Shingles

new M3 and S2000 both have hollow cams... yes hollow cams. Ie it's hollow on the inside. This is supposed to lighten up the drivetrain but the question is how much if any does this help?

Intersting concept though...

comments?

-Shing

Zprime

http://www.howthingswork.com/engine.htm

ok...I was not sure on what a cam is so..I decided to go to the site

anything light is good...especially for moving parts...the problem is just how strong will it be?
^_^

Micah95GLE

I wouldn't be surprised if it does make a huge difference at 9000RPM. Not only a little bit more power, but less strain on the related components for longer life.

ZuMBLe

iTrader: (1)

cams only rotate.. The lobes are in constant contact with the valves in one way or another. So the hallow cams shouldn't be a strength issue. I would think the lighter weight means less unsprung weight.. which means less loss.. which means faster spooling..

ZuM

Shingles

ACutally strength would be an issue.. the lubes are going to cause stress on the cams when they are pushing the springs back... if the cam is too thin, it'll probably snap at some point

Also, I think like you said, it'd spool faster.... Since the timing chain/belt would drive the cam, and there's less rotational mass, it'd be like having a lighten flywheel?

-Shing

Zprime

then you have to worry about torsion...especially it it rotates ^_^
and of course some shearing....hopefully not..cause that would be very bad
=]

ericdwong

I read somewhere that oil actually flows through the hollow cams.

got rice?

iTrader: (2)

here's a shot of the pass side intake camshaft on my Z:
<img src="http://www.cyberhosts.net/~gotrice/personal/60k/09.jpg">

ZuMBLe

iTrader: (1)

I'm sure they find some balance of strength and weight. having oil flow through them? Why?

ZuM

Max96

Yes, I have seen hollow cams in the past. From what I remember seeing, the oil would flow through them. Pretty good idea if ya ask me. This was back in the 80's from what I remember, so the concept has been around.

deathwish

Well, there's not a lot of bending stress or normal stress on a camshaft, most if it is in torsion. In torsion, hollowing out the center decreases strength by less than 10% usually, depending on how much you hollow out. But still, how much does a camshaft weigh? You're not getting a lot of weight savings, and since the weight you are cutting out is in the center, it's not saving you a lot on rotational mass. Who knows, maybe it's for cooling or something...

Keven97SE

Like Deathwish said, you could bore out half of the radius of the cam and only decrease the strength by something like 10%. Not much.

From a cross-sectional standpoint, the Moment of Inertia decrease from hollowing camshafts is small. Even considering that the camshafts are quite long, ultimately you're not removing enough material to cause a significant decrease in MI. (Note that MI is what causes resistance to acceleration - hence decreases power - analagous to weight added to a car's body that reduces the car's ability to accelerate.) Distance from centerline is far more important than the mass of the rotating part. That's why lightening a flywheel has a huge affect, lightening a crank pulley less so, and even less so lightening the camshafts. By far the biggest valve train loss comes from the stiffness of the valve springs. High-revving engines are going to have very stiff valve springs, and the resistance on the camshafts to rotate is large. Lightening the cams a little won't make any real impact on "rotate-ability" considering those huge valve spring forces.

Most likely, the reason for hollowing out the cams is to provide an oil channel that could be used to oil the cam lobes/lifter faces through holes at the lobes. The centrifugal forces are huge at higher rpms and would literally shove the oil out the holes in the cam lobes to provide really good oiling at higher rpms.

Jeff92se

iTrader: (82)

Have you guys ever lifted a cam? Ie.. taken one out and felt it? They are pretty heavy. ie.. my VE exhaust cam(you must remove to take the head off) is fairly heavy(ie..7-10 lbs.) Considering how small the chain sprokets are, that's a significant amount of weight to be rotating, especially x 2 + those long assed dohc chains. Any weight savings in the valve train helps the revability of the engine and the life of the valvetrain.

Ever wonder why hot rodders are so excited about roller rockers? They are stronger, have less friction and also let the user change the rocker ratio without changing cams. Nice huh?

Keven97SE

But remember, all that weight extends no more than ~1/2" from centerline. The Moment of Inertia is very small therefore. A 7 lb camshaft has a HECK of a lot lower MI than even a 7 lb flywheel. For a cylider,
MI = 0.5*M*R^2 (M=mass of shaft, R=Radius of shaft)

Assuming that the camshaft and flywheel are perfect cylinders, each weighs 7 lbs (just say 7 lb mass), and the radius of each is 0.5" (camshaft) and 7" (flywheel):
- MI, camshaft = 0.5*7*0.5^2 = 0.875 lb-in^2
- MI, flywheel = 0.5*7*7^2 = 172 lb-in^2
Obviously, the camshafts have a negligle affect on the acceleration of the engine from a purely mass/MI standpoint.

The losses in the valve train are primarily caused from the valve springs/lifters pushing on the cam lobes as the cam rotates and tries to push the lifter down. The reason why hot rodders lover roller rockers is because they decrease friction between the cam lobe and lifter assembly, hence reducing the rotating force on the camshafts, hence giving a net increase in power/torque.

Jeff92se

iTrader: (82)

So why do they go to the great expense of doing it?

Keven97SE

Oiling.

I think that's the reason. They can send oil through the camshaft, through holes on the cam lobes, right to the lifter/lobe interface. Works well under high rpms. Just my guess, though...I'd like to see whether or no there are actually holes on each lobe for this purpose. If not, then I don't know the reason for the hollowed camshafts. From a weight savings standpoint, however, hollowing the camshafts is a waste of time.

Jeff92se

iTrader: (82)

I don't think so. You can easily drill a small oil gally inside a solid cam and drill small oil holes in the cam lobes and bearing faces to help w/ lubrication.

I would think it would be too difficult to keep adequate oil pressure though such a large hollow cam anyway. If the cam is about 1/2 to 3/4" wide, you know how much oil that is and what kind of pressure it would take to keep the oil flowing though there? Too much I would guess. I think the VTEC hondas also feature this hollow cam thing. Ford also uses it for their 4.6 and cobra engines I think. It must be for lightness and valvetrain rev/life reasons. No other reason would justify the cost. imho.

Micah95GLE

You know what, though? S2000s require 5 quarts of oil. That's a lot for a 2.0L, so maybe it needs the extra oil for the hollow cams.

Jeff92se

iTrader: (82)

That's not really the point. I think it's an oil pressure issue. Normal oil gallies are like 1/8" wide at the most.

Maybe someone can elaborate.