I bought an auto about a month ago. Before purchase I test drove both drivetrains. The manual shift from 1st to 2nd was not as fast as the auto and lacked the ability to quickly force the rpm's into third gear. I found that the auto had less lag and rpm's rose much faster. Im sure there will be plenty of manual afficionados that will say the shift is as fast as the person shifting, but I feel that I am pretty adept. Just wanted to hear some thoughts about this topic?

Judson

Oh!!! This could be very important.

The 6 speed I drove had a very rough idle. In fact, had it not been for that my wife would have agreed to the 6 speed.

 

IMO on this subject...

The Auto Trans in the Xfire is the same in the CLK & SL and most of the faster Benzo's... They dont even make some of those cars in manuals... sorta like the Xfire SRT-6... there is a reason for that....

People say the manual is faster... but after chipping... and brake torquing like WM has taught us... you can pull off the same 0 - 60 times as the manuals... since chipping takes your RPM to 6200 instead of 6000 for shifting.. give it a bit more power...

I love my touchstick and wouldnt trade it for a manual at all in this car... would be different for different cars... but for the Xfire... i love it!

 

In a manual the 1st to 2nd shift is very quick. I'd recon its quicker than an auto. The 2nd to 3rd shift does take a bit longer, but once you get used to the car you can really improve the shift time.

As for the automatic climbing RPM's quicker than the manual, that is physically impossible. The lower gear ratios of the manual will result in quicker RPM gain. The lower ratios are a result of having an extra gear in the manual.

Automatics do have somewhat of an advantage over a manual off the line, unless the manual driver is very experienced with his crossfire. But like everyone says, the crossfire is not a drag car anyway... it belongs on a road course, which is where the manual is undoubtedly superior.

 

In theory this would seem correct. However, the automatic transmission will have internal slippage. So it makes sense that the rpms in the auto can climb faster than for the manual. The lockup feature on the torque converter eliminates slippage but only under certain conditions such as cruising speeds, top gear, etc. When accelerating in the lower gears the lockup feature is inactive and there will be varying amounts of slip.

 

I don't know about that. with no experience on this clutch I would probably agree but with a few thousand miles on it I am rather good a crushing the clutch in 2nd and 3rd gear.

I would not think the wheel spin I get in 2nd and 3rd slow me down so I can't see how the auto would do any better. If I could just figure out how to float to second and third with out the aid of the clutch and without destorying it then I would really be moving.

-marc

 

Have had my manual since April, and indeed, there is something of a learning curve to become proficient at getting through the gears smoothly and accurately. But once mastered, what fun! Can't imagine an auto in this car, but clearly understand how beneficial it must be if the xfire is your everyday car.




6sp graphite #16515

 

The torque converter will slip under normal driving and light acceleration, but under full throttle hard acceleration I do not think the torque converter slips. That would induce an awful lot of wear.

 

As best I can tell. I think our torque converters have aroung a 2,400 - 2,600 rpm stall.

For those who may not know... The "stall" rating is the point at which the converter locks up like a fully engaged clutch. This happens in each gear. Since the shift points are above 2,600 rpm at WOT (it enters the next higher gear above the stall point) the converter stays locked up as it goes through the gears as long as your foot is burried in the throttle.

 

...Which is determined by observing maximum RPMs while keeping the car stationary using the brakes under full throttle acceleration.

But even then there is still slippage since it is a hydrodynamic interaction. Unless in a mechanical lock-up mode there will always be a small slip percentage. I've learned that Mercedes (at least some of the newer models) have a really advanced lock-up converter that works in all forward gears. Anyone know if the Crossfire has that feature? Or does ours only work in top gear (like most other vehicles with a lock-up feature)? This increased efficiency must be why the auto gets slightly better mpg than the manual. Anyway, interesting topic. You guys got me thinking too much. :?: :idea:

 

I can tell you that it sure feels like it's locked in 2nd gear on an autocross course when you stand on the throttle when you appex a corner. I can't feel any slip at all. It's very possitive. But that could be because the chip increases the line pressure too.

