weight of chromoly pushrods vs regular hardened pushrods
Registered User
Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
For mass you could look up 4130/4140 and 1010 steel on one of the metallurgy sites to get some kind of an idea.
The thing that might be confusing is that some hardened pushrods are made from 4130 or 4140..... actually, some of the best in the industry are. They usually get a surface treatment too.
The thing of it is.... the pushrod itself is on the slow side of the rocker. What you want in a pushrod is ridgity, that's why the really fast cars usually run a tapered pushrod and the tallest lifter you can get.... that shortens the pushrod length and minimizes flex. It's all good.
If you want to lower mass, do it on the valve-side. For 6800rpm, you shouldn't have too much problem with the standard stuff.
-Mindgame
The thing that might be confusing is that some hardened pushrods are made from 4130 or 4140..... actually, some of the best in the industry are. They usually get a surface treatment too.
The thing of it is.... the pushrod itself is on the slow side of the rocker. What you want in a pushrod is ridgity, that's why the really fast cars usually run a tapered pushrod and the tallest lifter you can get.... that shortens the pushrod length and minimizes flex. It's all good.
If you want to lower mass, do it on the valve-side. For 6800rpm, you shouldn't have too much problem with the standard stuff.
-Mindgame
Thread Starter
Banned
Joined: Aug 2001
Posts: 3,505
From: looking for a flow bench so Brook and I can race
Originally posted by Mindgame
For mass you could look up 4130/4140 and 1010 steel on one of the metallurgy sites to get some kind of an idea.
The thing that might be confusing is that some hardened pushrods are made from 4130 or 4140..... actually, some of the best in the industry are. They usually get a surface treatment too.
The thing of it is.... the pushrod itself is on the slow side of the rocker. What you want in a pushrod is ridgity, that's why the really fast cars usually run a tapered pushrod and the tallest lifter you can get.... that shortens the pushrod length and minimizes flex. It's all good.
If you want to lower mass, do it on the valve-side. For 6800rpm, you shouldn't have too much problem with the standard stuff.
-Mindgame
For mass you could look up 4130/4140 and 1010 steel on one of the metallurgy sites to get some kind of an idea.
The thing that might be confusing is that some hardened pushrods are made from 4130 or 4140..... actually, some of the best in the industry are. They usually get a surface treatment too.
The thing of it is.... the pushrod itself is on the slow side of the rocker. What you want in a pushrod is ridgity, that's why the really fast cars usually run a tapered pushrod and the tallest lifter you can get.... that shortens the pushrod length and minimizes flex. It's all good.
If you want to lower mass, do it on the valve-side. For 6800rpm, you shouldn't have too much problem with the standard stuff.
-Mindgame
Registered User
Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
Don't know "Halbert", I was referring to Doug Herbert Performance Parts..... you know, Doug the dragster guy.
I think their website is still under construction Trey. You can call them at 1-800-444-7373. Get a catalog while you're at it.
edit: Yep, still down http://www.herbertperformance.com/
-Mindgame
I think their website is still under construction Trey. You can call them at 1-800-444-7373. Get a catalog while you're at it.
edit: Yep, still down http://www.herbertperformance.com/
-Mindgame
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Steel pushrod weight depends almost entirely on diameter and wall thickness of the tubing. Virtually all steel has the same 489 lb/cubic foot density, so lowcarbon (1018) or Chrome-moly (4130 or 4140) pushrods with the same diameter and .080 wall thickness will weight the same for the same length and end configuration. Heat treatment doesn't change the weight. The reason for 4130 (a steel with chrome and molybdenum as the alloying elements and .30% carbon) is that 4130 is the standard for tubing. Bars or "billets" are usually (not always) 4140, which is similar except it has .40% carbon. Plate is either 4130 or 4140.
Using Comp Hi-Tech pushrods as an example, the 5/16 (.3125) diameter rods use .080 wall 4130 tubing. They are case, or surface hardened (carbon added to the surfce during the heat treating process) to Rc 60 (about the same hardness as a ball bearing) for wear resistance and strength. If they were this hard all the way through they would be brittle, like a pretzel.
