Quick question on pushrod size.
well here is the relevant part then. that post was all about in general. in general use .075 from the top or bottom and that will get you close. close? oh ok so it only matters that you are close. well in general that is. specing pushrods for a camshaft without measuring and trusting them is a general bad idea. valve train geometry should always be checked. plus the matter at hand is also questioning the fact that predator said 2 diff things about 4 times in this thread alone.
but what do i know, my post count is small
but what do i know, my post count is small
That is one of my specs, dual lobed cam, I would use Comp Cam 5/16th, .080 wall thickness Hi Tech.
Why? Because they are quality chromemoly, hardened and with 3 attributes that are special to Comp:
1- They are light (yet tough)
2- The are designed to reduce unwanted cam harmonic frequencies.
3- They are recommended by Comp Cam and designed with those lobes in mind.
Why? Because they are quality chromemoly, hardened and with 3 attributes that are special to Comp:
1- They are light (yet tough)
2- The are designed to reduce unwanted cam harmonic frequencies.
3- They are recommended by Comp Cam and designed with those lobes in mind.
The .02lb weight increase is negligible, since we're on the slow side of the valvetrain (Hell, what's a lifter weigh?!)
We could even get silly and go to a 3/8" p-rod, gain .04lb over the 5/16, and be 60% more resistant to bending!
point 3- I really doubt comp designed a straight non-tapered pushrod in a rather standard 5/16" .080 wall with a specific lobe in mind.
But, back on topic, why not go bigger?
Last edited by Eskimo; Apr 17, 2009 at 02:56 PM.
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From: BFE
Why not go bigger, and increase the resistance to deflection? Since those lobes put extra pressure on the pushrods, I know I'd appreciate the extra 25% increase in bending resistance that even an 11/32" p-rod would give.
The .02lb weight increase is negligible, since we're on the slow side of the valvetrain (Hell, what's a lifter weigh?!)
We could even get silly and go to a 3/8" p-rod, gain .04lb over the 5/16, and be 60% more resistant to bending!
point 3- I really doubt comp designed a straight non-tapered pushrod in a rather standard 5/16" .080 wall with a specific lobe in mind.
But, back on topic, why not go bigger?
The .02lb weight increase is negligible, since we're on the slow side of the valvetrain (Hell, what's a lifter weigh?!)
We could even get silly and go to a 3/8" p-rod, gain .04lb over the 5/16, and be 60% more resistant to bending!
point 3- I really doubt comp designed a straight non-tapered pushrod in a rather standard 5/16" .080 wall with a specific lobe in mind.
But, back on topic, why not go bigger?
To keep the effective moving valvetrain mass as light as possible.
If you want such non deflective valvetrain, you are choosing the wrong type of cam. Then you should go solid.
If weight was so negligible as you say, why were Titanium retainers designed?
Why are light hollow valves designed?
The lighter the valvetrain, the more power is made at high rpm.
BTW, I have yet to see a .080 chromemoly hardened p-rod bend, unless it is from a mechanical over rev or a valve hitting the piston.
Also, stock lifters were not designed for heavy valves, heavy dual springs, heavy p-rods (not to mention all the added oil weight), which is one reason why I prefer .080>.100 range preload as well. Add to that sharp agressive lobes and high rpms, lifter failure is just a matter of time. How much time?
No one can say!
From here: (and I hope you know enough to respect what Terry Manton says when it comes to these things): http://www.mantonpushrods.com/Pushrod-Info.html
"Do not be over concerned about pushrod weight. The difference between a stock 5/16 diameter pushrod in a small block Chevrolet and a 7/16 to 3/8 tapered pushrod, represents a difference of approximately 2.5% of effective weight. This is because the pushrod is on the slow moving side of the valve train. The effective increase in weight between the two pushrods may be small but provides a huge increase in valve train stability. Remember the valve side of this valve train is the critical side where any weight savings will make marked improvements."
