oliver
Well-Known Member
It's pretty much always. Can you enlighten me on how bad geometry will not affect gross lift at the valve?
Which rocker arms would you run?
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Wyrmrider
Well-Known Member
Not hardly
If your shafts are "too high" the rocker gets to tangent with the stem at a low lift and you will loose lift
if the shafts are too low the rocker gets to tanget with the valve stem at a higher lift and you will have much more lift
also much more load on the parts as you are up on spring pressure
also you are getting to tangent, where you have the most leverage and most acceleration multiplication later
where the cam is slowing down acceleration prior to going over the nose- where acceleration and velocity is zero
in other words the rocker is trying to "fling" the valve which leads to valve float
best to fix
the best answer is not just to add bigger springs
cheers
put some dykem on your stems and post a pic of the witness stripe
what rockers are you running?
If your shafts are "too high" the rocker gets to tangent with the stem at a low lift and you will loose lift
if the shafts are too low the rocker gets to tanget with the valve stem at a higher lift and you will have much more lift
also much more load on the parts as you are up on spring pressure
also you are getting to tangent, where you have the most leverage and most acceleration multiplication later
where the cam is slowing down acceleration prior to going over the nose- where acceleration and velocity is zero
in other words the rocker is trying to "fling" the valve which leads to valve float
best to fix
the best answer is not just to add bigger springs
cheers
put some dykem on your stems and post a pic of the witness stripe
what rockers are you running?
oliver
Well-Known Member
The numbers I posted up were with the ductile rockers. I'll take a pic on Friday when I'm working on it again. With the harland sharps the roller to stem contact patch was pretty narrow and relatively centered.
Wyrmrider
Well-Known Member
the iron rockers are easier to set up
just do the lash cap trick
when you roll the motor over the rocker should look angeled up about the same amount as angled down from middle
If the iron rocker is too far up at closed it puts on more side thrust where there is the most leverage on the stem
too far down it puts pressure the other way at the bottom
biggest problem with iron rockers- well any of them is that the distance from the ball to the threads has really grown so the old "three threads" method of getting pushrod measurement does not work any more
so once you get the shaft to valvestem tip height correct (spacers and/or lash caps) then get the balls real close- like 1/4 inch (some say 9/32)
and get your pushrods and if you do not have lifters get the Magnum ones with hollow pushrods
Push rod length - Page 2 - Yellow Bullet Forums
just do the lash cap trick
when you roll the motor over the rocker should look angeled up about the same amount as angled down from middle
If the iron rocker is too far up at closed it puts on more side thrust where there is the most leverage on the stem
too far down it puts pressure the other way at the bottom
biggest problem with iron rockers- well any of them is that the distance from the ball to the threads has really grown so the old "three threads" method of getting pushrod measurement does not work any more
so once you get the shaft to valvestem tip height correct (spacers and/or lash caps) then get the balls real close- like 1/4 inch (some say 9/32)
and get your pushrods and if you do not have lifters get the Magnum ones with hollow pushrods
Push rod length - Page 2 - Yellow Bullet Forums
oliver
Well-Known Member
I'll pay more attention to the rocker through it's motion and report back. On a previous post of mine it shows how far the ball is out with the correct lash. I'm running a solid roller and I don't remember if I can oil through the pushrod or not. I'm thinking no.
I don't like needle bearings in an engine. So that throws them out, IMO. I am a huge fan of the ductile iron rockers. The issue is money. To properly set them up for a real high performance build requires some changes to be made that will make them as costly as a high end rocker. But, IMO, they are still better. When they are bushed and modified with good quality adjusters, they are top notch and can work with a large solid roller. Gary at Rocker Arms Unlimited can correct the ratios, bush them and make any necessary oiling modifications. Total art work when done. But as said, it costs.
I forgot to add the WHY as to why I do not like the needle bearings. Of course, the obvious, they can fail and fall out and cause major engine damage. The less obvious, IMO, the iron rockers have more surface area contact on the shaft. Once bushed and the proper center line found to correct the ratio, they are even stronger and more stable. With the side clearances properly set, they are nearly bulletproof. They may not have a cute roller on the tip, but they flat out work.
I forgot to add the WHY as to why I do not like the needle bearings. Of course, the obvious, they can fail and fall out and cause major engine damage. The less obvious, IMO, the iron rockers have more surface area contact on the shaft. Once bushed and the proper center line found to correct the ratio, they are even stronger and more stable. With the side clearances properly set, they are nearly bulletproof. They may not have a cute roller on the tip, but they flat out work.
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nm9stheham
Well-Known Member
Uuuumm..... not really. The loss of lift is the same if you get far off of the 'tangent angle' (as it is called above) either at the start or end of the lift cycle. If the shaft is .100" too low, you lose as much lift in the early part of the lift cycle as you would lose lift in the late part of the cycle with the shafts .100" too high.
