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M140i initial acceleration

12K views 74 replies 27 participants last post by  OneTwenty 
#1 ·
Hi
I just purchased an M140i (2017) to replace my old 2004 E85 Z4 3.0i and I'm a bit disappointed in its initial acceleration.
From standing to about 15mph the Z4 is more responsive. Could this be it is lighter?
After the 140 turbo kicks in, it destroys the Z4.
But pulling out of junctions, particularly on a hill, the Z4 is much nippier.
Am I missing something? - I have tried sports and sports plus modes but Z4 has the edge until the M140 turbo kicks in.
I'm guessing at low revs they are both 3 litre and pretty equal, so difference is inertia in the fact the Z4 is lighter?
Is this normal?
 
#27 ·
padders said:
OneTwenty said:
140ifan said:
M140i is a turbo, the z4 is NA

NA will ALWAYS be more responsive than a turbo car, the turbo has to build boost, once its done that though it will eat it alive. Launch control may help build the boost prior to launch but put a LOT of stress on the drivetrain.

Just accept it for what it is, ragging it from 0 to 15 is hard on the car anyway.
That may have been true in the 80s/90s when turbo cars had huge turbo lag, but the pickup on these is pretty much instant now due to the smaller turbo.

I don't believe a modern NA car will be more responsive than a modern turbo car, especially a 3L torque monster.
Totally agree. You'd have to force the B58 to pull in a very high gear at very low revs to experience anything like lag and in an auto it is virtually impossible unless you force it with the paddles. I regularly swap between a 3.6l 911 and my M240i and the BMW is noticeably stronger everywhere in the rev range, you have to rag the 911 to get it to fly (which is fun of course), whereas the BMW just goes and goes. The 911 weighs about the same as the z4 so I have a hard time thinking it is the turbo to blame here. My money is on either lack of traction or a poorly engine.
The issue is in very low in revs, before turbo, so just initial sensible pull away revs. So from idle to 1800.
Once turbo engages then I have other issues, but they are good ones as that means I have too much power and need an LSD :)
 
#29 ·
markm240i said:
I always thought the m240i and M140i autos could feel sluggish from initial take off unless you were quite aggressive with the throttle, but not to the point where you lose traction. The ZF8 is a fantastic gearbox once the transmission locks, but it can't initially hide the fact it's a slushbox torque converter.

WRT to the turbo kicking in, the B58 is pushing 500Nm from ~ 1750 RPM so even if it's torque limited in the lower gears (I don't know) it really shouldn't be an issue.

If it's a manual I've no idea what the problem might be!
Thats exactly what I'm experiencing. Up till 1750 rpm the response is not quite that of the Z4. But I have a manual. So not sure what's going on.
 
#30 ·
AngloSaxon said:
verfum said:
From standing to about 15mph the Z4 is more responsive.
ARe you sure the M140i isn't still wheel spinning? :lol2: :lol2:
You make a good point; I should be wheel spinning, but am not.
From a rolling start, say 5mph. If I plant the Z4 I get instant pickup, nearly wheelspin.
In the M140 if I plant the accelerator there are no revs, like an automatic from the 80s, then need wait till 2000rpm for the turbo to do it's stuff, and then very quick.
 
#34 ·
No, you should be able to do it on a Manual.

Try this:

- Press start button but do not start the engine, make sure it goes to all the lights being on the dash.

- Floor the throttle for 30-60 seconds

- Keep the throttle to the floor and press start button to power off

- Release the throttle and wait 2 minutes.

I've had to do mine a few times since buying.
 
#32 ·
Well that is an issue since the b58 has more torque everywhere and noticeably more from around 1400rpm (like 100s of Nm more). If you aren't feeling it until nearer 2k then something is wrong. You say you've tried with tc off, do you just mean sport plus mode or have you done the 3 second press on the DSC button? The tc intervenes without the light sometimes even in DTC/Sp+ mode which is only really a half way house to tc off. If not that then it must be either the clutch delay valve (likely), a boost leak or the throttle adaptions. I've not tried a manual b58 though so maybe they are tuned to be sluggish in the low gears to protect the clutch. Let's hope not.

Has the car been tuned/modded. If so then maybe that's the problem. Some maps are better than others.
 
#33 ·
verfum said:
tweeky said:
try resetting the throttle.
Would this only be for automatic transmission?
I doubt it the B58 throttle is fly by wire
 
#37 ·
Glad I bought the auto now, that sounds terrible. :redface:
 
#41 · (Edited)
Obviously that doesn't actually happen. I'm also not sure why the poster says you need to give it big revs unless they like burning their clutch or spinning their wheels. You only do that on a proper launch to maximise what you get out of the tyres.

Once the clutch is engaged unless you have wheelspin, the speed and rpm is locked.

Also given its a manual, the transmission behaves in the same way every time. A story that claims the m140i was out accelerated by a Qashqai suggests a problem with the driver.
 
#38 ·
The b58 and even n55 dont produce decent boost levels until 2500rpm looking at data logs, thats one of the reasons how bmw got good mpg from a 3litre engine ,
 
#40 ·
Got anything to back that up? It suggests that BMW are plain lying when they state that full 500Nm of torque is available from 1520rpm with the B58, and on balance I believe BMW. The B58 is strong as hell, especially from very low revs. The reason they get good mpg is because top gear is pulling 45mph per 1k rpm, on the auto at least. The manuals are noticeably worse.
 
