What happens to a car engine if you change gears ?

Question

What happens to a car engine if for example your going at high speeds eg 80mph (5th) and then you change to (1st) ? I know its not something you should do, I assume your gonna blow the engine.

In terms of engine pressure, cylinders, oil etc what exactly happens in there ?

Answer 1

Usually the transmission gears give out before the engine can do any damage to itself.  

Answer 2

It's like this; The gears allow you to slow down the engine so you can go faster without revving the engine to high. So you'll notice that as RPM goes up, you change gears and RPM goes back down, but you go faster.  If you're doing 80 and you switch to first gear, your engine will rev up so high, it will blow up. The pistons will move faster than they can handle, you'll probably throw pushrods from too much force, and the engine oil pressure will make it blow. Gaskets, oil rings, they can only handle so much pressure, and if you've ever noted, the oil pressure gauge on most vehicles will slightly rise as you accelerate.  It's just too much for the engine, it can only handle so much heat, pressure, speed, etc.

Answer 3

if you were to do this the drive tires would go into a skid due to the extreme slow down and you would probably loses control and crash.  the syncros in the trans wouldnt allow this unless forced, causing extreme internal damage to the trans and driveline. as for the engine the RPMs would be too much and the extreme internal pressure would cause the pistons conn rods and crank to crack/shatter, timing chain/belt would break causing the valves to collide with pistons totally destroyngthe valve train.  IF you got lucky, maybe the extreme pressure in the motor would cause the clutch to slip, saving the engine.

Answer 4

If you go from say fifth to first at 80mph you could, as you say, blow the engine or gearbox.

The engine and gearbox revs will desperately try to balance each other resulting in the road wheels not being able to keep up possibly throwing you into a spin.

Not really an advised thing to do :)

Answer 5

extreme pressure.  If you had good oil it would help alleviate the pressure, but it wouldn't  be wise to even think about something like this unless you were talking about taking it to the demolition derby, then maybe you could do it and see what would happen.  put it back up when you do it and tell us.

Answer 6

Basically, your engine would, metaphorically speaking, stick its head between its legs and kiss its arrr's goodbye.

Answer 7

If you do somehow manage to shift from 5th to 1st at 80, the following may occur

in Fifth gear the engine and transmission, will turn just over 1000 RPM, at crusing. At that gear also, your engine will be turning at the same speed, if not slightly slower of that of the tranmission and rest of the drivetrain. this means the engine is not putting much effort into pushing a car at the gear and speed,

Immediately when shiftting to first on your transmission from that speed, will bring the engine up over 5500 RPM, this caused by the transmission's lower gear ratio, to spin much faster than your engine.

The engine being the driving force of the car will immediately slow the car down and if kept in first.

This will cause you engine to overrev to keep up during this:

You will experience a huge shift shock, your car will slow down, it won't sound good at all as your engine redlines, (your trans is now pushing your engine, while it tries to slow the car down)

belts will slip because its going to fast,

oil pressure will climb as well as oil temperature,

transmission oil pressure will climb as well as temerature Lose a few gears

Clutch will not be happy with you

Timing will be off, and may misfire

Cylinders may seize

gaskets may blow due to sudden rise of oil and temperature pressure

oil rings may blow.

Smoke from super heated oils possilbly lots

burning smell as your engine stalls

loud not good sounding noises will occur

driver may lose control of vehicle

driver may lose control of bowel retention.

this may all occur within a matter of seconds

Answer 8

you probably cannot even shift into first gear at that speed, but if you did, the engine probably is not going to "blow".  Your drive tires will lock up, and you'll lose control of the vehicle.  Most likely your trans will suffer damage before the engine.  

Answer 9

I love some of these answers lol.Obviously some people have no clue what goes on inside an engine.Perry F gave you the best answer as to what could happen.

Answer 10

The valve train cannot fully cycle at very high RPM's due to it's mechanical properties and it's inability to dissipate the heat fast enough cause by the excessive internal friction.

Answer 11

compression.and IF,the trans manages to go into gear the trans will likely be the thing to go.

Answer 12

It would cause the engine to rev so high, the pressure in each cylinder would build up to beyond it's maximum working pressure and probably blow the engine causing castostrophic damage to itself. I know someone that did this - on purpose because he wanted rid of the car.... Not a very nice this to do to a perfectly good and usefull machine.

Answer 13

if your talking about a standard transmission, you probably won,t be able to, and if you did, it would tear the clutch out.

Answer 14

The transmission would not allow the shift.  If it did the engine or clutch would disintegrate because you would go from 2500 RPM to 11,000+ instantly.  At that RPM the valves would "float" which means they would not fully close, causing the piston(s) to make contact.  You can picture the rest. . .not a pretty picture.

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Answer 15

The engine will start to turn so fast that the mechanical parts can't cope with the stress and come apart (ie. blow up).

It will essentially tear itself apart, modern cars have safeties to prevent this.

Answer 16

If you are traveling at 80mph in 5th gear, it will be very difficult to get the car into 1st gear as the input speed of the gear box will be very high.

However if you were able to force the car into first and then you droped the clutch several things will happen at once.

First the clutch will slip like mad as there is major difference in engine speed to gear box speed.

Secondly the load on the gear box will probably result in first gear stripping.

If the clutch does not burn out or the gear strip the rev's of the engine will rise way above the red line, this will result in the rear wheels probably locking up and then the engine will probably blow.

Ja.

Answer 17

Most manuals will not engage due to the speed difference in the engine speed and the road speed, in order for the gears to engage they have to have the same or close to the same rotating speed, so it is unlikely that it would ever happen, an automatic has a governor valve that prevents a shuttle valve, or "shift" valve  from moving to the position that would allow the downshift.

"If" the transmission was placed in first gear at ,say 80mph, the engine would be forced past it's maximum RPM by the road wheels, likely floating the valves (the valve springs cannot return the valves to a closed position, this is  caused by  a cyclic vibration that collapses the spring) and the pistons may hit the valves, or each other-(intake and exhaust, in the case of a DOHC engine). The wheels would effectively drive the RPM of the engine past red line, causing catastrophic damage due to mechanical interference, not extreme cylinder pressure. You could stretch a rod causing the piston to hit the cylinder head, I have even seem rod bolts, stretch and break resulting in total engine destruction, thats termed catastrophic engine failure due to abuse.