Don Terrill’s Speed-Talk

We had a .135 wall to start. But when I changed heads to short. I said I wanted same so give the length required but that thickness. They said didn’t have tube that size but .083, no .135 but thicker. Asked my spring pressure etc said the .083 more than adequate. Oh my aching head. Lol

Steve be ready to throw about $350.00 down for a set. Just went through this and went with Smith Brothers. 3/8 .135 wall any length you need.

Thanks guys. I just ordered.

You gotta watch while checking lift with checking springs. Some rockers have engineered deflection in them and you can get a lot more lift with a checking spring than what you think you should have. With actual spring pressure, it will come back to normal.

I normally see about .020" loss with actual springs and the geometry on point.

I always opt for the biggest/thickest pushrod I can get.

Also, the difference in valve lash can be attributed to how hot the engine got. If you keep the water/oil cooler, the block won't expand as much. I normally see .014" difference from cold to hot on pretty much any aluminum block engine that I see, but that's at normal street water/oil temps. If you keep them cooler, they don't grow as much.

On the issue on the pushrod thickness and diameter has anyone ever seen any report or dyno results that a .135 wall pushrod over .080 wall pushrod will net an increase in hp/torque are even gains in rpm are does it just help stabilize the drive train.Just asking because I have not seen any real world results.Thanks

Realistically this engine made more power than it did with .135 wall. Lol. So now whats the correct answer. After all the tec at pushrod shop recommended these pushrods over .135 wall. He told me .135 was overkill for my pressure. I’m asking cause I really don’t know the answer. Must be someone on here who builds pushrods for a living.

With a given OD and wall thickness , the longer the pushrod , the more it will flex. That is simple physics. So there is no "one" answer on wall and diameter. Compound ( canted) valve angles can have more change than an "inline" . Add obscene RPM and that changes the requirement. Nascar engines typically use 1/2 major diameter pushrods to avoid valve train issues.
.020 is the amount of change I go with in a pushrod engine.

Been stated/proven/published many times....There is no disadvantage to running the biggest/thickest wall pushrod you can fit. Go diameter first, then wall thickness. The pushrod is on the slow part of the valve train and it's weight has very little effect on the valve train itself..Unless it's too small in diameter or too thin of wall thickness. Then it can flex excessively and behave more like a spring....

Coloradoracer wrote: ↑Thu May 21, 2020 12:22 pm The pushrod is on the slow part of the valve train and it's weight has very little effect ....

True statement ... and that means it has SOME effect.
So, if going bigger or thicker adds no more stability to the valve train then one smaller, it IS to large.

NO disadvantage is not a true statement as it sometimes will be; weight is one but, there are others.
I have the decision to using a bigger pushrod or making the port better ... more power will determine that advantage swaying to one or the other as long as the stability of the pushrod is adaquate.

double post

Steve.k wrote: ↑Thu May 21, 2020 11:17 am Realistically this engine made more power than it did with .135 wall. Lol. So now whats the correct answer. After all the tec at pushrod shop recommended these pushrods over .135 wall. He told me .135 was overkill for my pressure. I’m asking cause I really don’t know the answer. Must be someone on here who builds pushrods for a living.

I wonder if he thinks nascar 1/2' pushrods are overkill for their pressures.............less than 100 on the seat....lol.

I have no idea. What gets my goat is you phone these guys for their expertise. Do they just build for whoever wants what or actually do the testing? From what most are saying the .083 are basically mild street car rods.

Steve.k wrote: ↑Thu May 21, 2020 8:21 pm I have no idea. What gets my goat is you phone these guys for their expertise. Do they just build for whoever wants what or actually do the testing? From what most are saying the .083 are basically mild street car rods.

5/16" diameter x .060" wall is more like a mild street car pushrod.

Probably over a billion, (with a "B"), of them out there.

Thanks walter.