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]

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?

[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]

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]

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.

[thisisntjared]

Originally Posted by theclencher

I have read that the energy used to compress the valvesprings on the up-ramp of the lobes is returned on the down-ramp.

correct but you dont want that vibration.

[Ted Hart]

Originally Posted by theclencher

I have read that the energy used to compress the valvesprings on the up-ramp of the lobes is returned on the down-ramp. I believe that would be true BUT the friction losses need to be subtracted out. I'd think lighter springs would reduce system friction as long as valve bounce conditions are not encountered. I would speculate that lighter springs would reduce internal engine friction and increase FE with the caveat that engine redline would be lower.

If we neglect friction for a moment, all the lifting ramps tend to be cancelled by the closing ramps. This is a semi-static view. Add oil , add RPM, the picture changes. The operating engine imparts the pressures of the compression stroke and the power strokes...tending to hold the valves closed.

Certainly, lower tension springs are going to reduce friction (both lobe and bearing), but this will also upset all the geometries in the lobe ramps(they aren't just bumps on a stick!), the oil film behavior(s), tappet / lifter rotation(OHC owners disregard), and the harmonics inherent in any sprig-loaded system.I see some gain...but woe to (s)he who "puts the foot down", even for a second!

[MetroMPG]

Originally Posted by Ted Hart

I see some gain...but woe to (s)he who "puts the foot down", even for a second!

What would be the effect of valve float? Is it catastrophic? (My engine is non-interference.)

[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!