M6 first gear question

[third_shift|studios]

Sometimes when i'm stuck in heavy traffic, i'll just leave my ws.6 in 1st and either let it idle or i'll gently accelerate. Well, i've found that if i accelerate then let go [say @ 2000 rpm's] when it goes to about 1500 there is this "bottoming out" feeling i get almost as if it were an automatic doing a downshift...

something tells me this is normal, b/c i've felt it with big dump trucks too

[third_shift|studios]

bump

[Fran D]

Is this a question? I'm not sure I understand what you are describing. :dunno:

[third_shift|studios]

bah...sorry. the question is; what is the "bottoming out" feeling the car does when it's in first and idles down from 2000 rpms?

[t/as&dds]

It's probably the rear end clunking from the sudden change in motion. First you're giving it gobs of power by getting it to 2 grand then you're letting off and letting engine braking take over. I noticed that same thing.

[paul100]

Actually what i think you are feeling is the computer shutting down the fuel system. I beleive it does that when you are in gear at a low rpm with out the throttle being open.

[third_shift|studios]

It's probably the rear end clunking from the sudden change in motion. First you're giving it gobs of power by getting it to 2 grand then you're letting off and letting engine braking take over. I noticed that same thing.

that sounds about right...next time it happens i'll try to take notice if it's from the rear or not..

[GatorSS]

It's the rear end and it's normal.

[ButchN]

It's the rear end and it's normal.Never heard of that & my car doesn't do it.

[TransAm45]

It just has to do with physics. Considering your motor is directly linked to your rear tires.. and since you are in 1st gear (with a 2.97-1) ratio, everything your motor does will be maximized by your rear tires. As the motor is downshifting, you will feel it the rear tires slow down also (obviously) and it will seem as if you hit the brakes. Its just because the 1st gear ration is so high.. if you do the same thing in 2nd or 3rd you wont feel it nearly as much.

[GregP]

He's talking about the idle-down characteristics of the LS1. Once at rpm, say ... 1500 or more, it tends to stay at that rpm until the manifold pressure hits a point that says "we're deceleratting," and then it shuts the fuel down to idle level.

So, basically, if you accelerate and then back off, you'll travel some distance and will "coast" for some distance before you get much effective "engine braking." If you are on a road course, forget engine braking and use the brakes. The LS1's engine braking is almost non-existant until well after you already expected it ... until you drive it for awhile. Then, it's normal ...

Is that what you're asking about?

[oneBADDz]

I know exactly what you mean, my '97 does it too and it has nothing to do with fuel systems etc. It's just the point where the whole drivetrain makes the transition from pulling to being pulled. All of your gears are pulled tight against each other when you accelerate, and when you let off and decellerate they lose contact then pull tight against each other in the opposite direction as the drivetrain is being pulled by the car rather than the drivetrain pulling the car