What do you guys think about hollow camshafts? They help reduce valvetrain mass and improve engine response Could you just take a camshaft and bore it? Someone englighten.
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02:31 AM
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Rickady88GT Member
Posts: 10649 From: Central CA Registered: Dec 2002
Could you just take a camshaft and bore it? Someone englighten.
No.
The cams I have seen (I know there may be several type of hollow cam shafts?) are a tube with splines for cam lobes and the lobes are welded/brazed on. This tube is very rigid and does not flex. The cast iron cam shafts will brake if you could even bore it out. That is IF you could even bore it out? Have you ever tryed to drill a cast iron hole as deep as a cam shaft? Or drill half way from each end and meet in the center? It is not easy.
So a hollow one have to be made before the metal hardens by the way you talk. Sorry I've test drove an Evo twice in the last three days and I'm just researching it.... 0-60 in 3.5 was fun so I've been looking at ways to improve my upcoming Ecotec swap. Merging import technology with domestic technology is going to be very beneficial to the development of the turbo Ecotec project. Best of both worlds in a nutshell.....
edit: Anyone else have anything to share?
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[This message has been edited by IEatRice (edited 05-15-2005).]
From what (little) I know, hollow camshafts usually are made by taking a hollow tube, and fitting lobes onto it. A mandrel is then drawn through the tube, expanding it slightly and locking the lobes in place. It seems to me that an assembled cam is simply a way of making cams less expensive to manufacture.
I think that the Taurus SHO used an assembled camshaft, and it was the timing gear on the end of the cam "walking" out of place that caused many of the failures the SHO motor became known for. Correct me if I'm wrong on this, as I may very well be.
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04:27 AM
Fierobsessed Member
Posts: 4782 From: Las Vegas, NV Registered: Dec 2001
I've been thinking about this alot actually. I'm glad you brought it up. I think I can take 15-20 lbs out of the 3.4 DOHC's VERY HEAVY camtrain. My idea, is to take Quad 4 cams (because of there lift, duration, and relative compatibility), cut the cam at the end of each pair of cam lobes, center bore the cam lobe out to exactly 1" then cut the lobe off the cam. What you have left is a lobe with a 1" hole in it. Take a piece of 1" hydraulic tube, witch is NOT (E)lectro (R)esistive (W)elded, but rather or (D)rawn (O)ver (M)andrel type tube witch is seamless and very strong (can you tell who here is a hydraulic mechanic?) Well any way, its pretty much just slide the lobes on and carefully TIG weld them into the correct place. The cam bearings I believe could, with some patience and crafty machine work, could be replaced with ball or roller bearing sets. It would be a royal PITA to make these cams, but you would cut down significantly on the engines weight, the rotating mass (even though its very centered and therefore has a low polar moment, and at half crank speed) the cams drag if the roller bearings really drag less then the hydrostatic style from the factory. The stresses on the timing belt would be a bit less on free rev. And the best part, a significant improvment on lift and duration from the Q4 lobes. Overall its A LOT of work. The only problem I see with this idea, is that the welding of the lobes onto the tube might soften the lobe metal, or warp and bend the tube the lobes would be welded to, and the amount of machine work needed to do this. I am not sure if the Q4 lobes have a smaller base circle on the lobes then the 3.4 DOHC, but if they do, the whole thaught is pretty much scrapped due to the lack of lash caps, or longer valves.
Just a thaught Im throwing out there.
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05:25 AM
sheppard00 Member
Posts: 193 From: Denison Texas Registered: Jan 2004
The LS1 Engineers designed a hollow camshaft to take mass out of the engine. Also the camshaft has larger bearing journals, which in turn, allows larger lobes; thereby, reducing lobe stress. In doing so, engineers have added the capability to design a more aggressive cam profile, which gains performance. might no fit so well in the topic but I just happened to think of It when I read "Merging import technology with domestic technology"
An excerpt: **************** What makes the cams radical isn't the timing, but the construction. They are hollow steel tubes with the individual lobes, of powdered metal, sinter-bonded in place. In fact, the cams, being hollow, are used to bring oil to the intake lobes, which have oiling holes. Cam (valve) covers are cast magnesium. *******************
We have a metallurgist at our plant who used to work in the powdered metal forming industry. I will ask him more about the process, and if there is a possibility of getting custom work done. I also know a local machining supplier who has worked with Joe Lunati over in Memphis.
I have a 3.4 DOHC sitting in the basement now, and the idea here is intriguing. However, I see a lot of $$$ in making it happen.
Well how much money are we talking about here, hundreds or thousands? There's a Fiero meeting today here, I'll throw the idea around there to a few people. There's two or three guys that own a machine shop and would be interested in the project enough to cut me some slack on the price.
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11:16 AM
Marvin McInnis Member
Posts: 11599 From: ~ Kansas City, USA Registered: Apr 2002
What do you guys think about hollow camshafts? They help reduce valvetrain mass and improve engine response
Hollow camshafts do nothing to reduce reciprocating valve train mass. Think about it. While they may (or may not) slightly reduce total engine mass, even the reduction in rotating mass (i.e. the moment of intertia of that mass) is insignificant.
Historically, the engineering reason for hollow camshafts was lubrication; the center of a hollow camshaft makes a convenient oil gallery. The old DOHC Jaguar engines used hollow camshafts. Oil passed from the cam journals into the camshaft, and there was a small hole on the base of each cam lobe that provided very effective direct lubrication to the inverted-bucket cam followers.
