SBC valve geometry.

[Lizardracing]

Working on some 23’ Brodix heads with Ferrea 2.100 valves .100 long. Currently set up at 1.900.
I’m having trouble getting the half lift method of pushrod configuring to work out.
Does anyone besides Crower make a back set or rockers that reduce the trunnion centerline to roller tip centerline for 23’ Chevy stuff?

[mt-engines]

if you have a SBF Rocker near, try it. if memory is correct SBC is 1.450 pivot and SBF is 1.500

or measure the pivot you have, it might be a SBF rocker

[Paul Kane]

Working on some 23’ Brodix heads with Ferrea 2.100 valves .100 long. Currently set up at 1.900.
I’m having trouble getting the half lift method of pushrod configuring to work out.
Does anyone besides Crower make a back set or rockers that reduce the trunnion centerline to roller tip centerline for 23’ Chevy stuff?

Are you concerned with roller location on the stem tip? If the roller wheel is squarely planted most anywhere atop the stem and not falling off the edge, then it is fine--where the roller wheel rests atop the valve stem has nothing to do with valve train geometry. If you are concerned about premature guide wear, that will not occur in the extreme fashion as it certainly would with an off-center shoe-tipped rocker arm. That's the primary purpose of the roller wheel in the first place (to aim the forces of the rocker tip straight down atop the valve stem as the rocker travels throughout its radial sweep).

if you have a SBF Rocker near, try it. if memory is correct SBC is 1.450 pivot and SBF is 1.500...

Assuming a traditional SBC valve train with standard length valves, the trunnion-to-roller axle distance on a properly designed SBF rocker arm is effectively 0.060” long when installed onto the 23-degree SBC head.

[Lizardracing]

Thanks Paul
Using the Miller Half lift theory, The same one Chris Struab advertises
My issue is I'm getting a .140 wide pattern unless I make the pushrods really really long. like 8.050 long and the wheel runs off the exhaust side of the valve tip. It's also long enough to run out of threads on the studs.
Getting into PR length 'd expect, like a 7.800-7.950, This throws up a red flag so I was exploring options.
I need to measure my rocker pivot lenght and see if they are in the 1.450 range however I have had no issues on several other engines these have been used on from Gm casting to Dart Iron Eagles and now Brodix Track ones.

[novafornow]

Just my experience; 8.050 does not seem too long for a +.100 valve. BUT, running off of the valve...no bueno. Seems that you don't have the right rocker.

[Ericnova]

Straub sells a custom Harland Sharp's rocker with the reduced pivot length. Price isn't bad from what I've seen.

[Paul Kane]

Thanks Paul
Using the Miller Half lift theory, The same one Chris Struab advertises

I apologize in advance for going on a tangent : just for clarification, the Straub video (to which I think you allude) does not show the Mid-Lift standard; that video demonstrates what is known as the Minimal Sweep theory which focuses on the roller wheel side of the rocker arm to determine pushrod length but without regard to what is happening on the pushrod side of the rocker arm.

Conversely, the Mid-Lift standard addresses both ends of the rocker arm, with the forethought that the pushrod side is reading cam information and telling the roller-tipped side what to do. So in Mid-Lift, both ends of the rocker arm must be evaluated under the perception that the pushrod side is the primary side of the rocker arm while the roller tipped side is the secondary side (academically speaking, as ultimately both ends are considered equally important in the final setup). In short, we are sending critical information from the cam lobe to the valve stem, and so with Mid-Lift we start at the cam lobe and work our way toward the valve stem point-to-point, tuning the system for optimum efficiency along the way, from one end to the other (from lobe to valve). Most people don't understand Mid-Lift as entirely as they think, much due to the Minimal Sweep theory often receiving the "Mid-Lift" misnomer on so many forum discussions.