 

Torque Converter 101

A torque converter is basically made up of a pump and a turbine. Think of a hollowed out bagel and the way bagels are cut. Now imagine the two bagel halves being connected together through a bearing that allows each half of the bagel to spin independent of one another. The pump can be thought of one half of the bagel while the turbine is the other half. The pump half is connected to engine, and the other half (turbine) is connected to the trans. The trans fluid inside the torque converter (inside the hollow bagel) is is "flung" by means of little fins that are inside one half of the bagel (pump) to the other half of the bagel (turbine). The turbine also has fins attached to it on the inside, and these fins spin resist the fluid flung over by the pump and cause the turbine to spin. Since the turbine is connected to the trans, the car will start moving. (This is an oversimplification of course - there is a stator inside there as well.....)

The faster the engine spins, the more force the fluid gives to the transmission, until a point where the difference is so great, either the engine cannot spin any faster, or the car moves. That is the so-called "stall" point where, in the xfire, is about 2400 to 2600. It is at this point that the torque multiplication of the torq conv is the greatest, and in a good design, this multiplication is close to 2. Yes, the torque of the engine is mult by 2 or so, and this is the advantage a torque converter has over a manual, since a manual does not have a torque converter.

So, when you floor it off the line in the auto, the engine revs up faster than the car moves, and the cars speed "catches up" with the engine (the differential of the pump and turbine speeds) and the auto has this torque multiplication advantage over a manual.

So it sounds like the auto is superior to the manual, right? No. This 2x or so multiplication of torque does not make up for the parasitic losses in the auto trans. To make a long story short on the internal workings of the auto, the "overhead" of the complex gearing (planetary and sun gears) in a auto trans is far higher than a manual, and is, very roughly, about twice that of a manual.

To sum all of this up, the horsepower lost spinning the auto trans is more than spinning a manual (full race-prepped autos with super high stall converters excluded-the super high stall really multiplies the torque). Combine that with the fact that there is an extra gear in the xfire manual, and the auto CANNOT be as fast as the manual, provided the manual is shifted properly... and that is the auto's advantage. A missed shift by an overly excited driver (yours truly on occasion) is impossible to recover from. The auto is all about consistency....but it is NOT faster.

One last point regarding the lock up feature of torque converters. The efficiency (the difference in spinning speed of each half of the bagel) of the converter starts off at around 90 or so percent at the stall point, to about 95-98% at about 500 rpm higher than stall (in the xfire, probably around 3000-3200 rpm). Note that 96-98% is not 100%, and this equates to lost power (in the form of heat) and resultant loss in MPG. The lockup feature does just that - it forces the two halves to be "locked together". But the overhead of the gearing in the auto is still higher than a manual, and that is why in all cars (except for the xfire), the manual gets better MPG. (I still do not understand why the MPG number is better for the auto in the xfire).

So there!, you automatic loving xfire owners!!

 

Don't know if the Auto is "faster" than the 6 speed, but as far as my $0.02 go.....with the Upsolute ECU under the hood I'll take my Autostick over a 6 speed on any road course any day. Left foot braking anyone :-)
Now if I could get paddles on my steering wheel like in a 360....that would be the icing on the cake.

Plus and this is a big plus in the mess we call traffic here in SoCal......if you want to be lazy just leave it in D. No worn out calf after 25 miles of LA stop-n-go

 

I own a 6spd but drove an automatic for a week.....the auto isn't as quick as the manual. And I drove the heck out of it.



Dallas

 

thanks for the detailed explanation pelked1. that was very cool. i know the concept of the torque converter but didn't know the details. thanks a lot!

 

I think HDDP knows where to get some..

 

Just throwing in my .02. Well I know alot of people have problems with magazine times but that being said every magazine that has a manual and auto crossfire ran the manual is quicker. I think motortrend had a 6-speed do 14.7 and a auto do 14.8. 1 tenth is still 1 tenth and tenth is a car length :lol: and a high 14 is a high 14. I just like shifting thats why i bought the manual but i may buy a srt6 if the incentives hit it like they did my crossfire, i'd pay an extra 100 bux a mo for the srt6

 

Ah DRUNK... You're giving away my secrets for the SRT6 I have on order... Here is the vendor that is making the kit for me... I'm still going to hate the auto... But Supercharged 330hp outweighs the purist sports car mentality of my 6spd... And I drove a friends Porsche that has paddles and kinda liked the fact that I had full control of the wheel while shifting through turns...

http://www.bmw-paddleshift-retro.com/

 

HDDP... kinda does away with the airbag, right?