Sacrilicious
boom boom!
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- Cosmic Blue MS3 of hawtness!
ya, i never use the brakes if engine braking is an option...manual transmission 4tw...
What RPM to maximize fuel efficiency?
- Thread starter Stu C
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ya, i never use the brakes if engine braking is an option...manual transmission 4tw...
Yes... but I think we have established that engine braking does not cause significant wear on your clutch. So... I don't see how your post applies here. If it did, why would so many professionals recommend it? People do it all the time. In fact, trucks do it extensively. It is a misconception that engine braking causes clutches / transmissions to wear out so much faster than normal.
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ya, i never use the brakes if engine braking is an option...manual transmission 4tw...
Yep! It is also cool if someone is riding your ass... engine brake and then watch them panic because they didn't see any lights! (But don't do this if they are riding too close... unless you want them to hit you!)
Uh? Blip the throttle and dump it. Your matching rpms and the it will still be smooth as butter. I wish I could upshift half as fast/smooth as I could downshift =p
As far as RPMs.... My last car I was curious to find out that the manual recommended shiftpoints at 4k.
Doing so DRASTICALLY improved the day to day drivability of the car and I went from 22mpg to 25.
That was a K20 though so its very different =P
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Sacrilicious
boom boom!
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- Cosmic Blue MS3 of hawtness!
look, if you have the magical touch and you can shift without slipping your clutch at all, then all the more power to you, but i guarantee you that 99% of the drivers out there slip the clutch a little bit when they shift, because unless you're somehow godly enough to rev match perfectly every time, that's just what happens with manual transmissions.
With my double-clutch downshifts, my clutch doesn't slip at all (or very little). However, often times i'll let it slip slightly just to make sure I'm in the right gear and at the right RPM's, but most of the time, since I am in the right gear, and at the right RPMs there's no need for me to do that, and it won't slip if i just let it out. I double clutch, because I find that it's smoother than just rev matching, not to mention saving un-needed wear on the synchro, but i don't think it's really needed. With this car, I hardly ever upshift from 2nd to 1st just because it's difficult for me to match it exactly, so I end up using the brakes some of the time when coming to a stop, but my brakes feel like they did when I bought the car. It's my firm belief that the negative impact on my clutch from downshifting is minimal compared to how much wear i'd be putting on my brakes if I braked as if I were driving an automatic car.
Oh, and I'd like to add that I hate 1st to 2nd upshifts. Takes too long, imo, for the engine to rev down to the 2nd gears ratio. I sometimes end up slipping into 2nd because i'm impatient, lol.
Edit: oh and to be on topic.. For me, most of the time, I find that 2k - 2.4k is the most efficient for day to day variable driving (according to the onboard mpg monitor thingy). There's enough torque at those rpms to conquer any change in road level without applying a dramatic increase or decrease in throttle pressure, and gives you enough play in 4th-6th gear so you don't have to shift too much when going a steady speed.
Oh, and I'd like to add that I hate 1st to 2nd upshifts. Takes too long, imo, for the engine to rev down to the 2nd gears ratio. I sometimes end up slipping into 2nd because i'm impatient, lol.
Edit: oh and to be on topic.. For me, most of the time, I find that 2k - 2.4k is the most efficient for day to day variable driving (according to the onboard mpg monitor thingy). There's enough torque at those rpms to conquer any change in road level without applying a dramatic increase or decrease in throttle pressure, and gives you enough play in 4th-6th gear so you don't have to shift too much when going a steady speed.
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I couldn't agree more... Others tend to back us as well....
Petrol and diesel cars manufactured from 1990 onwards, are generally equipped with fuel injection combined with an electronic function that cuts off the engine's fuel supply under engine braking (accelerator released and a gear engaged). The advantages of this fuel cut off function can be used by releasing the accelerator in time, for example when approaching traffic lights. This also reduces wear and tear on the brakes, reducing maintenance costs. Engine braking, not only has a positive effect on fuel consumption, but also on exhaust emissions, traffic safety, traffic flow and passenger comfort.
http://www.ecodrive.org/The-golden-rules-of-ecodriving.249.0.html
Instead of using your brakes to slow your vehicle down on a steep grade, use what is known as "engine braking" (big-rig drivers use something similar called "jake brake").
This is a good idea if you want to:
a) save your brakes a lot of unnecessary wear & tear
b) actually HAVE brakes at the end of the hill!
In fact, you will increase the life of your brakes by a few months (or even years, depending on how much steep downhill driving you do) if you simply use engine braking whenever possible, rather than actually pressing the brake pedal to slow your vehicle.
In short, you are literally using the engine to break the speed of your vehicle traveling downhill.
This does NO harm to the engine itself or any of the inner working parts.
http://thefuntimesguide.com/2005/07/downhilldriving.php
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 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 leverage (mechanical 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 exhaust 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.
http://en.wikipedia.org/wiki/Engine_braking
Young Roids
Member
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- The pennies have been saved the MS3 is mine!
I suspect on this car we want to aim for lower rpms for max efficiency so that we stay out of the boost range. 4k would be well into boost. I am hoping that the cobb ap will have a fuel saving map that will basically get rid of boost and therefore let us use more of the rpm range for gas saving driving. Then maybe 4k would be about right.
has anyone seen a BSFC for our car that would tell you what rpm and load condition would yield the best fuel milage.
sheck this out
http://www.autospeed.com/cms/A_110216/article.html
sheck this out
http://www.autospeed.com/cms/A_110216/article.html
You misunderstand... im saying downshifting is a no brainer.. upshifting im a uncoordinated nerd often
Huh? You sure you're not getting the terms confused? IE 1->2 is an upshift, 2->1 is a downshift.You misunderstand... im saying downshifting is a no brainer.. upshifting im a uncoordinated nerd often
Young Roids
Member
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- The pennies have been saved the MS3 is mine!
That looks like exactly what we need.(wow)
As long as I've been driving manuals I have always tried to keep the rpms as low as possible without bogging, normally just above or below 2k depending on the car, where its being driven, etc. For this tank of gas I am trying to keep the rpms around 3k and trying to give it more throttle. This may yield a better mpg, but I'm not convinced yet. I'll post up when I get my next tank in a few days. Trying the BSFC thing....
I have gotten about 22mpg consistently since I had owned that car except for one all-highway cruise control trip which yielded 26.5mpg, and one tank when I was boosting generously which yielded 18mpg.
Some people have been talking about 26-28mpg, and I am just trying to figure out how there is such a drastic difference. Is there really that much difference in the way some of us drive our cars?
Some people have been talking about 26-28mpg, and I am just trying to figure out how there is such a drastic difference. Is there really that much difference in the way some of us drive our cars?
i went to atlantic city,NJ back and forth from new york and did 30mpg.. i got 360 miles out of 12 gallons
See in my lude, 3k was actually the correct RPM for cruising, but I'm pretty sure since I started driving at 2k, I'm getting better mileage.
