78 replies to this topic

[Liam Kelly]

yeah may need to get an adjustable, dont really want custom pushrods that i cant buy off the shelf (cost vs minimal gain) to get the best lift adjustment out of the rocker plus acceptable geometry with my head and valve train combo (its a slow street car). Its fine at the moment really except for slighlty smaller than theoretical max lift, so just curious why...

Edited by Liam Kelly, 22 August 2023 - 08:43 PM.

[Bruiser]

Sorry Liam, I missed your second link before having a spout before
That one seems to address valve train non-flexing mostly
It’s an intriguing subject, I ‘d like to know the answers to the
questions you are asking too, they are good ones
It seems you’re way ahead of me anyway
Maybe there’s a rocker design bloke at yella terra you could have a chinwag with?
About the in depth ins and outs of rocker design?

I have read that some brands of rockers are not constant ratio from top to bottom, and
some are have better numbers than others
That’s one of those things that reading articles about on Google only puts questions in my head,
and then there’s no info from the anywhere to help find a decent answer

[Liam Kelly]

yeah no probs and appreciate everyones help, I still havent learnt to leave the bloody car alone and enjoy.

 

I'll ask YT but i doubt im going to get one of their engineers. There seems to be some good info on that speed talk site but need to read it and in maybe 10 years ill understand.

 

Only thing i can think of is the pushrod angle slightly increases under the following circumstances which increases push rod cup to fulcrum point distance, which decreases the theoretical lift somewhat at certain points over the lift range

1. in general At max lift compared to mid lift more pushrod angle

2. When adjustable rockers are wound all the way out below the rocker arm

3. When using higher ratio rockers (They move the pushrod cup closer to the fulcrum point of the arm to get the higher ratio, but also increase pushrod angle so i.e. 1.65 at mid lift but only 1.6 ratio at max lift)

 

i dont know, beer time

 

Cheers

[warrenm]

David Vizard has done a comparison in one of his youtube channel not that long ago, some brands of rockers gain at low lift others are less. It's worth checking it out. Don't be afraid to use non std pushrods when you are looking at non std rockers etc.

[Liam Kelly]

Thanks Warren, those David Vizard videos are packed full of info and need to digest some of it.

 

I guess my geometry is too not bad at the moment with a tightish contact patch on the top of the valve stems, it's just if it could be improved a little with slightly different pushrods, shims etc to get closer to theoretical lift values. Will definitely do some trials when I can get some time.

 

As for the adjustable rockers it definitely seems like too much adjustment under the rocker arms loses some theoretical lift and I can maybe gain another 0.5mm - 1mm here without negatively affecting my contact patch then I might try.

 

It does seem that roller rockers do have a slight varying ratio over the entire arc, and this can sort of be visualised by the width of the contact patch on the valve stem.

https://www.performa...ocker-Ratio.htm

 

A contact patch that has a width of 1mm shows the lateral movement across the top of the valve stem which effectively changes the distance to the fulcrum point on the valve side. and even a movement of 1mm here can bump the ratio of rockers down .5 of a ratio or more.

 

Sent some questions to YT to see if their advertised value stamped on the rockers is a mid lift, not to have a go but just to understand what i'm seeing (rockers plus my entire valve train appear to behave more like 1.6 at max lift not 1.65) .

The roller probably appears to have a varying ratio range over the entire arc that needs to be understood but also that the other components dont amplify any of the variance.

 

Then after all that, getting around to actually seeing what I have at the moment is theoretically the best it can be.

 

Then actually get around to trying larger ratios and actually testing for any gains etc with the methods using by David Vizard (not ignoring new lash size and cam timing)

Edited by Liam Kelly, 23 August 2023 - 10:15 AM.

[Liam Kelly]

some interesting reads here also

https://www.speed-ta...pic.php?t=12213

Edited by Liam Kelly, 23 August 2023 - 02:02 PM.

