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6 sp manual downshifting effect mpg?

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Old 04-08-2011, 10:18 AM   #21
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The ECU control with the manuals makes the EPA MPG rating worse on the 6 spd than the autos.

I have noticed that when coasting in neutral the speed sensors must tell the RPMs to stay elevated (~1200) until you come to a stop and then it goes to warm idle (~800).

Because of this I usually leave it in gear while braking to keep the RPM's down and then I put in Neutral as I come to a halt.

I just wish an EE would come up with some sort of Flash fix to take the ECU emission control out of the equation. It takes the fun out of a manual when the RPM's don't drop when you let off the gas.
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Old 04-08-2011, 10:22 AM   #22
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Quote:
Originally Posted by thinkingman View Post
Downshifting neither helps you slow down or save fuel.
Add another to the TW misinformation machine.
The only benefit is to the mechanic that will be replacing your clutch at a much-too-early interval.
You guys kill me.
Your statements make no sense.

Downshifting does slow the vehicle due to engine braking, requiring less brake application to get the same amount of deceleration.

Downshifting with no accelerator input cuts injector pulses above certain RPM's. Downshifting does have potential to save gas. When your engine is at idle speed while coasting to a stop, the injectors are pulsing thus using gas to maintain RPM's. Downshifting does put additional stresses on the drivetrain and clutch plate, but that can be minimized with reasonable rev-matching.

Your talk about heel-toe has nothing to do with this thread. Heel-toe for your application on a track where grip is at it's limits is completely different in purpose for street driving and downshifting. How often are we downshifting while at the limits of traction on the street? You match-rev on a track to disrupt as little as possible the contact patch friction limits.
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Old 04-08-2011, 10:23 AM   #23
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While I'll let the others argue about something completely off topic... I'll add my two cents into the actual question.

I have a 4.0 liter 6spd and I was always curious about the effects of downshifting on MPG's. I broke down about a month ago and bought an ultra-gauge. This gauge has an instantaneous MPG window and also has a open loop closed loop indicator. When driving normally down the road it shows an closed loop. As I go to slow down at a stop light, I put it into neutral and watch the mpg's as I'm coasting. They take a large jump up, but then slowly drop down as my speed drops as well. Then at the next stop light I try it with a downshift. My loop indicator then shows an open loop (injectors are cut off). My mpg's go up quickly, but they dont seem to drop down quite as quickly.

So to sum it up, downshifting does seem to help with milage. I dont think it's hugely significant, but enough to notice. As long as your not revving the shit out of your motor or going from an extremely high speed to a slow speed by downshifting, then you should see an increase. As far as clutches go, like I said, as long as you're not abusing it and be gentle, you shouldn't have any problems. I downshift everywhere and my clutch still feels the same as the day I got the truck.

Thats my two cents.
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Old 04-08-2011, 10:27 AM   #24
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It does save gas according to my aeroforce gauge. The injectors don't shut off as some have claimed (Injector pulse width drops to about 2ms in a 20ms period meaning it's pumping gas about 10% of the duty cycle). It isn't much better than coasting though. So I doubt you'd save much over just coasting and braking.

Engine braking does slow the vehicle down though. To test it, put the vehicle in neutral and coast. The put the vehicle in gear and let out the clutch. You'll observe the vehicle slowing much quicker.
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Old 04-08-2011, 10:32 AM   #25
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Quote:
Originally Posted by hudhawk View Post
Considering downshifting will raise rpms, and at higher rpms the engine burns more fuel, i would think so. I also drive a trd offroad w/ 6spd manual, given it is an 05, not an 11, but i would think it would be the same. I stopped downshifting to slow down when im driving around town and started taking it out of gear and using the brake to slow down. My mpgs went up a little. What are you currently getting in terms of mpgs?
It's not burning more fuel. In fact the injectors are at their lowest fuel rate when you're off the accelerator. The reason the rpms are higher is because the drive train is mechanically linked to the engine. The engine has to turn at the same rate which is why the rpms jump.
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Old 04-08-2011, 11:35 AM   #26
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Quote:
Originally Posted by dhk View Post
On older vehicles, this won't be the case though. The engine spinning fast will draw more air through, which will draw more gas in. This fuel savings depends greatly on the vehicle being able to shut down or reduce its injectors in zero throttle high rpm circumstances.
Close, but not quite. With the throttle plate blocking the intake, you still save gas and use engine braking on gas engines. Diesel engines are another story, since there is no throttle plate. Diesel controls speed by fuel delivery. Jake/compression brakes contol valves to affect engine braking.
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Old 04-08-2011, 11:36 AM   #27
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Quote:
Originally Posted by thinkingman View Post
If you read the posits in the OP, and you have experience in the matter, you'll find that downshifting to a stop and maintaining speeds on downgrades are two entirely different matters.
In re downshifting, I'd be willing to bet less than 10% of the people on this thread know how to heel and toe properly and if you're trying it in a Tacoma, it's a raging fail, with the brake/clutch/accelerator and sloppy-ass shifter.
I learned to heel and toe in a Formula Ford and promise you, it wasn't for slowing the car.
Creeping downhill in 4wd is not the same as the OP.
No it's not.
Trucks using lower gears to control forward momentum on downgrades is not the same as the OP...some may use an exhaust brake for additional control, but that's a different kettle of fish.

