how is it safer to downshift to a lower gear to a stop? then throwing it in neutral and pressing on the brake?

that just wears on ur transmission and clutch id imagine...i

i dont get why people do that...

 

WRONG...in a 6MT, the injectors are shut off when you take your foot off the gas pedal...when you are coasting, your engine is still getting fed fuel to keep it going, just like when you're idling, or when your RPM goes below 700 (or 1000...I think it's 700 RPM)...

 

exactly why I'm writing this thread, everyone "thinks" or "imagines"...if you put your car into neutral (in stick or auto), the engine is not slowing down, thus, not slowing the car down...now if you drop into a lower gear (manumatic or manual), your RPM will rise and your engine will slow down...now, this is a practice commonly use in a 6MT and it is recommended for a 6MT to save fuel & pads, control and take off, etc...and we've established that it doesn't harm the 6mt tranny or engine...BUT, my question is what is the effect on a 5AT since downshifting doesn't go thru neutral...Engine braking became a habit for me in a 6MT...rev match, shift down...and I do feel more control and shorter stopping distance by engine braking (the latter may be just in my head)...

 

Subscribing.. good thread MeetJoeAsian... been wondering...

 

thanX...now help me find some facts...hehehe...

 

Just like you everything i've heard is hearsay... I want the cold hard facts too!!! I've done searches but have come up with very little....

 

What happens if your coasting in neutral to a stop and you suddenly need to get on the gas a bit to avoid an accident - you're screwed. That's exactly why it's good to downshift.

I downshift all of the time in my manual cars - it actually feels weird not to do it. Since i don't rev match very often i'm sure i'm burning my clutch out faster and probably stressing my synchros. But as long as i'm always downshifting one gear at a time and brining my RPM's up to 3,000, it's no big deal. I'd rather do that than burn out my brakes (especially if I have aftermarket rotors and pads)

As for the OP, I don't have any facts...but i would imagine the rev matching in the 5AT's is not only to reduce the stress on the transmission but also to provide a smoother ride. However, since the transmission is not making abrupt down shifts I doubt it causes much extra wear on the tranny. Sorry I can't be of much help.

 

Aite...here's something from Wikipedia explaining Engine Braking...but remember, Wikipedia is not a reliable source cuz it's written by ANYONE...and also, they do not mention anything about tiptronic transmission....

Engine braking

From Wikipedia, the free encyclopedia

Engine braking is the act of using the energy-requiring compression stroke of the internal combustion engine to dissipate energy and slow down a vehicle. Compression braking is a common legal term for the same mechanism. Large trucks use a device called an engine brake to increase the effectiveness of engine braking.

Design

Compression of gas and vapor requires energy as described by theories in physical chemistry and thermodynamics. Compression in an engine is driven by the forward momentum of the vehicle as well as the angular momentumflywheel. When a driver downshifts to spin the engine at high angular velocity (or RPM) of the without pressing on the gas pedal, the engine converts energy from the vehicle's speed, which is kinetic energy, into a temperature increase in the fuel-air mixture. These hot gases are exhausted from the vehicle and heat is transferred from engine components to the air.
This energy conversion occurs because most four stroke internal combustion engines require compression of the fuel-air mixture before ignition, in order to extract useful mechanical energy from the expansion. Diesel engines are adiabatic and have no spark plugs and use energy transferred to air charge during compression to directly ignite the mixture when the fuel is injected.

Advantages

The advantage of using the engine to dissipate energy is this immediate ejection of energy. Hot gases are ejected from the vehicle very quickly and the gases also transfer much of their heat directly to engine parts. In addition, friction produced within the engine system also adds heat to the engine parts.
This engine heat is taken away by the engine's integrated cooling system: usually a liquid circulation system and a radiator. Disc or drum brakes have no such energy dissipation mechanisms. They must rely on air flow to remove heat and they use their mass to retain heat without producing temperatures that would deform and damage the brakes.
Placing a vehicle in a low gear causes the engine to have more leveragemechanical advantage) on the road and the road to have less leverage on the engine. This is what allows cars to slow down using their relatively flimsy engine parts. The engine maintains a high rotational speed to dissipate a lot of power without forcing too much strain on the engine. (
The engine brake is used in large diesel vehicles because the rate of conversion of mechanical energy into waste thermal energy is low compared to the mechanical returns to kinetic energy from the air-spring effect in the engine.

Applications

Engine braking is always active in all non-hybrid cars with an internal combustion engine, regardless of transmission type. Engine braking passively reduces wear on brakes and helps a driver maintain control of the car. It is always active when the foot is lifted off the accelerator, the transmission is not in neutral, the clutch is engaged and a freewheel is not engaged. This is often called engine drag.
Active use of engine braking (shifting into a lower gear) is only advantageous when it is necessary to control speed while driving down very steep and long slopes. It should be applied before regular disk or drum brakes have been used, leaving the brakes available to make emergency stops. The desired speed is maintained by using engine braking to counteract the acceleration due to gravity.
Improper engine braking technique can cause the wheels to skid, especially on slippery surfaces such as ice or snow, as a result of too much deceleration. As in a skid caused by over-braking, the car will not regain traction until the wheels are allowed to turn more quickly; the driver must reduce engine braking (shifting back up) to regain traction.

