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  #16 (permalink)  
Old 11-04-2008, 03:26 AM
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My 2 cents worth
 
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Sorry guys, I have to agree with F-Bird on this for sure.

When using a 'degree wheel' and a 'dial indicator' gauge, to degree your camshaft. It does not make any difference on lift or duration at all, whether you take your readings at the camshaft, the lifter, the end of the push rod, or the push rod end of the rocker. The valve end of the rocker, will still show the same duration specifications, but will multiply the lift by the rocker ratio only.

Why do you think the Cam Card only comes with 'lift' spec's for the valve, and the camshaft @ .050? Valve lift is cam. lift times 1.5

Have you not noticed the 'cam' card does not show any other different "duration" spec's, per rocker ratio? Like .060, or .070.

This is because there is none.

I'm sorry to be so blunt.

Are we all still friends?

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  #17 (permalink)  
Old 11-04-2008, 07:14 AM
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Quote:
Originally Posted by F-BIRD'88
You have this preconceived notion of maximum "acceptable" streetable valve timing duration (probabily because you can't (yet) tune a carburator or ignition system currectly) and a false preconcieved notion of how rocker ratio effects valve action in a running motor that are both false and ill conceived. Probabily both from a lack of experience or know how and poor understanding of basic applied physical mechanics and high performance engine tuning.

Simple lever mechanics proves that you cannot change the valve event timing by changing the rocker ratio. the valves will start to.... and finish moving at exactly the same time reguardless of the rocker (simple lever) ratio.
The rocker ratio only effects the rate of lift of the valve, within that set motion duration as set by the cam lobe.
This has a very moderate and quite different effect on a running motor than a real change in actual camshaft duration. (a differnt camshaft)
Valve lash and its effect is a totally different thing and not comparable.

I didn't create the rules of mechanics and simple levers and reguardless of how you spin it you won't change those simple rules.
You'll find a lot more success (and a lot less knuckle damage) in fixing , tuning and hot rodding cars if you get the rules of applied mechanics straight in your mind and work within them.

Don't take it personally. We are not born with this knowledge or experience.

Do a google search "simple machine" there are 6 of them that haven't changed in 1000's of years. These are the basics of all applied mechanics.

Lash and preload are VERY simmilar when considering rocker arm changes. And I do know how a lever acts, I also know that the lash or preload of a lifter is filled in ever so slightly quicker with a higher ratio rocker arm. That's not even a simple machine, its just a simple action. And I don't hold your lack of knowledge against you. And I don't think that "expierence" means anything unless you fully understand what is happening. Without understanding no knowledge can be derived from expierence, just anecdotes.

I'm not saying there's a great deal of seat to seat duration change- a few degrees at most and only on lazy cams, nonetheless you cannot ignore the effects of preload or lash if you want to have a full grasp of the action of the valve.
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Old 11-04-2008, 09:15 AM
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Rusty,
rocker ratio's changes are explained on page #3 of this David Vizard article (but you need to read the whole article):

http://www.popularhotrodding.com/tec...ics/index.html

and here's a Dynomax's pipes to cubes/HP sizing chart pic'

malc,
thanks for the dyno graph chuckle...
8000rpm HP peak street motor combo (in your car?)!!!!!
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Last edited by red65mustang; 11-04-2008 at 09:47 AM.
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Old 11-04-2008, 02:02 PM
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Red,

Thanks for the link, the Wizard and I go way back - he mentioned that I had the rockers on the right side last time he stopped in at the garage for a beer and to see how the car was running...

I've got a handful of his books and he says essentially the same thing, but here's a line from your link:

As for the exhaust, we find that it is relatively insensitive to valve acceleration but is sensitive to duration. For this reason the rocker ratio used on the exhaust is best kept about 0.1 to 0.2 of a ratio lower than the intake ratio.

I started the post to see if anyone else had experimented with moving rockers around, something like what Malc posted (but somewhere less than 800 HP peaking at 8K?) Still very interesting though.

The exhaust will have to stay as is, even if someone dropped a 3" Dynomax exhaust system at my front door I can't say when I'm going to find time to swap it. Not 'til the kids get older then I can utilize that child labour!
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Old 11-04-2008, 05:41 PM
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Ok... I got frustrated and made a drawing. Its remedial, and not to scale, but it demonstrates my point.

The black arc represents the lift at the VALVE with 1.5 rockers. The grey arc represents the valve lift with 1.6 rockers.

Although both arcs still intersect the bottom line at the same point (same seat-to-seat duration) the point at which the VALVE reaches higher lifts is faster with the 1.6 rockers. The reason I was saying that it changes the effective timing is because what the valve SEES with larger ratio rockers would be equivalent to changing the lobe profile to have faster ramps and a taller lobe lift.

Rockers DON'T change the cam duration specs, but they in effect add .050" duration at the VALVE as indicated by the blue and red lines.

Increasing rocker ratio doesn't add seat to seat duration, but it DOES simulate additional @.050" duration. I think we're all arguing the same point using different words, but this drawing should help us all get on the same page.

I won't get into the disucssion about lash and seat-to-seat timing. I'm simply discussing area under the curve and valve opening/closing speeds.
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  #21 (permalink)  
Old 11-04-2008, 05:52 PM
How fast is fast enough?
 
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your drawing also has to have a line right below the red one that has an area for .010" travel of the rocker arm tip which is where the lash is taken up and the valve begins to move off of the seat. That's where my argument lies.
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Old 11-04-2008, 07:22 PM
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Quote:
Originally Posted by ap72
your drawing also has to have a line right below the red one that has an area for .010" travel of the rocker arm tip which is where the lash is taken up and the valve begins to move off of the seat. That's where my argument lies.
The lash value is taken up by lobe travel on hydraulic lifters, not rocker travel, so regardless of what is on the valve side of the rocker stud, the fact remains that on the short side, it will still require the same amount of lobe lift to begin activating the valve. THEN, once it opens it moves faster, but the lash is in the lifter. If it was .010" before the rocker swap, it will be .010" AFTER the rocker swap.

With solid lifters, i would agree since lash is physically determined at the valve. If you set lash to .010" at the valve before the swap AND after, then the lash will be taken up faster and add a fraction of a degree to the duration... but still, not enough to practically measure.
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Old 11-04-2008, 07:53 PM
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Quote:
Originally Posted by curtis73
The lash value is taken up by lobe travel on hydraulic lifters, not rocker travel, so regardless of what is on the valve side of the rocker stud, the fact remains that on the short side, it will still require the same amount of lobe lift to begin activating the valve. THEN, once it opens it moves faster, but the lash is in the lifter. If it was .010" before the rocker swap, it will be .010" AFTER the rocker swap.

With solid lifters, i would agree since lash is physically determined at the valve. If you set lash to .010" at the valve before the swap AND after, then the lash will be taken up faster and add a fraction of a degree to the duration... but still, not enough to practically measure.
Thank you Curtis.

AP72, I hope this helps, to better explain to you, what F-Bird, and myself, have tried to do.

Stephen
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Old 11-04-2008, 08:11 PM
How fast is fast enough?
 
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Quote:
Originally Posted by curtis73
With solid lifters, i would agree since lash is physically determined at the valve. If you set lash to .010" at the valve before the swap AND after, then the lash will be taken up faster and add a fraction of a degree to the duration... but still, not enough to practically measure.
Thankyou. and anything is measurable with the right tools.
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