Valve float is bad, but I'm interference, of course.
Anyway, I've thought of this myself. The easiest way to find weaker springs is to find springs that fit out of an engine with a lower redline. Also I've heard that springs will weaken with use, but I don't know how much so.
Don't racers get customs rates in their crazy titanium springs?
finding weaker springs would not be that hard just get the diameter and other specs and compare them to other springs to find what you are looking for. I don't think it will really gain a lot though because the cam has very little friction so practically all of the energy used to compress the spring will go to pushing the cam lobe forward as the spring expands.
Think of it this way the more friction the more wear so other than from lack of oil how many cams fail before 400k miles. on a sb chevy going to a roller cam only gets you a few hp but the steeper ramp rates that rollers can give is what really gets you some extra power. So maybe if you really want to do something nuts get a set of roller lifters off something and weld onto the stock lifters. Set the cam a bit higher so the new lifters match up and away you go
Really the only thing I see with going to smaller springs is that you will lower the rpm where you get valve float and it might be bad enough that you could hit a piston with a valve at some point due to the valve bouncing. Going to a spring that will lower redline from 6000 to 4000 isn't much difference in pressure really. To get significant reduction in friction it would take a roller cam.
I agree - I have no idea wher to get "softer" springs.
Would older springs be softer? I've only got 11,000 km on my engine, but I've got another 1.0 from the blue ForkenSwift with about 190,000 km on it. Would its springs be less springy from all those miles?
Less springy ...as in "tired"? Were they overheated or floated (over-revved) in their past life?
However...it really would bother me to know...spring steel has a finite fatigue life. The spring loses tension, then fails (breaks). There is a change in the crystalline structure of the metal...causing embrittlement( some say "work hardening")... this is why race engines get their valve springs changed very often! Springs are cheap; blocks & cranks aren't!
I would say that if you want to make your valve train more efficent, getting titanum valve springs (cryo-tempering might be a good idea, as Ti springs have a shorter life, and in theory it should make them last longer) and titanum valve keepers to reduce the recipricating weight.
how about getting a cam from an xfi? lower valve lift would give you a simaler affect, and more torqe, right?
I looked into this a while ago when comparing the motor in my car with newer versions. The spring seat pressure in my car is 66 pounds. The newer version is spec'd for 54 pounds and used a cam with slightly less lift (34.91mm vs 35.49mm) and more duration, which gives a more gradual lift ramp (less likley to float a valve). Both motors have the same redline, the newer motor made more power. Then the EVO came out and it had even lighter spring pressures and made even more power. Obviously there was more to each motor than just the cams and springs, but it shows a general trend.
WRT friction, this may just be semantics, but if there is no wear then there is no friction, but there will be viscous drag in the oil film, and more pressure= more viscous drag.
IMHO lighter springs will reduce power losses in the entire valvetrain (cam lobes, cam journals, timing chain or belt/ timing sprocket).
MetroMPG, your old head might have worn springs in it. It's easy to check, just remove the springs from the head and measure their free length. Hopefully you can find a specification for free length in a shop manual somewhere.
I replaced the valve springs in my Laser last winter after 190,000 miles of use and they were shorter than spec. For example, standard length is 48.31mm, service limit is 47.29, and mine were around 46.2 to 46.5mm. I took my motor up to redline many times with the old springs and the valves didn't hit the pistons, and my motor is an interference design. With new stock springs the motor regained it's power in the high rpms. HTH