A quick copy / past from another board discussing the same topic:
"Work is defined as Force * Distance. Say we have a valve spring with a seat pressure of 245 lbs. and installed height of 2". We also have a valve opening of 0.700 which gives an open spring pressure of 600 lbs. The work done is the area under the spring curve between the 2.000" installed height and the 1.300" open height. In this case about 296 in-lbs or about 25 ft-lbs.
Power is defined as the time rate of doing work, or Work/Time. At 7200 RPM the cam is spinning 3600 RPM, or 60 RPS, or 21600 cam degrees per second. For our cam, 264 @ 0.050, there are 66 cam degrees from 0.050 to max lift. Let's add another 24 degrees to from the base circle to max lift and call it 90 degrees.
This means it takes about 0.004 seconds to go from the lift ramp to max lift. So if we take our 25FtLb/.004sec = 6250 FtLb/Sec, and with 1 Hp=550 FtLb/sec, it takes 11.36Hp to open the valve at 7200 RPM. We can see that if the engine were only running at 3600 RPM, it would take twice as long to open the valve, so it would only take half the horsepower to open the valve.
Now that's just the power required to open the valve. It really doesn't answer the question about power consumed. That same energy stored in the spring at max lift has to go somewhere, so it delivers it to the cam on the back side. Theoretically, the net power should = zero in my mind. But there will be some loss by heat generated by the spring. Also, at higher RPM, as the cam tosses the lifter for a fraction of a second after max lift, the energy released by the spring doesn't return that power to the cam since the lifter isn't touching the lobe.
So I can see how there are some losses, but I just wonder how the claims of 20-30% came about. When you hear that stuff from several respected builders over the years, you just kinda take it at face value and don't question it."
The Honda CRX HF valve springs are much weaker than the regular Civic/CRX valve springs. And the HF did have a lower redline. 5000 RPM versus 6500 RPM.
The new gen IV Prius does produce less HP and torque from the same engine that is in the gen III. I wonder if peak revs were lowered along with lighter springs to achieve this?
OK Found it after all.
The numbers are lower than 25% and are reported as 19%
A quick copy / paste of the abstract is below:
Engine friction lubricant sensitivities: A comparison of modern diesel and gasoline engines
R. I. Taylor
Shell Research and Technology Centre, Chester, UK
Abstract
Engine friction models have been developed that take account of the variations in lubricants with temperature, shear rate, and pressure. These models have been used to study the lubricant sensitivities of modern diesel and gasoline engines. Total engine friction losses for a Perkins Phaser four-cylinder, 4.0 l, turbocharged, inter-cooled diesel engine, operating at 1300 rpm, with an SAE 15W-40 lubricant, were estimated at approximately 2 kW, with the piston assembly contributing 46%, the bearings 49%, and the valve train 5%. Total engine friction losses for a Mercedes Benz M111 2.0 l gasoline engine (used in CEC sludge and fuel economy engine tests) operating at 2500 rpm, and medium load, for an SAE 15W-40 lubricant, were estimated at 1.5 kW, with the piston assembly contributing 42%, the bearings 39%, and the valve train 19%.
Pete.
Would the 19% include:
*cam follower
*pushrods/rotators/ ends
*tappets/rockers
*springs
*valve guides
?
I a late 1970s SAE Paper about the Shell Mileage Marathon of earlier times,they showcased a 1920s Chevy which used lighter valve springs for their engine strategy.It did lower the useful rpm of the engine,but they topped out at around 55-mph coasting downhill and averaged in the 20-mph range over the course.
A metric which would be interesting about springs would be their hysteresis.
Unlike the rubber of a tire on a paved road,a steel valve spring may have virtually zero physical distortion during service and whatever power is used to open the valve may be almost completely liberated when the valve closes.
A stronger spring requires more effort to compress,but it returns most of that back?
PS I was shocked at how much effort it took to hand rotate the camshaft on the CRX.
If reducing friction is the goal, what about roller rockers? I understand they aren't available/ won't work for Geo Metros (and OHC engines), but they would achieve the desired results, no?
Quote:
Originally Posted by Old Mechanic
Maybe they should go back to the suction operated intake valves. Talk about low spring tension.
F1 engines use pneumatic valves. No springs.
Also, in my Fiat, the valves are hydraulically opened, the springs only close the valves, essentially halving the amount of time the springs are exerting friction on the cam (and friction is going to be minimal during the closing phase).
__________________
Last edited by oldtamiyaphile; 11-24-2015 at 07:38 AM..
The Following User Says Thank You to oldtamiyaphile For This Useful Post:
They're expensive,but they make a measurable reduction in engine friction.
Ford chose them for their Mustang engine many years ago as part of their friction reducing strategy.
*low tension piston rings also
*streamlined water pump impeller
Today
Other popular topics in this forum...
