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Roller Rocker arm Pics

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Trevor Jessie said:
OK... I think there is an issue there that needs to be addressed. But I'll leave it for an engineer. (I'm a scientist).
Click to expand...

what is that? Inquiring minds want to know.



mark
 
It is simple. The rocker rotates, with a OEM cam, 18.5 degrees so it's total movement, horizontally across the valve stem is .078. I centered the .078 on the valve dia of .281. So when the valve is is exactly halfway open the roller is at the exact center of the valve stem. Then by moving the adjusting screw closer to the the fulcrum point the valve will open more and moving the adjusting screw away from fulcrum opens the valve less. Think of a teeter totter. Using the CAD system I was able to move the screw closer to the fulcrum and still have clearance for the push rods. This whole process would change if a larger cam, more than .270" of lift, was used.
 
Tim,
did you take a look at valve spring clearance? Doesn't sound like .04 would be a problem but just to be sure the valve springs don't bottom out, if you know what i mean.


mark
 
OK,
You did two things that I understand

1)The adjusting screw was moved in towards the rocker shaft, but not far enough to cause pushrod clearance on a stock cam, but on higher lift cams there might be an issue.
2)The roller tip was moved out from the rocker shaft and centered at the valve half open point. Again, If a high lift cam is used then the roller has a potential of sliding off the edge of the valve stem.

So, you goal was to create a rocker set that could be bolted on to a stock engine to gain more valve opening. It seems like you have done this.

So what is the effective lift ratio?
 
Lift ratios baffle me. I have asked people at my local "Speed Shops" to explain rocker arm ratios to me. All I left with was the higher the ratio the more valve opening you have. Even Vizards book assumes the reader understands them. I know they are expressed as 1:50 or 1:30 but what do these figures represent? Is the 1:1 ratio "stock" and as the second number increases represent a percentage of more valve movement? Once I understand lift ratios as they pertain to this application I will be able to answer your question.
 
Trevor: I have sent you a PM. Please respond. Thanks
 
Actual ratio of valve to lifter, stock is something like 1.27 (a number off the top of my head), Theoretical ratio is based on the effective ratio of the lever arms (this is more troublesome because of the arc and contact pad/roller).
 
If the pivot of the rocker is in the center then the lift is one to one. move the pivot toward the pushrod and the effective movement at the valve is increased. Think of the see saw.
Graphic1.jpg


mark
 
whoa, that pic is a bit large...


sorry

m
 
So then the second number is a percentage of increase by moving the fulcrum?
 
the numbers refer to the ratio of the distances from the center of rotation to either end of the rocker. You divide one side by the other. Take the distance to the valve end and divide it by the distance to the push rod end. The result is the ratio of the arm.



mark
 
Right mark... in a 1.3 the valve opening is 130% of the cam lift. AND the length of one side of the rocker (measuring from the fulcrum) is 130% of the other side.
 
I have calculated that the rocker Arm ratio is 1:1.3876.
 
Dadandson said:
So then the second number is a percentage of increase by moving the fulcrum?
Click to expand...

Yes and this has to happen at the shaft, that why when significent ratio changes are made the pedestal holes must change. Titan rocker 1.5 ratio sets for example come with new pedestals, and the HS 1.3 units mess up the geomentry, and cause pushrod interference

I throw this in as well, since a roacker arms moves in a arc, and most engineers fiquire ratios horizontally, then almost all rocker arms lose ratio thru the arc, the more they depress the valve the more ratio is lost, and of course then most of us go out and get a higher lift cams so we lose even m more ratio, if the high lift cam lifts enough, sure we see a gain, but the ratio loss rate is enlarging the more we lift. The real rick is to get a racker that stay true to it's claim thru out the lift, Keith Dodds forged rocker are the only one I know that does.

Tim you can fiquire out your 'real" ratio of your rockers, by simply throwing ratio at them x cam lobe lift, until the applied ratio x cam lobe lift matches te actual measurement you are seeing in cam lift measured at the valve.

Amazing feat by the way Tim, but I think you can even further develop it, and come up with something people will buy. I like to talk to you more about this, and maybe lead you to someone that could be even more help in the etire theory of this. I have no idea if you just wanred to make a set of racker for yourslef, or if you wantto get into the rocker arm business, but if it's the later, then I have some builders that would love to talk to you in the development stages. Call me or PM me anmber wher I can reach you, all my contact info is on my website. Thanks.
 
Alloy 1.5:1 rockers with proper offset pedestals and adjusters, with tube spacers, now on sale from Minisport UK for 126 pounds plus 35 pounds UPS shipping. Exchange rate yesterday: 1 pound = $1.42
 
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