valve springs
 

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...)

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....

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?

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

Forgot to reply to this part:

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

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.

correct but you dont want that vibration.

Correcto, mundo!
 

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!

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

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!

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.

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

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

Here's that link I was looking for! Page 1 sums it up, tho there's other good stuff in that article as well.

https://www.physics.princeton.edu/~mc...101lab8_96.pdf

Softer springs will reduce losses but this of course lowers the RPM which the valves will float.
You will have to match it with a suitable cam grind to keep it below that critical RPM.

Of course now that the valve train is set up for a lower power the intake and exhaust ports will be too big (eg- no need to be able to flow 80hp when your new max will be 40 hp)

Reduce the size of these (epoxies are easiest) in the head (welding and then grinding to correct shape is best) and then construct new manifolds.

Its a lot of work , but possible.

I have just used normal epoxy on intake ports but not exhaust ports.
There may be specific fuel proof epoxies , but ime unsure of that.

Depending on its shape an exhaust port could be sleeved.

If anyone is interested, HERE is a link to an article I wrote on basic cam dynamics back in Fall 2003 (WARNING: geek content!).

And if you're REALLY bored, you can read the book I referenced at the end (I enjoyed it).

Synlube I think had an article on cam load and the effects of better lubrication on the cam with their lubricants - they got into power needed to open valves etc. and load on the timing chain/belt and the effects of wear reduction. Also the rate of cam lift on the closing side determines the spring rate as well as the valve train mass needed to be moved by the spring. If you lighten the valves and springs and retainers you can use a lighter spring without any problems and I am sure there is plenty of margin in the spring pressure for less than peak rpm operation. Isn't red line the max continuous operating speed??

The red line is the maximum recommended operating speed.
The continious operating speed (under full load) is considerably less.

Ok, here is my perspective on using weaker valve spring's to try to improve gas mileage. I wouldn't do it.

The problem's I have with using weaker valve spring's is that the spring's primary job is to close the valve's, quickly and firmly. In closing quickly and firmly, it allows the valve to sit against the seat more solidly. The amount of time the valve is closed and how solidly it is seated is a factor in how much time and how well the valve is able to be cooled by the valve seat, in the head of the engine. If the valve is unable to be kept cool, by the valve seat, the head, the cooling system and the valve spring pressure, then the valve will develop hot spots, warp, burn, split and all sort's of nasty thing's.

I can disassemble and rebuild the head on car's. However, I don't like doing it and IMO putting weaker valve spring's on a car is just inviting a significant overhaul problem for a unmeasurably small amount of possible fuel saving's.

The risk just isn't worth the reward, for me.

One of my initial assumptions is that the valve springs are over-engineered, so there must be some margin for reducing their strength before you compromise durability or performance of the valvetrain.

Also, I was only considering this on a car that rarely (if ever) sees 50% of its maximum RPM.

But I don't pretend to know what that margin is.

And I also agree the savings would likely be small, but that's OK.

DAX: read your page. Nice work.

Hi GP

?In closing quickly and firmly, it allows the valve to sit against the seat more solidly?
The speed that the valve returns is controlled by the profile of the cam lobe and not the springs pressure.

?The amount of time the valve is closed and how solidly it is seated is a factor in how much time and how well the valve is able to be cooled by the valve seat, in the head of the engine. ?
This again is controlled by the duration of the cam , and note that in milder tuned engines the valve is seated for a longer time than in high performance engines.
This is purely cam geometry.

?If the valve is unable to be kept cool, by the valve seat, the head, the cooling system and the valve spring pressure, then the valve will develop hot spots, warp, burn, split and all sort's of nasty thing's.?
Split head or burnt valves are caused by excessively lean conditions and rarely from a lack of spring pressure.

Intake valves are cooled by the incoming charge ,so they rarely burn.
Exhaust valves dont get much cooling during overlap so they rely on transmitting the heat to the valve seat (75%) and to the valve guide (25%) for cooling.

Exhaust valves (or just the valve head) are made from tougher alloys to handle the extreme heats.

The reduction of spring pressure that is being talked about isn't a reduction to almost nothing.
A seat pressure of 40 pounds would still work very well in a low RPM engine application.

gregW:-)


PS.. ford 351W V8 engines had a spring presure of 60 - 65 pounds.
A high performance cam for the same engine would have 120 pounds.
This almost double the pressure is required for the extra 1 or 2 thousand rpm redline.

ive read that jb weld works just fine in the intake ports.

