@simon posted:the same question, which brand /type hydraulic lifters ( non roller) is the best choice ?
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Sealed Power HT-900 hydraulic flat tappets, however, hydraulic flat tappets with a DLC coating are already available for Chevys. If or when they become available for Fords those shall be the flat tappets to use. A DLC coating on the face of flat tappets can reduce frictional forces by up to 66%. DLC coated flat tappets retain the light weight and mechanical reliability advantages of a flat tappet while drastically reducing the disadvantages of friction and wear.
Lets discuss the factory valve train
Replicas of the Cobra Jet camshaft (D2ZZ-6250-B) are available from Speed Pro (CS-650), Melling (SYB-29) or Howard’s Cams (237211-15). There is one difference between the factory camshaft and the aftermarket versions; whereas the factory camshaft had 117° LSA, the aftermarket versions have 115° LSA. The torque curve will be a little more lively.
Cobra Jet Camshaft Specifications: 270°/290° duration at 0.006 – 205°/220° duration at 0.050 – 0.481/0.490 gross lift – 115° LSA – 50° overlap – 119° ICL.
The factory Cobra Jet camshaft timing was retarded 4° for emissions. The convention is to advance the cam at least 4° to reverse the emission tuning. To advance the timing of the camshaft it will be necessary to use a double roller timing set with a 9 keyway crank sprocket. Ford Racing M-6268-A351 and Cloyes 9-3621X9 timing sets are two possible choices.
The factory Cobra Jet camshaft requires M code/Q code spec valve train; factory 4V heads were assembled with this valve train but Australian heads (i.e. 2V heads) were not.
Factory M code & Q code valve spring specs:
> 1.50 inch OD
> 90 lbs at 1.82 inch installed height
> 390 lbs per inch spring rate
> 0.500 inch max lift
The valve springs of a performance engine are equipped with tight fitting flat-wound dampers inside the main springs to prevent oscillation, bounce, and surge. Over time the flat wound dampers wear and their fit inside the main springs loosens. As the fit loosens the dampers no longer exercise the same amount of control over oscillation, bounce, and surge; thus springs equipped with flat wound dampers wear-out. When rebuilding 40 to 50 year old cylinder heads do not re-use the old springs, replace them with new springs appropriate for the application.
M code/Q code spec valve train includes Sealed Power HT-900 hydraulic flat tappets, Sealed Power MR-1811 factory rocker arm fulcrums, Sealed Power VS-717 valve springs, and Manley 23645-16 chromoly 7° valve spring retainers.
Sealed Power VS-717 valve spring specs:
> 1.51 inch OD
> 87 lbs at 1.82 inch installed height
> 424 lbs per inch spring rate
> ≈0.500 inch max lift
Factory cams are ground with “gentle” low-rate ramps, allowing them to use lighter closed spring force. This is done to reduce cam lobe, tappet, valve, and valve seat wear. The lighter closed spring force requires a higher spring rate in order to have adequate force over the nose. Aftermarket cams and factory springs are not a good combination because the cams won’t have the low-rate ramps and need more closed spring force to prevent valve bounce.
Valve springs for aftermarket hydraulic flat tappet cams should have about 122 lbs ± 8 lbs force when closed and 315 lbs ± 15 lbs force over the nose. The actual spring rate needed will be in the range of 330 to 360 lbs/inch.
Stiffer ⁵⁄₁₆ inch OD pushrods made from seamless chromoly tubing, with wall thickness of at least 0.080 inch are preferred over factory pushrods. The 581S series pushrods by Smith Bros. Pushrods are one possible choice.
-G