[Liam Kelly]

 

So after reading and chatting to people it seems the following

 

- Theoretical Rocker ratio value for the rocker arm (stamped on it) does not change but the 'effective rocker ratio' the valve will actually see changes through the arc of the rocker. This is due to the contact surface on the valve stem changing as the valve travels down while rocker is arcing (contact surface to rocker fulcrum point distance changing). The pushrod side, cup to pushrod contact interface distance to fulcrum point seems to change slightly also through the full arc, from the rocker moving over the ball of the pushrod. All rockers when installed will have this + and - of ratio value at the valve, when travelling through the arc with some designs like shaft mounted and roller less of a variance.

 

- The change in rocker ratio value from the advertised value, from the adjuster cup being down too much below the arm on adjustable rockers, seems to be a constant change in the advertised ratio. However the above mentioned variance when moving through the arc will still come into play. Maybe some small gain here by going to a pushrod .050 larger here.

 

- The value that is actually stamped on the rocker seems to be a theoretical value for standard pushrods, head, valve length, installed spring height etc and prob at mid lift (to be confirmed). This David Vizard said you have a 1/100th chance of having that lol, Probably changes for every manufacturer.

 

So when working out max lift from the theoretical rocker value only seems that there is going to be error there from the above and also any pushrod deflection from the actual valve spring pressures etc.

 

I guess I can get a cam degree wheel and plot my entire 'effective valve lift range' if I can find the time and maybe fit checking springs while doing that. Not sure I could be bothered but it is probably needed to determine any changes when comparing two types of rockers against each other.

 

Curious what others are getting when measuring max lift at the valve compared Vs theoretical max lift?

[Uncle Chop Chop]

...dont really want custom pushrods that i cant buy off the shelf (cost vs minimal gain) to get the best lift adjustment out of the rocker...

 

 

The cost of getting it wrong could get very expensive

[Liam Kelly]

Thanks Chop Chop, which scenario do you mean ?

In this instance im talking about solid cam with adjustable rockers. Car running for a year or so with acceptable rocker geometry and contact patch on the valve stem.

When i wrote that it was about scraping back 1mm or so of the rocker adjustment below the arm as it might be lowering the advertised rocker ratio slightly.

I see that you can get off the shelf pushrods at 0.05 inch increments for cheap but somewhere in between for the small gain i might get i just don't think would be a wise spend of my cash.

Any info welcome as trying to learn.

Cheers

[Uncle Chop Chop]

When you're going to extreme lifts and ratios, it's more critical to get everything spot on. Saving a few dollars on parts could mean the difference between hit and miss.

[Liam Kelly]

Yeah thanks

Only at .500 lift at the moment but looks like many of you guys running crazy non street motors. What tolerance in pushrod increments to you guys get down to with adjustable rockers?

Edited by Liam Kelly, 24 August 2023 - 08:15 PM.

[N/A-PWR]

If 1.5:1 equals .500 thou valve lift,

 then 1.8:1 with same cam equals .600 thou.

 

If dial gauge sees this,

 then rocker ratio is correct.

[Liam Kelly]

Hi N/A, should be .520 theoretically with 1.65 rockers. Im seeing around .500 with dial gauge measured with installed springs.

Thats why i asked the previous questions

Will check again with checking springs to remove any lost lift from defection.

[Bruiser]

Not sure my motor qualifies there, but I have not gone down the adjustable pushrod checker path, never used custom length pushrods
Mine has .354” cam lift with 1.6 rockers minus .018” lash gives (a not actually measured) .548”.
After all the machining and juggling of deck and seat heights, I was told that 186 pushrods would
be pretty close. Blued the contact patch one day, found it to be a bit off centre
Tried a 202 rod which got it pretty well centred.
Surprising, but it looked good so there they are
Always thought that the centring was the important thing, but there is a school of thought saying
the narrowness of the patch is more important than the central location, within reason
Just been reading about it in speedtalk here
Got me wondering wether I have done the right thing now

https://www.speed-ta...r rocker design

If you haven’t seen it already, I reckon you’ll dig this, Liam
these guys sure go into some depth here about all sorts

[Bruiser]

There’s some stuff in that link talking about losing or gaining actual lift at the valve
relative to the calculated lift you are expecting to see

Edited by Bruiser, 24 August 2023 - 09:13 PM.

