or know anyone who has? Good or bad? Worth it or not?

Thanks.

 

I use it.

IMO yes its worth it.

 

I use it and am also happy with it, and think it is worth the investment.

 

I've heard and read that, unless you professionally match the rev-kit spring rates and retainer mass to the stiffness and mass of the remainder of the valve train, don't do it. You can cause more damage than good if the resonant frequencies of the valve springs and the rev-kit springs occur at the same or similar rpm.

I would concentrate on getting the conventional valve spring pressures right. With a hydraulic cam, you want to run as much seat pressure as possible, while limiting the open pressure to around 350 lb. I've found that you can run over 140 lb seat pressure while limiting open pressure. Doing this will give you a rev ceiling of 6700 or so. If you need more rpm than that, you probably want to switch to a solid roller and run 180+ lb seat pressure.

If you want to talk to an expert on this, call Thunder Racing and ask for Geoff (the owner). He's done alot of playing with this and made trips to Comp cams to use their Spin-Tech (basically a valvetrain and a strobe light) to play with different profiles and spring pressures.

With a set of GTP-ported heads and a mild, but well-matched cam and valvetrain, he's made over 450 rwhp with a stock short-block LS1.

Mike

 

I cannot see how a rev kit is going to cause a "resonant frequency" that is going to cause a problem in my valve springs and/or REV kit springs.

Maybe I am missing something though.

Do you have any further information about this?

 

Well, here goes with my best explanation:

If you support a mass (valve, retainer, rocker, pushrod, and lifter) with a spring (valvespring), then add some damping (coil damper), the system has a resonant frequency - just like anything else (do a Google search for "Tacoma Narrows bridge" and click on the first hit for a dramatic example). When you exite this system at its resonant frequency, it causes some problems.

The spring is compressed, then released when the valve operates. If you compress it and release it at its natural (resonant) frequency, it will continue to compress and release itself until the energy is eventually damped out. So, even though the valve is supposed to be closed, the valvespring will bounce off of its seat, releasing tension holding the valve closed. This usually doesn't cause too much of a problem because the damper can damp these out. According to Vizard, this can happen as low as 3000 rpm.

But, if you throw another spring into the mix, such as a rev-kit or a second valvespring (dual springs), and the resonant frequencies are similar or the same, the damper can no longer damp out the exaggerated resonant motion. Cam companies go to great lengths to match (mis-match is probably a better term) valvesprings for dual spring arrangements. But with a rev-kit, no one has "mis-matched" the spring resonant frequency to your current valvespring resonant frequency. Furthermore, no one has increased a damping rate to damp out the resonant motion.

Clear as mud?

Mike

 

yes, but you are talking about 2 nearly independant systems(the valve spring and the rev kit spring). The rev kit spring soley controls the lifter, nothing else. The valve springs control the pushrod on up.

 

Good point Jordan. So I can opt for AFR's at $229 or:

http://www.primediapowerpages.com/cg...00216&2D101087

hmmmm......

Willie

 

The valvespring controls the entire valvetrain with the rev-kit acting as a helper on the lifter. Just because they they are both controlling different components of the same system doesn't make them indepentent, but it does complicate the issue quite a bit more.

Now you have two springs acting together plus a damper to control the lifter, and the rest of the valve train is controlled by one spring with a damper. Also, the springs act together when the valve is opening, but somewhat independently as they close. Jeez, this is even more complicated than I at first thought.

Which brings me to my original point, that a hydraulic cam can be set up with matched, tested, and shimmed conventional dual springs to meet the needs of the street-car racer. But, for very high rev ranges, you should switch to a solid roller. After all, if you're looking for 7000+ rpm, you'll probably want to take advantage of the steeper ramp rates and higher lift available with a solid roller.

Mike

 

hhmmmm....can that be used on a Lt1?....if so Im getting one

 

Im using Crower's rev kit. Install was a little hairy but if you have the heads off or the motor out of the car, installation is going to be a little simpler. I believe most kits are similarly designed.

My thoughts on the rev kits resonation. If it was that big of an issue, would people be using them? It cant be THAT big of an issue.

Good luck Willie.

 

Maybe Mikes point is valid... i dont know. But i think if it were a big problem we would be seeing failures with people that had rev kits. Yet i dont ever see any...

 

I don't think that the valvetrain would necessarily fail due to the resonances, just that it MAY lose power at some very specific rev ranges. For instance, 6100 and 6300 rpm power could be unaffected, but at 6200, the combination loses 30 hp. My point is, if a conventional hydraulic roller set-up can get the needed results, why make it more complicated than it needs to be and take a chance of messing it up?

Mike