#47 ·
I already asked you to post some after your first post. Feel free.
 
#49 ·
On another car yes but not on the B58 since I've left mine well alone. You are the one making claims about no boost below 2.5K, I would say the onus is on you to back it up. Show us on the N55 if that's where you've found it lacking.

How are you contending that the B58 makes no boost if you can't show us?
 
#51 ·
So mr paddy this is a data log of a m140i i know its stage 2 , but as you can read data logs very well, you will see the difference between boost target and actual boost at the inlet manifold even at 100 percent throttle, below 2,5 k
datazap.me | JSP_BMW_M140i | Log 1642500786
 
#54 · (Edited)
Both those logs are interesting and rather surprising I must admit, but I have serious reservations. What gear were those runs in? Also, at what point was the pedal mashed and WOT applied? For the log @i531m shows only 20% of throttle was applied until 1,560rpm (yes I can read a log thanks) and 100% only at 1800rpm. Boost takes time to build and you don't build it at 20% throttle so it is meaningless for showing boost lower down. More instructive would be WOT from idle, or 1K rpm.

Also regarding gear, I can see how in 1st there just isn't enough time for the turbo to make meaningful boost before running out of revs but I would be amazed if in a higher gear with longer to stabilise the B58 is only making 3-4psi at 2k. If that is the case, how the hell are they getting 500Nm at 1500rpm with just a couple of psi or less? No, I just don't buy it.

I too would like to see a standard tune car. At first glance, both those logs show what was suggested, that the boost isn't fully there until 2.5k, but if they aren't using WOT until near 2K then what use are they?
 
#56 ·
In 1st engine rpm accelerates faster than turbo can get going for any given rpm, so unlikely to hit peak torque at any given rpm at all in 1st gear.

ie, 1500rpm in 6th and floor it, rpm will rise slowly and turbo spools to max by maybe 1600rpm.
In 1st you floor it, it might be at 2000rpm by the time the turbo is at full speed.

ZF8 probably masks this in auto.

Manual won’t mask it.


I loved my E85 3.0i, great cars, very responsive, very taught chassis.
 
#59 ·
My m240i auto sometimes feels like 1st and 2nd are torque limited. I never launch my car but on the odd occasion I get caught out on approaching a roundabout. I’m rolling up to the give way line 5-10mph, ready to enter it but I’ve misjudged the speed of an approaching car so stop and then quite quickly get on the power again, the car accelerates in 1st upto about 3.5-4K revs before changing to 2nd and it feels like someone’s removed the turbo, there’s hardly any torque at all and this continues into 2nd. It’s not until I come of the throttle and get back on it get I feel the torque and ‘normal’ power return. I very rarely accelerate hard below 3rd gear so not sure if this is the gearbox having learnt my driving style being caught out by what it considers unusual behaviour or if there are torque limits in place orsomething else entirely. But to bring it back to the OPs question, a 3.0 na Z3 would destroy me in these circumstances.
 
#58 ·
I have the B58 auto, and think I get what the OP is talking about. Once warmed up, it likes to idle at about 600-700rpm, which I assume is an emissions/economy feature. If you're gentle on the throttle, even in sport mode, it can take maybe half a second to "wake up" -- whether this is an artefact of the emissions profiling or done deliberately because it spins one back wheel so willingly in anything other than a straight line in the dry (when it spins both), IDK. Adding the LSD vastly improved reliability off the line, but now it's even more tail-happy than in standard form, although the slight lag before pulling away is still there.

If I need to get away, I'll very softly launch it, running up to about 1100 rpm against the footbrake, and that fixes it entirely.

In the real world, I don't think you'll ever be WOT on boost at 1500rpm -- WOT in low gears will just light up the rear axle, and if you plant it from ~65mph in 8th, it'll have shifted down before the turbo has spooled up.
 
#60 ·
I think this might have been mentioned earlier in the thread but I'm fairly sure the drive-by-wire throttle has a variable/adaptive map related to driving style. At least it has on previous cars I've owned (3 series). The more frequently you mash the throttle pedal, the more responsive the actuation of the throttle is. Likewise in opposite - the more sedately you drive, the less the throttle will open (kind of) for a given input. There used to be a way to reset this throttle map manually but I couldn't tell you what it was, other than to use the throttle like an on/off switch for a few miles!!
 
#62 ·
I am surprised that nobody here has bought up the proactive traction control stuff? If I get considerable wheel spin in comfort/sport then the next time I pull off power will be limited until I next start the engine. I've never tried to clear this by turning the nannies off but I believe Sport+ will snap it out of it.

Does nobody here think that this could be the proactive traction control stuff?
 
#64 ·
It's nowhere near losing traction, at least for me and at least the way I interpret the OP's situation. It's merely trying to make swift progress but not flooring it, all while in 1st, there should be no traction worries at those levels. Normally, if setting off in a relaxed fashion the 'box will chage to 2nd almost immediately, but when pushing the pedal further like in these situations it will keep 1st for up to 3-3.5K rpm and then it will sound like it doesn't want to rev more.

Experimenting with it yesterday I found if you manually shift to 2nd just as fast as the 'box would do in a more relaxed driving off situation, this hesitation feeling almost goes away completely so maybe it's really just the gearing / un-necessary gear holding. Plus with all that torque you really have no reason to keep 1st beyond the first couple of meters.
 
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