Why do I spin out of control on an icy hill coasting in nuetral using my brakes but I don't when I'm slowly crawling down the hill in 1st gear without using my brakes?
Because you're not a very good driver and lack basic car control knowledge.
Low friction surfaces require very light inputs if you're nearing maximum traction. I know, without a doubt, I can modulate my brakes quicker and with more precision, than I can modulate the throttle, especially if I have to alternate between a closed throttle and an open one....in your example I italicised above, you're adding drivetrain backlash into the equation.....epic fail in low traction/downhill circumstances.
Stick to the example by the OP, not your own.
They aren't two completely different matters. It's 100% the same concept. You are using the engine to control the speed of the vehicle against momentum and gravity. Decelleration is decelleration regardless of the grade.

Your 10% comment is probably accurate. However it is possible in the Tacoma, I do it all the time. Sure it was an adustment compared to my previous vehicle but after a little getting used to it, I can heel-toe just fine in the truck. I do it to make downshifting a smoother, also similar to driving a racecar, it's makes downshifting for acceleration smoother.

Slowing down is the same thing as controlling forward momentum. Otherwise you would continue to move forward at the same rate of speed or faster if you're on an incline (obviously gravity and wind resistance affect this)

I have personally never spun out of control going down an icy hill, just using that as an example. Gearing down in low traction is not an epic fail, its actually better than using your brakes, there is no risk of locking up. Same concept that ABS accomplishes, which is modulating the brakes to even braking pressure to allow the wheels to continue to spin and to slow you down without locking up.

Anyways no more arguing for me, just based on the comments from others, it appears that you're in the minority here.

So according to people with a scanguage and other AFR monitoring devices, the consensus seems to be that downshifting does save gas over braking in nuetral.
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Old 04-08-2011, 12:11 PM   #28
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Quote:
Originally Posted by macgyver View Post
So according to people with a scanguage and other AFR monitoring devices, the consensus seems to be that downshifting does save gas over braking in nuetral.
It would be miniscule though. In gear, my gauge indicates 1.9-2.0 ms out of 20ms. In neutral, 2.0-2.3 ms out of 20ms. 300 microseconds difference. You'd probably never notice it at the pump. There are too many other variables that would affect it more.
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Old 04-08-2011, 12:24 PM   #29
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Quote:
Originally Posted by Evil Monkey View Post
It would be miniscule though. In gear, my gauge indicates 1.9-2.0 ms out of 20ms. In neutral, 2.0-2.3 ms out of 20ms. 300 microseconds difference. You'd probably never notice it at the pump. There are too many other variables that would affect it more.
hmm..interesting. I wonder if the narrowband sensor vs. wideband sensor has an effect on this.

When I had my wideband it would read "lean" (17:1+ AFR) if I decellerated in gear but if I were in nuetral it read 14.7ish. It wasn't a tacoma though but I doubt for it would be that big of a diff. Most cars idle at 14.7 (stoich)
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Old 04-08-2011, 12:28 PM   #30
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Quote:
Originally Posted by whippersnapper02 View Post
Most if not all modern vehicles are designed to shut down the fuel injectors when coasting. Some have said the still notice injector activity with their scangauges when coasting but at a reduced rate. So yes you save fuel by downshifting.
That's what I was just going to say. The injectors shut off when you're 'coasting' while still in a gear.

I usually don't down shift until I know the rpm's are going to be 2.5k or below though.
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Old 04-08-2011, 02:02 PM   #31
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Quote:
Originally Posted by dhk View Post
Let me suggest an experiment for your consideration;
Get going on the highway at, say 70 mph. Push in the clutch, get the stick into SECOND, foot off the gas, release the clutch. What happens? Did you just get thrown through the windshield because the vehicle slowed down too fast for you?

Oh, and just because you drove some ford pos doesn't mean that you know how to operate a manual transmission. I would suggest that YOUR lack of skill is NOT an indication of anyone else's ability to use the mentioned techniques.

