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I am about to start ordering parts and don't want to order something that won't work, so is thier a way to know valve to piston clearance without actually measuring it?
I will be running Pro Topline lightning heads with 2.02/1.6 valves. They will be going on a ZZ4 short block that has hypereutectic 4VR flat top pistons. The cam I will be running is comp cams XR276HR 224/230 .503/.510 112 @.05, that’s with 1.5 rockers. I would like to run 1.6s if that’s possible. Pro Topline website says "Recommended min: inlet .800" exh .100"".
Thanks for the help.
__________________ 1992 RS - ZZ4 short block, Pro Topline heads, comp XR276HR cam, Stealth ram with 58mm throttle body, T56, 4.10 gears.
Piston to valve clearance isn't just how much lift the valve opens since the valve isn't all the way open when the piston is at TDC. Duration and cam timing affect piston to valve clearance.
With flat top pistons and only .503 lift, you won't have any contact.
When checking clearance, .100" intake and .125" exhaust is usually the minimum. The best way is with modeling clay. Put some on the piston. Install the head. You need to use solid lifters since hydraulic ones won't give a proper reading. Set the valves for the cylinder and rotate the engine over twice by hand. Pull the head off and look at the clay to see if the valves left any marks.
Going to a higher lift cam or 1.6 rockers needs more checking than just that.
Factory springs don't like much more than .490" lift. At maximum lift, there should still be at least .060" between the spring coils.
Extra lift can cause the bottom of the spring retainer to hit the top of the valve guide.
Roller rockers or long slot rockers are required so the the slot in the rocker doesn't bind against the rocker stud.
__________________
Hardtail Racing
All engine, no power adders! Bests: 9.029@150.45 (at altitude)
Theoretical sea level performance 8.623@157.05
I plan on getting the springs and retainers that comp recommends. Also I may get new lifters because of the aggressive ramps speed of this cam (stockers are 12 years old).
I have been doing a lot of searching through the boards and found a guy that was getting valve to piston contact with the LT4 hot cam. Just wanted to see if it was something I was going to have to worry about.
The only heads that are likely to cause a problem at low valve lifts like that are the TF TW heads, because of their valve location and design. I doubt you's have any trouble until you reach at least .600" lift, maybe more, with normal valve timing.
__________________ "So many Mustangs, so little time..."
