Coasting with an Auto

[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.

[cfg83]

Compaq888 -

Originally Posted by Compaq888

this is the reason I stopped coasting with engine off. It can kill the tranny easy, and starter. I hate auto.

I am not sure. Did you stop coasting with the engine off on your auto or your stick?

CarloSW2

[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.

[JanGeo]

May be that the higher speed of the engine produces a quicker shift from the increase in automatic hydralic pressure. I think unless there is a freewheeling action in the torque converter than rev matching is a good idea. The clutch in top gear would wear much less if the RPM of the engine is closer to the normal RPM for the car speed. I would think that there would not be that many times when you would have to coast at that high a speed - more likely at lower speed when you would be shifting back into drive at less than 30mph. The last thing you want to do going down a mountain is to rely on brakes to slow you down if the drop is big enough leaving it in gear may be a lot safer.

[brucepick]

Originally Posted by Compaq888

... Whenever you let your foot off the gas the tranny goes automatically into neutral...

As written elsewhere in this thread, I also think it varies with different cars. I put a tach into my car so I could see better what was going on with engine rpms.

My car has auto trans without lockup converter, so ymmv, as always.

Leavng it in D on a nice long downhill coast will see the rpms drop to 1500 and stay there.

Putting it in N for a similar nice long coast will see the rpms drop to about 800. Idling in N when not moving, rpms = 700-800.

My take on it is, coasting in D has the car's momentum spinning the engine via the tranny. It's not fully "engaged" as when your foot is on the gas, but those rpms have to be coming from somewhere. My foot is off the gas so I think it must be the car that's driving the engine. Those coasts seem to lose speed faster than the ones where tranny is in N. That always gives me the best coast. Oh yeah - electric rad fan, so the airflow is NOT driving the engine!

I drive Rte 9 in CT daily, it has loads of long up and down grades where I pulse to about 70-75 going down, and then glide the max possible till I need to help it get up the next hill.