You can MOST DEFINITELY use engine braking to slow you down to a CRAWL withOUT even the use of brakes. That means at lights. Just need to plan accordingly, if you need to stop FAST, you still need to use the regular brakes. SOME PEOPLE seem to be entirely unable to think when they drive.... let me guess.... between lights your ONTHEGASONTHEGASONTHEGAS-BRAAAAAAAAAAKE!!!!!! Try relaxing a bit. You don't need to be the fastest car on the road or the first to stop at the next red light!

Note to OP: compared to this guy, anyone using engine braking to slow their vehicle will DEFINITELY be saving a TON of gas.


Regarding downshifting to save gas.... the theory works like this;
When you use downshifting to slow down, the vehicle's inertia is transferred into engine rotations, therefore the engine doesn't need to supply fuel to keep itself spinning. If you pushed the clutch and just used the brakes, the engine WOULD need to add fuel to keep itself spinning. So in theory, it CAN save gas to downshift!

On older vehicles, this won't be the case though. The engine spinning fast will draw more air through, which will draw more gas in. This fuel savings depends greatly on the vehicle being able to shut down or reduce its injectors in zero throttle high rpm circumstances.
Well, since you're a genius, I won't bother pointing out the ridiculous innaccuracies in your post.
No, I can't ignor them.
number one, you can't shift into second from 70mph.
Number two, you don't even know what a Formula Ford is, let alone posess the intelligence to know whether it's a POS or not...I'm pretty sure you've never driven a non-syncro close ratio 4spd.
Number 3, use some of that genius to show us your calculations for saving 'A TON' of gas.
301.783 gals?
329.326 gals?
I'll leave that question to the genius...bet you can't or won't figure out the what I'm even referring to.
4...I hypermile my 6sp...never rev over 2k except driving on the freeway where the pathetic 6th gear requires 2.4k rpm to maintain freeway speed.
thanks for our insight and wisdom....look forward to your response.
sorry for the hijack.
some people can't figure out the difference between deceleration and maintaining control of forward motion using engine compression.
BUT THEY'RE GENIUSES!
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Old 04-08-2011, 02:09 PM   #32
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Quote:
Originally Posted by macgyver View Post
They aren't two completely different matters. It's 100% the same concept. You are using the engine to control the speed of the vehicle against momentum and gravity. Decelleration is decelleration regardless of the grade.

Your 10% comment is probably accurate. However it is possible in the Tacoma, I do it all the time. Sure it was an adustment compared to my previous vehicle but after a little getting used to it, I can heel-toe just fine in the truck. I do it to make downshifting a smoother, also similar to driving a racecar, it's makes downshifting for acceleration smoother.

Slowing down is the same thing as controlling forward momentum. Otherwise you would continue to move forward at the same rate of speed or faster if you're on an incline (obviously gravity and wind resistance affect this)

I have personally never spun out of control going down an icy hill, just using that as an example. Gearing down in low traction is not an epic fail, its actually better than using your brakes, there is no risk of locking up. Same concept that ABS accomplishes, which is modulating the brakes to even braking pressure to allow the wheels to continue to spin and to slow you down without locking up.

Anyways no more arguing for me, just based on the comments from others, it appears that you're in the minority here.

So according to people with a scanguage and other AFR monitoring devices, the consensus seems to be that downshifting does save gas over braking in nuetral.
I'll help you with the difference between deceleration and maintaining downhill speed.....deceleration means your velocity decreases, maintaining downhill speed means your velocity remains constant.
There, see?
In re using engine compression to ease down an icy hill, stop fooling yourself into thinking you have better control using engine compression, you can't modulate the inputs as precisely as you can pressure on the braking system.
I learned this 30 years ago before ABS was prevalent.
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Old 04-08-2011, 07:49 PM   #33
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I've been driving a manual for 16 years. I put nearly 300,000 miles on 2 vehicles. I replaced 1 clutch. My 1st Gen taco had 196,000 miles (i put on the last 116,000 miles) on it when i traded it in, and still had very strong original clutch in it. I downshifted all the time. It was just part of how i drove the vehicle. IF you know how to drive a manual, downshifting doesn't cause any extra wear on the transmission or clutch.

Downshifting shouldn't waste anymore fuel. If it uses extra fuel, it shouldn't be enough to make you lose 2-3 mpg. The fuel injectors shouldn't be pumping out much fuel while you are out of the throttle.

If your getting bad gas mileage, change the way you drive. Easy on the gas, shift early, don't drive over 60 mph. Start with that and see where it gets you.
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Old 04-08-2011, 08:56 PM   #34
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Until they come up with a commercially available full rotor contact pad, engine braking trumps brakes. Brakes will lock long before you lose traction with the road, it's just the nature of the beast.
ABS corrects problems caused by the average driver. A good/expert driver can out-brake ABS every time.
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Old 04-09-2011, 08:09 AM   #35
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Quote:
Originally Posted by thinkingman View Post
I'll help you with the difference between deceleration and maintaining downhill speed.....deceleration means your velocity decreases, maintaining downhill speed means your velocity remains constant.
There, see?
It's the same principle with engine braking whether you're going downhill or running on a straightaway. The reason the speed stays constant going downhill is because there is extra force (gravity) being applied. Without the extra force, the vehicle would slow.

