I was looking at some articles on the Max and it said "...cruising at 65 mph at 3300 RPMs...". Is this right for an auto? I have a manual and I checked it out. 65 mph is 2650 RPMs and at 3300 it was at 80 mph. Is the auto geared that much differently? Top end must be a lot higher for the manual(I've never tried).
Thanks
Tom

 

Maybe with out the overdrive on I will have to take a ride and check.

 

4Gen automatics turn fewer RPMs than 5-speeds at any particular speed and in top gear. That's why the EPA fuel consumption figures are typically 1 mpg better for automatics. "65 mph at 3300 RPMs" might be right for an automatic with Overdrive off (i.e. cruising in 3rd gear).

Top end speed is determined by several factors including gearing. There are some 5-speed cars which will actually achieve a higher speed in 4th gear than 5th. I don't know if this is true for the 4Gen Maxima.

 

I have a 97 GXE auto and my rpm's have never been that high going 65. Im not exactly sure what they are but they dont get close to 3 until im goin around 80-85. Take Care

 

Ok. It didn't make sense to me. Thanks.

 

i tested it out today....@80 i was @ 2700rpms Se automatic w/overdrive on

 

i dont want to contradict you, but i've notice that when i was looking for my new car, all the 5spd's got better milage than autos by 2-3 mpg. is this just different for the max or do all cars vary?

 

In most cases, manuals get better gas mileage than automatics, all else being equal. But for the Maxima, the manuals have much shorter gearing to help them accelerate quickly, which also causes the higher rpms at any given speed and, thus, a decrease in fuel economy.

 

do auto max's have 5 gears or 4 gears? if they only have 4, doesnt our fith compensate to give us equal or better milage, given drivers accelerate at equal paces?

 

It's different for each model of car, and dependent more on gearing than transmission type. The numbers which come to hand are for the '99 Maxima (my car). The EPA highway mileage esimates are 27mpg for 5-speed and 28mpg for automatic.

 

The EPA rating shows the auto to have a 1-mile-per-gallon advantage in City and Highway driving. For Camrys and BMWs, for comparison, the manuals have 1-3 more miles per gallon than their automatic equivelents.

 

Maxima automatic transmissions have 4 forward speeds. However, the number of gears doesn't contribute much to good fuel economy. It is the overall ratio of the top gear that matters most.

 

Actually some of what you guys said is unaccurate. Actually the 5spds do run higher RPMs in 5th gear than the auto does in 4th gear. Whoever said that the 5speeds get reduced economy in 5th gear is wrong. Although our RPMs are higher, that doesn't mean that we're necessarily wasting more fuel. The fact is we have more available power at that RPM and when we need to pass someone we barely put our foot into the gas. Auto's require more throttle to accellerate and more throttle to stay constant. Throttle wastes as much if not more gas than higher RPMs. I personally wonder if running the car at 6000 RPM with very little throttle wastes more or less gas than flooring it at 1500-2000.

Daniel B might no the answer there.

 

That doesn't make any sense. If an auto is pulling up a long hill at a constant speed at, say, 1600rpm, it will be using much less fuel than a manual that has been downshifted to second or third and running at higher rpm. Flooring the accelerator is a very, very small part of driving, and doesn't compare to all of the steady-state driving that's done on street cars. And automatics don't require "more throttle" to stay constant. At any given speed, the automatic will be turning less rpms than the manual, which means less fuel consumption.

 

Flooring the pedal also doesn't put you in the highest power curve of the RPM band at speed either. When you need to accelerate at speed, the auto has no problem downshifting to get up and go. Anyone can answer this question but why are the auto's look at as 4 speed but when you get up to 80 to 85 it drops into another gear? or is it just the overdrive gear?

 

No throttle position has a lot to do with how much gas you're using. If you're trolling up a hill in overdrive at say 2500 RPM you'll need to put your foot in it deeper than us 5spds trolling at 3500.

Trust me throttle position has to do with gas mileage. You drive around at 1500 RPM in a 5spd all day long with it floored and you tell me what MPG u get.

 

This is a sweeping generalization. It depends on which gear the automatic is in, which gear the 5-speed is in, and at which RPM the engine operates most efficiently. Lower RPM is often, but not always, more efficient than high RPM.

In deceleration (under certain conditions) the 5-speed enters Fuel Cut mode which means it is using zero gasoline. The automatic doesn't have Fuel Cut mode.