The whole point in getting the rocker's height 'tangent' to the stem at mid lift is that it minimizes the lift loss in both early and late parts of the lift cycle. It does this by minimizing the maximum rocker angle from the 'tangent angle' in all parts of the lift cycle.
Makes sense...
furrystump
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So I have been thinking about this and I understand what you look for to obtain the correct geometry. Which would produce the smallest contact pattern. I made a quick sketch but can’t seem to post the picture right now. The suggested optimum is at mid lift a line running through the rocker shaft center line and the valve tip are perpendicular to the valve. So the valve speed off the seat and at max lift is the slowest and the fastest at the mid lift point. Here’s my hypothetical thought. There is no useable lift down low. I understand this is going to be hard on parts, but we want the valve snapped off the seat and up to a useable lift as quickly as possible. So why not have it so with the valve closed the rocker center line and the valve tip is perpendicular to the valve. The valve speed off the seat will be the fastest because the rocker motion is more linear. As another benefit the valve speed at max lift will be the slowest. So it will linger longer at max lift. Just spit balling here.
Wyrmrider
Well-Known Member
Oliver the roller lifters have to have the oil through the pushrod provisions- in your case make sure the oil squirters in the rockers hit above the pushrod cup- hit the ball
Rusty- three cheers I've seen TI valves cupped with roller tip rockers when they forget the hard tips or lash caps
furry- sounds good- people have tried what you are suggesting- the 1/3 lift method etc all trade offs
you loose lift
and teh cam lobe is not designed for that method (today) maybe back when that 1/3 method was more popular and springs were not as good
Let me explain another way
a rocker has a theoretical ratio here 1.5:1 but that is an AVERAGE and only true at the tangent to the valve stem
at valve closed and valve open the ratio is much less due to the angle of the rocker
(if the rocker was angled all the way to vertical at valve closed all the motion would start off sideways!)
many rocker vendors build in extra ratio so they do not get the "my valve is not getting 1.5 x my cam lift"
Chrysler rockers are short arms compared to most all others
the 1/3 method is much better than having the tangent down low where you do get MORE VALVE LIFT
but you get the FLING that I mentioned previously-- hard on parts, guides, stems
remember if you are using roller tip rockers the tangent is determined by a line through the fulcrum (shaft center) and the roller center
not the valve stem top like a Stock or Iron rocker
nm with the tangent low you get maximum ration down low where the valve is more open- hence more total lift-
some people think that is better
but it's not
Rusty- three cheers I've seen TI valves cupped with roller tip rockers when they forget the hard tips or lash caps
furry- sounds good- people have tried what you are suggesting- the 1/3 lift method etc all trade offs
you loose lift
and teh cam lobe is not designed for that method (today) maybe back when that 1/3 method was more popular and springs were not as good
Let me explain another way
a rocker has a theoretical ratio here 1.5:1 but that is an AVERAGE and only true at the tangent to the valve stem
at valve closed and valve open the ratio is much less due to the angle of the rocker
(if the rocker was angled all the way to vertical at valve closed all the motion would start off sideways!)
many rocker vendors build in extra ratio so they do not get the "my valve is not getting 1.5 x my cam lift"
Chrysler rockers are short arms compared to most all others
the 1/3 method is much better than having the tangent down low where you do get MORE VALVE LIFT
but you get the FLING that I mentioned previously-- hard on parts, guides, stems
remember if you are using roller tip rockers the tangent is determined by a line through the fulcrum (shaft center) and the roller center
not the valve stem top like a Stock or Iron rocker
nm with the tangent low you get maximum ration down low where the valve is more open- hence more total lift-
some people think that is better
but it's not
furrystump
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I could see it being very violent on parts and it would be easier to grind the cam to accomplish the same thing. Not worth the increase in valve spring pressure you would need, so the valve doesn’t bounce on closing. Plus the abuse on every other part.
yellow rose
Overnight Sensation
Did you read the tech pages at b3racingengines.com?
You should. You lose much more lift from the wacky pushrod angles than you do geometry on the valve side of the rocker.
nm9stheham
Well-Known Member
Very interesting thoughts there, FS.
One thing to spitball back on as far as a faster opening rate..... we have to deal with a matter that we don't typically think of, and that is the internal vibrations in the spring. Most of that energy that goes into making the spring vibrate and wobble around (and waste energy) comes from the valve opening phase. So the faster you make that opening, the worse this matter gets. The worse this gets, the stiffer the springs get to help that and the more important any damper gets.
Plus, getting the valve open further, very early, may just make reversion at overlap worse.
