Variable Duration Flat Tappet Durability
Variable Duration Flat Tappet Durability
(OP)
The Comp Cams catalog states that their variable duration tappets should not be used for extended street duty. I can imagine that increased valve seat wear might occur from valve velocity at closing. Is this the reason for Comp's warning or is there some other reason?
Thanks.
Thanks.





RE: Variable Duration Flat Tappet Durability
RE: Variable Duration Flat Tappet Durability
I would be interested in some actual engine performance data using variable duration tappets versus standard tappets.
RE: Variable Duration Flat Tappet Durability
As to why not to use them for street? I have heard a muffeled engine with them at idle and it just sounded like when I would 'lash' my hydraulic lifters on my 1964 Corvair turbo Spyder to get a few more revs. LOUD!
Rod
RE: Variable Duration Flat Tappet Durability
They worked for me in a everyday high performance street sleeper, but I now mainly have OHC and buckets, Hydraulic or Roller in anything I play with.
I would never consider useing them in a roller, for fear of cracking a follower. I don't know what a rev kit would do for them
Regards
pat
RE: Variable Duration Flat Tappet Durability
Rod
RE: Variable Duration Flat Tappet Durability
I guess a rev kit might bleed them down, even on the base circle until the tappets were wide opened, depending on oil supply rate and bleed of rate at the rev kit spring pressure.
I also guess that if the clearance is taken up on the base circle, there is no need for opening ramps, just closeing ramps.
I guess they would have some effect as the opening rate and total lift would bleed down a little at low speed, but the ramps would reduce the bleed down effect on the closeing side, not eliminate, but reduce the effect.
Now you got me thinking, a dangerous move at any time.
With a few experiments re oil supply rate, bleed down rate and rev kit spring pressures, I might only lose 3 or 4 cams before I got it to work. Then again, I don't get enough time to sleep as it is
Regards
pat
RE: Variable Duration Flat Tappet Durability
Reguardless, ANY HYDRAULIC lifter will decrease the natural frequency of the valvetrain, and thus will limit how fast you open the valve and the upper rpm range.
RE: Variable Duration Flat Tappet Durability
I finally gave up on all flat tappet/pushrod setups.
RE: Variable Duration Flat Tappet Durability
Has anyone done a roller tappet setup on the 230/250/292 Chevy? If so, I would appreciate any comments on what parts to start with and what alterations might be required.
How much can the variable duration effect be altered with oil viscosity? For an extreme example- how would 0W30 weight compare to 60 weight racing oil with regard to variable duration tappet action?
RE: Variable Duration Flat Tappet Durability
IIRC, I measured the hardness of the rubbing surface of a few lifters, and they were all about the same-close to Rc 60, I think. I suspect that Rhoades buys stock Chevy lifters and then mills the small bleed-down flat on them.