CLASS RACER FORUM - Flat tappet lifters

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Re: Flat tappet lifters

Quote:

Originally Posted by SuperStock172 (Post 561397)

Thank you for the response, starting to get a lot more confident with this type of setup. Given your Boss' past experiences within NASCAR would you be able to comment on a camshaft specific question? My question relates to cup style camshafts being apparently designed to loft the lifter and hence giving the valve additional "dynamic" lift whilst running. Is this something that you or he has encountered and if so how would a DLC coated lifter hold up in this scenario? As Alan mentioned above you don't want a DLC lifter bouncing around so to speak because it will have the same result as a Schubeck, thus it seems strange to want to design a camshaft to loft the lifter with this potential catastrophic result. Any input would be highly appreciated.

NASCAR cams have never been designed to have an inherent loft or separation at the nose of the camshaft lobe. This type of event would damage or destroy the valvetrain and engine, especially during a 500 mile race. Just imagine the end result of the engine due to lofting taking place at a constant 8700 to 9400+ RPM's during a race.

The main root cause for a lifter to loft or jump the camshaft nose is inadequate open valve spring pressure. Dwell nose camshaft lobe designs have less propensity to loft.

Nevertheless, in a nutshell, the key is proper selection of valve springs to prevent lifter lofting.

Re: Flat tappet lifters

Quote:

Originally Posted by SSDiv6 (Post 561420)

NASCAR cams have never been designed to have an inherent loft or separation at the nose of the camshaft lobe. This type of event would damage or destroy the valvetrain and engine, especially during a 500 mile race. Just imagine the end result of the engine due to lofting taking place at a constant 8700 to 9400+ RPM's during a race.

The main root cause for a lifter to loft or jump the camshaft nose is inadequate open valve spring pressure. Dwell nose camshaft lobe designs have less to loft.

Nevertheless, in a nutshell, the key is proper selection of valve springs to prevent lifter lofting.

That is the answer I thought I was going to get, doesn't seem right at all to have an inherent loft at those engine speeds and the given operating times. It seems that our past Schubeck lifter failure was the result of swiping the ceramic puck off rather than a valve float/loft issue. Looking at the failed Schubeck lifter it seems the failure mode of the puck has been due to a shear load rather than an impact load. Correct spring pressures and lash settings have always been constantly maintained with approx. 250-300# seated and around 700 over the nose with PAC springs. The remainder of the valve train has no shortcuts, with titanium valves and retainers used, jesel high end rockers and correct pushrod sizing. Do you have a preferred camshaft supplier for using the recommended DLC lifters with? Again thanks for the advice.

Re: Flat tappet lifters

Quote:

Originally Posted by SuperStock172 (Post 561435)

For starters, I would go with PSI springs in lieu of PAC springs. During an NHRA divisional race a few weeks ago, we were experiencing issues with PAC springs loosing pressure every other run on a Comp Eliminator engine.
Yes, your forensic assessment on what took place with the Schubeck lifter is correct.
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