valve springs

[MetroMPG]

I forget if I've brought this one up before. Here goes ...

Most of the energy needed to turn the cam is spent compressing valve springs. So what if you put in weaker springs?

(getting ready to duck...)

[thisisntjared]

i have thought about this myself and i bet its very possible. the possible gains depend on how the cam(s) are setup up with the duration and slope. if a cams lobes are configured such that the pressure from springs remains somewhat equal throughout 360 degrees of the cam's rotation the gains will not be as profound. (warning the rest of the paragraph is just a train of thought and may or may not be of value) in a motor geared for fuel economy, even softer springs may be of more value because the duration of the cams would be less so less likely to maintain constant spring pressure around 360 degrees of the cam(s)...

i know that with stiffer valve springs fuel economy is lost, so i really dont know... hmmm... maybe i am just pessimistic today...

i think softer springs would be harder to find, but maybe lighter valves are fairly abundant....

[MetroMPG]

Forgot to reply to this part:

Originally Posted by thisisntjared

if a cams lobes are configured such that the pressure from springs remains somewhat equal throughout 360 degrees of the cam's rotation the gains will not be as profound.

That's true too. In that case, the gains would be solely from reduced friction on the lobes.

[MetroMPG]

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?

[Ted Hart]

Originally Posted by MetroMPG

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!

[thisisntjared]

my swag-o-meter says yes, but i dont know if it will really be enough for an impact. i dont know metals that well.

how close are the springs to being fully extended while in the head? a very risky idea would be to shave them so that they would be just under full extension while in the head.... sorry to say, i will not be trying this out. i cant back down from 7200

[MetroMPG]

Originally Posted by thisisntjared

how close are the springs to being fully extended while in the head? a very risky idea would be to shave them so that they would be just under full extension while in the head

Hmm!

Could you just shave half a milimeter off the top and bottom, where they seat, not actually affecting the spring itself?

I admit I know nothing about spring physics or metals.

Fun thinking about it though.

[Ted Hart]

Originally Posted by MetroMPG

Hmm!

Could you just shave half a milimeter off the top and bottom, where they seat, not actually affecting the spring itself?

I admit I know nothing about spring physics or metals.

Fun thinking about it though.

A slack(er) valve spring encourages ... maybe not enough ... the valve to "bounce" when it reaches the seat. This is not good! Valves are brittle; they break! A spring with a longer than valve stem length (when closed) ensures no bouncing goes on....The lobes of the cam have "ramps" ground into the profile (you'll never see 'em!) to let the valve down onto the seat...instead of just dropping it. A slight amount of spring tension is required to force the lifter / rocker arm to "follow" the lobe profile!
There is a lot going on, here!

[SVOboy]

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?

[MetroMPG]

I've got an XFi cam coming actually. So yeah, maybe spring mods + the cam is a bit much.