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Discussion Starter · #1 ·
I'm pushrod shopping and have a few basic questions about the intended duty and "work" preformed by them.

1) How does the weight of a pushrod effect the valvetrain ??

2) When is the "weight" of the pushrod "ok", because of the needed additional strength (compression)??

3) Is defelction a serious problem with quality pushrods ?? Manton, Trend, Smith Bros.

4) How is harmonics detected and would it be noticable in the car ?? AKA...not in the dyno room.


This is a hydro. roller cam and a weekend warrior...
I'm running LSL/HUC 620ish/630ish, for those not familiar with these lobes they are relatively soft ramp rates.
spring info ~ 157lbs @ 1.800" & 471lbs @ 1.125"

I'm looking at either a 5/16" x .116" or the 3/8" x .049" both being 4130.

Thanks....and FWIW I spin this motor to 6800ish...got to see where the manifold falls off.
 

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I would like to start off by introducing LGM Racing and Development to the bullet. There have been a few threads on here that mentioned our taking on of the Probe line of rocker arms so a few may have heard of us already. We look forward to helping out here when we can and providing the best product we can at a price that everyone can afford to get out and race with! We have this account set up to provide support, gather feedback, and help out wherever we can.

I can shed a little light on our views when we work on program development for customers. When you look at mass in the valve train it's all relevant. What side of the rocker it's on dictates how much energy the springs see throughout the cycle and leads one to choose the overall spring pressure and rate. With that said, you always want the least amount of mass you can get away with while having it hold the desired geometry. Is there a point where you have to have mass? Sure, every engine program is an engineering optimization, not a 100% solution in every area. As for deflection, it is something that is looked at heavily either on the spintron or through computer simulations. A lot of builders put serious time into this and guard their views closely (that’s part of the premium you pay for a good builder). That being said, with the spring package that your lifter is limited to any of quality pushrods should be adequate. I hope our .02 helps.

Justin
 

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Discussion Starter · #3 ·
Thanks JRhoads...

Has there been any compressive destructive testing in reguards to pushrod O/D's and I/D's ??

Example...it takes "X"lbs to deflect a 5/16" x .049" as compared to "X" lbs for 5/16" x .116". And so on and so forth....

I understand I may be simplifing this a little, but you have to start somewhere. Harmonics, metallurgy, RPM ect....I sure these all play a role but just looking for some solid feedback.

Thanks....
 

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For sure, engineers do this type of testing all the time. Each builder will go about this in one of many ways depending upon their background and equipment. If you know exactly what the pushrod is made out of, exactly what dimensions it is, and exactly what forces are at play you can do the math and get the answers you seek (or have a computer do it for you). Once the part begins to yield the math becomes considerably more complex and in the end, you tend to enter into the realm of the professional engineer (with hardware and software equally as expensive as hiring one of them). The people that work on designing airframes for military aircraft do some very impressive things with computers to the extent that much of the destructive testing is a thing of the past (validation is the main reason that they do them now).

Many shops are substituting the spintron apparatus for the computer hardware/software run by the engineers. This allows them to perform trial and error runs with various configurations while doing an ok job of simulating actual conditions. It also takes less time to run through the scenarios but you also have to have all the components to run (so it tends to be a double edged sword). There isn't an easy answer to your question regarding your application; simulations and calculations are only as good as the data provided. If you can give me some specifics I can get you an 80% solution without too much trouble if you would like. Hope this helps.

Justin
 

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Discussion Starter · #6 · (Edited)
No offense taken....

But IMHO a dual purpose vehicle is a tougher build. IMHO a trailer queen is a lot easier...very little compromise in a trailer queen (aka..max effort on all accounts). One operating range, from idle to wot then on the trailer.

Meaning in a "street" application the components see a lot more variables. And this little "street" 346 will be in the neighborhood of 2.3hp per cube when under "power". Three hour drive to the track "with the a/c on", stop and go traffic, click off some 9.60's through a 6 speed then turn around drive three hours home. And what ever fun happens on the way to the track...if you know what I mean.

