Silver Sleeper

iTrader: (7)

i figured id ask...didnt find anything in my search specific to the PAC 1218's

can i use the stock 4.8 pushrods? FYI, im also using a stock 99 LS1 cam

thanks

PREDATOR-Z

yes you can

Silver Sleeper

iTrader: (7)

thanks

batboy

iTrader: (6)

Stock pushrods flex like spaghetti at high rpm even with stock springs. It would be better to get chromemoly hardened pushrods if you are upgrading the springs.

redtan

iTrader: (5)

If a cam requires such springs, then you can't use the stock pushrods.

If a cam does not require new harder pushrods, then you don't need such springs.

So what's the point of getting those? Why not a nice set of LS6 yellows?

vettenuts

iTrader: (4)

The hardened pushrods will flex just as much if the OD is the same. The OD increase is where pushrods can be stiffened.

wildcamaro

iTrader: (15)

That's not true as the hardened pushrods are stiffer based on the material properties...you can gain stiffness by a bigger od OR using the same od with a better material...

Silver Sleeper

iTrader: (7)

i have already installed them in the heads...reason i went with the 1218's was becuase they were recommended for boost. the cam is a 99 LS1 cam.

vettenuts

iTrader: (4)

No, that's not true. They are both steel, both have the same elastic modulus and both have nearly the same OD (stock are metric). The stiffness has nothing to do with "better" material.

batboy

iTrader: (6)

Chromemoly steel has an excellent strength to weight ratio and is considerably stronger and harder than standard steel. To claim they flex the same is simply incorrect. I suggest you do a bit more research.

mikezohsix

the 1218 has about 30# more load with the valve closed and the same valve open specs as compared to the LS6 springs. That's not a stiff spring, and should be ok for any stockish application from what I understand.

also note that all GM LS6 springs are not yelllow, and some have no marking on them at all - ask me how I know....

vettenuts

iTrader: (4)

Flex (stiffness) and strength are two different things and note I stated stiffness. Stiffness is controlled by four primary things: material modulus (pretty much the same for all steels), OD, ID and length although with the LS1 pushrod ID has very little affect. OD is the controlling parameter for stiffness not the type of steel or the degree to which it has been worked. The amount of flex you can undertake prior to premanently bending will be different for the hardened pushrods, but not the amount of flex under load. If you flex enough to premanently bend the pushrod either the setup has a major flaw or there has been some catestrophic event such as tagging the piston with the valve.

I don't need to do more research as I do this type of thing for a living. Here is a post that may explain more and provide more details: Link

blueshifty

This is the only issue I have with your theory.

http://www.matweb.com/search/MaterialGroupSearch.aspx

Based on a quick search of the material properties on that site just a high carbon steel can vary from 2000 - 34100 ksi. (1 KSI = 1,000 PSI) In material selection the elasticity is many times what dictates alloy/ material. You are right that most commonly used pushrod materials have similar characteristics and that the O.D. is the single most important factor, however, I disagree with the notion that all steels are pretty much the same.

wildcamaro

iTrader: (15)

I see what you are saying vettenuts but like bayboy said even though most steels have generally the same modulus the hardened pushrods are still an upgrade over stock pushrods. I'm not exactly sure of the exact id and od of one versus the other but I would think the hardened ones are made to reduce flex through better manufacturing process.

vettenuts

iTrader: (4)

Note that I did not state the strength is the same, but for two steels of different strengths that are not loaded to the point where they permanently deform the stiffness is identical.

Your referenice is to the material strength, which for all steels will have a large range of values depending on alloy and working (annealed, cold worked, etc). However, for all steels the modulus is 28.5e6 (or a value close to that) which denotes the stiffness. For a pushrod, the stiffness between two pushrods may be identical however the amount of load they can take prior to permanently bending will different and based upon the strength (or yield) value.

My point is that there is little stiffness gained using hardened pushrods over stock other than the stock pushrods are metric (and very slightly smaller OD). The real gain in stiffness is when the OD is increased.

vettenuts

iTrader: (4)

The flex of a hardened pushrod will be the same as the non-hardened pushrod. The only difference is the amount of flex they can sustain prior to permanently bending. The issue is that if they flex that much you have bigger issues with the setup and are likely lofting lifters and such.

blueshifty

I guess I am having a hard time with the terms you are using. I assume that you're using a FEA software of some type and that you are using these values to simulate differences? I also assume you're constraining both ends of the modeled pushrod? Overall, I agree with your philosophy so I don't want to detract from the CORRECT point you are making and that is that OD IS THE MOST IMPORTANT FACTOR IN PUSHROD RIGIDITY. There are a number of ways a pushrod can fail, harmonics being the more difficult to calculate. Stiffness relates to the structure itself and young's modulus (or elastic modulus) is just one factor in the calculation. There are about about a kazillion alloys of steel (with a vast array of carbon content) and they behave much differently.

vettenuts

iTrader: (4)

The alloys will not affect the frequency at all (assuming the modulus doesn't change), unless you start to look at failure. If the elastic modulus is the same and the dimensions are the same, the stiffness/frequency are the same. There are no structural failure criteria used to establish the stiffness or elastic frequency.

In the analysis done, ends were free-free not constrained.

blueshifty

Again, I think you're oversimplifying. Extrusion/ manufacturing method, porosity, material properties, etc all play a part in the "quality" of pushrod. The modulus is just one small factor in the equation.

I am not sure what program you're using for analysis, but I would've probably modeled the lifter and roller rocker as well. That way you can apply the load on the pushrod between a fixed lifter and the spring. (The roller rocker would be fixed through the bearing location.)

Kind of off topic, but modeling software only goes so far. At some point the anecdotal information engineers like to ignore becomes equally valuable. Tolerances can be too tight. Valve lash can give better performance. Stock pushrods are more likely to deflect with steep cam rates. We can mathematically prove whatever we want, but I think most of us in these forums prefer to do it on the pavement.

vettenuts

iTrader: (4)

OK, whatever. Not going to argue but the things you mention are in the noise. In this case, the material parameter is just a constant. Run a closed form solution and show me where I am wrong. The lifter and rocker play no role in the bending stiffness of the pushrod. They play a role in the overall system and are controlled by different parameters. The discussion here is the pushrod itself and there are only four variables that apply,two of which are constant and one that plays a minor role. Run the numbers for yourself and you will come to the same conclusion.