When I and my Taurus I looked into valve float because it was an interference engine. And found out that valve float occurred at 6600rpm sending multiples of valves into the cylinder as the piston is coming up to meet them. If i remember correctly(didn't read any of the links ill do that tommorrow) having softer springs on your valves would be bad. Because from what I understand if your reach the max rpm or get close to it your going to reach a point where both valves are open at the same time causing a decrease in mpg. What would happen in a non-interference engine when you reach valve float. Would the valve shoot upward instead of into the cylinder or would the spring collapse and seal closed that inlet/outlet valve?

I think you're onto something, although every car is different. I'm not sure how you'd test the safety margin on your motor.

I had the chance to test the safety margin built into my motor a couple of times. I did it by accidentally mis shifting. I was racing at the track and hit my shift point of 6800rpm in 3rd gear, then quickly shifted to 4th. At least I thought it was 4th, somehow I got 2nd gear instead! Ouch! My tach showed a peak of around 9300 rpm! :O And redline is 7000rpm. There was no catastrophic failure. I'm still driving it today. I don't recomend testing your motor this way. HTH! :)

Hi Rstb88

In a conventional sprung poppet valve system there will always be at some high REV a point reached where the valve will not follow the cam lobes profile and the valve will float.
Manufacturers will choose a spring stiffness which they think will return the valve correctly up to the maximum expected RPM of the engine.
Excessively low spring rates will limit high rpm use and on the other hand an excessively high spring rate will reduce power and cause valve and valve train failures and excessive wear.
So they guess a happy medium.

Normally valve float will be noticed by a marked drop in power ,,,or a wall like RPM barrier limiting higher RPM's.

Only in very extreme over revving cases would the valve head be still low enough to get slapped silly by the upcoming piston.(a dropped valve)

Softer valve springs would only be recomended with a cam profile that did not encourage higher RPM's
A cam choice with maximum power at around 4,000 , and maximum torque at 2,000 would probably work well for FE.

This would put the point of valve float above the usable RPM range so it is of no concern.

gregW:-)

PS.. especially on 6's and 8's valve train losses are not as bad as expected because as one valve is opening another one is shutting.
The compressed energy in 1 spring is being released helping another one to open.

Which suggests my antiquated 3-cyl 6-valve Metro motor might benefit the most (relative to engines with more cylinders) from matching valve spring strength to low RPM engine use.

Onegammyleg: I don't disagree with you, as far as the cam profile defining when the valve's can close. However, the fact is it is the spring pressure that makes the valves follow the cam profile and if you put to weak a spring on them, their going to float.

My point wasn't that you couldn't use less spring pressure. My point was that I don't like dismanteling and rebuilding engines, unless I have to and in my perspective, the potential gains are so small as to be virtually insignificant, in comparison to the problems with goofing up the valve's.

If anyone has the inclination to try this, go for it. I don't think your going to see any measurable gains, but hey, I just am not into rebuilding something if I don't have to.:rolleyes:

Good point. Honestly, I think I've only ever taken the valve springs off a head once, and that was so long ago I honestly don't remember how difficult it was. Also it was a pushrod engine.

Hi Gary

Well . .discounting the cam change there still would be measurable gains just by the springs alone.
Have you ever had a head on the table and tried turning the cam sprocket by hand ?
If you had you would appreciate that they don't turn easily , and when others in here are doing almost everything apart from shaving door handles off they probably are looking for that 1 horsepower loss/or advantage.

Even after the many years that I have rebuilt engines I am still amazed at what people expect them to do.
Idle smoothly , run well across a huge RPM range , live a long time and give good gas mileage.(and now days pass smog tests)
Its an amazing trick really that they do it so well.

But one of the problems with having an engine that can run across a wide powerband is that its not going to work PERFECTLY across it.

That is why ,,if a person desired to do so, modification to narrow the powerband (cam, springs and reduction in head port size) you could increase its efficiency in a lower RPM range....which should/would improve FE at those revs.

The car would loose its maximum power and flexibility would be less (no more tower out bogged Hummers in the Metro).,, and of course JUST a spring change (without a cam change) would be asking for trouble.

Of course extreme FE mods arent for everyone ..otherwise we would be all driving around in white metro's with clear vinyl sheeting stuck to the front and back to improve the aerodynamix . :D

"Of course extreme FE mods arent for everyone ..otherwise we would be all driving around in white metro's with clear vinyl sheeting stuck to the front and back to improve the aerodynamix . "

Don't you mean White Civic Hatch's? I know it's hard to tell sometimes. :)

Hehe , your rite ,its hard to see under all those mods. :D

i agree. definitely.