Yes, I do see what you're saying and I agree. The TC hasn't locked back up when I shifted back into 5th. The reason for that is because I was downshifting from 5th to 3rd and then going back to 5th for a very short period (about 1 second) and then downshifting from 5th to 3rd again. The video was to show you that the tranny, at least on my 03, will downshift from 5th to 3rd and skip the TC unlock and 4th if I want it too. I thought that's what we were debating here and not what the tranny does on a part-throttle upshift

As for the TC locking at full throttle, yes, it does it. You can see this when you're in 3rd at say 4800rpms and mash the throttle. With most autos, when you do this, the rpms will jump 300-500rpms and the car will start accelerating. With the G, the throttle response is instantous as if it were manual. The TC on the G is very loose (2800-2900rpm stall) and it would be very obviously if the TC was unlocked at full throttle above 4500rpms or so, especially in 3rd and 4th. The TC locking at full throttle is dependent on load, rpm, tranny temp, etc. There are tons of variables at play.

The G 5AT is well geared, is paired with a decent stall TC, and the tranny is pretty smart. All this explains why these 3,400lb cars with automatics and ~220whp/210wtq and achieve lower 14 second ETs in the 96-98mph range. Most cars with same power levels and 5ATs are in the higher 14s. A perfect example is the current gen Acura TL 5AT. They weigh the same, have 5ATs, and roughly the same power (slightly more HP, but 10wtq less), but they're .5-.8 seconds and 3-4mph slower on average. It very uncommon for a 2004+ TL 5AT to see sub 15.0s@93mph with a 2.3 60 foot. My stock G did 14.6s@97mph with high 2.3s 60 foots and with 2.1s it does 14.3s. That's a pretty big difference for two cars that look the same on paper. The major difference? The TL's poorly geared 5AT and tight TC that doesn't lock at WOT. The new TL-S 5AT with 3.5L 286hp and revised tranny are seeing 14.3-14.5s@97-98mph at Rockingham Dragway in NC. That's a pretty quick track too.

 

It would be interesting to compare the power curves of those two (hp/tq) as I believe the g generates a fuller tq line as compared to that of the TL.

Although the TL may be geared poorly relative to 1/4 mile times, I bet it doesnt cruise 70 mph @ +3k rpm (which is one thing I cant believe nissan over-looked).

 

I just tried this in a 03 sedan:

I was on the Fwy doing 60 in 3rd, and let the TC lock up. With partial throttle (very gentle), the TC stayed locked, but when I went WOT, there was an instant ~500 RPM jump.

I'm not sure if this is a result of the adaptive throttle, or if the tranny was taken care of differently. I do know whenever I left someone borrow my G, the shifting attitude was different, as well as the throttle response.

I do have to say that the 5->3 shift is absolutely seamless. I couldn't do a 4->2 though. It's fast, but not as seamless as the 5->3. I'd say blame it on the bigger RPM jump.

1st gen G's do roughly 3k rpm at 80mph. My honda does 4300 RPM at 80 mph. It puts down about 240 to the hubs and still consistantly deos 25+ mpg... My G regularly did 28+ on freeway only driving.

the TL creates less power, but FWD has less drivetrain loss as well...

 

I stand corrected (my kph-mph calc. was wonky).

My point was the G should be able to crank 2.5k rpm max at that speed, if it was geared more efficiently and less 1/4 mile aggressive.

 

^^ +1 .. who cares if the G cruises at 3k @ 80mph. I don't understand why folks always need to comment/complain about that.

It doesn't cost you significant MPGs over cruising at a lower rpm and the engine revs to 6800 rpm. As a bonus, you get a little pep for shift-free passing on the freeway.

Fuel burning in the cruising rpm range is directly related to air coming into the engine and air coming in is directly related to throttle position, not RPMs. ......Unless your ECU is broken and floods your engine with a very rich mixture just because you are at 3k rpm instead of 2k rpm.....

 

Right....?!?

http://autorepair.about.com/library/faqs/bl857g.htm

Note: I didnt want to hijack the thread but in my opinion I would take the slower 1/4 mile time to achieve that extra 3-4 mpg on the highway (when comparing tl vs. g35).

 

more RPM = more mechanical loss, but it also means you have more torque.

You just need to find a good balance between RPM and power.

E.G. my 3000GT will get better MPG in 5th than in 6th unless I'm cruising 85+. 6th gear RPM is simply too low, and I don't have enough power, so I have to step on the gas more. This results in positive boost from the turbos as well (side effect). In 5th, my RPM is higher, but I can step on the gas WAY less, and my boost will stay negative.

 

Check out Acurazine.com and go to the TL forums. You'll see that the real world TL mpgs aren't much better than the G. Most TL owners see 18-20 in the city and 24-27 on the highway. That's what my G sees. I've gotten as high as 29.8mpg.

 

DaveB how much did you bend the shift prongs can you take a pic? I thought about doing this when I reversed my MM direction the other day.

I see that it has been done before so I will give it a try.

I sometimes didn't push it far enough or tap it too lightly (I guess) when racing and it doesn't upshift until I do it a second time.

Which sucks being FI because I bounce off the rev limiter when that happens.

 

Today's engines are very low friction. You need to be very high in the RPM range for you to see a measurable difference in mpg. The difference between 1.8k and 3.5k on the tach in a cruising situation is minimal.

A fuel-injected engine is going to receive the same mixture of fuel-to-air at all times (except near redline). If your throttle is nearly closed, you're not going to inject a bunch of fuel into the engine just because the rpms are high. We're talking a tiny amount of fuel in those conditions. Increasing the RPM few percentage points (10-15%) isn't going to amount to a whole lot of net fuel use difference.

In fact, if you are fully cruising (completely off the gas pedal) and your rpms are above 1500, you are burning absolutely no fuel at all. The car's momentum is turning the wheels, the engine, the belts, etc and keeping everything going.

You can waste your time shifting early all day long if you want -- but all it takes is one jackrabbit start to make it across a busy intersection and you've devoured any possible savings and then some.

 

friction isn't the only issue here. It's the reciprocating action. The pistons are constantly going under acceleration in two different directions, and that acceleration has to come from somewhere.

That acceleration/deceleration/acceleration/deceleration is the primary reason engine braking is effective.

 

....wth... this started out with a G vs a GT .. and now we're bringin up ferrarris... lol and btw.. shame on u for gettin womped... smh.

 

Wow, 117 replies to this thread. Looks like I have some catching up to do.

.

 

I agree with you in principle -- there is more than just friction at play. I think it is minimal.

Engine braking is effective due to engine compression plus gearing. Ever worked on an R/C plane? It's difficult to get the prop to turn past the peak compression point. Then when you cross it the prop pretty much spins around the rest of the way by itself until it encounters pressure resistance from the compression again. Take the head off the plane's (one cylinder) engine and with no compression the prop will free-spin to the extent that the bearings on the engine are in good shape. Same concept here, just bigger engine, heavier prop, I mean, car.