Coasting with an Auto

[kickflipjr]

Today was the first time i tried drifting down a hill (engine not on). I just put into N, killed the engine, coasted down this one hill for about a mile, and then restarted when it was needed. I have heard that this can be bad for certain auto trannies. I have also heard that it isn't bad on saturns (i don't plan on doing this too often because it is hard on the starter).

[omgwtfbyobbq]

I was thinking, if the auto really does cut fuel when coasting, then breaking up driving into small P&G intervals should really help out with FE. The driver could pick a target speed, and window, so depending on how much of the time they pulse and how much they glide, pumping losses could be reduced by that ratio. I'm thinking something like a 20% increase in FE could be attained with this technique in an auto, but it really depends on whether the injectors shut off. Does anyone know how I can test this, for cheap?
I've seen the fancy induction tach the smog places uses, but is there a low tech solution that can tell me if there is a signal or not?

[SVOboy]

Hmm, just hook a light up to your injector's switched ground and if it's not flashing then the injector ain't turnin' on.

[omgwtfbyobbq]

So there's enough current to light an LED? I'm hoping the current draw won't screw with the pulse...

[SVOboy]

My injector powering lit up my LED very well when I was messing around the other day. I doubt it'll mess with the pulse, I have my superMID hooked it to my #2 injector without issue.

[omgwtfbyobbq]

Sweet! Probably try this out on friday.

[Traugbot]

i had a tranny go out in my old car (not from n-bombing) and it is not fun. I got stuck in an intersection, so if n-bombing is bad for your tranny i wouldnt advise doing it

[Erdrick]

Alright, so let's say that I am driving along at 40mph. I am coasting down a hill, and decide to put the car into neutral. I end up going about 50mph by the end of the hill, still in neutral. Without touching the gas, if I were to then, at 50mph, shift the car back into drive, would that hurt the transmission?

[kickflipjr]

Originally Posted by Erdrick

Alright, so let's say that I am driving along at 40mph. I am coasting down a hill, and decide to put the car into neutral. I end up going about 50mph by the end of the hill, still in neutral. Without touching the gas, if I were to then, at 50mph, shift the car back into drive, would that hurt the transmission?

well, you should rev up the RPM (while in neutral before you put it in drive) so they match what you would be at at 50mph (say 2,000rpm) and then put it in drive. Doing that will hurt your car less.

I really think costing with an auto may be more trouble then it is worth (unless you find a long gradual hill).

[Snax]

The effectiveness of rev matching is probably going to vary by vehicle. Not only that, but torque converters absorb the bulk of it and likely mitigate much of the wear associated with shifting in and out of gear.

Play around with it. Whatever works the most smoothly is the way to do it.

If I were to try to reve-match in our truck, it will clunk aggressively into gear every time at highway speeds. It produces a virtually unnoticeable engagement by simply leaving it alone until the gears are engaged again.