Camshaft lobe design by Billy Godbold

[David Redszus]

That is true. I do wish that when Billy was talking about the different acceleration that he would of had some graphs / plots of those curves.
Stan

Agreed. As you well know, Stan, give an accurate lift curve, the derivatives can be calculated and graphed.
Then we would know velocity, acceleration, and area under the lift curve; for accurate lobe comparison.

But that would only be lobe information, not valve lift information which is what we really need.

If some smart guy would only write a follower translation program that would produce valve lift
from lobe lift, I would buy him (or her) a beer, and even dinner if it is an her.

[gruntguru]

Here you go.

https://www.physicscurriculum.com/inter ... %20screen.

[David Redszus]

People think 4 valves are hard to improve and yet the same group of people are more than willing to change their cams.

Comparing camshafts can be a bit more complicated than often assumed.

Let's compare two camshaft angle area; that is to say the areas under their lift curves.
Assume both are 3-4-5-6 polynomial lobe designs.

Cam 1
Lift.....0.429"
Dur.....280 deg
Valve..2.0"

Cam 2
Lift......0.448"
Dur......260 deg
Valve...2 1/16"

Which cam has the greater angle area?
Which has the higher velocity?
Which has the greater acceleration?
Which requires a larger flat tappet?

In a given engine, which cam will produce more air flow?

[juuhanaa]

People think 4 valves are hard to improve and yet the same group of people are more than willing to change their cams.

Comparing camshafts can be a bit more complicated than often assumed.

Let's compare two camshaft angle area; that is to say the areas under their lift curves.
Assume both are 3-4-5-6 polynomial lobe designs.

Cam 1
Lift.....0.429"
Dur.....280 deg
Valve..2.0"

Cam 2
Lift......0.448"
Dur......260 deg
Valve...2 1/16"

Which cam has the greater angle area?
Which has the higher velocity?
Which has the greater acceleration?
Which requires a larger flat tappet?

In a given engine, which cam will produce more air flow?

A bit more?

Thanks for questions David. Sorry i cant answer just like that, but that makes me dangerous?

I tend to over simplify things but hell, its so complex that i better keep my OEM cam until i can answer those questions!

IMG-20211026-WA0017.jpg

[juuhanaa]

[quote=gruntguru post_id=926029 time=1664252387 user_id=25870]
Here you go.

[url]https://www.physicscurriculum.com/inter ... n%20screen.[/url]
[/quote]

Nice! Thanks,


[attachment=0]IMG-20211130-WA0025.jpeg[/attachment]

[LotusElise]

https://www.youtube.com/watch?v=K1DFrWcvTuc

Thanks for sharing it. Godbold has some greater passion for this topic, I really like his kind of talking about the valve lift design. This two valve engines are really different to the 4-valve heads. Over 20 mm valve lift on a valve which likely weighs around 80 or more g, have rocker arms and push rods, maybe 250 g of moving mass? In that kind the valve spring specification must be like a chassis spring .

I've just specified the valve springs for my 4-valve head (10,500 rpm redline) based on the kinematic, masses relative to valve axis and calculated the acceleration and acceleration force based on a 1° increment of the valve lift over crank angle. From that I calculated the contact force between cam lobe and roller follower. This week I measured all 16 valve springs on the single hander compressor to see what I really need on shim height to get the 10,500 rpm managed right.

A competitor company uses a specific spring on crazy drag cam lobes with, don't laugh, for a 4 valve head this are crazy valve lifts, up to 15 mm valve lift (below 0.6"). They reported to see no bounce on the Spintron at 11,000 rpm. If I calculate it on a more low acceleration design I still see contact force get's negative around max valve lift. Even though my model doesn't include dynamics of the system, the valve spring can't follow the lobe at that engine speed with proper contact. I assume a small oscillation can be introduced and need to be calmed on the deceleration phase before seating phase to be able to rate no irregular bouncing was seen. Beside that, the Spintron can't replicate reality as the scavenging phase has no power without proper pressure ratio, heat and the depended sonic speed, it was very interesting to see how edgy the valve spring design can come out, rated on the Spintron. Older approaches recommended 60-80 % safety margin to cover the dynamic effects of spring and damper systems of the valvetrain. Here the safety factor is already negative as the contact force was around -500 N for around 100 °ca around peak valve lift, increased again up to +3000 N and went down to +620 N at seat.

If I look into the valve lift of the above mentioned measured system I can't see what it translates into the 2nd time-based deviation of it. But there I can see the real cam design, here the real fine tuning get on the table. So I would be really interested in an previous NASCAR valve lift and acceleration curve of those who were allowed and able to rev to 10,000 rpm. NASCAR was the most valve spring challenging racing series of the world. The world leading valve spring companies (PAC, PSI, COMP, ...) refined here there knowhow and material. We have no racing series here in Europe which was more challenging as that application: huge valvetrain mass, lacking stiffness, amazing lift values and still 10,000 rpm covered by a spring for very challenging application with a lot of redline near operation, where 250 rpm more could change the field.

[Stan Weiss]

People think 4 valves are hard to improve and yet the same group of people are more than willing to change their cams.

