Downshifting bad for MPG?
#46
12-02-2005, 04:54 PM
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Originally Posted by cloud
a little off topic but just curious, when you guys revmatch, do you match precisely 100% of the time? I seem to be a little off at times like 100~300 rpms off.
I don't have my 6mt G yet (hopefully comes in this weekend
but when I used to downshift in my //M3, being 100-300 RPMs off was not that uncommon and did not yield bad or un-smooth results. This depends on how fast you let off the clutch.On a side note, I used to practice heal-toe when approaching a corner but not really at stop lights.
-Evangelo2
#47
12-02-2005, 04:57 PM
Originally Posted by RBull
I think you mean little gas consumotion as opposed to "no" or "zero" gas consumption. The engine is still running so there is fuel being used just as there is when it is at idle when stopped.
If the ECU is intelligently programmed, it would shut the fuel injection completely off anytime you have your foot completely off the gas pedal and engine RPM's are above the predefined idle RPM. If the engine is turning, it is running.... whether or not gas is being injected or not. The presence or absence of fuel doesn't matter... all that matters is that it's turning. Once the RPM's drop to idle RPM, fuel injection can then start up again to maintain idling RPMs.
#48
12-02-2005, 07:46 PM
Originally Posted by RBull
Originally Posted by Speedoholic
First, why would anyone put it in neutral and glide while depressing the brakes? - you're killing your pads as the car has more "mass" going down heel in neutral than if it was in gear. If anything, I would leave it in gear and brake. That way, the load is evenly divided between the engine braking and the brakes.
For the rest of my driving at different speeds my downshifting style is pretty much how you described yours.
#49
12-02-2005, 07:48 PM
Originally Posted by jayelleseven
man u guys are much less informed than the guys at 6mt.net First off, DONT engine brake too much, in the long run it messes with ur transmission and dont make me explain it cuz i cant word it right, jus know that ur are forcing revs and makin the transm. work harder
And who do you think are the members of that site? Same owners of the same car... Give me a break.
#50
12-02-2005, 07:49 PM
any tips for AT MM users? 
when you are in MM and coming to a stop from lets say...60mph (4th gear)
according to people saying "i'd rather brake than harrassing my motor," you just brake and let gears change by itself?
i downshift all the time...maybe i should stop doing this.
ridiculous thing to ask but...doesnt hurt to ask
thx
when you are in MM and coming to a stop from lets say...60mph (4th gear)
according to people saying "i'd rather brake than harrassing my motor," you just brake and let gears change by itself?
i downshift all the time...maybe i should stop doing this.
ridiculous thing to ask but...doesnt hurt to ask
thx
#51
12-02-2005, 07:57 PM
Originally Posted by RBull
I think you mean little gas consumotion as opposed to "no" or "zero" gas consumption. The engine is still running so there is fuel being used just as there is when it is at idle when stopped.
Read Partyman66's reply above, he pretty much nailed it. There is no need for the ECU to continue nourish the engine with gas as long as the engine is spinning from the wheels end. How do you think you jump-start a car by pushing it downhill and jerking it into gear? - Same element. The engine can be worked out the other way around as well. If the car reaches a complete stop and you haven't neither stepped on the clutch nor accelerated it will simply shutoff due to lack of power to continue spinning without either fuel combustion or a natural movement of the wheels that would spin from the other end.
If there was an endless downhill slop, you could technically run your car for months like that.
#52
12-02-2005, 09:21 PM
Originally Posted by Speedoholic
If that's what you want to do then by all means continue to do so. The engine will not shut off until you reach to almost a complete stop. I usually just coast in gear and when the car is close to stop I just tap on the shifter and take it out of gear - no clutch needed. As to your method... if you like to wear your brakes prematurely just because you're lazy... well, it's you car do as you wish with it.
#53
12-02-2005, 09:29 PM
Originally Posted by partyman66
I'm not sure how Infiniti's ECU is programmed to handle this specific situation... but the engine could very well use ZERO fuel when you do this(I'm just not sure if it uses no fuel, or if it uses the same amount as it does at idle). As long as the engine is turning(from coasting with the car in gear)... whether or not fuel is being injected into the cylinders is irrelevant, so long as the RPM's stay above idling RPM.
If the ECU is intelligently programmed, it would shut the fuel injection completely off anytime you have your foot completely off the gas pedal and engine RPM's are above the predefined idle RPM. If the engine is turning, it is running.... whether or not gas is being injected or not. The presence or absence of fuel doesn't matter... all that matters is that it's turning. Once the RPM's drop to idle RPM, fuel injection can then start up again to maintain idling RPMs.