And on top of that..I've spent alot of time reducing weight and stabilizing the valve train so....it sounds like your suggesting just throw some shelf pushrods in it and run it. Which may be the answer but...like you and everyone on here. This build is just knowledge for the next engine for the car.

Thanks....and by the way..what was your suggestion towards the pushrods ??
 

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Discussion Starter · #8 ·
Thank you.....I was leaning towards the 3/8 but didn't know the downside of running a pushrod that size.

Again thanks..
 

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Go with the biggest Dia. You can fit in the cyl head. A good 1 piece .080" wall 3/8" Dia. will be just fine. For what your building you want overkill in most areas so it's dependable.
x2 i have run both manton and smith bro's on my roller combo 250 on the seat both 3/8 .080 and never a problem spin to 8000 rpm
 

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I use Manton and have been very happy with them and the tech help I got when I ordered them.

I ended up with 11/32 .120 wall. 3 piece with .060 holes.

You want the biggest dia and thickest wall you can get. Weight is not a concern.

My springs are 150 -400 and 7500 rpm has not been a problem.

Tim
 

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Discussion Starter · #12 ·
Look up a little info on radius of gyration in supporting members. It will break down why a larger diameter is better based on the moment of inertia of the pushrod.

Thanks....and that is what I'm talking about.

The "why" of the parts, not just the "because".

Again thanks...
 

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This is a hydro. roller cam and a weekend warrior...
I'm running LSL/HUC 620ish/630ish, for those not familiar with these lobes they are relatively soft ramp rates.
spring info ~ 157lbs @ 1.800" & 471lbs @ 1.125"

I'm looking at either a 5/16" x .116" or the 3/8" x .049" both being 4130.

Thanks....and FWIW I spin this motor to 6800ish...got to see where the manifold falls off.
Curious.... how long is the push rod for this application?

As stated use the biggest push rod that will fix. I don't think your hyd roller is going to have an issue on bit with 3/8" push rod, but you might want to call Manton and ask a few questions.

I found out some interesting stuff about my 9"+ push rods when I talked to them.

G
 

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Discussion Starter · #14 ·
Holy smoke...9"....

I'm in the 7.4" +or- .050"

And if it helps, this is a zero lash fixed fulcrom setup.

Thanks....
 

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Long Live The King
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10.36" Deck A-460 block with TFS A-460 heads.

A .120" thick wall vs .080" is only 8% stronger as where a 7/16" vs 3/8" is 87% stronger.


G
 

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Discussion Starter · #16 ·
Thanks G-Code....

You confirmed what I've read....O/D plays a larger role than the wall thickness.

Thanks....
 

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Discussion Starter · #18 ·
Billyman...two questions.

What down side is there to running a 3/8ths pushrod ??

What data do you have telling you the 5/16ths were adaquate ??

Thanks....
 

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Billyman...two questions.

What down side is there to running a 3/8ths pushrod ??

What data do you have telling you the 5/16ths were adaquate ??

Thanks....

Only downside to running 3/8ths pushrods is head interference and weight. If those two problems are insignificant or nonexistent then rock 'em, but rock 'em for the right reasons................like, because they're needed.

Pushrod diameter and thickness is a job duty thing. You aren't really at enough spring, cam, or rpm to constitute overkill of pushrods. Data? Well......I've got few friends with spintrons that I have acquired hard data over the past few years. It's neat to have the numbers and look at different variables of deflection depending but after all the "ooh" and "ah's" are done, it pretty much goes hand in hand with an ungodly amount of years of experience. Engines and power go way back. :D
 

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I would have to agree with Billyman on this one. I think a 5/16 .080 wall pushrod for your app is more than enough. I have smith brothers 5/16 .112 restrictor pushrods in my hyd roller engine and rev it to 7500 every time i start the damn thing up--never had one single problem with them.Do yourself a big big favor and call smith brothers--tell them what your doing and they will answer all your questions and recommend exactly what you need---just my opinion---p.s. ask for Pieere at smith brothers--great guy


I have 285 seat and over 550 over the nose of the cam
 
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