I don't remember......it's bin a long time since the last time I drove mine.

 

i dont think s4's n/a have a fuel cut. only the tIIs have it. and as for hitting a wall on 8250, the needle may stop there and the engine can still spin. i wouldnt recommend it though

 

Mine definately had some sort of rev limiter. It stopped and sputtered at 7800 or so, it seemed like fuel cut to me.

 

get VLC media player.

 

I think there is some sort of rev limiting device, either fuel/ignition or something, because i have heard my engine hit a "wall" many times, usually in first gear over revving, even if you are going straight line and hear the engine go and go, just remember that both the gauges are slow to react, and the tach is very inaccurate imo (redline buzzer coming on at different rpms all the time). So like if you rev your engine just sitting there with no load, by the time the gauge maxes out the motor is already doing probably close to 9k. And if you are straight line accelerating and the tach maxes out, but the speedo still says your are increasing speed, its probably just taking longer to get to the appropriate speed compared to the car itself.

 

I miss-shifted and hit 9800 (according to my safc). My compression went to 0 within a week.

 

wow, you must've been mashing on the throttle while tryinhg to rev-match??

 

S4 NA's have a rev limiter at ~8250 rpm, I hit it almost everyday in my car.

 

IDK ive been told S4's don't have rev limiters at least the TII doesnt. Maybe a fuel cut but i have revved to about 8200 and the car hasnt cut on me. Maybe a fuel cut somewhere higher than that but not a rev limiter. Oh and BTW i wouldnt sweat it as long as you are not doing it often you should be fine.

 

err,.. so what exactly do you consider the difference between a rev limiter and an rpm-dictated fuel cut?

 

by the sounds of it no one seems to care about overev
s..... i mean ive never taken the 7 past redline, sept once when i wasnt paying attention....

but as soon as the buzzer kicked on i shiffted.....

do you guys not consider passing redline to be a unwise idea?
8250 rpm isnt gonna burn that engine out?
you dont think its gonna blow a seal?\

 

On a Series 4, The ECU will cut fuel to the rear rotor at around 8250. Also called a Fuel Cut. People have different ideas about the meaning of "rev limiter". Some say if you car has a rev limiter that its ignition only and that we have a fuel cut. Some say rev limiter is just a term used to explain that there is a safety system in place to limit the revs.

Either way S4 has a fuel cut. Most of the time your tach is off up high. My tach has gone near 8500 and the engine kept reving higher then it hit fuel cut, but I know for a fact that it was near 8250.

 

The way I see it, a rev limmiter is something that limmits revs. Anyway, taking the engine to the fuel cut for a small amount of time isn't going to hurt anything, especially on a rotary. I hit fuel cut in my 5.0 mustang a few times and nothing happened. Generally, manufacturers put the fuel cut before an harm could come to the motor if run there for a short period of time. Also, it takes something major like a detonation to pop a seal. There was a video of a couple idiots who took a 7 with a blown front rotor and ran it floored for 3 minutes straight. The only reason it died then was because it ran out of coolant.

 

actually it would be harder on the drivetrain because the tires are already rolling and therefore are harder to break traction. when you dump the clutch and the tires break loose it is much easier on the drivetrain then a dump and the tires just sit there and grab

 

Not really rxspeed. The drivetrain doesnt really get worn all that bad, say if your cruising at like 30-40 mph, then rev to 6k and dump the clutch in 3rd gear, if you dont break traction, your clutch just slips until it drops down to match the rpm. So the only thing taking damage in your "drivetrain" is the clutch. Tranny/driveshaft/differential/driveshafts dont really care that much. The clutch is usually the weakest link after the output shaft on the motor, the only thing that will slip first is usually the tires, unless ur clutch is pooched/you have really good tires. And thats only on a hard launch.

 

I'd rather change tires than a clutch.

Coincidentaly, in reference to the video I posted above coming out somewhere near 9krpm. The water passage cracked and broke free on the front plate few months later of driving in such manner occasionaly. Related, unrelated... either way, still an engine needing rebuilt.

Kent

 

Maybe you're right, but it seems to me that if the transmission is rolling along at 4000 or 5000 rpms, and you rev the engine to 8000 or 9000 rpms and dump the clutch on it, you're talking about a difference of 4000 or 5000 rpms. If you rev the engine to 8000 or 9000 rpms with the car at a stop and dump the clutch on it, then you're talking about a difference of 8000 or 9000 rpms, and I can't help but think that would be worse for the car.

Or let's view a few other relevant analogies:

On a relatively flat surface, is it easier to push a car from a stop, or to push it faster once it's already going?

Or here's a better one,
If you're driving along and you hit a car, would it do more damage if that car was at a complete stop, or if it was already moving in the same direction you are?

 

most any of the cars I have owned are faily underpowered I admit but everyone of them if I dump the clutch at higher rpms while rolling the clutch grabs more or less right away.
in that case most the shock still goes to the drivetrain and has actually led to the destruction of one driveshaft which in turn spun around and hit the tail end of the tranny taking it with it. that really sucked somehow though no cats where injured in that event.

now maybe if your clutch is worn it will slip but if you have any sort of decent clutch in there it can and should grab right away and since the tires are already rolling are going to be much harder to break free and instead the drivetrain has to absorb all that shock with the clutch only taking and absorbing a very minor part of it.

