valve train questions

after suffering a roller lifter failure I have been investigating trying to find the root cause. My first question is does a thicker push rod wall thickness necessarly mean less deflection and ensure better valve train control. Is there such a thing as to thick? I know the Predator heads use alot more spring pressure than conventional heads such as Stage 6 and Trick Flow. Is .080 thick enough with say 250 lbs seat pressure and 600 open or should it be thicker. Thanks Birdtracker

Diameter is more important to stiffness than wall thickness.

Assuming all are made of the same material and length, a .060” wall thickness 7/16” pushrod is stiffer than an .080” wall thickness 3/8” pushrod...... which is stiffer than a .100” wall thickness 5/16” pushrod.

Lobe design, rocker ratio, and spring force are also key elements in determining what is required for a given combo.

A change in wall thickness is not very effective, in 3/8" OD going up from .080" to .100" only adds 7% to stiffness.
However, increased OD is way, way more important, even another 1/16" is very helpful. Bending resistance varies roughly as the 4th power of the tube OD.
Example: Keeping the .080" wall constant, 7/16" OD is 74% stiffer than 3/8" OD - if you can fit it into the PR relief holes. A single or double taper may give more room.
I would ask Smith, Trend, or Manton what they suggest based on your RPM, 250 & 600 sounds low but they certainly know better than I do.

I will have to check to see if I have the clearance for a pushrod that the outside diameter is bigger. I have checked my installed heights and the spring pressures. 250 with the valve closed and 630ish open.This is a solid roller. I was going to say I thought that was a safe pressures for the Harland Sharpe rocker arms I have. Thanks for the info. Birdtracker

Up till a week ago, I've been running 3/8 .065 wall Smith Bros. push rods with my Isky .680-.660 soild roller cam w/210-540 ish lbs seat pressure initially and now 245-620 and never really paid attention to it then but started hearing horror stories so I called SB and told them what they sold me 15+ years ago and he was shocked someone even recommended those. I got .120 wall based on several recommendations stating the cam can whip around especially at higher rpm's and create issues and even valve float. Plus on the cam side it's apparently less important weight wise like it is after the fulcrum to the tips of the rockers and I can't honestly say I feel a difference cos with the t-ram this puppy goes past 7000r's quicker than ever.....Track time soon a a 5.99 or better pass soon hopefully to follow.....

I think mine was doing that. I call it porpoising. It beats the rollers out of the lifter and cracks the body of the lifter down by the axle. Then the really bad things happen. Birdtracker

Guess I've been very lucky cos so far no damage that I can see.......

On your and Dominics deals I would and do use Manton series 3 3/8 by .120 wall, good up to 700+ lbs. open and 7000 RPM.
Next step up would Manton series 5 with the same measurements Good up to 1000 Lbs. open and 8500 RPM +
I had Smith Bros make me a custom set of 3/8 that where suppose to be .120 wall, one failed, broke in half, on the dyno and took out the one beside it and also broke the top off of the Crower roller lifter and gouge the lobe of the cam when the broken part drop down onto the cam lobe after the lifter getting tossed out at 5600 RPM in the middle of a pull
The one that broke had a defect in the middle of the tube that was very visible after it broke, I took both of them back to Smith Bros and found out that they had made me a set of their 3/8x.083 wall, not the 3/8x .120 wall I had ordered and paid for They made me two new ones like I had and didn't charge me for them, they didn't offer to pay for the lifter or for fixing the camshaft
I order a set of 3/8 x.120 wall series 3 from Manton and did back to back dyno pulls, the Mantons pushrods where worth 8 HP gain and increase, raised the peak RPM HP by 300 RPM with no other changes
No more Smith Bros pushrods for me since then , back in 2008 or so. Much better parts at a better price
Manton on line or call at 951-245-6565

As Dwayne said bigger is better just not always practical. I would rather see an .080" 7/16" than a .120" wall 3/8" but sometimes it just is not practical. As Dom pointed out the pushrod weight is not relevant when considering valvetrain weight. Most people would be shocked how much is lost to deflection, not just with the pushods either

Agreed. If I had the foresight to clearance my hemi block more I would have ran 7/16. As it is I could only fit single taper 3/8 to 7/16 (.165)

Intake valve lift with checker spring was .658

With 600lbs open it was .631

My springs are set up at 250-260 seated and 600 ish open With pushrods that are 9.750 effective length. The guy at Manton assumed I was gonna use 3/8 pushrod and said the stage 5 .120" wall but I said a 7/16 will fit my exhaust and and we went with stage 3 ..120 wall straight 7/16 on my exhaust but on the intake there wasn't much room for that on indy ez heads with harland rockers and B3 correction kit. I made room for a custom taper pushrod form manton thats a stage 3 7/16 to just a few thousandths smaller than 3/8 at the top under the cup with a .168" wall thickness after a lot of clearancing the pushrod areas. Manton told me the same thing everyone else here says. The bigger the diameter the better for stiffness, wall thickness doesn't do much. He said the same as far as ugrading to the stage 5 material as well after I asked. Most people say my pushrods are overkill though lol.

Pushrods bend in the center, tapered with reduced diameter ends don't affect stiffness - just lightens your wallet.

Extra pushrod weight does matter, but much less than on the valve side, it varies inversely with the square of the rocker arm ratio.
Example: the effect of pushrod weight with a 1.7:1 rocker is equivalent to 34.6% (1 ÷ 1.7^2) of valve weight.

Not that this answers the OP question but i thought it was ?interesting?...this is a bent checker pushrod which is 5/16 and about .085 wall. I was capturing the difference between the checker spring and the actual spring which is about 750lbs open to gauge system deflection. this is an 8.7 long pushrod using an SR head and offset lifter and homemade spacers to straighten the angle. Actually snapped about about 3/4? the way to peak lift so 600? lbs. I didn't believe it so i swung it around to the exhaust side and wouldnt ya know if snapped that one too...lol I used Manton 7/16 straight with intergrated meter orifice for PR oil regulation....VERY HAPPY with MANTON service and price BTW!!!

thats really interesting. With winter here and the motor out of the car I want to test fit 7/16 pushrods in the motor and see if there is clearance on the Trick Flow heads. Birdtracker