There's 2 types of bending... bending where it deflects but hasn't reached the Modulus of elasticity, and bending where it has. Have you watched a high-video of a pushrod engine even at idle? it's amazing how much smaler diameter p-rods deflect, and 5/16" is a stock diameter. material change helps, sure (though I'm not sure what type of metal an OEM p-rod is made of), but an increase in diameter helps far more.
Also, stock lifters were not designed for heavy valves, heavy dual springs, heavy p-rods (not to mention all the added oil weight), which is one reason why I prefer .080>.100 range preload as well. Add to that sharp agressive lobes and high rpms, lifter failure is just a matter of time. How much time?
No one can say!
No one can say!
Im sorry can you tell me what the weight of a stock L92 valve is? It is heavy, that is all we need to know. Do they make special L92 lifters that only the L92s have? Um no....
There's 2 types of bending... bending where it deflects but hasn't reached the Modulus of elasticity, and bending where it has. Have you watched a high-video of a pushrod engine even at idle? it's amazing how much smaler diameter p-rods deflect, and 5/16" is a stock diameter. material change helps, sure (though I'm not sure what type of metal an OEM p-rod is made of), but an increase in diameter helps far more.
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From: BFE
Because they're on the "fast" side of the valvetrain where it matters far more...
From here: (and I hope you know enough to respect what Terry Manton says when it comes to these things): http://www.mantonpushrods.com/Pushrod-Info.html
"Do not be over concerned about pushrod weight. The difference between a stock 5/16 diameter pushrod in a small block Chevrolet and a 7/16 to 3/8 tapered pushrod, represents a difference of approximately 2.5% of effective weight. This is because the pushrod is on the slow moving side of the valve train. The effective increase in weight between the two pushrods may be small but provides a huge increase in valve train stability. Remember the valve side of this valve train is the critical side where any weight savings will make marked improvements."
From here: (and I hope you know enough to respect what Terry Manton says when it comes to these things): http://www.mantonpushrods.com/Pushrod-Info.html
"Do not be over concerned about pushrod weight. The difference between a stock 5/16 diameter pushrod in a small block Chevrolet and a 7/16 to 3/8 tapered pushrod, represents a difference of approximately 2.5% of effective weight. This is because the pushrod is on the slow moving side of the valve train. The effective increase in weight between the two pushrods may be small but provides a huge increase in valve train stability. Remember the valve side of this valve train is the critical side where any weight savings will make marked improvements."
The biggest mistake lots of poeple make is to missmatch components.
There's 2 types of bending... bending where it deflects but hasn't reached the Modulus of elasticity, and bending where it has. Have you watched a high-video of a pushrod engine even at idle? it's amazing how much smaler diameter p-rods deflect, and 5/16" is a stock diameter. material change helps, sure (though I'm not sure what type of metal an OEM p-rod is made of), but an increase in diameter helps far more.
It is not the size that matters, it is what it can do at that size.
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From: BFE
106 grams for L92 OEM and 101 grams for LS1 OEM so hardly what I would call so heavy to warrant special lifters, they do not run LS1/LS6 lifters
Compare that to a stainless L92 aftermarket of 122 grams, now that is heavy.
A good substitute are LS9 valves (Hollow stem at 91 grams
) Last edited by PREDATOR-Z; Apr 17, 2009 at 06:23 PM.
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There's 2 types of bending... bending where it deflects but hasn't reached the Modulus of elasticity, and bending where it has. Have you watched a high-video of a pushrod engine even at idle? it's amazing how much smaler diameter p-rods deflect, and 5/16" is a stock diameter. material change helps, sure (though I'm not sure what type of metal an OEM p-rod is made of), but an increase in diameter helps far more.
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Just want to correct a couple of things here, I certainly don't want to get into the middle of this fray. All the pushrods being discussed have pretty much the same modulus of elasticity as they are all steel. Unless you hit material yield, which can be different for different steels, then the pushrods shouldn't bend. The bigger issue is the harmonics or natural frequencies (stiffness if you like), which will be a function of length and OD/ID to the fourth power. Thus a small increase in OD is worth much more in bending stiffness then changing the thickness (ID with the same OD).