A particular gear is only going to allow the truck to go so fast without extra fuel input. The gear that keeps the vehicle at say 20mph downhill is also going to slow a vehicle to 20mph on a straightaway and it will do it much faster than letting it coast. The point is that the engine is doing it.
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Old 04-11-2011, 05:33 AM   #36
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Old 04-11-2011, 06:36 AM   #37
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Quote:
Originally Posted by dhk View Post
The throttle plate will never be fully closed and/or able to stop air flow. The harder the engine sucks on the carb (i.e., the faster it spins), the more air and thus, the more FUEL will be drawn into the engine.
True. The throttle plate will not completely stop the flow of air. The throttle plate stop screw is what sets idle on carbs. It still offers a great deal of restriction, thus engine braking. A carb will not give you the control of fuel injection, and will constantly be fueling the engine regardless of speed.
If you put the trans in neutral on a carb engine, you save gas, but lose engine braking.

I'm unsure of the point you are trying to make. We seem to be in agreement.
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Old 04-11-2011, 10:55 AM   #38
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jspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shed
Name: Jim
Joined: Jan 2009, #12342
Location: Knoxville, TN
Age: 27
Gender: Male
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Quote:
Originally Posted by thinkingman View Post
Downshifting neither helps you slow down or save fuel.
Add another to the TW misinformation machine.
The only benefit is to the mechanic that will be replacing your clutch at a much-too-early interval.
You guys kill me.
I'm going to just avoid all of the crap you spewed afterwards, and rehash what everyone else has said because I can.

Downshifting slows you. Your assertion is provably false. Go 40mph, then downshift to second. Then, go 40mph and go to neutral. You will slow faster in second, period.

Whether it saves fuel is dependent on the automobile design. As others have mentioned, if the designers allowed for fuel shutoff while coasting in gear as the wheels drive the engine to turn over (which a source on this forum, I can't be bothered to search where, indicated that they did), then it is possible that it will save some fuel over coasting in neutral.

Make your Tacoma a Prius? No. Good idea to do? Up to you. But does any of that make it untrue? Absolutely not.

Shut the fuck up.
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Old 04-11-2011, 11:12 AM   #39
Senior Member
thinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shedthinkingman is one of the sharper tools in the shed
Joined: Apr 2008, #5971
Location: redmond WA
Posts: 1,081
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Quote:
Originally Posted by jspadaro View Post
I'm going to just avoid all of the crap you spewed afterwards, and rehash what everyone else has said because I can.

Downshifting slows you. Your assertion is provably false. Go 40mph, then downshift to second. Then, go 40mph and go to neutral. You will slow faster in second, period.

Whether it saves fuel is dependent on the automobile design. As others have mentioned, if the designers allowed for fuel shutoff while coasting in gear as the wheels drive the engine to turn over (which a source on this forum, I can't be bothered to search where, indicated that they did), then it is possible that it will save some fuel over coasting in neutral.

Make your Tacoma a Prius? No. Good idea to do? Up to you. But does any of that make it untrue? Absolutely not.

Shut the fuck up.
Thanks...I spewed coffee out of my nose.
Are you all so obtuse as to think I don't know what my 6speed Taco does when I let off the gas?
Apparently so.
Thanks for the education.
For those of you experts that think using the gearbox and clutch to slow your car is an effective use of the machinery, keep going. Your repair shop thanks you.
In re Formula Ford=POS, you lack the intelligence to know what you don't know.
I love you idiots.
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Old 04-11-2011, 11:14 AM   #40
Senior Member
jspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shedjspadaro is one of the sharper tools in the shed
Name: Jim
Joined: Jan 2009, #12342
Location: Knoxville, TN
Age: 27
Gender: Male
Posts: 2,981
jspadaro's Tacoma Gallery
Quote:
Originally Posted by thinkingman View Post
Thanks...I spewed coffee out of my nose.
Are you all so obtuse as to think I don't know what my 6speed Taco does when I let off the gas?
Apparently so.
Thanks for the education.
For those of you experts that think using the gearbox and clutch to slow your car is an effective use of the machinery, keep going. Your repair shop thanks you.
In re Formula Ford=POS, you lack the intelligence to know what you don't know.
I love you idiots.
Effective? Arguable. Does it work? Yes Did you say it doesn't and then call all of us idiots for saying that it does, when it in fact does? Absolutely.
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