Increasing ~.030 lift worth it?
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Joined: Nov 2001
Posts: 3,515
From: Kansas
Increasing ~.030 lift worth it?
My LE heads are going on in about 2 weeks so I decided to take a look at Comps webpage to see if they had any new lobes out there for SBC. I happened to run across the old XE charts and noticed my cams max lift is .536/.544(3314/3315 lobes). If i ran a 1.7 RR I would increase lift to .570/.578 or If i got a new cam with the 3192/3194 lobes with 1.5 RRs my lift would increase to .567/.584 and get a more agressive cam out of the deal. What do you guys suggest? Is it even worth my trouble to pick up the extra lift? Thanks
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Joined: Oct 2001
Posts: 368
From: Cincinnati, Ohio
Re: Increasing ~.030 lift worth it?
I can tell you not to run 1.7 rockers on an XE lobe...I tried that with my 218/224 XE cam and snapped a pushrod. I called Comp afterwards and they told me not to do it again and that I should only run 1.5s or 1.6s (1.7s put too much stress on the springs/pushrods/lifters with that kind of lobe profile). I switched back to 1.6s and all has been fine.
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Joined: Oct 2002
Posts: 6,518
Re: Increasing ~.030 lift worth it?
If you snapped a PR then you overloaded it. One thing to remember is that the rocker arm mulitplies the load the spring has on the valve the same amount that it increases valve lift. Going to a thicker PR or a higher quality PR would help. If you snapped a Comp 5/16 Hi Tech then a 3/8 is the way to go. Only thing is that they are really short on a HR LT1 so you would have to have them made. Sticking with the 1.7's only on the intakes would help too.
So lets take Turbo_z's example with a 977 Comp spring on there, not only does the over the nose load increase because of the added lift the spring load on the PR increases. So the over the nose pressure that the pushrod sees goes from 630lbs to 690lbs. An increase of 60 lbs over the nose. You are also going to see faster accleration and velocity on the valve which could have some issues too.
Pushrod and ROCKER ARM stiffness is important when going to a higher ratio rocker arm. If you are not running at least 7/16 stud Hi Tech's in a situation like above you are going to have rocker arm deflection which leads to inaccurate valve motion and usually a loss of max lift. Shaft mounts and stud girdles always help.
Bret
So lets take Turbo_z's example with a 977 Comp spring on there, not only does the over the nose load increase because of the added lift the spring load on the PR increases. So the over the nose pressure that the pushrod sees goes from 630lbs to 690lbs. An increase of 60 lbs over the nose. You are also going to see faster accleration and velocity on the valve which could have some issues too.
Pushrod and ROCKER ARM stiffness is important when going to a higher ratio rocker arm. If you are not running at least 7/16 stud Hi Tech's in a situation like above you are going to have rocker arm deflection which leads to inaccurate valve motion and usually a loss of max lift. Shaft mounts and stud girdles always help.
Bret
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