5/16 or 3/8 pushrods on 241s
Thread Starter
Staging Lane
Joined: Apr 2014
Posts: 55
Likes: 0
5/16 or 3/8 pushrods on 241s Hey guys. I slipping in a sns stage 2 this weekend or the next.
I need to order my pushrods from BTR since I already have their dual spring kit but I am not use which is better. The 5/16 or 3/8. Any help would be appreciated. Thanks!
I need to order my pushrods from BTR since I already have their dual spring kit but I am not use which is better. The 5/16 or 3/8. Any help would be appreciated. Thanks!
Launching!
Joined: Jan 2008
Posts: 225
Likes: 1
From: Fargo, ND
3/8 pushrods can only be used if you clearance the holes in the head. otherwise they will hit the head and not work.
A little rubbing is okay, but a lot is bad and they dont even fit without opening up the hole.
a thicker wall 5/16 pushrod will help with deflection if that is what you are after.
A little rubbing is okay, but a lot is bad and they dont even fit without opening up the hole.
a thicker wall 5/16 pushrod will help with deflection if that is what you are after.
Thread Starter
Staging Lane
Joined: Apr 2014
Posts: 55
Likes: 0
Ah okay. I understand now. Thanks for the help! 5/16 it is!
3/8 pushrods can only be used if you clearance the holes in the head. otherwise they will hit the head and not work.
A little rubbing is okay, but a lot is bad and they dont even fit without opening up the hole.
a thicker wall 5/16 pushrod will help with deflection if that is what you are after.
A little rubbing is okay, but a lot is bad and they dont even fit without opening up the hole.
a thicker wall 5/16 pushrod will help with deflection if that is what you are after.
It all depends on your valvetrain setup.
A heavy wall 5/16 should work fine with a light valve, stock rocker, titanium retainer, dual spring with under 400lb seat, and a mild lobe.
Aftermarket rockers, heavy valves, Increased spring pressures, and aggressive lobes will require a 11/32 or Trend dual taper to keep deflection at bay which causes lofting... (the lifter comes off the cam lobe).
A heavy wall 5/16 should work fine with a light valve, stock rocker, titanium retainer, dual spring with under 400lb seat, and a mild lobe.
Aftermarket rockers, heavy valves, Increased spring pressures, and aggressive lobes will require a 11/32 or Trend dual taper to keep deflection at bay which causes lofting... (the lifter comes off the cam lobe).
Tick has the dual tapers from Trend for $250 shipped. Martin posted this in a recent thread and they plan to stock the common sizes or you can order custom length. I have Trend dual tapers and they make a nice pushrod.
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Diameter is the key, not wall thickness .And yeah 3/8 can be run but they need to be double tapered
I got 243 and im running Manton 5 series(bestyou can get) 3/8 double taper pushrods and they clear my stock opening in my head without rubbing.I order only 2 of them in the beginning to test fit them.Sprayed them with machinist blue ink, install them and spin the engine a lot.No rubbing so i ordered the other 14.
If you dont wanna do the fit test, You should go with some 11/32(59% stiffer than 5/16) from either Manton or Trend.Do yourself a favor and forget the 5/16.
Go read this thread.Very instructive :
http://www.corvetteforum.com/forums/...post1572507024
I got 243 and im running Manton 5 series(bestyou can get) 3/8 double taper pushrods and they clear my stock opening in my head without rubbing.I order only 2 of them in the beginning to test fit them.Sprayed them with machinist blue ink, install them and spin the engine a lot.No rubbing so i ordered the other 14.
If you dont wanna do the fit test, You should go with some 11/32(59% stiffer than 5/16) from either Manton or Trend.Do yourself a favor and forget the 5/16.
Go read this thread.Very instructive :
http://www.corvetteforum.com/forums/...post1572507024
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I would just go with the 11/32" pushrods from Manton. If I remember correctly they were only $160 or so for the set and it costs you nothing extra for custom lengths since the build the pushrods per every order.
Diameter is the key, not wall thickness .And yeah 3/8 can be run but they need to be double tapered
I got 243 and im running Manton 5 series(bestyou can get) 3/8 double taper pushrods and they clear my stock opening in my head without rubbing.I order only 2 of them in the beginning to test fit them.Sprayed them with machinist blue ink, install them and spin the engine a lot.No rubbing so i ordered the other 14.
If you dont wanna do the fit test, You should go with some 11/32(59% stiffer than 5/16) from either Manton or Trend.Do yourself a favor and forget the 5/16.
Go read this thread.Very instructive :
http://www.corvetteforum.com/forums/...post1572507024
I got 243 and im running Manton 5 series(bestyou can get) 3/8 double taper pushrods and they clear my stock opening in my head without rubbing.I order only 2 of them in the beginning to test fit them.Sprayed them with machinist blue ink, install them and spin the engine a lot.No rubbing so i ordered the other 14.
If you dont wanna do the fit test, You should go with some 11/32(59% stiffer than 5/16) from either Manton or Trend.Do yourself a favor and forget the 5/16.
