Would pushrod length make this much difference?

Posted by: BradH

Would pushrod length make this much difference? - 02/07/18 05:28 PM

A couple of diagrams I did trying to get a sense for how much difference might result from running the shortest possible pushrod vs. one at the max exposed adjuster length.

Seems like -- on paper, at least -- there's a significant ratio difference... and not something I'd given much thought to before.

Oh, the reason why the tip of the adjuster ball in the first picture isn't the actual point of measurement is that I was trying to account for my using that same style of rocker with a brand of adjuster screw that's noticeably shorter than what's pictured.
Posted by: AndyF

Re: Would pushrod length make this much difference? - 02/07/18 06:01 PM

Yep, using a pushrod that is as long as possible will give you more valve lift. But you have to watch out for the gotchas. For example, with Harland rocker arms on my 470 I toasted the pushrod ends since the long pushrod puts the cup out of reach of the oil squirt. Pushrod oiling solved that problem. With T&D rocker arms you have to have the adjuster in the correct location or else they won't oil. So you can't screw the adjuster all the way in or all the way out, it has to be in the middle of the range or else you'll kill the rocker arms.

This trick is also dependent on the design of the rocker arm. If you get a bunch of different Mopar rocker arms and put them on the same shaft you'll see that everyone designs their rocker arm differently. So the angle of the backside of the rocker arm is different. The pushrod to rocker arm angle can vary a lot between different rocker arms so the long pushrod trick may or may not work.
Posted by: hemi-itis

Re: Would pushrod length make this much difference? - 02/07/18 06:13 PM

Pushrod oiling is the answer to anything that has an issue with burnt cups.
Posted by: mopar dave

Re: Would pushrod length make this much difference? - 02/07/18 08:55 PM

Yep, turn your adjuster all the way up, then 1 turn down. From there you only have 1 turn either way. The closer you get to 1 full turn either way the less oil you get.
Posted by: Sport440

Re: Would pushrod length make this much difference? - 02/07/18 09:35 PM

Your pics don't give the minute differences justice.

Longer pushrod equals more max lift while a shorter pushrod gives quicker more mid lift but with less max lift.


Significant difference??, in the scheme of the whole overall lift event, either way, long/short pushrod, doesn't make any significant difference in performance on the engine involved. The valve train, does like the longer pushrod though, less stress on the rocker arm because of the lesser angles involved. IMO
Posted by: polyspheric

Re: Would pushrod length make this much difference? - 02/07/18 10:47 PM

The minimum adjuster length isn't a specific number of turns. What matters:
1. no contact throughout the range of travel
2. enough adjustment to get lash
Posted by: Cab_Burge

Re: Would pushrod length make this much difference? - 02/08/18 01:37 AM

I've seen adjusters and pushrod cups broken off due to using to short of pushrods, way to short work
To long can and may beat up the bottom of the rockers also so my choice is to see between 1/8 of a thread to three complete threads max exposed under the rocker arms up
As already mention on the single shaft T&D system they like 1 1/2 turns out to three turns out max on their adjusters for oiling the push rods properly shruggy
I think I have 1 1/2 threads exposed on my 440-1 with the Jesel pair shaft system with pushrod and spray bar oiling up
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/08/18 10:50 AM

I've read where both Jesel and T&D say to set their cup adjusters to one turn out from seated in order to limit the exposed (unsupported) amount of the adjuster, and to keep the oiling passages aligned.

Seems like part of the cup-style pushrod-to-rocker clearance concerns could be addressed by converting to cup-style adjusters. Is going from ball-type to cup-type adjusters as simple as changing to hollow pushrods, as long as the lifters support pushrod oiling?
Posted by: mopar dave

Re: Would pushrod length make this much difference? - 02/08/18 10:56 AM

My point on the on the 1 turn from seated up was to get enough oil to the pr tip. With TD rockers i always seat lash from that 1 turn down from seated position. I latter added spray bars and it didnt matter.
Posted by: Cab_Burge

