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08-27-2009, 10:13 PM | #1 |
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Why is 0-60 so much faster with MT ?
The 0-60 spec on 135i is 5.1(MT) and 5.2(Auto), but for the 128i its something like: 6.1(MT) and 6.7(Auto).
Why would the difference between the two be so much bigger in the 128 than the 135 ?? (P.S. How much does that auto-trans weigh?) |
08-27-2009, 11:42 PM | #2 |
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The 128 has an inferior automatic gearbox compared to the 135 and also the gearing might be diffrent which will also play a role.
So for 135 manual ratio = 3.06, auto = 3.46, this shorter gearing combined with good gearbox acts to close the gap between the manual and auto. |
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08-28-2009, 12:55 AM | #3 | |
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MT: 128---- 135 I/II/III: 4.30/2.46/1.66---- 4.06/2.40/1.58 IV/V/VI/R: 1.23/1.00/0.85/3.94---- 1.19/1.00/0.87/3.68 Final DR: 3.23---- 3.08 AUTO: 128---- 135 I/II/III: 4.065/2.37/1.55---- 4.17/2.34/1.52 IV/V/VI/R: 1.20/0.85/0.67---- 1.14/0.87/0.69/3.40 Final DR: 3.73---- 3.46 Do these numbers account for that big difference in 0-60 for 128 that you don't see in 135? It seems odd that the Vth gear ratio in AT is not 1.00. The ATs appear to have 2 overdrive gears ?? |
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08-28-2009, 01:14 AM | #4 | |
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I compared several E87 123d and 130i (Euro cars) and look at figures, too. MT AT 130i 0-100 km/h 6.0s 6.2s 123d 0-100 km/h 6.9s 7.0s The point is how harmonically develop engine's power with shifting algorithm. When I changed ECU software and brought 125i power to stock 330i level (272 HP) I carefully compared car real world performance with both 130i MT and AT. Due to fact that 125i has even shorter final drive ratio than 130i, it was not surprise that 125i with AT was slightly quicker than both stock 130i both with AT and MT (7 HP more are compensated with some 40 kg more weight of tested 125i). Both stock 125i and US 128i show very big difference in result between MT and AT, although on 125i is exactly same gearbox as on 130i (and I believe 128i, but didn't check this). With power elevated to around 130i stock values the difference evaporated. So, the difference (0,7 s in Euro spec) was melted down when engine characteristic became better optimized to initial characteristics of the gearbox. Practical conclusion is that acceleration difference here depends on engine and ECU algorithm much more than gearbox itself. After further power enhancing (to around 300 HP) power gains were clearly reflected in car acceleration and feel (further around 0,6 s improvement 0-100), so car, although not exectly same, can hold its own very, very close to 135i (both AT and MT). I believe that 135i has heavier duty gearbox (not better in terms of acceleration) due to its huge torque in lower revs (here is the biggest difference to N52 engine). |
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08-28-2009, 02:45 AM | #5 |
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raceman what software did you get?
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08-28-2009, 07:48 AM | #6 |
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@raceman: What automatic transmissions come with the 123d and 130i? Is it the ZF transmission from the 135i coupe, the GM transmission from the 128i - or are they different altogether? And what is the gearing like in the 123d/130i?
Thanks. |
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08-28-2009, 07:57 AM | #7 |
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In the 135i the automatic would be slower, but the engine stays under boost during the gear change (which isn't possible on the manual) and that probably closes the gap. Turbo cars with automatic transmissions always have that advantage.
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08-28-2009, 09:59 AM | #8 |
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It's rubbish....my stock 135i will never do 0 - 62mph in 5.3seconds!!