If the ECU is intelligently programmed, it would shut the fuel injection completely off anytime you have your foot completely off the gas pedal and engine RPM's are above the predefined idle RPM. If the engine is turning, it is running.... whether or not gas is being injected or not. The presence or absence of fuel doesn't matter... all that matters is that it's turning. Once the RPM's drop to idle RPM, fuel injection can then start up again to maintain idling RPMs.
#54
12-02-2005, 11:04 PM
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Originally Posted by Hotrod
There is really no reason on the street to heel toe because you really don't have to be on the brakes and the gas at the same time when downshifting on the street. I have been racing cars for over 30 years and I fully understand heel toe downshifting and rev matching as well as the potential of locking up the rear tires if you dont rev match, but that is on the track. I have never had to heel toe my car in street driving. If you just take your foot off the gas and as the car slowes and you want to go into the next lower gear just blip the gas a little and downshift the car, there is really no reason to use the brakes (while slowing) unless its an emergency if you are paying attention and not following to closely to the car in front of you. Again I agree with you 100% on using heel toe downshifting on the track but it is not necessary on the street.
#55
12-03-2005, 12:50 AM
Originally Posted by partyman66
Most gasoline-powered street cars run in the 8:1 to 12:1 compression range, whereas diesel-powered engines run at a much MUCH higher compression range of about 15:1 to 25:1. Compression is how the diesel fuel is ignitied..... rather than by a spark plug, like with gasoline engine. Diesel engines are usually equiped with some sort of a "glow plug" that sort-of makes the diesel engine function like a gas engine(spark plug-like) when the engine is cold and compression is lower, but once the engine is warm... it runs off of only compression to ignite the diesel fuel.
#56
12-03-2005, 12:54 AM
i have a buddy with a ferrari that had driving lessons, as well as another buddy with an eclipse gsx and his dad having a lotus espirt v8tt, both hardcore autoX'ers. they asked me this question... so let me ask you...
DO YOU THINK IT IS ALWAYS GOOD TO BE IN GEAR?
if you asked yes, then you will understand or realize why it's better to downshift rather than brake. i'm sure you can think of a few reason or situations.
DO YOU THINK IT IS ALWAYS GOOD TO BE IN GEAR?
if you asked yes, then you will understand or realize why it's better to downshift rather than brake. i'm sure you can think of a few reason or situations.
#58
12-03-2005, 07:28 AM
Originally Posted by chilibowl
What do most of you folks do? You guys do the usual put it in neutral and use the brakes to slow down the car, or do you downshift? I ask this, because I would assume downshifting lowers MPG because of the rpm's spiking up on a downshift.
About a month ago I was slowing down as I came to an intersection since the traffic light went to amber. This was a six lane road with the inner lanes designated for turns. Anyway as I approached the intersection going about 30 MPH and downshifting in prepartion for a stop, a woman in the turn lane decided to abruptly get out of that lane and pulled right in front of my car. For some reason she didn't see my car approaching the intersection. If I merely hit the brakes, I would have smashed into the side of her car. Since I was in an appropriate gear I was able to accelerate around her car into the adjacent lane. If I had drifted to a stop in neutral, this manuver would not have been available to me and my car would have collided with hers.
#60
12-03-2005, 03:15 PM
Originally Posted by FAST1
If the downshifting is done appropriately, it should have minimal impact on gas mileage. The gear ratios on the G are close and in a constant deceleration mode, there won't be much of a blip on the tach when downshifting. From a safety perspective I would never recommend putting the tranny in neutral and coasting to a stop. Sometimes the differance between being involved in an accident and avoiding one is a fraction of a second or the time that it may take you to shift out of neutral.
About a month ago I was slowing down as I came to an intersection since the traffic light went to amber. This was a six lane road with the inner lanes designated for turns. Anyway as I approached the intersection going about 30 MPH and downshifting in prepartion for a stop, a woman in the turn lane decided to abruptly get out of that lane and pulled right in front of my car. For some reason she didn't see my car approaching the intersection. If I merely hit the brakes, I would have smashed into the side of her car. Since I was in an appropriate gear I was able to accelerate around her car into the adjacent lane. If I had drifted to a stop in neutral, this manuver would not have been available to me and my car would have collided with hers.
About a month ago I was slowing down as I came to an intersection since the traffic light went to amber. This was a six lane road with the inner lanes designated for turns. Anyway as I approached the intersection going about 30 MPH and downshifting in prepartion for a stop, a woman in the turn lane decided to abruptly get out of that lane and pulled right in front of my car. For some reason she didn't see my car approaching the intersection. If I merely hit the brakes, I would have smashed into the side of her car. Since I was in an appropriate gear I was able to accelerate around her car into the adjacent lane. If I had drifted to a stop in neutral, this manuver would not have been available to me and my car would have collided with hers.