Re: Would pushrod length make this much difference? - 02/08/18 12:27 PM

Brad, the Jesel adjusters are hollow and don't have any provisions for oiling the axles or valve tips shock shruggy
I called them about this and they said that splash oiling was good enough confused
So I added the spray bar valve covers luck
Posted by: Stanton

Re: Would pushrod length make this much difference? - 02/08/18 03:03 PM

I'm curious as to why pushrod length affected the lobe lift.
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/08/18 03:13 PM

The lobe lift only changed because I reversed-engineered the lobe lift for the same valve lift to account for the ratio change. If I'd left the lobe lift the same, then I'd have had to increase the lift curve on the valve side. It was simpler to leave the rest of the rocker diagram the same and only tweak the pushrod adjuster arc to match the ratio difference.
Posted by: fast68plymouth

Re: Would pushrod length make this much difference? - 02/08/18 04:42 PM

Be a good excercise with the rocker on the head, an adjustable pushrod, a checking spring, and a dial indicator.
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/08/18 04:53 PM

Originally Posted By fast68plymouth
Be a good excercise with the rocker on the head, an adjustable pushrod, a checking spring, and a dial indicator.

Yep. scope
Posted by: Sport440

Re: Would pushrod length make this much difference? - 02/08/18 05:21 PM

Originally Posted By BradH
Originally Posted By fast68plymouth
Be a good excercise with the rocker on the head, an adjustable pushrod, a checking spring, and a dial indicator.

Yep. scope



Yep, and Your just the right kind of guy to do it. Put the car on hold for just a little bit longer. laugh2 up
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/09/18 09:51 AM

More "stuff" to think about... the location of the pushrod contact point w/ respect to the rocker arm fulcrum also affects whether the lift curve translated by the rocker arm from the cam lobe is linear or regressive. The diagram below came from an old Crane Cams presentation that shows an example of how the leverage ratio actually decreases across the lift curve as the valve is opened.

Posted by: WedgeFED

Re: Would pushrod length make this much difference? - 02/09/18 10:08 AM

http://tdmach.com/wp-content/uploads/2018/01/Instructions-P-N-05899.pdf
Posted by: Cab_Burge

Re: Would pushrod length make this much difference? - 02/09/18 12:29 PM

I wonder if these instructions apply to stud mounted rockers only? shruggy
Posted by: madscientist

Re: Would pushrod length make this much difference? - 02/09/18 03:41 PM

Originally Posted By Cab_Burge
I wonder if these instructions apply to stud mounted rockers only? shruggy


Nope. Adjuster position affects geometry on stud and shaft rockers.
Posted by: EV2Bird

Re: Would pushrod length make this much difference? - 02/09/18 04:28 PM

Interesting info posted.

Folks mention the cup oiling window of setting, so when also taking into account possible rubbing issues, scrub pattern at the end of the day what, say does .050 off give or take just for an example in terms of usable power/rpm amount to?
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/09/18 04:47 PM

Probably nothing you'd ever notice.
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/09/18 04:53 PM

Originally Posted By madscientist
Originally Posted By Cab_Burge
I wonder if these instructions apply to stud mounted rockers only? shruggy


Nope. Adjuster position affects geometry on stud and shaft rockers.

Adjuster position on a shaft system has no effect on geometry; that's determined by the rocker fulcrum location with respect to the valve.
Posted by: sixpackgut

Re: Would pushrod length make this much difference? - 02/09/18 06:19 PM

Geez, and I'm just happy when the pushrods stay where they belong
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/14/18 06:13 PM

Originally Posted By sixpackgut
Geez, and I'm just happy when the pushrods stay where they belong

Ain't that true. IIRC, my first trip to Dwayne's dyno we ended up bending a couple because I hadn't noticed there were clearance issues w/ the heads. I'm an idiot. eyes
Posted by: AndyF

Re: Would pushrod length make this much difference? - 02/14/18 06:59 PM

You aren't an idiot, you just haven't learned everything the hard way yet. Once you learn everything the hard way you'll be a bitter, grumpy old man with no patience for whipersnappers who haven't learned everything yet.
Posted by: WHITEDART

Re: Would pushrod length make this much difference? - 02/14/18 07:11 PM

Pushrod length was one of the things we explored when I went to competition engine building school.. by adding .050 a pushrod length we gained about .06 at Max lift.But the early and mid numbers suffered slightly... made absolutely no difference on back-to-back on the dyno.. I would say picking a pushrod length with the adjuster set and it's recommended location would be your best bet
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/15/18 01:03 PM

Originally Posted By AndyF
You aren't an idiot, you just haven't learned everything the hard way yet. Once you learn everything the hard way you'll be a bitter, grumpy old man with no patience for whipersnappers who haven't learned everything yet.

