Cam Lobe Design

[SteveHuck]

I am in the process of designing a camshaft and need some help.

When I increase the flank radius of the lobe, the positive G's go up and the negitive G's go down.

I assume that the more positive G's, the more wear on the cam and stress on the valve train.

Fewer Negitive G's and the spring pressure required would be reduced.

The question would then be, where do i strike the balance.

This cam is for a V4 model engine designed by the late Bob Shores. He passed away before finishing the project so the drawings have been "not so good" so i want to verify everything before i build it.

Base circle = .350
Flank radius = .693
lift = .065
Duration = 260 (130 cam degrees)

Positive G force = 88
Negitive G force = -38

Any camshaft grinders out there willing to lend some wisdom?

Thank you!

Steve

 

[EngJW]

Designers stopped using graphical methods of dimensioning cam lobes back around the 1930s. From the 1950s on, polynomial equations have been used to derive the profiles and then these are converted to a lift table (follower lift vs. cam angle). You also have to add an opening and closing ramp at each end. For a fee you could get someone like Harvey Crane at cranecamdesign to design a profile.

 

[thundair]

Try this guy he is real knowledgeable about cam design.

UD Harold
662-562-4933
brookshire@panola.com

Cheers

I don't know anything but the people that do.

 

[SteveHuck]

"For a fee you could get someone like Harvey Crane at cranecamdesign to design a profile."


I don't think that will happen. This is just a model engine.


"Try this guy he is real knowledgeable about cam design"

I dont want to bother anyone off list. I am just looking for some basic guidelines. I will copy an existing lobe from a cam in the garage first. Just want to build something better than a triangle on a stick.

 

[Tmoose]

I might try plotting the lift every degree or finer, then running it thru Excel's FFT function, and, when that did not work, I'd spend some time trying to use the SUM nd PRODUCT functions in Excel to calculate the individual slopes ([lift@2-lift@1]/[time per degree]) to create the velocity curve, and repeat to create an acceleration curve, and maybe even cut-and-paste again to get the "jerk" curve although I am unsure of what that would really mean.

 

[dicer]

UD Harold is the best. I'm sure if you called him and explained what you were doing he would give you some tips.

 

[pmtoo]

Gordon P. Blair has a few good articles in Race Engine Technology that are available as .pdf on his website. This is most likely more than you wanted to know, but it may answer some questions.

http://www.profblairandassociates.com/RET_Articles.html

 

[SteveHuck]

Thanks Pmtoo!

Looks like some good reading.