What is the best rpm to let these cars shift at for maximum economy? I know with my honda it liked about 3k rpms, my powerstroke diesel likes about 1800rpms, and well really, every car is different. Whats the optimum rpm to shift at in these cars (automatics) for economy?

Matt

 

Leave it on the non-sport mode setting and it will shift itself pretty much at maximum economy. Modulate that with your foot of course.

 

Well I understand what your saying, but I'm sure your idea of economical my vary from myself and other peoples. I can lay my foot down on the peddle holding it to the ground and it certainly wont shift economically. Do you see what I mean?

 

If you hold the pedal to the floor the car "automatically" won't shift at the most economic RPM because you are calling for power, and it will provide it until it hits the rev limter.

With a 5 speed manual you could do some things like skip shifting from 1st to 3rd or 2nd to 4th to take advantage of some economics with the RPM's. But with the auto you are stuck unless the model is programmed to skip shift (like newer Corvettes are).

I don't really know how to respond to the question in any other way. If you want precise figures or graphs or something you'd probably have to go to Jaguar for that or do your own dyno testing.

 

You aren't understanding what I'm saying.

Obviously there is different degrees to which the pedal can be depressed. It can be depressed so that it shifts at 1400 rpms, or 7000 rpms. Which is the most efficient rpm to shift at in these cars? With my honda I get the better mileage shifting at 3,000rpms instead of 2000 rpms. With my powerstroke I get way better mileage shifting at 1800rpms than 2200rpms. So whats the sweet spot on these cars.

 

I completely understand what you are asking. I just don't properly know how to formulate a response apparently. I am guessing you are going to use the J-gate to determine shift points rather than let the autobox do it.

"what we have here, is failure to communicate"....

maybe somebody else can provide a different way of responding.

where I live is very hilly. I don't often have much of a choice for RPM derrived shift selection with any type of consistency. Not enough to conduct a mpg comparison across rpm shift points per gear anyway. That would be a lot of data.

 

And what is the meaning of "T-Type" in your sig line? Just curious.

 

No I plan to let the autobox do it.. I'd just rather have some good quality guidance on where to start over guessing lol. I've been trying to keep rpm's around 2k.. we'll see what happens I guess. It's sucking gas this tank though due to the CEL I have on (I think the pcv line is the culprit), so I might have to wait another tank or two. I have like 130miles and already over half tank!

Ya I dunno how I messed that up, but good catch! Thank you.

 

Well, I don't know if anyone really can give any quality guidance on your topic that isn't just anecdotal evidence. At least I have not read anything on this board or others that fits the bill. You might get some "it seems to be better here, or there" but I doubt anyone has actually done anything scientifically.

You might be the pioneer on this one if you are going to start a systematic data collection and analysis. Good luck and let us know how it goes.

 

lol it looks that way! I guess I might be pioneering this here subject! It's just such a pain in the *** with not having a beginning point. But here is a quick compilation of my theories
Four cyls love to be reved. They dont make power or torque, but are capable of high rpms, and with rpms comes power and torque. Mileage is dependent on throttle blade opening, and as long as the throttle blade is kept near closed, no harsh fuel consumption will be induced.
Six cyls like a medium shift cycle.. they are generally bigger motors with higher basic fuel consumption requirements, so therefore they dont like to be revved TOO high, but they also make much more power of idle with fewer rpms' than four cyls
Eight cyls make extreme power off idle, and do NOT like rpms (modern day 8cys are slowly being produced to run higher rpms). The v8 can handle drastic gearing and over drives as they produce power off idle to propel the car. Keep rpms low.


So with this being said, this is an American car retrospect. European cars tend to be smaller displacement, higher revving motors. Sooo this is going to be tricky for me to try figuring out. It might take several months to get an idea.

 

Maybe I am missing something here, but if I am understanding the point of this discussion you are trying to get the best fuel economy you can by trying to "feather" the accelerator at the most optimal point so that it shifts to a higher gear thereby giving you the "best" fuel economy. Just sems if you go to that much trouble to even find that "g-spot" what is the end result? Would you gain a tenth of a mile per gallon? Two tenths? Just seems to me that even if you get to that point the net gain in fuel economy would be minimal at best, especially having to make you you accelerate at just that perfetc sweet spot. Seems like a lot of work for virtually no gain. Probably better off just being light on the throttle or J-Gating to higher gears sooner.

 

I think your analysis of engine characteristics by number of cylinders is way off, but that's not relevant. Does your car not have an instant fuel consumption indication? If so that will give you your answer.

My S-type's fuel consumption has relatively little to do with transmission shifting points and everything to do with throttle position while accelerating.

 

No you are correct. But as I stated earlier, I got better mileage shifting at 3k rpms than 2k rpms in my honda.. an average of FIVE miles per gallon better by shifting higher. Whereas if I overshift in my powerstroke and dont keep it around 1800rpms, I can consume as much as 4mpg worse than shifting optimally.

That was the lamens condensed version. I know there is far more to it. You are also correct in the throttle plate input. RPM's dont so much matter as does throttle plate positioning.
Yes I have an instant mpg reading, but it's not really "instant". It doesn't show on-the-spot differences. It keeps the numbers linear, therefore the shift in economy as per the readout varies at a slower rate (but perhaps more long-term reliable, of a rate?)

 

Layman? I'm not a layman, but your understanding of engine dynamics is incorrect. I'd suggest that you abandon making these types of broad generalities to help in your quest for optimum fuel consumption. Torque/HP curves or max. RPM have little or nothing to do with the number of cylinders.

 

Some light reading to get you ready for your test: http://www.physicsforums.com/showthread.php?t=349129

I would hesitate to compare diesel vs. gasoline engines directly however. Something to keep in mind as they are designed to operate with different characteristics.

 

As I've already stated, I know this. It has to to do with throttle blade positioning. You are losing sight of my question though: Around what rpms do these motors function most efficiently

I wasn't making a comparison of diesel vs gas motors, just that EVERY motor has it's sweet spot for economy.

 

Now you're asking a different question. Operating 'most efficiently' is not necessarily the same RPM as 'best fuel economy'.

 

I understand this. But between appropriate throttle input and the correct rpms, maximum economy can be determined. So what kind of throttle input makes these cars feel all warm and gooey inside

 

The transmission will sort that all out for you, just let it do it's job. Forget trying to second guess it and just drive the car.

 

I think you're confusing issues between different kinds of vehicles. A Honda isn't going to have the same torque as a diesel so naturally you're going to have to rev a lower torque engine just to get the car moving. A diesel, with it's high torque can be lugged all day and not stall.

All you really need to know is your best economy comes from your highest gear capable of sustaining constant forward motion. For the 3.0, get the car to 40mph (non-sport mode) as gently as possible and that's the most you can do. Once in fifth gear, you can slow to about 35mph without it downshifting as long as you don't step on the gas. I'm not sure about the 2.5 limits.

In a nut shell, the sport mode revs too high to yield high mpg and the standard mode lugs too much on hilly terrain which causes it to drop a gear and lose mpg. In the end, just remember you're paying at the pump for the luxury of AWD, there is NO getting around it.