Throttle strut?

[scottzg]

Well, this evening marks the 3rd time i've been in a car that 180'ed because of lift off oversteer. No harm, no foul, but it's still a disconcerting experience. Although this has never happened while i'm driving, i'd rather keep it that way, and so i got to thinking.

Why not stick a small strut on the opposite side of the throttle? The idea being that when you lift off, the throttle doesn't snap shut, rather eases back closed, slowing the engine more gradually. It couldn't be very agressive, as it would affect throttle and shift timing and whatnot, but even slowing the last 10 degrees of motion should make a considerable change.

Of course lift off oversteer is great on the track, but some of us don't live on a track. I was wondering if anyone had any opinions on this idea, ie, e-throttle, that wont work, how it might be set up, you're fkn brilliant, etc etc etc. Cool.

[THAWA]

Stop lifting off the throttle.

[BAC5.2]

You can prevent it by driving correctly.

[scottzg]

Stop lifting off the throttle.

You can prevent it by driving correctly.

How nice it would be if we could live in a fantasy land where the only result of a driving error was bouncing off the magical marshmellow guardrail and back onto gumdrop lane. Unfortunately, until the transit authority places more budget money into confections, that isnt the case, and a generally good driver can get bit by lifting. Myself, i can't initiate that much rotation in a parking lot, and so i worry that i won't recognize the situation until it's too late.

Does anyone have anything to ADD?

[THAWA]

But serisouly, you might be able to give the throttle cable some more tension by tightening the screws that hold it mounted to the manifold. If you could get it just right the plate wouldn't slam shut so forcefully. Or maybe you could have a very small tube bypass the throttle body so that even if you slam it shut there's still enough air getting there or something to keep the revs up a bit? I dunno, just stabbin in the dark.

[vrg3]

The functionality you're describing is that of a dashpot. Dashpots used to be physical valves that would damp the action of the throttle, allowing air to pass through momentarily after the throttle slams shut.

Our cars have a virtual dashpot. The ECU operates the IAC valve based on input from the throttle position sensor and idle switch in order to achieve dashpot functionality. In short, the car already does what you're describing. Just not as much as you might want.

If the dashpot were more pronounced, though, it would start to adversely affect drivability. Ever driven a car where it seems like the throttle butterfly is only vaguely connected to the gas pedal? That's undesirable as well, since it limits your control.

[BAC5.2]

If you can get bit by lifting, then don't lift. Nip the problem on the input end, and be conciously aware of what lift-throttle oversteer is, and how to prevent it. The only time I have ever fallen victim to lift throttle rotation is on purpose. Education and knowledge of the situation can help in preventing it.

To ADD, lift throttle oversteer is like all other types of oversteer. Just countersteer and apply the throttle as necessary to control slip angle.

If you would like to practice extreme situations, head out in the snow. Roll in 2nd or so, and start to turn slowly. Slam the throttle shut and the car should lock momentarily and the rear should swing around. It's a very similar feeling to what happens during lift throttle oversteer. Make actions slow, smooth and calculated.

What's different about the street, is the resistance YOU feel as the driver. When sliding on the street, there is a moment of "floatiness." Learn to recognize this moment, because that's the point of no return. If you start to feel the floatiness, you start to countersteer. If you feel it, then it ends, you are pretty much fucked.

To get this idea in the dry, you should be able to simulate it in a parking lot (auto cross style). In a parking lot, a slide will just slow you to a stop, but it should give you a good feeling of what it feels like when the rear breaks loose on the street.

Understand how it all works, and performing it on the street makes more sense. The biggest hurdle, is telling yourself to move with confident, smooth, and slow movements.

Not that I recomend and condone this type of behavior, but if you have an area with a decent grass runout on the side, you should give it a shot so you can learn your boundaries. That, and play lots of GT3. The dynamics of slip are pretty realistic in that game, and it helps you to remain focused and control the harshness of your actions.

[Brat4by4]

Not a good idea. So the next time you are in an emergency braking situation and come off the throttle, it powers you for another 50-100 ft depending on the speed?? No thanks.

The only mod needed here is to tighten the nut behind the wheel. Driver skill is the problem. Fix the problem, not symptoms of what they do. I really don't think I want more namby-pamby electronic/mechanical stuff that's meant to protect me like I'm an idiot. Thank you, car, for putting half of my seatbelt on for me...

[G-reg]

05's with the Elec throttle do this constantly....and it blows ass It sucks because when you lett off the throttle to shift or blip for a down shift the engine keeps rising 500rpm or so....not ideal and VERY annoying

[evolutionmovement]

Left foot braking could be a way of easing out of this problem for you. You could keep the gas on while using the brake to tighten the line. I use it all the time in the snow (especially with these summer tires). It also defaults to giving you a smooth transition from brake to gas by design.

Steve

[scottzg]

Well, i spent the morning experimenting with this idea, and although it worked, im not gonna leave it set up. I personally don't have a problem with lift off oversteer, and the time/hazard required outstrip the reward. I used a pen pocket clip epoxied to the throttle to slow the throttle for it's last bit of movement. Aside from messing the idle up a little if you eased off the gas to a stop, it worked pretty much as i planned.