[Liam Kelly]

Thanks ill check it out! heaps of info on that site.

When i was reading a similar thread on there i had to wade through if each comment was related to hyd or solid cams and if the rocker was adjustable or not, in the way of pushrod and geometry changes and effects.

Edited by Liam Kelly, 24 August 2023 - 09:41 PM.

[N/A-PWR]

The Big Block Red Six,

 does not breathe well, as it has asthma.

To get it to breathe better is to port it in such a way,

 that the flow of air has a smooth travel without too much turbulence to the bore.

(normal atmospheric pressure N/A)

Having said that,

 the valve does not have to be too much bigger than the standard valve,

 but the cam timing of the valve needs to be longer apart.

(i.e. a big Cam)

Then to get more out,

 we need more RPM,

 plus higher compression.

Then the good ole river of fuel running into the bore.

(not fancy fuel mist)

 

NOS, JZ heads etc and Turbo's are the next step in making more changes.

 

p.s. no point having a valve held open longer,

 when the bore is already filled. 

[Liam Kelly]

Good summary mate,

 

Seems that most of us play with these old holden 6s is the challenge of getting N/A power rather than buying a 500hp crate motor for less than spent on a fancy holden 6 head... Some of the topics I raised above in this thread seem to be directly related to this, even though more about fixing up efficiency losses for a mild street car rather than max N/A power. Still curious to hear others thoughts on their measured lifts vs theoreticals.

 

For the fuel injection, yeah at wide open throttle (engine at operating temp) the engine needs a river of fuel and not a fancy mist. However the fanciness that comes from controlling the fuel timing is advantageous for driveability in a street driven car, for improved cold starts, injecting after valve overlap events at low revs (not shit it out the exhaust) and being able to easily tune out flat spots etc. Once again depends what you are trying to achieve here and if an all out drag car than prob not.

 

Just for the closing of the inlet valve comment, I know what you are trying to say mate and I'm sure you already know this and were trying to say this. Just if the bore is already filled, the piston coming back up with the inlet still open and you have some inlet air inertia still flowing and ramming air in at slightly higher than N/A pressure, then that's what should determine the inlet valve closing time. Really requires tuning your cam timing to your inlet manifold dynamics.

 

Also seems if you have a large overlap cam and evacuating the exhaust too early can be detrimental to making use of the scavenging event. This would be at the expense of some reversion into the inlet manifold at low revs. I'm keen to get more lift on my inlet here to take advantage of the flow my head still has in it but maybe not on the exhaust as the percentage of flow between the inlet and exhaust is already pretty high. I can see in my manifold I have a little reversion going on at the moment but the ITBs and fuel injection seem to handle this fine with not having to have a high idle speed.

 

Yeah I could probably choose a better cam and chuck it in (less agricultural) but maybe after I have eventually tried out some 1.7 or 1.8 rockers etc and then actually do some testing on a dyno to see what's improved.

 

Before new rockers, first going to try an off the shelf  5/16 9.05in pushrod with a .110in, 210deg ball wall to see if I get any of my theoretical lift back from a) lose one turn out of the rocker adjuster and maybe slightly better rocker geometry less deflection with the thicker wall c) bees dick better geometry on the pushrod side from different angle ball. As previously mentioned if you guys think i should go down to custom 0.025in pushrod increments here please let me know.

 

Then after that I finally get around to measuring the clearance I have from the valve to the bore walls and thinking about 1.7 or 1.8 rockers for a trial, if i stick with the same brand rockers then there should be a relative increase in ratio rather than two different manufacturers having differences between their stamped ratios.

 

Thinking I should base my clearance from valve to the bore wall here of my larger theoretical value rather than the lower actual value for caution.

 

 

Bruiser you may like this article also.

https://www.motortre...train-geometry/

 

Cheers

Edited by Liam Kelly, 25 August 2023 - 10:45 AM.

[Bruiser]

That’s a good one there, supports what I have been seeing on speedtalk, too.
As you have probably seen, Jim Miller himself has popped up in a couple of those discussions and explained that further.

