Has anyone out there tried a 3/8" pushrod to see if it fits? The Modified block is very tall and the pushrods are long and subject to flexing.
What worked for you?

R.

 

They would just be overkill unless your going to use a solid cam with lots of spring psi..

 

Does anyone have a real answer for this question?

R.

 

Of course a 3/8 pushrod will fit, IF you get the proper length. But again, a 3/8 pushrod is overkill for most engines.

 

Yes you can run 3/8" push rods. I run .650+" lift hydrualic cam and use them (3/8" x .135"). You can use a .105" wall thickness 5/16" pushrod to gain strength without adding undue weight. I don't see a problem with going to a 3/8" rod when you start using a rod longer than 9.5" plus the weight isn't as much of a problem when you are talking lifter side of the valvetrain. Racers running .800"+ lift cams are currently running 5/8" x .188" diameter rods. It really depends on what your intended cam lift, valve spring pressure, and engine rpm will be. That said, I have used 3/8" x .135" rods on 400s running .550" lift cams just because I don't like the small diameter, 9.5" stock rods on anything more than a wimpy stock cam rebuild.

 

Thank you for the factual reply. For those saying "overkill" don't knock it 'til you've tried it. The 400 pushrods are longer than a big block chevy and they routinely run 3/8" pushrods and for high perf use, 7/16" pushrods have been used for decades.
Especially with today's aggressive cam lobes, you can't get too big a pushrod. Case in point: A few years ago Subaru switched from pushrods to overhead cams. They found with exactly the same cam profile there was something like a 10% horsepower gain with the elimination of the pushrods. The guys at Comp Cams have been doing extensive Spintron work and found that pushrod stiffness is a major factor in valvetrain stability. So additional mass on the lifter side isn't harmful and most times the gains from the stiffer pushrod more than offset the losses from the increased mass.

For those inclined to learn more than they already know, study columnar loading which is a key component of the engineering course Strength of Materials. The pushrod is a column unrestrained on either end. As such it isn't very stable. Increasing the diameter increases the stiffness greatly. It is possible to increase the diameter while decreasing the wall thickness and come out ahead.

R.

 

You might have a point if you had a performance 400, but I suspect you don't. I ran a couple of different high lift cams with stock rockers over the years and the pushrods were never a problem.