Why would an engine blow when running too long past the redline?
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From: Oakland, CA, Bay Area
Car Info: Subaru WRX MY02
Why would an engine blow when running too long past the redline?
Would an engine blow when running too long past the redline?
Why and how?
This is a serious question. No jokes. Lets say for instance your running in third gear and youre constantly running the car past the redline. For instance, were using a wrx tachometer which redlines at 7000 rpm.
Since the tachometer goes up to 9000 and the car is pushed for a period of time past 7000. At this point, Im assuming that the air intake should be glowing hot red at this point.
The engine would pumping hot air through the intakes, the chamber surrounding the pistons would also get too hot, and throw the camshaft through the casing, and destroy the engine. Anyone care to add more or clarify this more for me?
Thnks,
- U.
Why and how?
This is a serious question. No jokes. Lets say for instance your running in third gear and youre constantly running the car past the redline. For instance, were using a wrx tachometer which redlines at 7000 rpm.
Since the tachometer goes up to 9000 and the car is pushed for a period of time past 7000. At this point, Im assuming that the air intake should be glowing hot red at this point.
The engine would pumping hot air through the intakes, the chamber surrounding the pistons would also get too hot, and throw the camshaft through the casing, and destroy the engine. Anyone care to add more or clarify this more for me?
Thnks,
- U.
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a lot of it would have to do with valve float, which is when the engine is moving too fast for the valve springs to keep up. so they end up "floating" or not being where they should at the right time, thus bending, breaking, melting and otherwise destroying things.
-PJ
-PJ
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valve float is murder on engines. you don't have to look to hard to find pics of someone's motor that got overreved, and snapped a valve stem, and the stem went through a piston.
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given the design of the EJ20, i'd imgaine that by the time you're in rod throwing territory, there is a serious danger of a) the crank failing due to the opposing forces being placed on it b) failure of crank bearings, causing the crank to wobble and tear the motor apart.
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Obviously you'd have to somehow remove the rev limiter to try this out. Let us know how it works out.
Just kidding. Like everyone else said, the springs in the valves can't keep up for starters. Sport bikes and F1 cars can rev higher because their cams/valves are built to rev that high AND they generally have a much shorter stroke relative to the bore. Less distance for the piston to travel means it can spin faster. Emissions laws (which don't apply to bikes) prohibit doing someting like this in cars.
Just kidding. Like everyone else said, the springs in the valves can't keep up for starters. Sport bikes and F1 cars can rev higher because their cams/valves are built to rev that high AND they generally have a much shorter stroke relative to the bore. Less distance for the piston to travel means it can spin faster. Emissions laws (which don't apply to bikes) prohibit doing someting like this in cars.
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Let's see. What else. They covered the valve float thingy. Which in alot of but not all cases can cause trouble. Most engines now are non-interference type engines, but that doesn't mean that nothing can happen. You biggest problem with valve float, if you don't bang a piston, is a SERIOUS loss of power and possibility of an intake backfire. Not a good thing. The rod throw...you've now exceeded the limit of the rods ability to spring back from being stretched out during an intake cycle. You are now causing a rapid hardening of the rod because of the loss of elasticity and it fails. OR...you've pulled on the top of a piston during an intake cycle, which is when the rod pulls on the piston the hardest, and the wrist pin area of the piston just gives up.
After all of that, what you have is a real nice doorstop or a whole bunch of paper weights...
After all of that, what you have is a real nice doorstop or a whole bunch of paper weights...
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the other reason that sport bikes are capable of revving so high, are the differance in piston weights. consider a 600cc sport bike with four cylinders, versus a 2000cc car with four cylinders. the sport bike's cylinders displace 150cc/cyl. while the car's displace 500cc/cyl. the pistons in the bike are much, much lighter, and therefore can travel at a higher rate of speed while exerting less stress on the rods and crank (which are both lighter than the car's).
F1 is a completely differant story. F1 cars don't use valve springs to open and close their intake and exhaust valves. the valves are pneumatically actuated, and open/close much, much faster than any spring is capable of. that's and stupidly strong and light internals are what allow those cars to rev to 18,000 RPM.
F1 is a completely differant story. F1 cars don't use valve springs to open and close their intake and exhaust valves. the valves are pneumatically actuated, and open/close much, much faster than any spring is capable of. that's and stupidly strong and light internals are what allow those cars to rev to 18,000 RPM.
I don't think intake will ever glow red hot.
Imagine a car with red hot FMIC, that'll freak me out.
If it does, sensors and wires are gonna melt and stop the motor.
The intake air will be compressed and get hot but not glowing red hot.
Basically valve springs won't be able to compress and spring back fast enough and then valve won't open and close at the right timing. Then something mechanicaly breaks or melt from uncontrolled explosion.
someone did 5th to 2nd misshift in RSX
i wonder what was the rpm it went up to...
Look at that chunk of metal that used to be a piston LOL
http://forums.2gnt.com/dcboard.php?a..._id=40306&page
Imagine a car with red hot FMIC, that'll freak me out.
If it does, sensors and wires are gonna melt and stop the motor.
The intake air will be compressed and get hot but not glowing red hot.
Basically valve springs won't be able to compress and spring back fast enough and then valve won't open and close at the right timing. Then something mechanicaly breaks or melt from uncontrolled explosion.
someone did 5th to 2nd misshift in RSX
i wonder what was the rpm it went up to...
Look at that chunk of metal that used to be a piston LOL
http://forums.2gnt.com/dcboard.php?a..._id=40306&page
Last edited by go go go; Jun 7, 2003 at 08:05 PM.
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