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Pushrod Recommendation? One Step Above Stock for LS3

 
Old 03-07-2019, 03:32 PM
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Default Pushrod Recommendation? One Step Above Stock for LS3

What’s the consensus on pushrods? Doing a stock LS3 build, would assume stock pushrods are the ticket? Will be auto trans with 6k max shift points.

I would not mind going up one step for safety margin. Would that be just material change at stock diameter and wall? Up one size on OD, thinner wall, and material change?

I see lots of advice to slam in the largest pushrods possible, but doesn’t that play a part in the valve train weight and reciprocating mass equations? I would think a heavier pushrod is same as a heavier valve (stem). But maybe there is something I am not considering here. Why would some drill out their heads to go telephone pole sized pushrods and yet hollow stem valves?

Thanks for any advice. So far I’d guess to go 11/32 diameter, 4130 material, thin wall, stock length?


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Old 03-07-2019, 09:56 PM
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On a stock rebuild, with equivalent valve spring ratings, there’s no need to put in a stronger pushrod. It’s when valvespring ratings get higher, that’s when a stronger pushrod is necessary to eliminate flex and harmful harmonics in the pushrod, which hurts power.
Pushrod weight won’t effect what the valvespring sees, in such a way to negatively add weight on that side of the rocker (fulcrum). If you were building a 10k rpm setup, then there is consideration for weight, but it always reverts back to making the valvespring choice correctly, since it controls all valve function.
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Old 03-07-2019, 11:41 PM
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Biggest/stiffest pushrod you can fit in the head holes is generally the rule of thumb if you want to make the most power.
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Old 03-08-2019, 01:38 AM
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push rod weight is not that big of a deal on that side of the rocker, every thing on the other side, valve, retainer etc is very important
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Old 03-08-2019, 12:20 PM
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Why is weight not relevant on the push rod side of the rocker? The spring has to control the valve spring retainer, the valve, rocker arm, push rod and lifter.
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Old 03-08-2019, 01:55 PM
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Above was my thinking as well. The valve spring is what keeps the lifter on the cam lobe. The valve spring is what pushes everything back into place after a lift event.

I’m not trying to start a fight, but I am just trying to see the other side of “use the biggest pushrod you can”, yet a hollowed out valve stem.
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Old 03-08-2019, 02:05 PM
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Because of the ratio effect of the rocker. It makes the pushrod/lift/lobe side of the spring seem stiffer due to less leverage vs the valve side. The valve side is traveling much farther to and thus moving at a higher rate.
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Old 03-08-2019, 02:29 PM
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Nice post. That’s making great sense, a point I did not consider. So it has an effect, but not nearly of the same magnitude as being on the longer side of the fulcrum (valve side of the rocker arm).

I know there was RPM limitations with stock (heavy) hydraulic roller lifters when they first came out, they would not follow the lobe ramp down, and could also cause hydraulic lifter pump up if unloaded on the downstroke. I don’t see this mentioned anymore, so it must be less pervelant than it was in the 80’s and 90’s.

Thanks for the input. New thoughts to play with.
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Old 03-08-2019, 02:33 PM
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Physics hasn't changed since the 80's. Lighter is better.
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Old 03-08-2019, 06:07 PM
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Of course.

What is the most common thin wall 11/32” pushrod of upspec material?

Thanks.
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Old 03-08-2019, 06:42 PM
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Summit just posted about new 11/32 pushrods they have available.
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Old 03-08-2019, 06:54 PM
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I’ll check it, thanks. Heads are still off, so I guess I could consider 3/8” as well, but would want thin wall.

Thanks again all.
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Old 03-08-2019, 09:49 PM
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Stock Build (cam.springs & rockers) & 6000 RPM limit..... 11/32 are more than sufficient.
But a good upgrade and I would do it.
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Old 03-09-2019, 06:47 AM
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Originally Posted by L78steve View Post
Why is weight not relevant on the push rod side of the rocker? The spring has to control the valve spring retainer, the valve, rocker arm, push rod and lifter.
Your push rod is on the 1 side your ratio is 1.7 to 1 on the tip side of the rocker you are multiplying the force, go to enginebuilder.com read their thoughts. the added stiffness more then makes up for the weight
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Old 03-09-2019, 06:50 AM
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Originally Posted by FormulaBoat View Post
Of course.

What is the most common thin wall 11/32” pushrod of upspec material?

Thanks.
summit's 5/16 11/32 and 3'8's all have .105 wall I'm running Pac duals that came on my trick flow heads. I have guide plates so I'm going 5/16 .105 wall
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Old 03-09-2019, 10:50 AM
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I’ve decided with 11/32 x 0.080, 4130 material. Seems a good upgrade for stock and future small-medium aftermarket cam.

In conclusion, the weight does matter, but only at about half as much as mass on the valve side of the rocker.

This is was a good discussion. Thanks everybody.
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Old 03-09-2019, 10:53 AM
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Yea .....diameter is more important than wall thickness.
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Old 03-09-2019, 01:26 PM
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If I go up +2 on diameter to 3/8”, what if anything needs to be done for them to fit? Heads are still off so no big deal to hit them with a drill or mill if need be.

On the 3/8, would they need to be “dual tapered”, or even tapered at all to fit and work with stock lifters and rockers?

Apology my learning may be driving you crazy. We’re almost done, I promise.
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Old 03-09-2019, 08:32 PM
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Summit HDR pushrods are all thickwall. 5/16 .105, 11/32 .120, 3/8 .135. Run the biggest one that fits. 11/32 in this case. The weight is of no consequence compared to the good things it does when they aren't acting like pole-vaulting sticks on your rockers and springs. When they unleash their own spring, it adds way more action than the lobe designer ever intended and are the biggest factor in rocker and spring breakage. They are priced extremely reasonably for what we've put into them.
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