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Engineering/Technical Ask technical questions about cars. Do you know how a car engine works?
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Old 04-04-2001, 10:25 PM   #1
Dimex
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What determines a redline? Am I just thinking about it too much and it's simply the maximum engine speed, or is there more to it? Just a thought.
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Old 04-05-2001, 01:17 PM   #2
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The engineers that work at the car manufacturers generally take a lot of things into consideration in order to determine the redline. Things like:

Long term durability

Catastrophic failure (bending valves, breaking conn rods, etc.)

maximum accelerations of pistons, rods, etc

In the end, I'm sure everone on the design team agrees on a "safe" RPM that the engine can live at in the long term.
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Old 04-07-2001, 01:22 AM   #3
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Yes, but...

That doesn't mean that an engine can take redline or let's say almost redline, all of the time.

You'll end up having head problems and probably crank bearing, or even crank itself, problems.
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Old 04-09-2001, 10:33 AM   #4
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Often the valves and bearings are the first parts that set a redline. But there come always new technologies e.g. some brands are working on introducing air controled valves(like F1) to regular cars that would raise the redline:bandit:
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Old 04-09-2001, 09:35 PM   #5
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yep, Bean Bandit is dead on, it's almost always the valvetrain that limits maximum engine speed. Piston speeds and other factors can come into play later, but the old limits people imposed to fps (feet per second) piston speeds continue to be reliably surpassed as better metalurgy techniques become commonplace. For instance, the old hot rodders thought anything over 3000-4000 fps of piston movement was going to be disasterous, but production motors are pushing around 6000 fps now in some cases.
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Old 05-02-2001, 12:18 PM   #6
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In turbine engines when a power turbine or gas producer turbine speed is exceeded mechanical inspections are required to determnine if the centrifical force has caused cracks in the turbine blade or caused a blade to contact the engine housing.
I've also seen rods thrown in 2 and 4 cycle engines caused from old exsessivly worn engines combined with high RPM. High RPM can also cause valves to float or not fully close, but I'n not much of an expert. Sounds like Texan knows alot about it.
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Old 06-18-2001, 05:03 PM   #7
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I think that the main readon is valve float, once you get to a certain point the springs on the valves cant close the valves quick enough, so that is one way the redline is determined. I was reading an article recently about a new valve technology, it uses spheres with slices cut out of them, when a whole part of the sphere is over the opening, the valve is closed, when part of the slice is over it, the valve is open. They tested this on a ford v8 from a lincoln that previously dynod at 240 hp after the new valve technology was installed, the engine made 576 hp and could easily rev to 17krpm. The power increase is from the lack of drag from the valvetrain, the rev limit is from the directnes of the valves, no springs to limit the rpms, i think that it was called radial sphere valve, but i could be wrong
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Old 06-18-2001, 06:00 PM   #8
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That's the Coates spherical rotary valvetrain you're speaking of death...
http://www.coatesengine.com/
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Old 08-17-2001, 08:26 PM   #9
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im not looking forward to the advent of electromecanial valve trains were insted of a cam opening and closeing the valves it is a eletrical sylonoid. and when the sylonoid eventuly wears oout and stickes in the oppen position WHAM instant bent valve. but it would be a great hp gain due to less engine effort being used to opperate the valve train.
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