Comparing camshafts can be a bit more complicated than often assumed.

Let's compare two camshaft angle area; that is to say the areas under their lift curves.
Assume both are 3-4-5-6 polynomial lobe designs.

Cam 1
Lift.....0.429"
Dur.....280 deg
Valve..2.0"

Cam 2
Lift......0.448"
Dur......260 deg
Valve...2 1/16"

Which cam has the greater angle area?
Which has the higher velocity?
Which has the greater acceleration?
Which requires a larger flat tappet?

In a given engine, which cam will produce more air flow?

David,
Using 3456 and a lobe designed for a rocker arm ratio of 1:1

Cam2 has a peak velocity of just under 0.006
Cam1 has a peak velocity just about 0.0052
The greater velocity of cam2 will require a tappet with a larger diameter that cam1.

Cam2 has a peak acceleration around 0.000127
Cam1 has a peak acceleration around 0.000105

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____30.00_|__70.00_|_280.00_|__27.46
_________0.00600____11.98_|__51.98_|_243.95_|__27.42
_________0.01000_____8.33_|__48.33_|_236.67_|__27.40
_________0.02000_____2.01_|__42.01_|_224.02_|__27.32
_________0.04000____-6.50_|__33.50_|_207.01_|__27.06
_________0.05000____-9.87_|__30.13_|_200.26_|__26.92
_________0.10000___-23.18_|__16.82_|_173.64_|__25.89
_________0.15000___-33.90_|___6.10_|_152.21_|__24.65
_________0.20000___-43.65_|__-3.65_|_132.70_|__22.92
_________0.25000___-53.18_|_-13.18_|_113.64_|__20.66
_________0.30000___-63.07_|_-23.07_|__93.87_|__17.89
_________0.35000___-74.15_|_-34.15_|__71.71_|__14.29
_________0.40000___-88.74_|_-48.74_|__42.51_|___9.01
_________0.42500__-102.19_|_-62.19_|__15.61_|___3.21

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____20.00_|__60.00_|_260.00_|__26.62
_________0.00600_____3.53_|__43.53_|_227.06_|__26.60
_________0.01000_____0.20_|__40.20_|_220.39_|__26.58
_________0.02000____-5.57_|__34.43_|_208.87_|__26.49
_________0.04000___-13.32_|__26.68_|_193.36_|__26.25
_________0.05000___-16.38_|__23.62_|_187.23_|__26.12
_________0.10000___-28.46_|__11.54_|_163.08_|__25.23
_________0.15000___-38.13_|___1.87_|_143.73_|__23.97
_________0.20000___-46.88_|__-6.88_|_126.23_|__22.58
_________0.25000___-55.35_|_-15.35_|_109.29_|__20.56
_________0.30000___-64.02_|_-24.02_|__91.97_|__18.07
_________0.35000___-73.47_|_-33.47_|__73.07_|__15.12
_________0.40000___-84.97_|_-44.97_|__50.06_|__10.99
_________0.42500___-92.85_|_-52.85_|__34.30_|___7.70

Stan

[CamKing]

If some smart guy would only write a follower translation program that would produce valve lift
from lobe lift, I would buy him (or her) a beer, and even dinner if it is an her.

That's the exact opposite of what we use for design.
We design the valve lift curve, and then translate it into the lobe lift curve.
There are multiple programs available, that will do this. This is essential in designing cams for "finger Follower" applications.

Here's one, but Lotus also has a nice software package that will work. Both will cost a lot more then a dinner.
https://www.gtisoft.com/valvetrain/

[hoffman900]

If some smart guy would only write a follower translation program that would produce valve lift
from lobe lift, I would buy him (or her) a beer, and even dinner if it is an her.

That's the exact opposite of what we use for design.
We design the valve lift curve, and then translate it into the lobe lift curve.
There are multiple programs available, that will do this. This is essential in designing cams for "finger Follower" applications.

Here's one, but Lotus also has a nice software package that will work. Both will cost a lot more then a dinner.
https://www.gtisoft.com/valvetrain/

Billy has said the same thing “I design valve lift curves”, but I mean this applies to all of you actual designers and all would say the same thing, and as we all know, this is why finger follower lobes look the way they do.

I think the Blair program tried to be an all in one program and does this as well. I suspect the GT packages to be beyond that.

[CamKing]

I think the Blair program tried to be an all in one program and does this as well. I suspect the GT packages to be beyond that.

I wanted to buy the Blair software to see how well it works, but I was told it's no longer for sale.

[Stan Weiss]

I think the Blair program tried to be an all in one program and does this as well. I suspect the GT packages to be beyond that.

I wanted to buy the Blair software to see how well it works, but I was told it's no longer for sale.

Mike,
About 4 or 5 years ago I had a thread on here about trying to generate a cam for a Pontiac to match Blair's STA targets. Some one on here was able to generate some S96 files and sent them to me. When I have sometime I will see if I can find the thread and who it was. I am not sure but I believe they used Blair's software.

Stan

[LotusElise]

We design the valve lift curve, and then translate it into the lobe lift curve.

