7AT = 5mpg higher EPA rating?

[rn79870]

I just watched a preview of the new FX50 on the news here in San Diego. They demoed all the features of the car and meh, it isn't anything more than a G35 with side and rear view cameras. (at least it looks almost like the G with the S interior.)

They played down the 5.0 V8, referring to it as a "stronger motor." Never once mentioned the HP rating.What they did say that made me sit up and take notice was that with the 7AT, the car is rated at 5mpg MORE than last years model.

Now, we need to start a campaign to get that 7AT in the next G. If we're lucky, the 2009 sedan will be a G37 with a 7AT. If that happens, BMW better add another couple of turbos, and 2 more cylinders to its 335.

[gwoods]

Interesting side bar.

the transmission behind every Hemi ram is a 545RFE which is the SAME transmission as the 45RFE that is in every Dakota V8 and Jeep Cherokee.

In the Hemi its a 5spd automatic in the Jeep/Dakota its a 4spd automatic. The only difference is what the ECU does with the transmission.

In the Hemi it is actually a 6spd but 2 of the gears are both 2nd gears, 2 different ratios's. The ECU makes a lower 2nd gear for full throttle kickdown by using 4th gears clutches.

So my point (finally)

The 7 spd auto COULD be the same 5 spd auto we already have with some computer tricks.....

I'll take the 5spd over the 7 spd anytime. More gears means more shifts, more shifts usually mean a slower 1/4 mile time. I wish I could keep it in 3rd for the 1/4 mile now but my tires are too short.

[C-Kwik]

More gears generally does equate to better mileage if driven correctly. Less gears means each gear must have a much bigger range of operation for a given load. This tends to mean a motor will operate within a wider range of RPMs. Having more gears can narrow this range so that the engine's operation occurs more closely to the most optimal RPM (for fuel efficiency), which will likely reduce fuel consumption. It also allows a motor to have to rev less in each gear. As we have discussed in other threads, higher RPM tends to be one of the biggest contributors to fuel efficiency.

To put it another way, think of Continuously Variable Transmissions. They are in theory, the most fuel efficient transmissions. The more gears you have, the closer it gets to a CVT. If you have taken Calculus or worked with limits, think of x as the number of gears and what would happen if a limit was taken as x approaches infinity.

This same principle applies to acceleration as well. Only its operation will be more centric around the peak HP area of the motor. Shifting is quite fast in a modern automatics. So I doubt a couple of additional gears will make that much of a difference. Chances are, in a 1/4 mile, you might only experience one extra shift anyways.

[Q45tech]

"This same principle applies to acceleration as well. Only its operation will be more centric around the peak HP area of the motor" ?????

Maximum instanteous acceleration occurs in each gear where ever the torque peak rpm occurs.

[C-Kwik]

"This same principle applies to acceleration as well. Only its operation will be more centric around the peak HP area of the motor" ?????

Maximum instanteous acceleration occurs in each gear where ever the torque peak rpm occurs.

Absolutely. But for a given vehicle speed, maximum acceleration will occur when the engine is at the peak HP. Basically, the torque multiplication will result in more torque at the wheels there. Which is really what matters.

[redhed]

just checked here:

http://nissan.iconicweb.com/as...l.pdf

new FX gets anywhere from 1 to 3 mpg improvement (city/highway) over old '08 depending on model.

it's been my impression that more gears in the slushbox usually gives only a small improvement in fuel economy. however...the improvement in acceleration can be significant.

i'm a bit disappointed nissan hasn't employed an AMT and is instead sticking with a conventional slushbox...