The "myth" of M3 "lag" at low (< 5K RPM)

[fernande-bmw]

This is from an off-side conversation I had in another thread. As suggested, I started a new thread to get a better perspective.

Prior to the F80, my understanding was that although the M3 has been traditionally good at providing high power at high RPM, they were "laggy" at low RPM compared to its 3 series sedan twin turbo sibling that provided peak torque at lower RPM.

From the other thread:

Originally Posted by CanAutM3

That is a myth perpetuated by 335i drivers . It has been demonstrated many times that, at the same road speed, the E9X M3 puts down more torque at the wheels in any of the same gear than a E9X 335i.

However, to quote a fellow member from an older thread:

Originally Posted by vAnt826

I've owned both an E92 335i and now an E92 M3.

One of the only things I missed from the 335i was the torque down low. I still to this day miss the lovely power available from low revs from a twin turbo engine (I had an N54).

So, was this an issue of numbers vs. driver feel?

The new S55 engine (I6 with the twin turbos) should address the lack of torque at lower RPM with 406 lb-ft of torque between 1,850 and 5,500 rpm, and still keep the power at higher RPM with 425 hp between 5,500 and 7,300.

I guess I am still not clear on the performance of the F80 M3 at low RPM compared to the 3 series sedan it is based on, because the 340i, for instance, has peak torque produced at an exceptionally low 1,380 rpm.

I am looking at this from a daily driver point of view where you are less likely to rev to the limiter. You would keep the RPM around 2-4K for the majority of driving needs including overtaking maneuvers or even coming out from a full stop. For spirited drives, you are more likely to go full throttle to around 6K RPM for a short time.

Does this mean that the 340i has a better kick and does a better job at overtaking maneuvers than an M3 F80 in the lower RPM range?

Thanks!

[Sedan_Clan]

There is no real perceptible lag to me. The F8X's S55 reacts more or less like an N/A motor in stock form. It has significant torque on the low end, so anybody complaining about low speed driving is on crack. Don't over think it.

[saleen556]

I highly doubt it. The M3 is a purpose built race car for the street. I Believe much lighter as well. The 500 rpm difference when peak TQ comes in will make little difference.

[BwoodBMW]

I had an N54 E90 335i that I just sold for my M3. As far as driver feel I can definitely say that the F80 does seem to lag a bit more at low RPMs in regular city driving. It's bizarre because when the F80 pulls it pulls much harder and no doubt is a better car by 10x but you do have to drive it more aggressively to get the same feel. The N54 was a gem for city driving.

[BwoodBMW]

I'll caveat that with the fact that if you put everything in sport plus you have more available to you in the F80 at all times but at that point its a bit to aggressive and jerky for regular daily stop and go traffic driving.

[dmk08]

Originally Posted by BwoodBMW

I had an N54 E90 335i that I just sold for my M3. As far as driver feel I can definitely say that the F80 does seem to lag a bit more at low RPMs in regular city driving. It's bizarre because when the F80 pulls it pulls much harder and no doubt is a better car by 10x but you do have to drive it more aggressively to get the same feel. The N54 was a gem for city driving.

Is this in efficient mode?

[MFNATIK]

I agree that in efficient mode there is a bit of a lag at low rpms but I think its more of a function of the fly by wire accelerator pedal buffering so that the take off is smoother. When I switch to Sport or Sport+ I find that it is very responsive off the line and can be too aggressive for daily driving (especially Sport+). So yeah, there is lag in Efficient mode but its most likely on purpose to make the driving experience more smooth and relaxed.

[Warranty P]

Originally Posted by dmk08

Is this in efficient mode?

It's gotta be otherwise this guy smoking crack.

[DaBean]

The mode only remaps the throttle; it doesn't add more power.

As for torque / driveability compared to the 340i. I haven't driven that car, but I can tell you that the M3/4 has more than enough torque down low to move you around traffic. Coming from an E46 M3, the gobs of torque at any speed are remarkable.

[dmk08]

Originally Posted by DaBean

The mode only remaps the throttle; it doesn't add more power.

As for torque / driveability compared to the 340i. I haven't driven that car, but I can tell you that the M3/4 has more than enough torque down low to move you around traffic. Coming from an E46 M3, the gobs of torque at any speed are remarkable.

