorporate different OR SIMILAR amounts of lift into their cams. The two Comp cams are the best example because they only have .003 (.555 vs .558) difference in two different rpm range cams.

Howards on the other hand has a .044 difference (.539 vs .583) in their cams. One manufacturer .044 the other only .003. The point to me is that if Howards can make a cam with .583 intake lift, there isn't any reason that their milder cam couldn't also use a higher lift (as long as piston clears). Comp did exactly that in their two cams.

So, I'm not trying to be difficult, but I still believe that the manufacturers can easily expand the lift in a cam while keeping the same duration and it won't destroy the lifters. If a .583 lift cam with 233 duration doesn't destroy the lifter, then a less aggressive cam with similar lift won't destroy one either......and the Comp cams are a perfect example of it.:)
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Thanks everyone! (y)
 
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