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.120 vs.080 wall 3/8 pushrods sbc

General engine tech -- Drag Racing to Circle Track

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blackford
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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by blackford » Thu Jun 25, 2020 8:18 pm

af2 wrote:
Thu Jun 25, 2020 7:11 pm
It has nothing to do with weight, That is why MadBill and I use .187 wall 3/8 pushrods.
Ha Ha very funny...that's a solid rod...oh no wait...it has a .001 diameter oil passage :)
65 Mustang FB, 331 custom built with 289 H beam rods and 383W piston, 282S cam, Ported DOOEs, T5z, 9" 3.89 gears. 430HP@6500

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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by 6.50camaro » Thu Jun 25, 2020 9:40 pm

af2 wrote:
Thu Jun 25, 2020 7:11 pm
It has nothing to do with weight, That is why MadBill and I use .187 wall 3/8 pushrods.
So you have a .001 hole for the oil to lube the top end :wink: Dan
Sorry ,I did not see blackfords post till after I posted this

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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by swampbuggy » Thu Jun 25, 2020 10:12 pm

Don't want or mean to make your stuff seem small Adam, but mine will be 9/16 x .156 on the intake side and 5/8 x .165 on the exhaust side, appx. 9 to 9.300 long. Mark H.

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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by panic » Thu Jun 25, 2020 11:36 pm

In much the same manner that pushrod stiffness (bending resistance) increases exponentially with larger diameter, the reverse is true of pushrod length: stiffness decays exponentially as length is increased.

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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by MadBill » Fri Jun 26, 2020 10:04 pm

af2 wrote:
Thu Jun 25, 2020 7:11 pm
It has nothing to do with weight, That is why MadBill and I use .187 wall 3/8 pushrods.
Ah, it seems Kevin Johnson has a challenger re mining the S-T depths! =D>
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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by af2 » Sat Jun 27, 2020 3:32 pm

MadBill wrote:
Fri Jun 26, 2020 10:04 pm
af2 wrote:
Thu Jun 25, 2020 7:11 pm
It has nothing to do with weight, That is why MadBill and I use .187 wall 3/8 pushrods.
Ah, it seems Kevin Johnson has a challenger re mining the S-T depths! =D>
And you don't have to pipe cleaners to reduce the oil...........So JK Adam

,135" 3/8 push rods is the ticket for what I am building.
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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by af2 » Sat Jun 27, 2020 3:34 pm

blackford wrote:
Thu Jun 25, 2020 8:18 pm
af2 wrote:
Thu Jun 25, 2020 7:11 pm
It has nothing to do with weight, That is why MadBill and I use .187 wall 3/8 pushrods.
Ha Ha very funny...that's a solid rod...oh no wait...it has a .001 diameter oil passage :)
Yep I had to add humor sorry..... :mrgreen:
GURU is only a name.
Adam

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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by af2 » Sat Jun 27, 2020 3:40 pm

The reason is that people seem to think the push rods are part of the weighing the valve train and they get sideways on the equation. If you want a pole vault use .060" if you want stout use the .135". I hear loft and such but! I want make sure the lift is what it is when measuring my PV without guessing loft. That's all.
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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by panic » Sat Jun 27, 2020 4:06 pm

What I don't understand (yes, it's a long list):
There are engines with otherwise high RPM capability (CFM, pistons, rods, rockers, oil) but tight pushrod clearance in the head and/or block. This limits pushrod diameter and introduces pushrod bending and lagging valve action (the valve opens later than the tappet wants, but not linear) with some lift lost. Even a large taper (.625" bottom, .375" top) may not be small enough to clear the head, with a water leak as the penalty for a bad guess.
But the problem is the mid-point (of the unsupported span, without the ends), in which even a small diametric change is priceless.
If a 10" tube (with OD as large as can clear the target head/block tightest spot) is vetted for bending stiff by length (with OD & wall constant @ .375" & .100"), a change to 9" length increases stiffness by 37%, This may be had by using a taller tappet, lowest rocker fulcrum position, etc.
How about shortening it to 2 × 5"? Off the scale: each half is 700% greater.
Now slip the cut ends into a .100" wall sleeve 2" long, .575" OD (which probably has clearance to the inside cylinder wall, etc. as it's only .100" closer) and braze them (silver solder? epoxy?). The sleeve stiffness is 475% greater than the original 10" tube.
If there's a clearance problem in the block, the two halves may be very different as to length (3" and 7", etc.) to put the sleeve where it fits best and still achieve superior results.
Only one special part must be made (the 10" pushrods are a shelf item), and two operations added.
Yes, there's a weight penalty.

Now the questions: where is my error? It can't be that easy, or it would have been done.

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Re: .120 vs.080 wall 3/8 pushrods sbc

Post by blackford » Tue Jun 30, 2020 5:22 pm

I agree that a thicker pushrod provides some insurance with little down side. I just wanted to kick this can down the road a bit more though.

Those Spintron vidoes show the pushrod flexing, but they are not bending permanently. All steels generally have the same resistance to bending elastically (where the force is such that the deflection or deformation is not permanent and the material returns to its original shape when the force is removed). No matter the thickness of the walls, there is some deflection, and the thicker the wall the less the deflection. Even if a 10" pushrod were to bow .100 in the middle (that's a lot, but this is just an example), the overall length of the pushrod only changed by .002 which is virtually nothing. A thinner wall smaller diameter pushrod is going to bend permanently before a thicker wall larger diameter pushrod. Both will deflect, but just not the same amount.

I'm not really trying to say anything one way or another or trying to "push" an agenda, just adding to the discussion.
65 Mustang FB, 331 custom built with 289 H beam rods and 383W piston, 282S cam, Ported DOOEs, T5z, 9" 3.89 gears. 430HP@6500

2013 Corvette 427 Convertible daily driver

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