When one ran in first up to 5000 and stepped off the gas, no longer did the car lurch like it normally does because of confused efi. Rather it would ease back (quickly) down to a lower speed, with a small 'step.' There was very little change to shifting, it would be about 200rpms higher than it normally would be when doing the "subaru mt sucks slow-shift" and the clutch could easily compensate for that. Driving in the hills was the same, except on slow tight turns (15mph) where it was actually better.

I won't be keeping it though, as in town the idle problem was irritating, and the pen clip kept loosening its hold every so often. I'm sure these things could be worked around, but i'm tired of messing with it and the thought of the clip jamming the throttle open is somewhat disturbing. I also dont know how the ecu is gonna like it long term. The other thing is that at this point im pretty convinced that the 180-ing is not caused as much by throttle as it is by the vehicle dynamics. Ya just can't control enough just by monkeying with the throttle to do anything significant. If i'd had any sense i would have just read a little about porsches; im sure they have looked into the issue quite a bit already.

Its interesting that the iac does this. The only other car i've had to deal with the iac with was my bmw, and it was just a plastic/rubber doohickey that expanded when it was cold, i didnt even know the iac was electronic.

In all, probably a waste of time, but i learned from it.

[BAC5.2]

Lift-throttle oversteer is caused by rapid weight transfer, not the EFI system. Just to clear that up. All cars, to some extent, express lift throttle oversteer. Some more than others, and it's often based on alignment and suspension design. With our rear suspensions, camber goes positive under unloading, which can't help the scenario.

The S2000 I drove had very little lift-throttle oversteer, which was probably attributed to the double wishbone suspension, which retains alignment through the travel.

[scottzg]

Lift-throttle oversteer is caused by rapid weight transfer, not the EFI system. Just to clear that up.

Who said that?

[Yukonart]

Lift-throttle oversteer is caused by rapid weight transfer, not the EFI system. Just to clear that up. All cars, to some extent, express lift throttle oversteer. Some more than others, and it's often based on alignment and suspension design. With our rear suspensions, camber goes positive under unloading, which can't help the scenario.

The S2000 I drove had very little lift-throttle oversteer, which was probably attributed to the double wishbone suspension, which retains alignment through the travel.

Should try mine sometime when you get out here, Phil. Jesus. . . mine'll swing around on your like a mutha when you do that in a turn. Even with the coilovers to dampen the weight transfer!

[BAC5.2]

When one ran in first up to 5000 and stepped off the gas, no longer did the car lurch like it normally does because of confused efi.

I thought you were equating the confused EFI lurch as being a contributing factor to lift throttle oversteer. You go on to mention the ECU, and the throttle in general, which made me think you had the wrong idea about the condition.

You said later in that post, "...im pretty convinced that the 180-ing is not caused as much by throttle as it is by the vehicle dynamics." That's correct, it's not caused by throttle. It's caused by weight transfer caused by the lifting of the throttle.

Like I said, suspension design and driver competency are the major factors. It is a driver induced problem that can be prevented.

Art - But your rear suspension still has lateral links and a trailing link with a macpherson strut assembly. Camber goes positive when unloaded. I bet it feels loads better with the coilovers though, doesn't it?

[scottzg]

Here it is again:

low speed turns- oversteer is much less agressive
higher speed turns- oversteer is exactly the same

reason- efi bucking has less effect as speed increases, while suspension design has more.

decision- remove device as it is not worth persuing.

I am not confused. I'm reporting results from a 1 variable experiment.



Art's coilovers reduce weight transfer and camber change.

[BAC5.2]

It just seems like you are trying to solve EFI bucking, not lift-throttle-oversteer. Two very different conditions, not related.

Lift throttle oversteer is a driver induced condition. No throttle spring, or ECU modification will prevent lift throttle oversteer. ECU modification will reduce or eliminate EFI bucking. Like William said, tighten the nut behind the wheel to "tune out" lift throttle oversteer.

Art's coilovers reduce weight transfer, thus reducing camber change, but camber change still occurs through the motion of the suspension, and when the rear is unloaded, camber goes positive. Coilovers or not, weight transfer still occurs, and thus, camber goes positive in the rear.

I'm done with this. Good experiment, glad you learned something.

[Brat4by4]

It's not really the camber. Its the load on the rear wheels. If anything, if he has stiffer rear springs, this would make lift-throttle oversteer worse if the rear has less sway.

With the STi's acceleration, the transfer is greater and the balance more easily upset. If the car in question has a humongous drag inducing downforce causing rear wing, then you can lift throttle all you want because there is still force on the rear wheels.

[91White-T]

Hey, I wish I had some lift-throttle oversteer. Damn thing will barely oversteer in the snow if I left foot brake the snot out of it.

[Legacy777]

Left foot braking is a good way to help fine tune/modulate weight transfer.

I left foot brake with AT's all the time. It's the only way to drive them. I don't so much with the MT because I can modulate weight shift a lot easier with the throttle, assuming I am in the "correct" gear