I have. They help marginally with controlling valve float, but that's not the main advantage.

The main advantage is for roller cams, as they keep the roller in contact with the base circle.

Other advantages are that they increase valve float controll with zero increase in seat and nose presures, thereby reduceing load on the valve stem, retainers, collets, rocker arms and pushrods.

Dissadvantage is they add extra components, are a bit awkward to assemble, and you can only get weak springs in there, which minimises the advantage.

Regards
pat

Pat,

Thanks for sharing your experiences.  The class I compete in does not allow this, or any, modifications.

Why only weak springs?  Seems like you'd have the entire lifter valley to play with.  Even if the diameter is somewhat small as the pushrod is close to the block, you should get decent force from the length of the spring...

You have to be able to get them in without damageing anything.
I have never seen a valve spring compressor designed for it, so you squeeze one side to get it in, then lever the other side down with a screw driver. It normaly does some minimal damabe to the ally bar that contains the spring seats. If they were really strong, a pliers type compressor would be necessary, but then you have to extract the compressor. To take them out with really strong springs might involve removing the head. It seems easier to put 90% of the spring tension on the valve were it controls everything except the roller on the base circle, leaving that job alone to the rev kit. It does not take all that much spring to control thre follower from tappet clearance to base circle.

Regards
pat

Rev kits have their place especiall with Hydraulic Rollers when solid rollers are not allowed. We have seen big gains in power at 6000 RPM's and higher.  

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

Why just hydraulic rollers?  The physics are the same reguardless of lifter design.  

The Hyd rollers Float because of the plunger in the lifter.
They do work on solid rollers too, but the big gain comes when you use them with Hyd rollers. I hate Hyd Cams.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

Actually, something else probally screwed up in the valvetrain, eg poor cam design, valvespring surge, lack of valvespring force.  Something got wacky and caused excessive lash, the hydraulic lifter is just doing it's job.  

The gains come because some people are turning Hyd Rollers nearly 7500 RPM's. This is why the lifter floats, not necessarily anything getting wacky other than the RPM's. Any hyd lifter will love a rev kit when it is being ran in a motor turning upwards of 1500 RPM's in excess of it's dynamic stability. Accept for the case of the "rules", a hyd cam, be it a flat tappet or roller, is totally wrong for a perf/race motor. Hyd lifters can't hang in that environment and need the help of the rev kit. A rev kit will give upwards of 50+extra horsies in V8's running Hyd cams in extreme(RPM) environments.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

Shaun,

The last time I was invloved with a hyd cam, we ran 0 pre-load/lash to avoid pump up on a dirt track car running in a hyd class (mid 80s).  It seemed to work pretty well with the lifter being "maxed out" at all times.

Would the rev-kit still apply in that situation?

If it runs 6500+, then Yes. I don't like running the lifter at 0. I also don't like it more than a 1/4 turn past 0. When it runs at 0, the plunger runs against the snap ring and will eventually if not sooner come apart. You know what happens next!!!

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)