 

Huh? At 80, the car can be in 2nd, 3rd or 4th gear. The car is @ ~6300 in 2nd, ~3300 in third and ~2700 in 4th. To me, all other things being equal, an engine running at a lower speed would have to be more fuel efficient, because not as much fuel is injected into the cylinder during a minute secondary to the reduced engine speed. The car doesn't care whether you are at 1500 and floor it so that it downshifts to ~6000 or you are running steady state at 6000, it would inject the same amount of fuel into the cylinder every cycle. The engine just asks for a faster fuel rate as the RPMs increase. The auto and manual tranny Maximas top out about 3 MPH away from each other , about 137 for the auto, 141 for the manual.

 

I respectfully disagree.

The fuel management system does respond to "flooring it" by providing more fuel per engine revolution.

1) The fuel pressure regulator operation is controlled by intake manifold vacuum. When the vacuum is relatively high (engine idling or cruising at a steady speed) the fuel pressure is 34psi. When the vacuum is relatively low (Wide Open Throttle or heavy engine load) the fuel pressure rises as high as 43psi. See Chilton (page 5-3) or Haynes (page 4-3).

2) The Throttle Position Sensor signals WOT to the Engine Control Module. The ECM momentarily abandons Closed Loop mode, and ignores those frantic "Too Rich! Too Rich!" signals from the Oxygen Sensors. See Chilton (page 4-18) or Haynes (page 6-8).

These measures allow the engine to deliver maximum performance during WOT acceleration. During this brief time the engine does not deliver optimum fuel economy and does not minimize exhaust emissions.

 

Question: The maximum amount of 'power' you can get from the engine is relatively dependent on the maximum amount of fuel that can be burned in one cycle (yes, I know I oversimplified, but follow me here). Are you telling me that the engine would make more power if you WOT it at the theoretical maximum HP and torque points? Wouldn't that mean that the car would make more than 190 HP at 5600 RPMs if you floored it at that exact point? BTW, I use alldata.com and they only gave me two fuel line pressures, 34 PSI at idle and 43 psi when starting. I will have to check Chiltons or Haynes to read further.

 

The "active" control that the ECU has over fuel & fuel/air ratio is injector pulse width: how long the injector is open. There are a number of sensor inputs that it uses for determining pluse width, and of course, throttle position is one of them. During WOT the mixture goes rich so the extra fuel provides cooling for the piston. (To a lesser extent with newer vs. older cars, due to emmission laws.) Fuel pressue does have an effect of mixture, since for a given amount of time that an injector is open, the one with higher pressure will flow more fuel. This is why different/modified fuel pressure regulators are used on turbo & SC cars.

Traveling at a constant speed, on a level road, with the same car you will get better gas milage in a higher gear, turning a lower RPM.

 

Yes. The reason is that at anything less than WOT the engine management system strives to achieve good fuel economy and minimize exhaust emissions. At WOT it "throws the rule book out the window" and does everything it can to maximize power.

No. The 190hp what you get at WOT. When cruising on a level road at 5600 rpm the engine develops only enough power to overcome air drag and friction losses, and that is much less than 190hp. The published figure of 190hp is the maximum power the engine is capable of delivering.

 

why you aruging? you own a GLE-R .. it has a manually tranny

 

All those years of schooing and no one ever told me about that. I always thought that the engine was making exactly the same HP and torque at the same RPMs no matter what the gear. Nice to know. Thanks.

 

Definitely not, I know The 4th Gen NEEDS 5th to get top speed. In 4th, the torque runs out at around 6000 RPM at around 125 or so mph. You drop it in 5th and you're back in the torque band, and the car pulls you up to 137 or so.

DW

 

I know we are just talking about Maximas but I have seen what Daniel is talking about with the 6 speed Corvette ZR1's. You could achieve a higher top speed in 5th than in 6th.

 

I know we are just talking about Maximas but I have seen what Daniel is talking about in the 6 speed Corvette ZR1's. You could achieve a higher top speed in 5th than in 6th.

 

Typically, the manual version of a car gets better mileage because a manual transmission is more efficient in delivering engine power to the wheels than an automatic. However, at highway speeds, the auto will lock up, becoming just as efficient as a manual. In the case of the maxima, the manual runs at a higher rpm at highway speed than the auto, thus it suffers ~1 mpg in mileage. In city driving, the manual would prove more efficient, if speeds were kept under, say, 40mph. If you have an auto, push the gas at highway speeds and the rpm wont jump, the car will just go. Push it at slower speeds, and rpm will jump up a little. When I say push it, I dont mean enough to make the transmission drop a gear, just enough to accelerate in the same gear.

 

Automatics waste a certain amount of power in the tranny and torque converter where a manual is essentially a direct connection. So auto's usually suffer from lower mileage due to the lost power. However, if the manual tranny is geared to run at higher RPM's most of the time, then the auto may have an advantage.