Of course if one wishes to attain ideal installed geometry utilizing the Mid-Lift standard, he must first have a rocker arm body with the correct design geometry for the specific engine in question. Since virtually no rocker arm manufacturers are following any agreed upon standard and instead make their own independent designs, the majority of people building an engine default to random alternative theories such as the Minimal Sweep theory shown in Straub’s video. Personally I'm a disciple of Mr. Miller and prefer a Mid-Lift rocker to the point that if there isn't one for a given application I will try numerous brands & part numbers on an engine until I get the closest with Mid-Lift that I can.
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My issue is I'm getting a .140 wide pattern unless I make the pushrods really really long. like 8.050 long and the wheel runs off the exhaust side of the valve tip. It's also long enough to run out of threads on the studs.
Getting into PR length 'd expect, like a 7.800-7.950, This throws up a red flag so I was exploring options.
I need to measure my rocker pivot lenght and see if they are in the 1.450 range however I have had no issues on several other engines these have been used on from Gm casting to Dart Iron Eagles and now Brodix Track ones.

Obviously if the roller wheel finds its way off the stem tip then the trunnion-to-roller axle dimension is too great in the current application. I agree you should opt for another rocker arm...and which is wise because usually when people are uncomfortable with the location of the roller wheel, they make the mistake of adjusting the pushrod length in order to swing the wheel toward center of the stem--in other words, they reposition the wheel at the expense of optimized valve train geometry.

As far as other alternatives, you might look at the Crower aluminum--they are so close to Mid-Lift that MEI once sent Crower a Cease and Desist letter. Or, if you want an SBF rocker arm that might work with your SBC head, try calling Jim Miller. In fact he might even still have some SBC rocker bodies.

PS: feel free to PM me your number if you want to brainstorm on your current setup.

[FloydODB]

i have a set of the crowers. i think they're 1.5/1.6. 1 season in a 434 23deg modified engine. (7 nights) class got to expensive, sold the heads. $600

73677-8 & 73674-8 prbly some pushrods to. ill check the length.

i'll have to double check those #'s. i see 90 and 50 backset in the catalog.

[FloydODB]

I got .050's. 73690-73692

[panic]

With the best geometry the scrub path will be minimal (use trigonometry to calculate this).
When the valve is closed the roller will contact the stem at a point close to its near edge. As the valve opens, the contact point will travel away from this point (and away from the rocker shaft or stud) toward the center of the stem tip, and reach its farthest point of travel at 50% lift, ideally toward the far edge of the stem tip. From this point on to full lift, the contact point will reverse direction and “walk back” toward the rocker shaft, and finish where it began.
As the valve closes, the path is reversed, and again terminates at the same point close to its near edge.

[Lizardracing]

I'm getting there with it now. My rocker pivot length is 1.423 so a bit shorter than usual.
Using a 8.000 long Push Rod the pattern is about .080 wide, starting on the intake side and migrating to the the exhaust side across the center. I have two more push rods coming to try. 8.050 and 8.100.
This is not max effort power/lift etc deal. I'm am aiming for max reliability so I'm hoping to get in the .040-.060 wide and centered but I'll take it anywhere in the center 2/3rd of the stem.

[novafornow]

my gen 1 sbc pushrods are 8.200". Do not worry about the final number, if its right, its right.

[skinny z]

I've a .100" longer valve in my RHS heads and the only way I could achieve a minimal sweep (< .040") and not run too close the exhaust side of valve stem was to use the Crower .050" backset trunnion rockers.
Pushrod length didn't exceed 8.0, more in the 7.5" ( I'd have to check my records) but we can't compare my combination of parts to yours. All the various bits can stack up.
FWIW: There's a solid argument regarding the downside of getting too close to the valve tip edge. Namely, it's of secondary consideration when compared to the sweep. I believe this is further supported when a roller tip is used. Mechanically speaking there's certainly an element of the sideways force placed against the valve guide but it seems it's not as much as some make it out to be. It's there one way or another regardless.

[Walter R. Malik]

A lot of rocker arms are just not manufactured to be run with "mid lift" or "Minimal sweep" geometry,
Many, ROLLER rockers in the marketplace are intended to use the "low pivot" geometry which Jesel recommends.

Trying to use a rocker arm with another type geometry than for which it was manufactured, can become a nightmare.

[skinny z]

That's a new one on me.
Does this include the typical stud mounted rocker as in a traditional SBC?