red hot valve springs
red hot valve springs
(OP)
A motorcycle tuner with a good reputation spanning decades hangs around another bulletin board. He reported that a ProStock drag race (car, I think) builder had told him that their valve springs get red hot in operation. I find that kind of hard to believe, and would just ignore the comment coming from a lesser source. To be fair I have never been at a ProStock engine dyno session, but the valve spring metallurgy required to buy durability would seem to require operating temps way less than 1000F. And I'd expect the oil to char way below red heat as well. (Maybe the existence of char is the source of the red hot theory)
Any supporting experience here ?
thanks
Dan T
Any supporting experience here ?
thanks
Dan T





RE: red hot valve springs
RE: red hot valve springs
RE: red hot valve springs
Valve springs can certainly char mineral oil in some racing applications like sprint cars, and mineral oil tends to be more compatible with alcohol fuels.
I very much doubt actual red heat though as the temper would quickly disappear. I suspect the term red hot was used to describe very hot, then quoted as literal. They do get hot enough for carbon to form on the springs and spring seats.
Regards
Pat
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RE: red hot valve springs
"Red hot" steel implies a temperature of 1000 to 1200 degF. Most valve spring steel alloys lose temper strength above about 475 degF. So the notion that steel valve springs can endure even very brief periods of operation at "red hot" temperature is sheer fantasy. As for the presence of carbonized oil deposits on valve springs subjected to severe duty, that is entirely conceivable. Engine oil can produce these type of deposits at temperatures below the temper limit for alloy steel springs.
RE: red hot valve springs
RE: red hot valve springs
These real high output race engines almost always have aluminium heads. If the springs where red hot, they would melt their way down through the head.
Regards
Pat
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RE: red hot valve springs
RE: red hot valve springs
RE: red hot valve springs
RE: red hot valve springs
RE: red hot valve springs
I am certainly not a metalurgist, but the number 600 seems to spring to mind in association with aluminium having a dramatic drop in strength.
Regards
Pat
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RE: red hot valve springs
RE: red hot valve springs
Franz
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RE: red hot valve springs
F1 engines have to last between 2 and 3 entire race weekends including qualifying. Ironically, or predictably(?), they are much more reliable under these rules than they were when they only had to do one race. But everything is critical and super expensive. At least they don't have to worry about red-hot valve springs since they use air springs. 18,000 rpm is only about 75% of the rpms they would be doing by now had the rules not limited them (some were already at 21,000 back in 2006).
RE: red hot valve springs
Regards
Pat
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RE: red hot valve springs
RE: red hot valve springs
BigClive, it belatedy dawns on my numb skull that when you drop a valve spring squarely onto a hard floor, it bounces back to only 90-something percent of its starting height. I think the loss is a few percent. A little is, of course, air drag, but what remains is the inefficiency of the spring. That directly results in the heating of the metal. How much power does it take to compress the spring? A few percent per cycle of that is what heats the spring. There is also friction in the rest of the valve train contributing to the total power cost to run the valves. Note that at low rpms, the spring pushes back on the cam, returning power in valve closing, but at float rpm, the spring is not able to deliver power back to the cam. I assume the stored energy in the spring gets progressively dissipated in spring surge and coil collisions as the rpm increases. You can imagine that the heating of the spring increases faster than the rpm..