Bob

 

So here's my little confusion. I know in reality our auto max's have only 4 speeds. Three plus overdrive. But how conme if I'm in overdrive and add a little gas the car seems to drop to an intermediate gear? Like it's out of overdrive. Then if I tap that overdrive off button it drops to third and really jumps. - Kevin

99Max SE Auto - Full Mods thanks to Maxima.org

 

Torque converters 'lock' at speed to maximize fuel economy. The 'shift' that you feel is the torque converter locking and unlocking.

 

I drive everyday to work on the Garden State Parkway.
I have a '97 with o/d. When I need to get on the road
at entry 129 in Islin, NJ, it is an upward climb to
get my speed up to the limit. I start accelerating
once I approach the main highway. My start speed is
about 30 MPH and I need to move fast to catch up to
and blend in with the highway flow which is about
65 MPH. My tach goes from 1600 to 3500 and in about
30 seconds I am about 55 MPH. As I settle around
60 MPH, my tach shows 2200 RPM. But mind you, Jersey
is flat as a pancake and maintaining 60 at 2200 is
easy.

This is only my experience with this fine car. Hope
others can concur with my findings.

 

The torque converter locks up under ideal conditions. Lockup eliminates the inefficiency due to slippage in the torque converter. When you are cruising in 4th and feed a little bit of gas, you are feeling the torque converter unlock. Then if you shift down to third (that's what the O/D OFF button does) you feel a true gear change.

 

Going up a hill --high load condition -- in a lower gear will burn less fuel than going up that same hill in a higher gear assuming the speed is the same --

With a lower gear, torque multiplication is higher to the wheels -- if the torque multiplication is higher, then the engine doesn't have to make as much torque to keep the car going up the hill at the same speed -- If the engine doesn't have to make as much torque, then it also doesn't have to burn as much fuel --

As for increased RPMs burning more fuel --
parasistic engine losses go up exponentially with RPM -- actually I read it is to the 4th power exponent --
But the Maxima engine is very efficient -- microfinished rods/cranks / cylinder linings -- etc.. Unless you are in the upper half of the RPM range, engine losses due to RPMs probably aren't making a big dent in fuel economy --

Another big factor for the 5 speed is that the transmission is far more mechanically efficient because is doesn't have a torque converter to waste power -- A solid mechanical link is far more efficient than a viscous fluid link --

So given the extra mechanical efficiency of a 5-speed and the fact that they have one extra gear -- effectively spacing the gear ratios closer -- and the fact that the gearing overall is a little shorter -- the 5 speed will have better real world fuel economy and "fun to drive" factor --- EPA Fuel Economy numbers is not real world -- If you have to do a lot of stop-and-go, driving in unsmooth traffic, hilly terrain, etc.. the Maxima 5-speed will always outperform the automatic in fuel economy and acceleration -- Now, I am only speaking a gear vs. gear comparison --

Each gear in the 5 speed will produce more acceleration than the corresponding gear in the automatic -- Even 5th Gear in the 5 speed outaccelerates 4th gear of the automatic --
Even if 5th gear of the 5 speed was geared exactly as 4th gear of the auto, it would outaccelerate the auto because it wouldn't have a torque converter to deal with

So when a driving situation is not dependent on driver skill for shift speeds vs. auto tranny valve bodies and torque converter modifications, the 5 speed is better -- Because the purpose is to provide driving versatility and thrust without burning as much fuel --

I think a torque converter with higher stall speeds is only useful for acceleration if the mid-range torque of the engine is a lot higher than the low RPM torque --- i.e. supercharger, turbos, etc... where the increase in torque outweighs the increase in viscous losses -- the faster you run up the torque converter in viscous mode, the more you lose through it --- and once that is all done and you let off the gas, you are burning more of it to keep the car at the same speed as the engine works harder to slush through the converter coupled with higher gearing ---


cv
proud owner of 95 automatic

 

So beyond the theoretical physice to application. Does anyone know the Torque a Maxima generates and at what RPM it is achieved? And while were at it the ideal shift points for a 99 Max SE Auto? - Kevin

99 MAx SE Auto - Full Mods

 

Steve Cutchen's excellent MaxFAQ site
http://web2.airmail.net/scutchen/max_faq/
gives these specs for the VQ30DE engine:
190hp @ 5600rpm
205ft-lbs @ 4000rpm

 

...and:
178 ft-lbs @ 5600 rpm
156 hp @ 4000 rpm

 

it all depends on the driver of the manual transmission. If he can shift effiecntly (mostly smoothly) he/she will inherently get better gas mielage than a rookie.