Good find, Pete. Nice to see some numbers on the subject.
They make it clear why Suzuki went with a 2-ring piston on the higher-efficiency Metro XFi rather than the 3-ring pistons in the garden variety engine.
I've never seen any mention of valve spring differences between the two though.
Yes, good find. Still wondering about the savings or potential savings from spring changes. Also should find out more about those two engines- one with 5% valvetrain losses, one with 19%. What's the diff?
Diesel vs gas engine Frank. Makes sense the gasser would have an higher percentage of losses from the valve train since they rev higher and have lower compression.
19% of 1.5 kw is roughly .38 hp. Suppose you halve the valve train losses, and your car uses 15 hp going down the road at 55 mph, that's 2.5% better FE.
Making the valve train lighter can also help reduce the forces needed to keep adequate control of the valves. If you know that you're never going to run the motor over 3000 RPM, for instance, you can likely get away with an awful lot of lightening of the rocker arms, retainers, and so on. Going to a lighter material (e.g., titanium) for the valves themselves will pay potentially large benefits for weight reduction.
That can let you reduce the spring pressures even further...
I don't know enough about the subject to begin to guess at how light you can go with the parts, or with the springs. But note that often times the super lightweight materials are super expensive... Titanium valves in particular!
The spring resist rotation when opening, but aids rotation when closing.
Not sure what that means just yet.
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I think it's a zero sum situation, because there'd always be another lobe resisting rotation while one lobe is aiding. The net effect is just a lot of friction on the cam. Moreso without rollers (as is the case in the Suzuki motor).
I think it's a zero sum situation, because there'd always be another lobe resisting rotation while one lobe is aiding. The net effect is just a lot of friction on the cam. Moreso without rollers (as is the case in the Suzuki motor).
I think that depends somewhat on the number of Cylinders (and arraignment
For example I was adjusting valves on a 7m (I6) last week and it "feels" easier to turn the cams than a 5sfe (I4). Very very not scientific, I'd guess it is a case of smoother, not less energy, just thinking . . . .
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2016 Tesla Model X
2022 Sprinter
Gone 2012 Tesla Model S P85
Gone 2013 Nissan LEAF SV
2012 Nissan LEAF SV
6 speed ALH TDI Swapped in to a 2003 Jetta Wagon
Let's remember that valve train losses are pretty much linear with RPM, while other internal friction varies with load. There seem to be many benefits to lower speed engines. Too bad racing formulas were based on displacement, rather than weight or fuel.
one with 5% valvetrain losses, one with 19%. What's the diff?
Frank ,
Apart from the obvious RPM differences for the two engines mentioned (1300 for the Perkins and 2500 for the Mercedes) I a guessing the detail design differences (finger roller valve operation versus bucket tappet operation etc) may account for the rest.
The comments about the actual values of the valve springs themselves being basically a zero sum item is essentially correct as Metro MPG stated above.
The force needed to compress the valve spring is returned as the compressed spring releases the energy stored in it.
There is a small amount of internal friction within the steel and this is released as heat.
The differences in spring pressure add to the friction component of the engine by the added pressures they apply to the items they contact like camshaft bearings , rocker bearings and pushrod contact points.
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