(And before anyone says, its not my driving...I am a qualified race driver and advanved police driver) Best 0-60 time i've had in my 135i is 6.6 sec |
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08-28-2009, 10:12 AM | #9 | |
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So how exactly do you explain that fact that numerous magazines and independent tests have matched BMW's claims. There are people on this forum who've clocked low 5 second 0-60 times. |
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08-28-2009, 10:17 AM | #10 |
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6.6 seems to be far higher than average (by about one second)
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08-28-2009, 10:36 AM | #12 |
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the 135i has the ZF auto and the 128i has the GM auto that's the difference I believe
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08-28-2009, 10:40 AM | #13 | |
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This is my results from my 135i, and from a G-dyno and other tested means. That was theres... It's very annoying! |
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08-28-2009, 01:02 PM | #14 | |
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Tom |
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08-28-2009, 03:43 PM | #15 |
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To go back to the original AT vs MT in a 128i question, I had to do this twice so somebody should check my math but I think the AT 128 is in 3rd gear at 60 mph and the MT is still in second.
Using the above gear ratios, I did not check them, I get a final drive ratio of 7.9458 for the MT 128 and 8.84 for the AT (final drive ratio is the transmission ratio times the rear end ratio). Using the fact that in the RT 135 test, they got the manual transmission to 69 mph in second (at 7000 rpm), I get a maximum of 64 for the MT 128 and 58 for the AT. So most of the difference is the extra shift with the AT. In the real world you should not see this big a difference (the MT would be shifting a split second later too). Jim
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08-28-2009, 04:29 PM | #16 |
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Jim, I calculate redline in 2nd as 66 mph for my '08 128i, so I think you are pretty close with your numbers. But shouldn't the shorter ratios and torque convertor more than make up for the extra shift? And does the steptronic 2-3 shift really take over a 1/2 second at 7,000 rpm? If so, I'm really glad I opted for the MT!
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08-28-2009, 04:46 PM | #17 |
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My local tuning shop does that and guys have many years experience of manipulating ECU software.
In theory, like some German tuners do it, ECU software can be easily loaded to original ECU block, but in reality they check all aspects and adapt SW to each particular car. Also, they give full warrantly and will re-load software in case of necessity later (if dealer 'updates' ECU to original data). Point is that it's not big issue for software crackers to do it, but requires some equipment and experience. There is really no need to 'suffer' from somehow underpowered 125i engine, when 100% same engine produces 272 HP with OEM software for X3/330i. |
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08-28-2009, 04:52 PM | #18 | |
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I tested two 135i with AT and they did something around 5,2-5,3 s for 0-100 km/h, also two 335i with around same result. As point of reference stock 135i with AT is just slightly quicker (0,3-0,4s to 100 km/h) than tuned to 300 HP 125i with AT what is adequate for torque difference. With 6.6 s, your 135i is in 125i range what doesn't sound right. |
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08-28-2009, 07:30 PM | #19 | |
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A.) Something is seriously wrong with your car B.) Your driving skill is Sub-Par I can fairly easily hit high fives without a huge launch, and mid-low 5's beating the hell out of it when all my car had on it was an axleback exhaust and SSK. FWIW, most car magazines have hit sub 5 0-60mph times... The car is capable in proper working order and a skilled driver. |
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08-29-2009, 08:22 PM | #20 |
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Tom,
I thought of the same thing as I was doing the calculations. The quoted speed difference suggests that the GM transmission in the 128 is not so good. The higher ratios should get the automatic 128 accelerating harder so it should be ahead when the upshift to third occurs. But that is if there is no slipping in the torque converter. There is always some slipping from a standing start but if it continues to slip effectively reducing power to the wheels, that could offset the ratio difference (and could be the reason for the ratio difference in the first place). It still seems odd, however. There are lots of AT cars with acceleration similar to MT. And the mileage of the AT 128 is good. It would be nice to know what other cars this AT is used in. If it is a bit weak for the N52, they could be trying to protect it from damage under hard acceleration by letting the torque converter slip to take up shock. That would make things hang together. Jim
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08-29-2009, 08:42 PM | #21 | |
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08-29-2009, 09:29 PM | #22 |
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I notice that on the BMW UK website, the 120i, 125i, 318i, 320i and 325i have an average 0~100 kph difference of about .6 seconds between MT & Step. But all other models (including the various diesels) only show a difference of .1 or .2 seconds - like our 135i.
Sounds like Jim & SJ are on to something. Tom |
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