I was considering the AFR Hydra-rev kit. I shift at 6000 rpms and although I don't experience valve float, it got me thinking. Does valve float just "happen" at a certain rpm and cause power loss? Or does it start to happen gradually and you slowly lose power as rpm's increase? If the latter is true, then even though I shift at 6000 rpm and don't have valve float, if it gradually happens, I would probably see a gain from the Hydra-Rev? Is this correct?

 

Two different scenarios with valve flow.

1. The cam is driving the valve/spring into a harmonic frequency. At a certain speed the valve/spring will act kinda like a paddle ball. The initial hit is from the cam and the valve/spring will bounce.

2. There is not enough spring pressure to keep the lifter against the cam. This would get worse as RPMs go up.

Both of these will leave the exhaust valve as the biggest culprit of robbing power. Now if there is no valve float, you will not see any gains from adding the rev kit.

 

The first thing that usually happens is that the valves bounce when they hit the seat... that's where the spring pressure is lowest. Then as RPMs continue to increase (assuming that they still can), some of the other modes that a73 described start to come into play.

IMHO a rev kit is entirely unnecessary on a mild street cam like those Lingenfelter cams. There's not enough lift or "intensity" on the ramps to require that sort of thing. Using the proper valve springs is adequate: and I don't mean the cheapest springs (GMPP, K-Motion) with "specs" that claim to be adequate, I mean real springs from a reputable manufacturer that will warranty them as suitable for the application.

Contact Comp, Crane, Lunati, ot Ultradyne and give them the specs for the motor you are using them in, see what they say.

By the way - the head mfrs. are all real bad about putting cheap springs on their heads; World, Edelbrock, and AFR all come in for criticism that way. If you are still using the springs that came on them, you need to ditch them and get something decent on there anyway, before you worry about work-arounds. Your heads should be set up to accommodate 1.45" springs; in Comp, those would be part # 986.

 

Excellent guys, thank you.

 

Like RB83L69 said about those springs. As nice as the package deal seems with fully assembled heads, the manufacturer has no idea what camshaft you're going to use. The majority of those springs are for a stock or very slightly mild cam.

It's better to buy bare castings then have everything setup for your cam.

I just had my springs replaced in my heads with the proper ones for the cam. There was nothing wrong with the old springs but they were wrong for my current cam.

While they were at it they also installed new 10* retainers and hardened locks. The ones that came with the heads were starting to get pounded out. The new springs were set up to take a cam that I'll be putting in this winter.