1. I've told my friends & family for years, I learn EVERYTHING the hard way.

2. I'm already a bitter & grumpy old man with no patience for others... and I still don't know sh!t.
Posted by: Cab_Burge

Re: Would pushrod length make this much difference? - 02/15/18 09:52 PM

I, like Al Aquire, do know that I don't know what I don't know work whistling
I'm willing, and still learning, to learn a little now and then haha
Posted by: Greenwood

Re: Would pushrod length make this much difference? - 02/15/18 10:30 PM

I also don't know what I don't know. Kinda makes sense. I think. One of the things I set about getting a handle on this year was making sure my pushrods were the proper length. Trying to measure actual valve lift with the engine in the car was always a struggle. I was of the opinion I was giving up .030" of lift. After poring over a few treatises on pushrod length and rocker geometry (none of which made acertain light bulb go off like BradH's diagram), I have determined that I'm within .020" of optimum pushrod length. Can't really say that's worth buying new pushrods for my heap. Actual valve lift is within .005 of theoretical so...
Posted by: Cab_Burge

Re: Would pushrod length make this much difference? - 02/16/18 01:33 AM

Don't forget that actual valve lift at the retainers with the race valve springs will never be as much as the advertised valve lift or exactly the same as when using light checking valve springs work
I've seen as much as .040 loss due to pushrod and valve train deflection shock
Good thick, stiff, pushrods can make up for a lot of that loss up scope
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/16/18 11:11 AM

Originally Posted By Cab_Burge
...actual valve lift at the retainers with the race valve springs will never be as much as the advertised valve lift...

That's entirely dependent upon how the rocker arm is designed. AndyF's rocker arm articles touched on how some of the brands he checked were "over-ratioed" w/ checking springs, but came in at or above the advertised ratio when checked w/ the actual valve springs.

As far as deflection, I believe it can be in the pushrods, the rocker bodies, and/or the shafts, depending upon the components used. Not sure Joe Average's budget can eliminate it entirely, but I've seen some cases where it certainly went beyond my idea of an "acceptable" amount in terms of lift/ratio loss.
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/16/18 11:28 AM

Oh, I came across some pics of "stuff" that Mike at B3RE did w/ some Hughes rockers used on Trick Flow heads that included switching to cup-style adjusters (requires pushrod oiling). I can't say exactly what differences would result from such a mod, but it's pretty obvious the pushrod tip's relation to the rocker fulcrum would change big-time.
Posted by: Brewzer67

Re: Would pushrod length make this much difference? - 02/16/18 10:15 PM

Originally Posted By BradH
Oh, I came across some pics of "stuff" that Mike at B3RE did w/ some Hughes rockers used on Trick Flow heads that included switching to cup-style adjusters (requires pushrod oiling). I can't say exactly what differences would result from such a mod, but it's pretty obvious the pushrod tip's relation to the rocker fulcrum would change big-time.

I'm curious where you found these pictures. These look like my heads and rockers. They came out great with Mike's kit and the change to cup adjusters. The sweep is small and centered and there is minimal lift loss. I am running dual taper 9/16" (.165 wall) oil thru pushrods from Trend and lose less than .008 lift on a .716 lift solid roller. With the change to the cup adjusters there is almost no change in pushrod angle from full closed to full open. Even though the pushrod side doesn't add too much in the way of harmonics issues, I can't help but think this minimal movement goes a long way to promoting valve train stability.
Posted by: BradH

Re: Would pushrod length make this much difference? - 02/17/18 10:18 AM

I think there were some pics posted on FABO that I stumbled across. I had a link somewhere, but not at the moment.