Anyone using a half-speed camshaft on a flathead??

Are you absolutley sure?
I suspect it isnt quite that straight forward since the cam lobe is not the same shape. Article says required much less spring pressure for the same RPM limit. If it hadnt been by such noteworthy people it would be easier to dismiss it. Blow up the picture of the cam for a better look. It is quite a different lobe shape when running 1/4 speed. I suspect there is a little more at play here than meets the eye at first glance. May not be the answer to all our problems but it cetainly is very interesting. Was it as good at 6000 as a 1/2 speed cam is a 3000? (both Lobes would be moving by the lifter at the same speed) Probably not, but still the idea has some merit if only to make us stop and think about what is actually going on in that situation.

 

If you can use a lower pressure spring and acheive the same result, the engine should see less mechanical loss. Valve float may be less of an issue due to the dual lobe design and slower rotation of the camshaft. Would this allow for a more aggressive lobe profile? After work today, I'll go into the shop and take a couple of pics.

 

I have not yet tracked down the articles...I remember that a claimed benefit was extremely gentle valve action, illustrated by holding a roller against a rotating cam spinning in a lathe. A person could easily hold roller against the Schaller, but not against equivalent normal cam.....I just don't remember any more. I know the articles are in the upstairs bathroom somewhere.
And--whyinhell can't I find any patents on the thing??? They must be out there.

 

Picture I snapped of one of these cams for a SBC at the Hot Rod Reunion in 03.

 

If the cam is geared 4:1, rather than 2:1 to the crank, doesn't that mean that it only takes half as much power from the crank to drive it ?

 

seems to me that the slower rotation speed of the cam would reduce lifter (and the rest of the valve train) "float" on the back side of the lobe, due to a less violent movement. So, the same springs that would float with a give cam profile, might not with the slower speed, because the movement is less violent.

 

BL I have the article here. 1963 Hot Rod Annual. it actually as two article about it in the one book.

 

The picture i remember best had a tiny grinding wheel to do those hollow flanks; the guys trying to grind one must've invented some new words.
Add to that the tiny, pointed noses (anybody who's wiped a lobe knows where i'm going) & i just smell lots of trouble.

 

OK, I should be able to find the Annual; i think I have articles in various Fawcett hot rod books too.

 

if this cam is running 1/2 the normal cam speed ,or 1/4 the speed of the crankshaft..what do use you to drive it? the normal gears for a flathead , or chain and gears for the SBC won't do it

 

I certainly have no idea how to drive one in a flathead...seems like you'd need a gigantic external gear, or a layered gear train of some sort...then the oil pump...then the distributor!! The cam would look pretty cheap after you solved for the peripherals!

 

"layered gear train"

That's the key.
The ratio between the 1st and last gears in a single train is the same regardless of how many intermediate gears there are: none or 20.
However: if the crank sprocket were extended forward by its own thickness, it could drive an intermediate dual-row sprocket, which then drives the cam sprocket. The reason for moving the crank sprocket is that the front cam bearing won't take any overhang load.
As long as the tooth count of each "pair" is the same, the center (pitch) distance to the idler will be the same. The idler post can be offset to increase the sprocket tooth count (and/or chain length).
17 tooth crank sprocket drives a 34 tooth intermediate outer sprocket at 50% speed (17:34 = .50). The 17 tooth intermediate inner sprocket (behind the 34) drives a 34 tooth cam sprocket at 50%. The ratios are multiplied: crank drives cam at 25%.

 

You can see some pics of the full SBC kit on this page.

They are quite small, but you can definitely see that as well as the cam, you also got a gear drive setup with a large cam gear and small crank gear, valve springs, roller lifters, timing chain cover and distributor.

Since the cam, gear drive and distributor are all supplied, there is no problem with the fact that the cam is being driven backwards with the 2 gear setup.

http://www.my-creative.com/SchallerC...%20stories.htm

 

well I cant see any benefit, the valves have to go up and down the same as a 1/2 speed cam so it has 2 ramps every 1/4 turn, which is twice as many as a half speed cam? What kind of cam does a radial aircraft engine have? How many ramps do they have? As I understand they have a large ring with a lotta bumps on it? I read about it back then but still dont get it?

 

With 2 lobes instead of one, wouldn't the HP required to turn it be the same because it's traveling at half speed? The cam is still doing the same work. The benefit is in the ramp angle, right?

 

Do not ignore the fact that you have to open the valves at the same speed regardless of how many lobes on the cam.
And that means that if the cam is slower in rotation the ramp has to be steeper to get the same acceleration. And if you have a steeper ramp there is more pressure on the cam itself , and the cam would be subject to much more wear.
it will work the same, but stresses are higher
The normal cam has half of the circumference to get the valve open, more or less. this cam has 25% of the cam to raise and lower the valves and that means the cam has to have steeper ramps to get the cam up in the shorter space
Carrying it to extremes you will see that the more lobes on the cam the steeper the slopes have to be to get the same accelerations and duration. Until , that is, there is no room for the lifters between the lobes.

LOL

traderjack

 

Traderjack, that's kind of what I was trying to say. The cam is doing the same amount of work, even though it is going slower. So I think it would take the same amount of energy to turn it. I'm not seeing this as being an advantage. Just for discussion, roller cams are nothing new. The Premier race car in the Indy museum has a OHC hemi with roller rocker arm setup from 1903, 927c.i.{I think} four cylinder. Buicks used roller lifters most of the way through the '20s.

 

The pressure/wear on the cam is related to how much valve spring pressure the lifters are pushing against, as well as how steep the ramp is.

Since the 1/4 speed cam uses lighter valve springs, maybe the combination of lighter springs and steeper ramps cancel each other out ?


Anyway, the point I was trying to make earlier about the drive ratio was not that it takes less power to spin the cam, but that the mechanical advantage provided by turning the cam at 1/4 engine speed means it takes less force from the crank to provide the same rotational force at the cam.


Think of it this way ...

If you disconnected the timing chain from an engine and put a wrench on the cam retaining bolt, you would be able to turn the cam with some amount of effort.

If you slipped some pipe over the wrench to make it twice as long, it would take half the effort to turn it.

Changing the drive ratio between the crank and cam from 2:1 to 4:1 has the same affect as doubling the length of the wrench in the above scenario.

 

Hoo Hah! Found a patent. Haven't read it yet, still looking for more.

http://www.google.com/patents?id=Ff...&as_miny_is=2008&as_maxm_is=1&as_maxy_is=2008

 

This is a picture of my Schaller 1/4speed cam kit. sbc