Knowing absolutely nothing about cars engines....ok just the very basic stuff - I would like to know what happens when a car over revs. Will it cut out, will there be damage (in modern engines like that fitted to the 9N with ECU's and stuff like that)? Not being a fan of 'dicing' or 'one-on-one racing', because of the fact that I don't like taking the car above 4500rpm (except when I'm on the open road and doing something like 105mph on a closed circuit).
Why I am asking is, I just had an experience where I (in the heat of the moment - actually just wanted to get home quickly and NOT wanted to race) raced another guy and when I looked at the rev-counter once, it was at 5500rpm (or something near to that in 2nd or 3rd) I took my foot off the gas and let the guy pass, 'cause I feared damage.
So what could happen?
Revving....
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polo2k
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well the engine has a rev limiter that is ment to protect the engine from damage however there is another way to over rev an engine, this is in down gearing for example if you went into 2nd gear at 60 mph then the engine would over rev and possibly turn on the engine check light
the parts that can be damaged in an over rev can range from things like the alternator running too fast but there can be some very severe conciquences such as snapped timing belts, bent con rods, bent valves, scored bearings, "corkscrewed" cranks, snapped cams, oil pump failure, holed pistons (if a valve sticks) so you get the idea
in my experiance a well aintained vw engine can take the occasional over rev as my polo occasionally gets over reved on down shifts when trying to shrug off speed coming into corners, the worst i have ever over reved was in my golf doing the best part of 100 mph ( on a cosed road with no public access
) and went to shift into 4th gear (from fifth) to accelerate but when i went for 4th i missed, hit second gear and by some simple calculations * i am fairly sure (that without clutch slip) i actually got to 12,000 rpm for a few seconds and since you are at twice the rev limit the engine starts to come back out of the rev limiter as the sensor gets saturated with pulses however at theese kind of speeds the possibility of SEVERE engine damage is almost certain but i was lucky and only got some valve bounce which is where the valce is moving so fast that it bounces off the valve seat as it closes and then the valve takes on a harmonic resonence that makes things worse.
* on a aex engine fitted to a golf the rev limiter is at 6,000 revs and in second gear this gives 50 mph so if we double the speed then we must also double the engine speed
so 50 mph x 2 =100 mph
and 6000 rpm x2 = 12,000 rpm which in turn = a very confused ecu and risking total engine failure
the parts that can be damaged in an over rev can range from things like the alternator running too fast but there can be some very severe conciquences such as snapped timing belts, bent con rods, bent valves, scored bearings, "corkscrewed" cranks, snapped cams, oil pump failure, holed pistons (if a valve sticks) so you get the idea
in my experiance a well aintained vw engine can take the occasional over rev as my polo occasionally gets over reved on down shifts when trying to shrug off speed coming into corners, the worst i have ever over reved was in my golf doing the best part of 100 mph ( on a cosed road with no public access
) and went to shift into 4th gear (from fifth) to accelerate but when i went for 4th i missed, hit second gear and by some simple calculations * i am fairly sure (that without clutch slip) i actually got to 12,000 rpm for a few seconds and since you are at twice the rev limit the engine starts to come back out of the rev limiter as the sensor gets saturated with pulses however at theese kind of speeds the possibility of SEVERE engine damage is almost certain but i was lucky and only got some valve bounce which is where the valce is moving so fast that it bounces off the valve seat as it closes and then the valve takes on a harmonic resonence that makes things worse.* on a aex engine fitted to a golf the rev limiter is at 6,000 revs and in second gear this gives 50 mph so if we double the speed then we must also double the engine speed
so 50 mph x 2 =100 mph
and 6000 rpm x2 = 12,000 rpm which in turn = a very confused ecu and risking total engine failure
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polo2k
- Bling Bling Diamond Member
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- Joined: Tue Dec 10, 2002 1:01 pm
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s long as you donp pin your car to the limiter when shes cold then your safe but when the engine gets hot then your ok to get the needle round towards the red zone once in a while
Last edited by polo2k on Sun Jul 13, 2003 3:02 pm, edited 1 time in total.