I would sign this too. The need of the engine in terms of alterantion of load, translated into valve lift, should be the basis for the service agent supplying, which is the valvetrain and finally the cam. Only if the valvetrain FMEP or wear goes to high then compromises in iterations should be done on the alternation on load.

[David Redszus]

People think 4 valves are hard to improve and yet the same group of people are more than willing to change their cams.

Comparing camshafts can be a bit more complicated than often assumed.

Let's compare two camshaft angle area; that is to say the areas under their lift curves.
Assume both are 3-4-5-6 polynomial lobe designs.

Cam 1
Lift.....0.429"
Dur.....280 deg
Valve..2.0"

Cam 2
Lift......0.448"
Dur......260 deg
Valve...2 1/16"

Which cam has the greater angle area?
Which has the higher velocity?
Which has the greater acceleration?
Which requires a larger flat tappet?

In a given engine, which cam will produce more air flow?

David,
Using 3456 and a lobe designed for a rocker arm ratio of 1:1

Cam2 has a peak velocity of just under 0.006
Cam1 has a peak velocity just about 0.0052
The greater velocity of cam2 will require a tappet with a larger diameter that cam1.

Cam2 has a peak acceleration around 0.000127
Cam1 has a peak acceleration around 0.000105

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____30.00_|__70.00_|_280.00_|__27.46
_________0.00600____11.98_|__51.98_|_243.95_|__27.42
_________0.01000_____8.33_|__48.33_|_236.67_|__27.40
_________0.02000_____2.01_|__42.01_|_224.02_|__27.32
_________0.04000____-6.50_|__33.50_|_207.01_|__27.06
_________0.05000____-9.87_|__30.13_|_200.26_|__26.92
_________0.10000___-23.18_|__16.82_|_173.64_|__25.89
_________0.15000___-33.90_|___6.10_|_152.21_|__24.65
_________0.20000___-43.65_|__-3.65_|_132.70_|__22.92
_________0.25000___-53.18_|_-13.18_|_113.64_|__20.66
_________0.30000___-63.07_|_-23.07_|__93.87_|__17.89
_________0.35000___-74.15_|_-34.15_|__71.71_|__14.29
_________0.40000___-88.74_|_-48.74_|__42.51_|___9.01
_________0.42500__-102.19_|_-62.19_|__15.61_|___3.21

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____20.00_|__60.00_|_260.00_|__26.62
_________0.00600_____3.53_|__43.53_|_227.06_|__26.60
_________0.01000_____0.20_|__40.20_|_220.39_|__26.58
_________0.02000____-5.57_|__34.43_|_208.87_|__26.49
_________0.04000___-13.32_|__26.68_|_193.36_|__26.25
_________0.05000___-16.38_|__23.62_|_187.23_|__26.12
_________0.10000___-28.46_|__11.54_|_163.08_|__25.23
_________0.15000___-38.13_|___1.87_|_143.73_|__23.97
_________0.20000___-46.88_|__-6.88_|_126.23_|__22.58
_________0.25000___-55.35_|_-15.35_|_109.29_|__20.56
_________0.30000___-64.02_|_-24.02_|__91.97_|__18.07
_________0.35000___-73.47_|_-33.47_|__73.07_|__15.12
_________0.40000___-84.97_|_-44.97_|__50.06_|__10.99
_________0.42500___-92.85_|_-52.85_|__34.30_|___7.70

Stan

Thank you Stan. I use cam angle rather than lift to drive the calcs so my numbers come out
very slightly different than yours. But the principles are the same.

Given a lift curve, cam velocity, acceleration, and other derivatives can be calculated. Adding a valve diameter we can determine valve angle area, which in the above examples are the same. Even with different lifts and durations, the areas under the curves are the same.

However, to Mike's point (and Billy's) though the areas are the same, it does not mean they will run the same.
We have not yet accounted for rocker ratio (if any), lash, and cam indexing. The required spring forces will be different depending on valve train mass and rpm.

As Mike said, what we really care about is the valve lift curve, not the cam lift curve. In direct acting tappet valve trains (1 to 1 ratio), they are the same. With rocker followers, they are not. Neither are rocker ratios constant with lift.

In some applications, we can obtain all the information we need from cam data. In other systems, the cams must be installed with push rods, rockers, etc, in order to measure valve lift.

But even then, we only have static valve motion data. The dynamic conditions of a running engine can produce an unexpected valve lift curve; including float and bounce.

[vannik]

I think the Blair program tried to be an all in one program and does this as well. I suspect the GT packages to be beyond that.

I wanted to buy the Blair software to see how well it works, but I was told it's no longer for sale.

I have it, I was one of the Beta testers for Prof Blair, but more on the kinematics and dynamics side. I have written parts of a vehicle dynamic simulation package so had some background. Unfortunately Dr Charlie McCartan no longer has time for sales and support.

[CamKing]

. Unfortunately Dr Charlie McCartan no longer has time for sales and support.

That's too bad. I wanted to see how well it worked for generating the lobe lift curve from the valve lift curve.
The system we use is accurate, but not the quickest or easiest.