Pushrod Length for more lift
Thread Starter
Instructor
Joined: Mar 2003
Posts: 239
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From: Toronto Ontario
Pushrod Length for more lift
Can I obtain .590 +/- lift with just a pushrod change instead of a roller rocker change.Right now I'm using a 1.5 rocker and a 5/16 7.2 long pushrod for a .520 lift .What length pushrod would I need for a .590 lift?
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
The cam "lift" is increased by grinding the cam base circle lower, so I think you need a push rod longer by 1/2 the lift difference. That would put your new push rod length at 7.200" + (.590-.520)/2, or 7.235".
But you should still verify that the rocker rolls symmetrically across the center of the valve stem.
But you should still verify that the rocker rolls symmetrically across the center of the valve stem.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
The reason for changing push rod length is to adjust the sweep of the rocker across the valve stem tip. The object is to sweep equally across the center of the stem.
If you want to change valve lift change the cam, the rockers or both. BTW, going to 1.7:1 rockers would get the job done.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by Pete K
This is true.BUT to some extent, if you have the wrong length push rod you can effect overall lift and the rate/timing of the valve opening......
only at the instant the rocker arm is perpendicular to the pushrod does the rocker move the same distance as the change in cam lobe height....
BTW wrong push rod length can really screw things up....
Just so no one misunderstands me, you don't control valve lift by changing push rod length, even tho push rod length can effect valve lift
From CompCams.com
. Determine correct valve train geometry
What is the correct length pushrod for your application? The one that produces correct valve train geometry. What is correct valve train geometry? When the rocker arm roller tip rolls from the intake side of the valve tip, across the center of the tip (at approximately mid-lift), to the exhaust side of the valve tip (at full lift) and back. See Diagram A.
Last edited by LT4BUD; Aug 21, 2005 at 10:02 PM.
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Le Mans Master
Joined: Dec 2002
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From: Seattle Area WA
I wish!
CFI, are you sure those vc's will clear the wiper motor then?
LT4Bud, that is dead on! Though it will have a slight effect on lift, it will probably have more of an effect on your valve stems failing!
Originally Posted by CFI EFI
Darn! It looks like I'll be canceling that order for 10 foot push rods.
RACE ON!!!
RACE ON!!!
CFI, are you sure those vc's will clear the wiper motor then?
LT4Bud, that is dead on! Though it will have a slight effect on lift, it will probably have more of an effect on your valve stems failing!
Last edited by USAsOnlyWay; Aug 22, 2005 at 02:34 AM.