I found this idea there and have been out in the shed with rocker cover off giving it a looksee

Checking for pushrod length down in the engine bay of a 69 Mach 1 is no easy thing. Looking at the Manton site on determining pushrod length, ''a light turned on'' and this is to me the best method. I put a piece of masking tape on the side of the rocker. Drew a fine line on the tape that intersected the centers of the roller tip and the trunion axles ( you can see the machine marks so the centers are pronounced).Installed, set up dial indicator and opened valve to half lift. Now, heres the trick.I used a piece of 3/16'' square high speed steel, layed it on top of the retainer and let the piece lay beside the rocker. Now I made adjustments to pushrod length until the drawn line on the masking tape and the high speed steel bar are parellel.

And the next reply, which makes sense

That's slick should work well, assuming your also keep the valve at mid lift
that would change as you very the pushrod length.

My .theoretical 550” cam lift was actually .530”ish, and exhaust down the same amount
Swapped back to 186 pushrods and not much difference, sadly.
But, using the method above, the lines were not very parallel , and it looks like the pushrod cup needs to
be maybe 2mm or so to achieve close to that.
The longer 186 pushrods were better than the 202 ones, though.
I need an adjustable pushrod to mess around with it any further, until then the 186 rods are staying in

[Uncle Chop Chop]

If it's a solid cam, then the clearance between the vale tip and rocker is obviously removed from the lift. It won't be much, but it all adds up.

[Liam Kelly]

Yeah it would seem we are loosing static theoretical max lift values after lash, from either varying rocker ratios, deflection from spring pressures , slight lift loses from geometry or a combo.

Check out this one also bruiser
https://www.speed-ta...opic.php?t=3971

Edited by Liam Kelly, 25 August 2023 - 10:49 PM.

[Bruiser]

That’s good info, too
I think you are right with the missing lift
I reckon at an eyeball guess, my mid lift lines are about 4 x- 5 degrees out.
ThInking about the imaginary circle traced out by the rocker tip axle, the maximum vertical travel (lift)
will be if the mid lift point is on the 90degree, with equal travel above and below.
If the rocker could theoretically point vertically, the vertical travel per degree of rocker movement
would be at it’s lowest. Must be losing some if not perfectly right, but .020”?
I have factored in the lash, too.
They reckon there is a difference to be seen when using light checking springs
so the spring pressure loss must be a factor as well

Have you seen this one?

https://www.w8ji.com...r_geometry.html

[Liam Kelly]

Are your rockers shaft or stud mounted ones ?

 

yeah i was reading that article today actually and turns out the shaft mounted YT rockers i have, geometry won't change with pushrod length only pedestal height. So my contact patch width (currently 1.25 inlet- 1.5mm exhaust @ .500in lift) won't change. Double checked everything and it is within spec of the YT instructions etc so im just going to leave mine i think with the 9.00in pushrods and not try to scrape back a bees dick of lost lift here by trying to get the contact patch tighter.

 

Seems when wading through this info a lot of people talking apples and oranges in the same threads with shaft and stud mounted rockers etc.

 

I might fit some checking springs to confirm the actual static rocker ratio and max lift, but seems like many people just dont bother with these anymore after coming to the realisation of the lost lift from defelection etc. Prob a good thing to do if comparing different rocker ratios against each other though (my original intention).

 

Some interesting info in this one from Bill Jones even talking about defelction in the cam etc.

https://www.speed-ta...opic.php?t=1133

[Liam Kelly]

Seems with the higher ratio rockers, as the pushrod cup moves closer to the valves, the pushrod angle increases and getting closer to the cylinder head wall.

 

Shims for the pedestal and 9.05 pushrods already in the mail though, so might do a trial to see if i can better the pushrod angle a little with the longer rod / rod & shims (and have enough lash adjustment) and if not now at least i have some options when going to the higher ratio rockers.

[Bruiser]

Mine are stud type, 186 head just the street terra line.
I had to relieve them a bit when going to the bigger cam too, they fouled on
the posi-lok. Haven’t broken yet at 6000 rpm
I was wondering what sort you had too, actually
Hope your new rods get you what you need