I haven't sectioned one, but I would expect the case depth is maybe .010 deep. During the heat treating process the core (or area below the hard outer wear surface) will also harden to around Rc40, similar to a Grade 8 bolt, so it is very strong, tough and not brittle. They are also centerless ground on the outside diameter, both for size and straightness control and to make the surface very smooth, and with no imperfections which could become stress risers, or the site for a crack to start. The black oxide treatment ('gun bluing' ) is mainly for appearance.
A low carbon (1018 or probably 1015-1026, a tubing grade steel) pushrod can still be case hardened, but the core won't get anywhere near Rc40, so it's more like a Grade 3 or 5 bolt, but with the hard outer case. In Comp, these would be 'Magnum' pushrods. I don't think they are ground, either. The price probably reflects the lower cost steel and fewer manufacturing operations.
Comp also has 3/8 (.375) diameter .065 wall thickness Hi-Tech pushrods. Larger diameter tubes, even with thinner walls, are stronger and resist bending under compressive loads (which is what pushrods get) better than smaller diameter ones.
A 3/8 x .065 wall pushrod is about 8.3% heavier than a 5/16 x .080 wall pushrod. That's about 4.4 grams in a 7.00 long pushrod.
Don't forget that you need to look at the resonant frequencies of the entire valve train system. Every component (lifter, pushrod, rocker and valve) has mass and a spring rate. They all have different spring rates, with the pushrod perhaps the "softest", so there are many resonant points. The valve spring(s) have to control all of this so choosing the correct components isn't always easy. Fortunately companies like Comp, Crane, etc. study these component motions extensively, and can usually recommend parts which will work together in certain rpm ranges. Be honest about how high you'll rev; if you say 6500 max, and then run it to 7000, the components that did well at 6500 might be jumping all over he place by 7.
For 6800 I'd use at least 5/16 Hi-Tech pushrods.
My $.02
Using Comp Hi-Tech pushrods as an example, the 5/16 (.3125) diameter rods use .080 wall 4130 tubing. They are case, or surface hardened (carbon added to the surfce during the heat treating process) to Rc 60 (about the same hardness as a ball bearing) for wear resistance and strength. If they were this hard all the way through they would be brittle, like a pretzel.
I haven't sectioned one, but I would expect the case depth is maybe .010 deep. During the heat treating process the core (or area below the hard outer wear surface) will also harden to around Rc40, similar to a Grade 8 bolt, so it is very strong, tough and not brittle. They are also centerless ground on the outside diameter, both for size and straightness control and to make the surface very smooth, and with no imperfections which could become stress risers, or the site for a crack to start. The black oxide treatment ('gun bluing' ) is mainly for appearance.
A low carbon (1018 or probably 1015-1026, a tubing grade steel) pushrod can still be case hardened, but the core won't get anywhere near Rc40, so it's more like a Grade 3 or 5 bolt, but with the hard outer case. In Comp, these would be 'Magnum' pushrods. I don't think they are ground, either. The price probably reflects the lower cost steel and fewer manufacturing operations.
Comp also has 3/8 (.375) diameter .065 wall thickness Hi-Tech pushrods. Larger diameter tubes, even with thinner walls, are stronger and resist bending under compressive loads (which is what pushrods get) better than smaller diameter ones.
A 3/8 x .065 wall pushrod is about 8.3% heavier than a 5/16 x .080 wall pushrod. That's about 4.4 grams in a 7.00 long pushrod.
Don't forget that you need to look at the resonant frequencies of the entire valve train system. Every component (lifter, pushrod, rocker and valve) has mass and a spring rate. They all have different spring rates, with the pushrod perhaps the "softest", so there are many resonant points. The valve spring(s) have to control all of this so choosing the correct components isn't always easy. Fortunately companies like Comp, Crane, etc. study these component motions extensively, and can usually recommend parts which will work together in certain rpm ranges. Be honest about how high you'll rev; if you say 6500 max, and then run it to 7000, the components that did well at 6500 might be jumping all over he place by 7.
For 6800 I'd use at least 5/16 Hi-Tech pushrods.
My $.02
Last edited by OldSStroker; Mar 14, 2003 at 09:44 PM.
God bless...
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