Just want to correct a couple of things here, I certainly don't want to get into the middle of this fray. All the pushrods being discussed have pretty much the same modulus of elasticity as they are all steel. Unless you hit material yield, which can be different for different steels, then the pushrods shouldn't bend. The bigger issue is the harmonics or natural frequencies (stiffness if you like), which will be a function of length and OD/ID to the fourth power. Thus a small increase in OD is worth much more in bending stiffness then changing the thickness (ID with the same OD).
By the way, I would say this mis-matched pile of parts revs out pretty clean for a 224° based cam.. but what would we know, what with light pre-load, beehive springs, and heavy pushrods.. And this isn't a "happy" dyno...
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From: Texas and Qatar
Eskimo, can you post the SAE numbers and make sure smoothing is set to 5.
I always wanted to roll that out on someone to see what it's like. Eh, I feel the same as before.
On pushrods I'm in agreement on larger diameter. Someday I plan to engine dyno test some, but I'll have to make sure the baseline has valvetrain issues, shouldn't be too hard to setup though. I have dyno'd engines that had valvefloat symptoms, but had 5/16" pushrods and aftermarket rockers, going with slightly better pushrods (5/16" .120" wall) and stock rockers cleaned up the pull. I didn't have time to test the thicker pushrods with the yella terras though.
I always wanted to roll that out on someone to see what it's like. Eh, I feel the same as before.
On pushrods I'm in agreement on larger diameter. Someday I plan to engine dyno test some, but I'll have to make sure the baseline has valvetrain issues, shouldn't be too hard to setup though. I have dyno'd engines that had valvefloat symptoms, but had 5/16" pushrods and aftermarket rockers, going with slightly better pushrods (5/16" .120" wall) and stock rockers cleaned up the pull. I didn't have time to test the thicker pushrods with the yella terras though.
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You can get a .065" wall 3/8" pushrod from Terry Manton. Vettenuts said it quite well about the advantages from a larger diameter pushrod. The weight on the valve side of the rocker arm is a lot more critical than on the lifter side of the rocker arm.
As OldStroker has said in the past everything is a spring. The idea is keep the springing to a minimum. The videos of the valve train with the Spintron are amazing. I never knew how much things flexed including the valve stem itself. As for me I will be using the Manton .065" 3/8" pushrods in my build.
As OldStroker has said in the past everything is a spring. The idea is keep the springing to a minimum. The videos of the valve train with the Spintron are amazing. I never knew how much things flexed including the valve stem itself. As for me I will be using the Manton .065" 3/8" pushrods in my build.
Pred Z talks about the disadvantages of a heavy pushrod on the lifters, but what about heavy *** valve springs and way too high springs rates? That's what causes lifters to collapse. Hence why I've always thought that running a beehive spring was a better option than dual springs. That's why I went with PAC made 918s and titanium retainers, but did go with a 3/8" pushrod.
Pred Z talks about the disadvantages of a heavy pushrod on the lifters, but what about heavy *** valve springs and way too high springs rates? That's what causes lifters to collapse. Hence why I've always thought that running a beehive spring was a better option than dual springs. That's why I went with PAC made 918s and titanium retainers, but did go with a 3/8" pushrod.
give me some lobes for example.
I was not aware that heavy springs could be harmful to lifters.
A few years back I was concerned on lifters and started investigating who had had lifter problems and what their setups were. I did this through the search function and a few PM's to some of the guys. This was stock lifters, I went with Morels because the offshore boating guys beat them badly without problems and a boat engine is under much heavier loads than a car engine. Anyhow, what I found was that if you were over a certain load on the lifter guys were starting to have issues with the lifter. This load is valve spring open load times the rocker ratio, which is the feedback to the lifter. I can't seem to find the spreadsheet I did on this but there appeared to be a definite break point in the limited data I could find.