Legal implications

Compression braking, a form of engine braking, produces extreme amounts of noise pollution if there is no muffler on the exhaust system of the engine. Use of an engine brake produces similar effects, due to release of compressed gasses, but the mechanism is distinct from regular car engine braking. Anecdotally, it sounds similar to a jackhammer, however the loudness is between 10-20 times the perceived loudness of a jackhammer. Numerous cities, municipalities, states, and provinces have banned the use of unmuffled compression brakes.
This is often a source of dissatisfaction to professional truck drivers, some of whom believe that municipalities are taking advantage of them due to their transient nature, and thus disregard the law, believing that they will be gone before a complaint can be lodged.

 

I would not be so absolute, but me thinks a number of members have already stated this. An air brake is VERY useful in a dirt bike when you screw up and fail to make it to the top of a hill climb.

 

There's a very good reason for what happens when you get a big jolt of power. Typically, when you push the pedal to the floor board to pass, the car will usually go down 2 gears. So in 5th, depending on how fast your going and your RPM mind you, the car will typically go into 3rd gear.

when you just move the stick to the right, into Manumatic mode, it only dumps to one gear. If you don't realize this, then just move the stick to the right and quickly pull it back....same effect.

Also, re: Manumatic and rev matching, that works a bit, not perfectly. The engine DOESN'T slow down, it revs up - usually substantially, but that does also depend on your RPM's to begin with and what gear you downshift to, as in the example above. Many hit the stick to the right and pull it back, resulting is typical over rev for engine breaking.

Now - yes, as I wrote earlier in this thread, racing and spirited driving: engine breaking can be very useful, like others have written already, such as; limiting speed on a hill, going through canyons, and other emergency needs to stop quickly.

This is really a very simple topic, and why it gets so much attention is beyond me...simply put again, over revving and downshifting properly, will provide for increased drivetrain wear and tear, doing it right, will cause less, but you still have to deal with an increased rev, which will cause more stress overall. How measurable it is, is something that really has never been studied. You can build 2 identical engines, and one will and could last far longer than the other. Even if driven under controlled environments.

Rick

 

lol what? that may be the stupidest thing ive heard in 3 weeks. honestly, i dont look into getting into an accident anytim soon when i drive.

and what kind of accident can u avoid with needing gas? if someone pulls onto ur lane from oncoming traffic, he'll be going fast and u'd be f*cked either way. our daily lives arent like fast and furious

 

lol i was thinking the exact same thing.

 

If you guys are so worried about wearing out your engine, then leave it in the garage. If you own a Z, and drive it like a little girl, then maybe trade it in for something a little more practical. Or just lease one. I drive a 5at. I downshift it. I beat the crap out of it, and I love it. It's a cheap sports car, not collecable, and I don't see the point of worrying. Most of these cars are still under warranty, so if it breaks, nissan can fix it. If you modified your z, and voided your warranty, then chances are, you bought this car to drive it, not whine about it on the forum. Get off the computer and go drive your damn Z! Drive it like a man.

 

LOL - I drive my 5AT hard. I do the same to my daily, 99 Accord 4D V6. After 162K+ on the Accord, she still drives great and strong. Regular, routine maintenance is the key.

Yes, they are totally different cars. BUT - As long as you don't drop two gears and over-rev the crap out of your engine, change the fluids regularly, use 93 octane gas, and keep up with all other maintenance, the Z should hold up fine.

On that note, I am going out for a nice drive. The weather is too good right now to not be rolling!

 

No doubt. I read his post and was like WTF?
There are times when hitting the gas can help avoid an accident. For example, a truck starts to merge into your lane and you nail the gas to get out of the way.
But for the life of me, I cannot think of a single example when you would need to hit the gas to avoid an accident while coming to a complete stop?
I personally never downshift to help me stop. Downshifting is a help when going downhill. You can shift to a lower gear to help keep you going slower and you don't need to ride the brake as much.

 

You might want to take your car for a check up because my manumatic shifts exactly when I want it to with less then a second delay.

 

Agreed. The only delay my AT had was when first switching to manual mode. After that, the shifts were fast and crisp.

 

yea its really smooth on shift other than 3rd gear 30% of the time. Back on topic, I personally downshifted on my old 98 automatic corolla ALL the time for 75,000 miles with constant 75-100 shot of nitrous with no tranny problems. My aunt has been driving it and it has 150,000 miles an still no tranny issues.

 

my question is not regarding safety when slowing down, but rather being in a lower gear in higher RPM so I can take off when I floor it should I NOT stop...otherwise, gear searching takes forever...when I'm hitting coming up to a red light, I like to downshift to the lowest gear possible (in an automatic, all you gotta do is shifft down several times, and it'll stop at the lowest gear "possible" for you), and if I needed to take off should it turn green, I have all the power right there already...

it's a driving habit a lot of people get used to once they've owned a 6MT: rev-match, downshift, coast/engine brake, slam on the gas and have this surge of power at hand...

 

hi guys....
Rick, downshifting the 5AT like you would a 6 Speed will not hurt the engine\ trans much at all. Thats just being paranoid....... no pun intended.

I just picked up an 07 Enthusiast 5AT, love the "manumatic" and its rev match capabilities. I drive it just like I would if I had a manual. I really can't see it degrading it. Really, the failure of most automatics is due to overheating caused by slipping due to simply overpowering the trans, towing, failure to maintain the fluids clean, and not using an appropriate trans cooler.

First mod to be done on mine will be the addition of a B&M trans cooler w/ a built in-fan & auto switch. Keeping the stock cooler which runs into the radiator can be a problem for some making power/not changing fluid often because it can clog rather easily.

We'll be offering a "built" 5AT very soon, something like what we use in the Z32.