It definitely holds back throttle so much it holds back boost and makes the car feel "laggy". I have to pretty much floor my car to get it to go in efficient.

[MFNATIK]

BMW setting the default to Efficient mode is sure fooling some people who test these cars and unknowingly don't adjust the modes. That's unfortunate! Too bad for them b/c this car is freaking amazing and I was HOOOKED on my first test drive.

[AW BMW]

Originally Posted by dmk08

It definitely holds back throttle so much it holds back boost and makes the car feel "laggy". I have to pretty much floor my car to get it to go in efficient.

I agree with this statement, I have to do the same with my car if it's in efficient mode. I never have it in efficient mode but sometimes I forget when I start driving. My tuned 335 had no driving settings but it was a strong performer down low but passing 4500 rpm nobody was home, it was uneventful! I drive the m3 in sports setting most of the time and when I feel like getting on it more I put it in sports +. The 335 was laggy though, the m3 in sport+ to me has virtually no lag.

[dkhm3]

N54 was a very non linear engine compared to the N55 and S55.

As far as the lag, there is a slight delay if you are WOT from 2-3k rpms and downshift to a lower gear... if you are intending to go WOT, stay in the 4k range and you will not have any lag.

[s0ul]

Ah yes. Easy fix to this solution, right foot made of lead with a dash of scream "POWAAA!!!!"

[CanAutM3]

There are two prongs to your thread.

The first one probably belongs in the E9X forum, but I will answer it anyway:

Yes, it is driver perception. Since the S65 pulls so hard high in the RPM range, it can give the perception of being weak in the lower rev range. But if you do the math, comparing 6MT to 6MT, you will find out that the E9X M3 has more pulling power at any given road speed in any given (same) gear than a E9X 335i (see this post for an example). Further, there is no "lag" on an S65 since it does not have turbos. With 8 individual butterflies just a couple of inches away from the intake valves, throttle response does not get any better than that .

Now to the second one regarding the S55:

First, you should not confuse turbo lag with boost threshold. I will simply steal the definitions from Garret, since they know a thing or two about turbos :

Boost threshold is the engine speed at which there is sufficient exhaust gas flow to generate positive manifold pressure, or boost.

Turbo lag is the time delay of boost response after the throttle is opened when operating above the boost threshold engine speed. Turbo lag is determined by many factors, including turbo size relative to engine size, the state of tuning of the engine, the inertia of the turbo's rotating group, turbine efficiency, intake plumbing losses, exhaust backpressure, etc.

Since the S55 has smaller twin turbos, it is less likely to suffer lag than the bigger single turbo in the B58. Also, the S55 is likely to have a more sophisticated anti-lag system than the B58 (not sure the B58 even has one). Further, it is also important to understand that most manufacturers test their engines in steady state for the published power ratings. In transient sate, at low RPM, the engine will likely not produce the torque advertised in the rating since the turbo does not have time to spool-up and catch-up with the constant demand for more air coming from the engine as it increases in RPM. So the actual transient boost threshold is most likely higher than what the published specs suggest for both engines.

All that being said, the S55 is a very torquey and responsive engine. While there is perceptible lag when mashing the throttle at pretty much any RPM, it remains very responsive compared to any other turbo engine I have driven. This "lag" does not hamper my enjoyment of my car even when driving on track. I would not be worried at all.

[mrduder]

so here's what I've noticed in the 7 months I've owned my F82. I do notice a bit of lag at times, just not all the time. I feel like it's usually only when the turbos aren't spooled up though that I get that lag. so for instance, if I'm just cruising and want to push it, but the car hasn't been pushed yet, that first WOT I notice like a 2 second delay before the car gets going. like it just doesn't rev at all for like 2 seconds and then all of a sudden it kicks in and the car goes. there's like a complete lack of throttle response. but, once that first WOT happens it's all good from there. no more lag issues.

[secretariat]

The only time my car is in efficient mode is when I'm warming the car up, especially now that it is cold out. I don't know what difference it makes if you have the car in efficient mode just for cruising around then why would you be looking for a lot of thrust. One poster said he forgets to put it into sport or sport+ I understand that if you are new to the car, otherwise I would think that you can't wait for the car to warm up so you can hit the M1 or M2 button. Once the M1 or M2 button is selected there is no lag.