The other tidbit I will throw out there as well. A lot of guys have had ticking problems after a head swap where the lifters have been out of the car. When I worked on mine, it was like a surgeons room. Very clean. I was fortunate to have a laser powered articulating boroscope that I borrowed from work. Both times I had the lifters out, upon inspection I found specs of dirt in the oil gallery just prior to lifter installation that would easily make their way into the lifter oil port. Now I don't know if this is the cause of the lot of guys problems but I was pretty surprised to see this as I took great care not to get dirt in the motor while working.
Can't emphasize enough, you have to keep things absolutely clean when working on the lifters.
The other tidbit I will throw out there as well. A lot of guys have had ticking problems after a head swap where the lifters have been out of the car. When I worked on mine, it was like a surgeons room. Very clean. I was fortunate to have a laser powered articulating boroscope that I borrowed from work. Both times I had the lifters out, upon inspection I found specs of dirt in the oil gallery just prior to lifter installation that would easily make their way into the lifter oil port. Now I don't know if this is the cause of the lot of guys problems but I was pretty surprised to see this as I took great care not to get dirt in the motor while working.
Can't emphasize enough, you have to keep things absolutely clean when working on the lifters.
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Let me expand on my reply. If I already had a motor with quality 5/16" pushrods I would leave them in there as long as there does not appear to be any problems. My decision to go with the Terry Manton 3/8" pushrods is I'm building a new motor that may turn to 7000rpm depending on the dyno chart for the best shift point. I have to buy pushrods anyways and I consider the 3/8" pushrod cheap insurance for valve train stability.
One more thing don't forget that GM went with the 3/8" pushrod on the LS7 motor. Their testing must have showed them something and that there was an advantage to the 3/8" pushrod.
One more thing don't forget that GM went with the 3/8" pushrod on the LS7 motor. Their testing must have showed them something and that there was an advantage to the 3/8" pushrod.
Throwing a few pennies into the pot...
We just did a H/C swap using LS7 lifters. VRX3, Patriot 59cc milled heads, MLS gasket. I somehow screwed up the measurement on the pre-load the first time we did it and used 7.400 pushrods. NOISY! Could not live with the sewing machine ticking. Pulled the covers and re-measured using a slightly different method and found we had 115 mil (0.115 inch) of pre-load. Seemed we should go to a 7.350. Asked questions, got no help on Tech, but a local shop recomended we go down to a 7.300 pushrod. I was skeptical of it, but the difference is incredible. Night and day difference in the noise. We now have 15 mils of pre-load, and the engine is almost as quiet as stock. I am not educated enough in the valve-train dynamics to understand why this would be a problem. The empirical evidence says it works good. Also, those clearances are measured in a garage at 50* F. Once warmed, the Pushrods, Lifters, Valves, everything will want to expand, not contract. I don't see how this could be a problem. Just wanted to throw that out there...
Oh, and I think I screwed up in locating the zero lash the first time.
We just did a H/C swap using LS7 lifters. VRX3, Patriot 59cc milled heads, MLS gasket. I somehow screwed up the measurement on the pre-load the first time we did it and used 7.400 pushrods. NOISY! Could not live with the sewing machine ticking. Pulled the covers and re-measured using a slightly different method and found we had 115 mil (0.115 inch) of pre-load. Seemed we should go to a 7.350. Asked questions, got no help on Tech, but a local shop recomended we go down to a 7.300 pushrod. I was skeptical of it, but the difference is incredible. Night and day difference in the noise. We now have 15 mils of pre-load, and the engine is almost as quiet as stock. I am not educated enough in the valve-train dynamics to understand why this would be a problem. The empirical evidence says it works good. Also, those clearances are measured in a garage at 50* F. Once warmed, the Pushrods, Lifters, Valves, everything will want to expand, not contract. I don't see how this could be a problem. Just wanted to throw that out there...
Oh, and I think I screwed up in locating the zero lash the first time.
