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Valve Clearance Problems with this Little Cam?

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Old Oct 29, 2011 | 09:21 PM
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Question Valve Clearance Problems with this Little Cam?

I was just reading a HotRod article and they said this:

Comp's fourth most popular cam, the 277LR HR-113, idled at only 10.75 inches in our 6.0L test engine. With the stock GM LQ9 truck short-block and stock cast pistons with shallow valve reliefs, piston-to-valve clearance was right on the edge, only about 0.050 inch. That was enough to scrape by on the dyno, but we wouldn't want to rely on going that tight for real-world use...so you're looking at a set of custom, aftermarket, forged, deep-notch pistons to really make this setup run safely with about 0.080/0.100-inch intake/exhaust valve-to-piston clearance.

Read more: http://www.hotrod.com/techarticles/e...#ixzz1cEAXA5a2
That cam is 227/235. How can it need fly cutting?
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Old Oct 29, 2011 | 10:07 PM
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If the intake opening flank is very aggressive AND the lobe is advanced to
trap or build more cylinder pressure then it could be close.
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Old Oct 29, 2011 | 10:12 PM
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I just noticed that they used L92 heads on and LQ9. Perhaps it is the combination of large valves and flat top pistons?
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Old Oct 30, 2011 | 09:16 PM
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Originally Posted by speedtigger
I just noticed that they used L92 heads on and LQ9. Perhaps it is the combination of large valves and flat top pistons?
Are the heads milled? That cam wouldn't be an issue with a 243 or 317 head.
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Old Oct 30, 2011 | 11:20 PM
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Originally Posted by speedtigger
I just noticed that they used L92 heads on and LQ9. Perhaps it is the combination of large valves and flat top pistons?
Pretty sure the L92 stuff has the big intake valve. That's where the issue is coming in. With a 317 head they would have had tons more clearance.
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