Push rod limitations
 

I run a 350/ 330 IHRA crate motor with .435/ .465 valve lift. we just pulled the engaine apart for freshening and some of the push rods have slight rub marks on them from where they come up through the heads. i am definately going to add more clearance in these areas but i also have been reading lots on the trend to go towards larger diameter push rods. Mine are the 5/16 - .083 wall and was thinking of going to 3/8 dia. Any thoughts?

Thanks
Ian

Re: Push rod limitations
 

push rods that rub slightly in the guide slots are norman. make sure there is enough/not too much clearence. i dont think that size a cam and springs warrent 3/8" units. be sure the ones you have are hardened. .083" should be fine & lighter.

Re: Push rod limitations
 

You cannot determine pushrod needs based on lobe lift only. You need to consider lobe profile as well as the spring pressure, I didn't see that you were running guide plates, however assuming you are it would be normal to see some rubbing. I found at bleast on my setup that going to larger pushrods actually made more power, of course every combo is different. Joe

Re: Push rod limitations
 

Ian, the marks you're seeing are normal with that diameter pushrod. no need for 3/8, if you are uncomfortable, get some .116 wall 5/16 to reduce the flex. a small amount weight added on this side of the rocker is not as big a deal. do not enlarge the opening unless you're going to use guide plates.

Wade

Re: Push rod limitations
 

Go with the bigger diameter pushrods and thicker wall thickness. You can't get a stiff enough pushrod so it doesn't deflect.

Re: Push rod limitations
 

Ian,

do you have guide plates or self-aligning [rail type] rockers?

Re: Push rod limitations
 

2x. And if you follow this advice I'll bet you won't need to clearance the push rod slots in the heads or have guide plates. The issue is flex, not lack of plates. Right? Fix the problem. Go faster.

Re: Push rod limitations
 

thanks for the replies and PM's. i do run guide plates and clearnaces look good by eye, the holes are tight but i wouldn't have assumed that much flex in the push rods or movement in the rockers. i will be opening the clearances in the head and will for certain purchase new push rods when the cam and lifters are ordered.

Ian