Also, do M3 drivers really put there foot down as soon as they pull out of the driveway, because I really don't think that is a good idea. This car is good for cruising around town or taking over anything on the highway or twisty mountain road.

[Gearhead999s]

Autocross one and you will see lag!On the street or on the track it is not an issue.

[ASAP]

Originally Posted by CanAutM3

There are two prongs to your thread.

The first one probably belongs in the E9X forum, but I will answer it anyway:

Yes, it is driver perception. Since the S65 pulls so hard high in the RPM range, it can give the perception of being weak in the lower rev range. But if you do the math, comparing 6MT to 6MT, you will find out that the E9X M3 has more pulling power at any given road speed in any given (same) gear than a E9X 335i (see this post for an example). Further, there is no "lag" on an S65 since it does not have turbos. With 8 individual butterflies just a couple of inches away from the intake valves, throttle response does not get any better than that .

Now to the second one regarding the S55:

First, you should not confuse turbo lag with boost threshold. I will simply steal the definitions from Garret, since they know a thing or two about turbos :

Since the S55 has smaller twin turbos, it is less likely to suffer lag than the bigger single turbo in the B58. Also, the S55 is likely to have a more sophisticated anti-lag system than the B58 (not sure the B58 even has one). Further, it is also important to understand that most manufacturers test their engines in steady state for the published power ratings. In transient sate, at low RPM, the engine will likely not produce the torque advertised in the rating since the turbo does not have time to spool-up and catch-up with the constant demand for more air coming from the engine as it increases in RPM. So the actual transient boost threshold is most likely higher than what the published specs suggest for both engines.

All that being said, the S55 is a very torquey and responsive engine. While there is perceptible lag when mashing the throttle at pretty much any RPM, it remains very responsive compared to any other turbo engine I have driven. This "lag" does not hamper my enjoyment of my car even when driving on track. I would not be worried at all.

I know mathematically what all of this means... but what then does this mean-

M3 - 295 lb ft @ 4400 rpm
335i - 300 lb ft starting at 1800 rpm

I mean the number is higher at a lower rpm which gives the 335 the advantage which is why it feels faster down there. What you are talking about is mathemetical tq multiplied by gearing, this doesnt always translate to feel... at least it certainly wont to any driver.

[BwoodBMW]

Originally Posted by Warranty P

It's gotta be otherwise this guy smoking crack.

I think you are missing my point... I have an F80 and until recently I had an N54 E90. There is no doubt that the F80 is a better and faster car. From my experience the 335's power FELT more accessible during regular day to day driving in Los Angeles traffic (big surprise, that's what the car was made for).

And anybody who says there is no perceptible lag in this motor probably doesn't understand what turbo lag is. It isn't bad, but like every turbo motor there is absolutely perceptible lag in plenty of situations. I'm not bashing the F80 at all, I love the car. Just responding to OP's thoughts based on my experience with both motors.

[ASAP]

Originally Posted by BwoodBMW

I think you are missing my point... I have an F80 and until recently I had an N54 E90. There is no doubt that the F80 is a better and faster car. From my experience the 335's power FELT more accessible during regular day to day driving in Los Angeles traffic (big surprise, that's what the car was made for).

And anybody who says there is no perceptible lag in this motor probably doesn't understand what turbo lag is. It isn't bad, but like every turbo motor there is absolutely perceptible lag in plenty of situations. I'm not bashing the F80 at all, I love the car. Just responding to OP's thoughts based on my experience with both motors.

I agree and feel the same...

smaller turbos are smaller turbos

[Sedan_Clan]

Originally Posted by BwoodBMW

And anybody who says there is no perceptible lag in this motor probably doesn't understand what turbo lag is.

Describe a driving situation in which you feel that the lag is beyond minimally perceptible. I'm asking out of curiosity because I've owned plenty of turbocharged vehicles (..FD RX-7, 335i's, etc.) and driven plenty of other makes/models with turbocharged engines, and the F8X's "lag" is minimal, if even noticeable. I've been driving my F82 for almost a year and a half, and I haven't run into any situations where I feel that lag was an issue. If you're in the wrong gear for the situation, there will be lag, but if you're in the proper gear there really isn't an issue. I don't think you're giving people on the forum enough credit. Many people with opinions have come from other FBO or fully modded turbocharged platforms.