Go read this thread.Very instructive :
http://www.corvetteforum.com/forums/...post1572507024
This is an excellent reply. Just to clarify for those reading in the archives...
What is meant by ("Diameter is key, not wall thickness") is that the outside diameter has the greatest effect related to pushrod deflection w/ wall thickness playing a significantly lesser role.
For example, a 5/16" .105" walled pushrod is better than a 5/16" .080" walled pushrod. It's just not nearly as beneficial as a larger OD 11/32" .080" wall pushrod would be.
Wow, $250 for dual taper 3/8" vs $108 for 3/8" straight. Quite the difference. For less than the $140 difference, we could pull the head and make the straight fit, assuming no Cometics.
In the link that always faster posted, vettenuts said, "As for the harmonics, the stiffness of any of these pushrods pushes the first harmonic well above the engine RPM. However, they will still flex to some degree."
I had heard before that a tapered pushrod dampens harmonics. Resonant vibration is controlled because stiffness is constantly changing along the length of the taper. Like spring surge is dampened by a beehive spring because of the change in diameter. I thought resonance was controlled by softer materials like oil, the rubber or fluid in a harmonic damper or (though I hate them) a belt driven camshaft.
I have great respect for vettenuts but I don't understand his statement.
In the link that always faster posted, vettenuts said, "As for the harmonics, the stiffness of any of these pushrods pushes the first harmonic well above the engine RPM. However, they will still flex to some degree."
I had heard before that a tapered pushrod dampens harmonics. Resonant vibration is controlled because stiffness is constantly changing along the length of the taper. Like spring surge is dampened by a beehive spring because of the change in diameter. I thought resonance was controlled by softer materials like oil, the rubber or fluid in a harmonic damper or (though I hate them) a belt driven camshaft.
I have great respect for vettenuts but I don't understand his statement.
Wow, $250 for dual taper 3/8" vs $108 for 3/8" straight. Quite the difference. For less than the $140 difference, we could pull the head and make the straight fit, assuming no Cometics.
In the link that always faster posted, vettenuts said, "As for the harmonics, the stiffness of any of these pushrods pushes the first harmonic well above the engine RPM. However, they will still flex to some degree."
I had heard before that a tapered pushrod dampens harmonics. Resonant vibration is controlled because stiffness is constantly changing along the length of the taper. Like spring surge is dampened by a beehive spring because of the change in diameter. I thought resonance was controlled by softer materials like oil, the rubber or fluid in a harmonic damper or (though I hate them) a belt driven camshaft.
I have great respect for vettenuts but I don't understand his statement.
In the link that always faster posted, vettenuts said, "As for the harmonics, the stiffness of any of these pushrods pushes the first harmonic well above the engine RPM. However, they will still flex to some degree."
I had heard before that a tapered pushrod dampens harmonics. Resonant vibration is controlled because stiffness is constantly changing along the length of the taper. Like spring surge is dampened by a beehive spring because of the change in diameter. I thought resonance was controlled by softer materials like oil, the rubber or fluid in a harmonic damper or (though I hate them) a belt driven camshaft.
I have great respect for vettenuts but I don't understand his statement.
3/8" taper tip is not the same nor does it react the same as a tapered pushrod. It was my understanding that he had calculated the harmonics based on using a 3/8" pushrod w/ a tapered tip in order to clear the head openings. Additionally, the calculation results are related to the pushrod alone. It does not look @ the effect of any dampening from other devices coupled to the pushrod like hydraulics or springs.
Although the dual tapers are costly compared to your "run of the mill" push rod, the fact that you don't have to remove the heads from your engine for another 150 bucks, saves you a crap ton of labor and sweating in your garage.
For those that don't mind or already have their heads off the engine, it'd be a no brainer to clearance the passages for a 3/8" straight.
For those that don't mind or already have their heads off the engine, it'd be a no brainer to clearance the passages for a 3/8" straight.
3/8" taper tip is not the same nor does it react the same as a tapered pushrod. It was my understanding that he had calculated the harmonics based on using a 3/8" pushrod w/ a tapered tip in order to clear the head openings. Additionally, the calculation results are related to the pushrod alone.
Was that taken into account in the calculations? Does the double (relatively continuous) taper dampen harmonics as suggested in Squalor's post?
Yes, the taper dampens harmonics. A given cross section resonates at a certain frequency. Since the cross section changes so does the frequency required to resonate.
Given that, flex does come into play. The pushrod can still flex without reaching its first harmonic. It is possible to have a pushrod that has its first harmonic above the range that would be excited within the valve train, but the flex would cause issues with valve bounce. Therefore, the stiffest pushrod you can fit in without having valve float is the better solution. I wasn't sure the double taper would fit when I bought them but rolled the dice and checked them out once I had them in hand. They cleaned up my upper RPM quite a bit. I wasn't looking for a hp increase, rather better valve train stability to prevent issues with valve bounce which will wipe out cam lobes and lifters.