I'm not really familiar with Cam Shaft geometry and how quick you can build lift.
I'm fooling around with something and I need to decrease the cam duration by about 20 percent or so.
My concern is that with the same lift level this will make a much sharper cam lobe which will result in an increase in valve transitional acceleration.... which increases the forces on the valvetrain exponentially.
Basicly I was wondering if there is some limit to valvetrain acceleration.... so duration vs lift.
Anyone know a formula or guideline for cam lobe geometry?????
((( And yes.... I know that reducing cam duration will reduce power.... I'm working on a slightly different design... hard to explain... it's still on paper)))
Cam Shaft grinding
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PrecisionBoost
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I've been looking at this recently as I wanted a cam for my engine that had stock (or nearly stock) duration but more lift.
How much valvetrain acceleration you can get away with will depend on the type of cam follower, weight of the valvetrain and valve spring rate.
Flat followers are the worst for quick opening and closing rates whilst roller followers are the best (as far as production engine technology goes).
The limits of valvetrain acceleration are going to be determined by the follower type and strength of the components used. As valvetrain acceleration goes up, higher spring rates are needed to control the valve. Higher spring rates mean higher contact (Hertz) stresses on the cam, valve tips, etc. This may mean the use of special alloys, hardfacing the cam lobe or special surface treatments to withstand these contact stresses.
I don't know of any handy formulea to work this out. I guess you'd need to work out the forces involved using the weight of the parts used, spring rate etc. and then perform stress analysis on the valvetrain parts either by classical methods or FEA.
It may be best to discuss the basics of what your doing with a cam manufacturer. You could also try www.eng-tips.com and post something in the Automotive section. I'm sure I've seen proper books on the subject too, maybe the SAE or ImechE could help? They've got lots of books/papers in their libraries on this stuff and I know that the ImechE will search for info for you if your a member.
Stef
How much valvetrain acceleration you can get away with will depend on the type of cam follower, weight of the valvetrain and valve spring rate.
Flat followers are the worst for quick opening and closing rates whilst roller followers are the best (as far as production engine technology goes).
The limits of valvetrain acceleration are going to be determined by the follower type and strength of the components used. As valvetrain acceleration goes up, higher spring rates are needed to control the valve. Higher spring rates mean higher contact (Hertz) stresses on the cam, valve tips, etc. This may mean the use of special alloys, hardfacing the cam lobe or special surface treatments to withstand these contact stresses.
I don't know of any handy formulea to work this out. I guess you'd need to work out the forces involved using the weight of the parts used, spring rate etc. and then perform stress analysis on the valvetrain parts either by classical methods or FEA.
It may be best to discuss the basics of what your doing with a cam manufacturer. You could also try www.eng-tips.com and post something in the Automotive section. I'm sure I've seen proper books on the subject too, maybe the SAE or ImechE could help? They've got lots of books/papers in their libraries on this stuff and I know that the ImechE will search for info for you if your a member.
Stef
Vauxhall Astra.
T3 60trim, Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Cast T3 Manifold With External Wastegate + More...
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PrecisionBoost
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Thanks for the tips Stefan
I might be getting into the expensive side of things because this valvetrain will be opening and closing quicker and with less duration so valvetrain forces will be really high.
I guess I could limit it to a 2500rpm redline just for the tests... this should make things functional enough to test my theories without destroying the factory valvetrain.
I wish I could get into the engine design more but it's a new type of engine cycle ( not an Otto cycle ) so I don't want to say anything until I know if it will work or not.... it's really wild.... should make in the order of four or five hundred horsepower per liter if I can get it to start up... once it gets through about 60 cycles it should be able to run on it's own but the first 10 seconds will be the hard thing.
I need a research assistant... I'm too lazy... I have over 900 pages worth of inventions but I never see any of them through to completion... I allways get side tracked with another cool idea.
I might be getting into the expensive side of things because this valvetrain will be opening and closing quicker and with less duration so valvetrain forces will be really high.
I guess I could limit it to a 2500rpm redline just for the tests... this should make things functional enough to test my theories without destroying the factory valvetrain.
I wish I could get into the engine design more but it's a new type of engine cycle ( not an Otto cycle ) so I don't want to say anything until I know if it will work or not.... it's really wild.... should make in the order of four or five hundred horsepower per liter if I can get it to start up... once it gets through about 60 cycles it should be able to run on it's own but the first 10 seconds will be the hard thing.
I need a research assistant... I'm too lazy... I have over 900 pages worth of inventions but I never see any of them through to completion... I allways get side tracked with another cool idea.
If you really want fast opening and closing rates, get in touch with the SAE and have a look at some papers on valvetrain technology. You don't have to use a cam to open and close those valves! 
That may mean a new head casting or radically modified existing one though......
Stef
That may mean a new head casting or radically modified existing one though......
Stef
Vauxhall Astra.
T3 60trim, Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Cast T3 Manifold With External Wastegate + More...
T3 60trim, Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Cast T3 Manifold With External Wastegate + More...
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PrecisionBoost
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Well... I've been thinking... and I think I will share this alternate engine design which is a hybrid of a miller cycle and a modified two stroke Otto cycle.
Let's face it... I'm lazy and I probably will never make this engine.... I actually have a 2 stroke diesel engine that I'm more interested in anyways.
So... I'm going to post the engine design on this forum just for the heck of it.
The cool thing is that this alternate engine cycle could very easily be put into use in a normal 4 stroke engine like the daewoo engines we all have.
Realisticly you could probably make this thing work for a couple grand but I don't know how the valvetrain or crankshaft would handle the extra stress.
So if anyone is interested see my post
Let's face it... I'm lazy and I probably will never make this engine.... I actually have a 2 stroke diesel engine that I'm more interested in anyways.
So... I'm going to post the engine design on this forum just for the heck of it.
The cool thing is that this alternate engine cycle could very easily be put into use in a normal 4 stroke engine like the daewoo engines we all have.
Realisticly you could probably make this thing work for a couple grand but I don't know how the valvetrain or crankshaft would handle the extra stress.
So if anyone is interested see my post