Unless used as part of the lubrication system design, I can't think of a valid engineering purpose for hollow camshafts ... although they may (or may not) reduce total engine mass and may (or may not) be cheaper to manufacture.
Unless used as part of the lubrication system design, I can't think of a valid engineering purpose for hollow camshafts ... although they may (or may not) reduce total engine mass and may (or may not) be cheaper to manufacture.
Uh oh, sounds like we have a politician in the house. So the historical reason was to fill it with oil, that's okay. But the reason the Evo has them is reduce valvetrain mass and improve engine response, like I said, not an oil delivery system. There's a number of online pages I've seen that prove it so.
Uh oh, sounds like we have a politician in the house. So the historical reason was to fill it with oil, that's okay. But the reason the Evo has them is reduce valvetrain mass and improve engine response, like I said, not an oil delivery system. There's a number of online pages I've seen that prove it so.
Well, it depends on the engine. The camshaft is rotating mass, not reciprocating mass, so lightening up the camshaft will have no effect on valvetrain performance whatsoever. On the other hand, as rotating mass if you reduce the weight the engine can rev faster. However, that only matters on an engine where the camshaft(s) represent a significant amount of the overall rotating mass. On the typical Fiero motor the crankshaft, flywheel, harmonic dampener, timing chain assembly, and rod big ends add up to a whole lot more than the camshaft itself, so reducing the weight of the cam by a pound or two isn't going to do anything at all. In fact, if you want to reduce rotating weight you should investigate lightening the flyweel, it's mass has a greater moment and any changes there will have a dramatic effect.
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12:33 PM
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Will Member
Posts: 14280 From: Where you least expect me Registered: Jun 2000
Cadillac Northstar cams through '99 are hollow. Oil enters the center of the cam at the front cam bearing and supplies the other four cam saddles with oil from the center. Hollow cams can not be cast. They must be gun drilled. GM's hollow cams are assembled from separate lobes and what basically amounts to hollow bar stock.
My thinking on this was in the direction of the oiling system. Much of what I read on the 3.4 DOHC indicates limitations on that system.
Its length and complexity were the factors cited.
However, one would have to modify other things to take advantage of a gallery down the camshafts. This is where the $$$ start to really kick in.
Another thought. Given the belt drive system for the four camshafts, how much gain in longevity would be obtained by the reduction of angular inertia? A tuner working in the range of 6000 to 8000 rpm might see an advantage.
Just a guess, but well over $500 per cam to realize this configuration. Cost-to-benefit ratio? I would not even venture a guess there.
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01:59 PM
fierosound Member
Posts: 15236 From: Calgary, Canada Registered: Nov 1999
The roller cam in my 3400 block is a hollow cam. I believe GM won an award for this technology. It's less expensive to produce, is lighter, and unlike a cast iron camshaft, won't break. It's still used in the 3400's in Montana vans and the like. I'd expect the 3800's to have them as well.
hmmm - good stuff yes, this reduces rotating mass. if you wanted to reduce reciprocating mass - the lobes would have to be hollow too. and, since they slide onto a splined hollow tube, I dont see why they dont hollow them also. this could make for quite the oiling system for the cam & lifters/followers. this is quite a weight reduction. and, I also would beleive the would put the cost about $500 for a cam. yes, thats more than double & for a DOHC V motor, thats $2000 just in cams - YIKES! but - as we all know - speed costs.....sucks being poor....
Uh oh, sounds like we have a politician in the house.
No, you have an engineer in the house. There was nothing wrong with your original question, but the laws of physics and mechanics (at least at the level of everyday phenomena) are non-negotiable.
1) As stated by me and others here, a hollow camshaft will do nothing to reduce the reciprocating mass of a valvetrain. The camshaft is not even part of the reciprocating mass.
2) Concerning rotating mass: What matters is the moment of inertia of the rotating mass, and that varies directly as the square of the radius from the center of rotation. Thus, removing mass from near the axis of rotation of a part (radius near zero) will have much less effect on the moment of inertia of the entire part than removing an equal mass from the exterior surface (highest radius). Gun-drilling a camshaft (i.e. removing mass near the axis of rotation) would not be very effective at reducing the moment of inertia of the entire shaft. Conversely, if you were to put the camshaft in a lathe and grind the lobes off, that would reduce the moment of inertia substantially.
Your profile says you are in Norman. Take a walk down to University and Boyd (Campus Corner) some afternoon, drop into the engineering building and/or the library, and open your mind.
(Edited for accuracy, clarity, and humor - AMM)
[This message has been edited by Marvin McInnis (edited 05-16-2005).]
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10:09 AM
Pyrthian Member
Posts: 29569 From: Detroit, MI Registered: Jul 2002
The weight reduction would be equivalent to roughly 8' of steel 3/4" rod stock or exactly 12lbs. Thats a reasonable loss in engine weight. But like I said, I would only do this so I can use bigger lobes with a longer duration. It's like cheeting around getting the cams welded up and reground. The reduction in the rotating mass is not significant seeing as how its farthest point from the center of rotation is about 3/8" and also its spinning at cam speed witch doesn't go much over 3500 Rpm anyway so the reductions are really only a matter of physical weight.
