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Will a stock 427 handle .520 lift?

5081 Views 5 Replies 6 Participants Last post by  dreis454
1969 427/385HP/all stock/app .140 domes/063 heads/10.25 claimed compression.
Seems like a fairly common engine. Certainly someone here has done this cam install. How much valve/piston clearance does the stock cam (461/480 lifts) have and is there ample room for .520 lift?
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It's not so much lift as it is duration. Generally aftermarket Mfgr's design their products to co-exist with Stock OEM Components. Pistons for Example: Speed Pro (TRW) design the Domes & Valve Reliefs to work with OEM Heads with say, 3 Specific Dome Volumes to fit in the Open Chamber 820(113cc), 781(118cc) and 049(124cc) Castings to provide 9:1, 9.5:1, 10.5:1, 11:1 11.5:1, 12:1 ... etc Static Compressions depending on the combination used. Stock Heads generally will not accept a lift of more then .670" lift without the retainer striking the top of the Valve guide using Stock Valve lengths and Deck Height but your more then likely to hit a Coil Bind before this happens and require longer valves for lifts higher then .670".

Advancing or Retarding the Cam Installed position generally will move the Valve approx .010" closer to the piston with each 2 Degrees change. The valves are closet to the Piston immediately after the intake Opens and just before the Exhaust Valve Closes; so a cam with a Long Duration and Fast ramps will cause the Valves to be closer to the Piston.

One thing you have to consider when installing Larger Valves is: Is the edge of the Valve Head going to interfere with the edge of the Valve Relief in the Piston. This again is taken into consider by the Mfgr for all OEM Stock Valve sizes, it's when you go beyond the OEM Specs that you have to worry.

It's always best to Mock a Head, Piston and Cam Assembly with #1 Cylinder Loaded using the intended head gasket and use something like Plumbers Putty "X'd" across the Valve reliefs and rotate the engine through 2 full cycles to determine the Valve to Piston Clearance for a Specific Cam and make note of the results; such that, if you ever decide to install larger valves, advance, retard or change out the cam you have some idea what the clearances may be.

There likely will be no problem with Piston the Valve Clearance with cams under 300 Degrees Advertised Duration in a MK IV using Speed Pro or other Reputable Piston Mfgr with the Engine at OEM Specs - That is: Head not milled, Block not Decked, using the OEM Head Gasket, Cam installed Straight up as per Mfgr Specs Stock rocker ratios or no altered specs that may cause the Stock Valve Seat Location to be closer to the Piston.

Closed or Open Chamber the clearance are respectively the same. I run a CB288R-10 Camshaft installed at 104 Deg (2 degrees advanced) 288/288, 246/[email protected]" - .623"/.623" Lift 110 LSA with TRW Forged Speed-Pro L2465F30’s Pistons in a 10.25:1 454 with 781 heads sporting 2.19"/1.9" Valves. Engine is at OEM Specs. My piston to Valve Clearance is .100" intake and .140" on the exhaust. Minimum values are considered .080" intake and .100" exhaust; however, I know some running as close as .060"/.080" Int/Ext without problems.

I don't know what you running, a Chevelle, I suppose ;o) with what tranny and Gears? But a 10.25:1 427 with Large Port 0val 101cc 063 heads is a very respectable mill, especially if the rotating assembly is forged. If you have the money, I would seriously consider something like a Lunati Solid Roller: The 502A1LUN or 60230 with either Crower Hippo or Isky EZ Rollers and say Comp Cam 933 Springs, Harland Sharp Rockers, 2" ARP Rocker Studs with extended Poly Locks to mount a Girdle and spin her up. These SR Retro-Cams are easy on the valve train and you can still cruise with close to 7000rpm & 600Hp on the pedal.
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