 

I can understand what your saying but when your dumping from a stop chances are your tires should give fairly easily. when those tires give a lot of the force of the drivetrain goes through the tires and the tires give just pumping that energy int movement. if your already rolling though those tires aren't going to give as easily and instead that shock will get absorbed slightly as extra movement of the tires in acceleration but the majority of that shock gets put to the drivetrain.

when those tires give it's like going with the punch.

since you seem to like the anology try this one. I have a car driving along and your walking on the road car hits you doing 20mph. sure it will hurt (been there done that) but since your just walking in open space your body will move and give into the impact letting you kinda roll with it. now same car moving at lets say 10mph but your standing next to a wall that just won't budge much. which do you think is going to hurt more?

sure in the first one just like as you say dumping the clutch at (7000rpms from a stop) might have a higher initial energy to the body as the movement of the car is faster. but within a very split second your body should start to move with the car overall absobing much less average energy. now when your against the wall your just fucked. nowhere to go and nothing to do but absorb most all of the energy of that car which in turn leads to many squished and broke bones. initial first split second might not absorb as much but your body has no choice but to abosrb everything so again overall average is much higher.

it is easier to push a car once it is already moving. but when you dump the clutch when your moving most of that energy doesn't transfer into acceleration most of that energy instead gets transfered into the drivetrain. if the drivetrain can not absorb it then it breaks. from a stop most of that energy has a higher initial shock but a lot of it ends up being transfered to the tires in the form of heat leading to smoking tires and lots of fun


as far as your second question it should be explained above, but to further explain it I would rather hit an object already moving with me as you are trying to imply but a big difference is even though both objects are moving with each other since the object being hit doesn't budge reletive to the object doing the hitting it's a little different. so in essence even though both objects are moving with one another it is as though the drivetrain isn't moving. explain the difference to me here. take your car somehow prevent the tires from moving now rev the car up to 4000rpms dump the clutch. now take the car drive down the road doing 4000rpms then rev up to 8000rpms and dump the clutch. chances are when you finish dumping the clutch and it grabs your going to be doing fairly close to 4000rpms still. so whats the difference then in this case? relative to each other they are the same.


kinda get what I'm saying?

 

No.

Your analogy of the person and free space vs. wall is completely different. We are talking purely about rotational forces and the force of friction exhibited by the tires and the clutch. Your talking about a mass with a lateral vector and the impulse (change in momentum) exerted against a stationary object. It has no relevance here.

When you drop a clutch while rolling, the rotational force required from the drivetrain is much greater than when stopped to break the traction of the tires free. Thus, the clutch is put under more load, and begins to slip, and not near as much force is delivered to transmission and thereon because it is dissipated as energy from the clutch as heat caused by the friction, instead of the friction being greater than the required force. Now given that its a stock vehicle, the clutch is still strong enough to overcome the motor head to head, but it slips at first because of the massive amount of energy being dissipated from the high speed rotation of all the rotating mass such as the flywheel and engine internals.

Now do you get what IM saying?

 

1. Correct for the most part, i guess.

2. That really isnt relavent, because pushing a car is dependent on your body strength, and the slower you travel the longer you can apply the force from your body, and the force is only applied while you make contact with the ground (feet). So, as the car picks up speed you start to run and the time your feet are on the ground are longer. Also, if it begins to move fast enough, frictional forces start to play a roll (bearing drag, transmission drag, aerodynamic drag, etc etc.)

3. Thats purely because the impulse is less if the car is already moving.

 

too early in the morning still but I get what your saying and I still disagree if there is a decent clutch as trying this before hasn't always led to a slipping clutch but instead has led to grab followed by driveshaft going boom


as far as what I said having no relevence being it is based upon a mass and change in momentum what happens when you dump the clutch? you have a heavy mass known as the flywheel and the motor transfering energy to the drivetrain trying to change it's momentum correct? as I said too early in the morning though. just being that one is rotational and one isn't rotational doesn't mean that there is no energy tranfer or attempts there of to change momentum

 

Well if you want to get technical if you are in a different gear when comparing rolling clutch drop to standstill clutch drop, the torque will be less in a higher gear, and torque is the only measurement we are interested in here. So obviously if you have a better clutch it will obviously provide more force than a weaker one, but since the gearing is being changed in the transmission-more rpm with the sacrifice of torque- then the force is less than with a standstill clutch drop. Also, if you think about it, the weight transfer when you drop the clutch is much greater than a rolling clutch drop, so the tires offer an even better Ff (force of friction) therefore more resistance and more stress on drivetrain. Its confusing, i know, but im trying to explain things as best i can.

Oh and just an fyi, although i am confident (95% sure) with my answers, i MAY be wrong. I only have 2 years of high school physics under my belt, so please correct me if im wrong. But if you do say im wrong, please let me know why, i am always up for learning more physics .

 

that beep is for the exaust temp schwag cause rx's have such high exaust temps

 

Uhm no its not, its to tell you your redlining. Thats why it goes on as soon as u go above just under 7k rpm. I personally have never had my exhaust temp buzzer go off. Is there even a buzzer? I know theres a light... Then again i just got straight pipes and oem type mufflers. The flow is probably too good to even heat up too much. Id imagine clogged cats would make it heat up fast as hell tho.