So it is not all a free ride.
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nm9stheham
Well-Known Member
Not more total lift... the geometry equations clearly show that. Maybe an 'area under the curve' thing, but not total lift. This is for the valve side only.
try degeeing your cam with the dial indicator off center from the lifter or valve.... you will see how angles effect the lift.
Wyrmrider
Well-Known Member
nm
mid lift gives you the most area
Think this way
if the shaft was up where the rocker was pointed down 45 degrees at max lift the rocker would be moving sideways as much as up and down and the rocker ratio (pushrod lift to valve lift) would be much less than say 1.5:1
if the rocker is tangent to the valve stem at max lift all the motion is up-down and pushrod lift to valve lift is 1.5:1 giving you the most lift possible
there are those that argue for lower tangent but the trade offs make it not a good idea
and YR is correct unless the shafts are way off- like with roller tip rockers
the whole idea is to make the valve motion smooth and the lifter angle certainly does not help
having the shafts at the wrong height does not either
for the above poster - if your stock rockers are hitting your retainers something is not right-- larger diamater springs? long valves? what?
stud rockers just raise the adjustment and use longer pushrods (actually do the mid liff procedure) - Mopar takes some more work
mid lift gives you the most area
Think this way
if the shaft was up where the rocker was pointed down 45 degrees at max lift the rocker would be moving sideways as much as up and down and the rocker ratio (pushrod lift to valve lift) would be much less than say 1.5:1
if the rocker is tangent to the valve stem at max lift all the motion is up-down and pushrod lift to valve lift is 1.5:1 giving you the most lift possible
there are those that argue for lower tangent but the trade offs make it not a good idea
and YR is correct unless the shafts are way off- like with roller tip rockers
the whole idea is to make the valve motion smooth and the lifter angle certainly does not help
having the shafts at the wrong height does not either
for the above poster - if your stock rockers are hitting your retainers something is not right-- larger diamater springs? long valves? what?
stud rockers just raise the adjustment and use longer pushrods (actually do the mid liff procedure) - Mopar takes some more work
oliver
Well-Known Member
Couldn't find my dykem, then saw it overturned in the lathe tray. oops. i used a sharpie and it kinda worked.
Heres the iron rocker
Comp magnum
Crane gold
Harland Sharp
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I think it's pretty funny how well the old iron rocker does. LOL It's a little wide, but that's how it's designed. It's the best centered of all of them.
I’m not seeing this (granted I just skimmed the first 40 ish posts), but what is your spring pressure? Reason I ask is, with a solid roller, you normally need a lot of spring, which would really limit your options on rockers...well, it would limit your choices on long lasting ones anyway.
My old setup with a similar small solid roller (Comp XR286R), I had the old version of the Comp pro-mag rockers (no bushing) with hardened banana grove shafts. I used comp 939-16 springs setup at 1.800”. This worked pretty well and didn’t put too much pressure on the rockers, but it still controlled the lifters well to my self-imposed redline of 7k (normally shifted @ 6500). Too little spring pressure will cause a lifter to bounce, which will destroy your lifter, cam, etc. I was told to keep the spring pressure at or below ~450#’s for these rockers, because anymore spring pressure could cause the rockers to gall the shafts. If you bush the rockers they would be good for whatever you can throw at them (700+lbs).
My old setup with a similar small solid roller (Comp XR286R), I had the old version of the Comp pro-mag rockers (no bushing) with hardened banana grove shafts. I used comp 939-16 springs setup at 1.800”. This worked pretty well and didn’t put too much pressure on the rockers, but it still controlled the lifters well to my self-imposed redline of 7k (normally shifted @ 6500). Too little spring pressure will cause a lifter to bounce, which will destroy your lifter, cam, etc. I was told to keep the spring pressure at or below ~450#’s for these rockers, because anymore spring pressure could cause the rockers to gall the shafts. If you bush the rockers they would be good for whatever you can throw at them (700+lbs).
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oliver
Well-Known Member
I put another pair of the iron rockers on and rotated the engine through a dozen revolutions and here's the resulting pattern. Not the best.
oliver
Well-Known Member
165 @ 1.8 and 385 @ 1.2, it's a very small street roller. I shift at 6500.
No it's not but having them bushed will fix all that.
oliver
Well-Known Member
Why would getting them bushed fix that? Truthfully, I'll either run them as is or run the crane gold's. Cheapest and quickest would be run the irons as is.
MopaR&D
Nerd Member
Because it changes the arc the rocker tip travels in relation to the valve stem. It's all on the site YR linked there's no good reason not to read it.
oliver
Well-Known Member
I've read it. That would mean each rocker would need to be bushed in different positions to do the correction. That would be amazingly costly.
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