Weaker Valve Springs
 

Background info:

When I was 15 years old I bought a '68 Charger. The charger had a 383ci big block with a huge .509 lift, 292 degree duration camshaft. The engine builder did not install proper load valve springs for the large camshaft, so at 6000 rpms the valves would "float" and power would decrease dramatically. I installed heavier valve springs and my problem was solved.

My sophmore year of college I wrote a research paper on alternative powertrains including: electric, hybrid, diesel, and advanced otto internal combustion engines. One technology was a camless engine design. The engine used electronic actuators to open and close the valves. This way the engine gained back the parasitic losses from opening the valves and rotating the cam and a computer could open the valves small amounts for low rpms and large amounts for higher rpms. Horsepower and efficiency in one design. The system boasted 30% increases in fuel efficincy.

A few months back I began testing on springs that will be used in my Single Trip Tool at FMC Technologies.

These experiences lead me to think of a cheap way to decrease some of the load on the engine and increase low rpm power and Fuel Efficiency....

Hypothesis: Using weaker valve springs in an engine will decrease the power lost to turning the camshaft and opening valves. This will increase fuel efficiency and very slightly increase LOW rpm power. Power will only be obtainable to a certain rpm range of about 5000rpm. A rev limiter should be used. The camshaft should be ground to a lower lift where power is made from idle to 5000rpms. This will also increase fuel efficiency.

Opinions?---Advice (other than going to a mental institution)?

Tech Questions: (Anyone have a Haynes for 92-95 civics?)

1) What is the valve lift for VX engines camshaft (big intake, small intake, exhaust)

2) Did honda D-series engines always have the same valve size?

3) Anybody have experience with weak springs for high rpms other than me?

Thanks for your time,

Kent

I don't have any advice for you. But I have long thought that this would work. Its one of those idea's I'll use if I ever do a FE engine build.

Low lift cam, cam timing, weaker valve springs, lightweight hardware, ceramic coated tri-y header, tuned intake manifold, total seal rings, knife edged crank, windage tray, electric water pump, etc..

I say go for it.

We had a similar but different experience. My Dad had 68 Pontiac with a 389 2 barrel. When he pulled out to pass on a 2 lane road the car shifted down and started sputtering. It was clearly valve float. Soon my Dad pulled the engine. Money was tight then and he re-rung it and installed a new camshaft and followers. He ground the valves but did not even shim the old springs. With the new camshaft the valves would not float as far as you would want to push the engine. This was my first experience where I witnessed valve float due to a worn camshaft profile and it was repaired without changing the valve springs. I ran into a very similar experience with th 365 hp 327 chevy once.

Another problem that can occur with weaker valve springs is hydraulic lifter pump up. Small Continental aircraft engines have done this at less than 2500 rpm with heavy oil in them. I have heard of three cases of this happening though I never experienced it. It seems odd that a lifter would be built in such a way that oil pressure could open the valve but that is the way it has been presented. I never studied the lifter close enough to determine if that was really the explanation.

Cam profile and harmonics play a big part in this. This probably is of little use to your real question though.

usedgeo

No, it is useful. Hydraulic lifters are pretty much just hydraulic cylinders. Engine oil acts as the fluid and oil pressure pressures up the cylinder to keep the lifters tight to the push rods. I will search...

I bet that the Prius uses lighter springs than the non-Atkinson version of the engine, meaning some really smart guys at Toyota agree with you.

Not to discourage discussion, but here's an earlier thread on just this topic:

Weaker valve springs for better FE?

Can't address the Hondas, but the XFi efficiency cam has lower lift & shorter duration (and advanced valve timing) to increase cylinder pressure for more low end torque.

The result however is a higher lift rate, which causes the car's redline to be lower than the stock engine. This is possibly due in part to the likelihood that valve float may be caused at a lower RPM.

So, with a low lift/short duration efficiency cam, weakening the springs may not be something you want to do.

I'm no expert. Just putting out some things I've learned since the last time this came up...

Here is a somewhat relevant link. Not exactly about springs but certainly interesting with respect to valves. Diamondlarry has some of this guys headwork on his car.

https://powrehaus.com/2007/01/26/powre-valvz/

Another point. Many old slow speed engines ran for years with no intake cam at all. You can see these at most fairs and museums. We had a couple when I was kid. We pumped water with one. These run a really weak spring because atmospheric pressure must open the valve. These engines obviously run very slow and the spring decreases volumentric efficiency. The principle is very similar to the two piece valve mentioned above.

Two more examples. My father-in-laws 400 ci ford was overhauled and the rotators were left off the exhaust valves in a stellite valve seat conversion. Not my choice, but anyway, the wrong keepers were used with the new retainer plates. It ran though poorly for 20,000 miles before I took a look at it. It was amazing that it never dropped a valve. The retainers were coming up and hitting the rocker arms as well as relaxing the spring about 3/16 of an inch. At high vacuum it could pull the exhaust valves open and cause erratic running. It may have been typical float but seemed to require high vacuum not just rpm. This was certainly exploring one of the limits. The proper valve keepers fixed it.

A very similar situation was done by a neighbor on a chevy 6 when I was a kid. It was a mismatch of parts from two different engines. In that case my Dad just slotted some washers and slipped under the springs.

Conclusion you will need enough pressure on the exhaust valve to resist high vacuum but not necessarily that much pressure on the intake valves.

Now you got me thinking. I could pull the intake rockers. Install super light springs on the intake valves along with solid stops to limit valve opening to less than interference and have perfectly optimizd intake valve timing with a huge power loss. I could easily live with this power loss.

Geez I swear I have not been smoking anythign funny this morning.

The same effort used to run the cam lobe up on the spring is returned when the spring helps the cam on the valve closing stroke. Stiffer or softer valve springs makes little difference in the cam actuation of the valve versus the valve rotation of the cam. Less effort to open the valve means less force from the valve 'helping' the cam rotate when the valve is closing. Stiff springs require more energy to compress, but they also return more when they expand.
The parasitic loss reduction of lower spring rates on the valves is mostly due to the characteristics of the oil film between the cam and the lifter or follower. Less spring pressure means less sliding friction at the cam lobe and that's about all. Or retrofit a roller follower set to really cut the sliding friction more than lighter springs might.
Lower mass valves won't require as much spring force to bring back closed and can benefit from lower rate springs, but lighter springs are not recommended without lightening the valve's mass.

Ducati has a method of using two cams and no springs for valve actuation. One cam lobe pushes the valve open, another then pulls the valve back shut. Complex, with two sets of lash adjustments, and the rotating / reciprocating mass isn't less, and it adds cost, but it is possible to produce a high rpm valvetrain without spring parasitic loss, if willing to compromise in other aspects.
Formula1 builders use air pressure to open and to close the valves in their 14,000 rpm engines.
Spring-less valve trains are possible, but the reality is that the springs aren't that big a percent of the losses to consume so much effort and expenditure.
Piston rings are a greater parasite. Remove all your rings for greater fuel savings than you'll ever see from lighter valve springs. It'll be about as practical, too.

So maybe half baked? What if the camshaft's angles would be setup so less power would be used to open the valves and force closing the valves? I understand the intake and exhaust profiles would change but just a thought...