04-22-2021, 10:58 PM | #1 |
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The S58 is certainly not an S55
This is obvious.
Now that I've pushed the car more I'm kind of surprised how dramatically different the characters of these two engines are. A few thoughts I've had so far: Noticeable turbo lag Kind of bland in the sound department Dramatically more thrust at and near 5(still breaking in) Not as sharp and violent as the S55 i.e On/off throttle movement kind of mushy.. I'm not sure how I'm going to feel about all that by the time 5k miles rolls around but at this point I'm kind of missing the s55 and all it's sounds and character. How do you guys who've come for f8x cars feel about it? |
04-22-2021, 11:51 PM | #2 |
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Background: I've been mashing on my S58 with regular redline drives for a year now.
Boost threshold and tuning for linear power is not turbo lag. The S58 has almost no turbo lag when on boil >3.5k rpms. It does have a boost threshold though, not really starting to develop power until about 2500 rpms and by the time you hit 3k torque is strong with Hp rising linearly until about 6500 RPMs then strong to 7.2k. It feels more naturally aspirated than S55 with a smooth and powerful powerband which is generally more desirable than the character of the S55. If you like a spiky more wild character you may prefer S55. |
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04-23-2021, 12:27 AM | #3 | |
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04-23-2021, 12:41 AM | #4 |
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Boost threshold = the RPM at which an engine needs to be at to generate the desired boost pressure from the turbo
Turbo lag = the time in which the turbos themselves need to spool to reach optimal boost pressure S58 has both a higher boost threshold and more turbo lag than S55 because of its lower compression ratio and bigger turbos. The "linear" powerband is just a byproduct of the classic big turbo formula. If you're driving below say 3.5k (as the above poster suggests) you will be out of the boost threshold whereas S55 is within or closer to its boost threshold. When out of boost, S58 will take slightly longer than S55 to spool - which is usually represented by throttle response which I think you are describing above. S55 throttle response is greatly aided by its high compression ratio and smaller turbos (theoretically S55 is producing more natural power relative to its total output due to the higher ratio and therefore needs less help from the turbos - i.e smaller turbos), the expense of which is less objective top end power and tuning potential (which is why S58 is such a monster). Simplistically, that's really all there is to it - I've driven X3M and noticed both the higher threshold and slightly more lag in "normal" driving, but both of those aren't a problem if you're driving in a performance context as the engine is always under load and you're always in boost and above the threshold.
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04-23-2021, 12:59 AM | #5 |
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Bottom line in my experience is that if you want to stay in the powerband, don't be afraid to go into first gear at slow speeds and keep revs >3k RPMs. 4-7k in 3rd gear (8AT) is the real monster.
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04-23-2021, 03:15 AM | #6 |
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All valid points. I recommend reserving final judgment until you have an opportunity to play with the entire rev range. As you said, it has a different character, and the best parts of the S58 are higher up. The decision will be whether those thrills make up for the more tame experience between 0-3500RPM.
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04-23-2021, 10:12 AM | #8 |
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From the various dyno charts I've seen, the S58 is much stronger than the S55 on the top end, which IMO better fits the character of an ///M car.
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04-23-2021, 11:01 AM | #9 |
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Yeah if you are a fan of the old NA M-engines the S58 is probably as close as you will get to that feeling (minus intake music of NA) with turbos. If they kept the DCT for one more generation it would be even better with the higher 7500 rpm redline the engine is capable of.
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04-30-2021, 01:55 AM | #10 | |
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05-02-2021, 11:23 PM | #11 |
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Amen brother
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05-06-2021, 12:37 PM | #12 |
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Max torque come on at 2750 and stays flat until 6250. Easy to keep in the power band using the paddles, and the hp rise is like a powerful NA engine. This is new to me coming from 6.2 liter NA V8s, and I'm just learning. But it still surprises me off the line in M2 with maybe 1/3 throttle how the torque slams you in the head at ~2800. Can't wait to floor it. Good thing I have the HUD, as I feel like I'm going 65 but actually 20mph faster!
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05-06-2021, 02:32 PM | #13 |
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05-06-2021, 03:12 PM | #14 |
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LBbluem2 Have you passed break-in and had a chance to go to redline yet? If so, have your thoughts changed, or still the same feeling about the powerband/sound/etc?
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05-06-2021, 04:25 PM | #15 | |
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It is a more rewarding experience to keep it between 4-5.5 than it was in the s55 especially coming from a 6mt. The way the car shifts from 3-4 is just an epic feeling and sound. Even making the change at a max of 5.5k with 3/4 throttle. Once I pick it up next week I'll also have the break in service done that day and I'll post how she really goes |
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05-10-2023, 03:22 AM | #17 |
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Dyno runs done by Evolve on a stock G80 Competition, a stock F80 and stage 2 F80. The S58 turbos spool around 1k later than the S55 so they are significantly bigger = more HP up top. S58 also has a lower compression ratio of 9.3 compared to 10.2. They probably done this to reduce NOx however it also means you can push more boost safely without knock. This explain the turbo lag however it is the perfect recipe for SERIOUS whp with just turbo supporting mods and a tune. BMW engineers knew exactly what they were doing. Gotta love em. |
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05-10-2023, 05:12 PM | #18 | |
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05-10-2023, 05:17 PM | #19 |
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That must be a rwd g80 they dynoed, the xdrive gets peak torque around 3000rpm.
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05-11-2023, 12:43 PM | #20 | |
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The biggest problem with the F80 was the ability to put the power down with such a spikey S55. The S58 corrected this with more linear delivery, which, to me, is more advantageous as power is not only more usable, but there is more of it.
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05-18-2023, 04:15 PM | #21 | |
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I have the same feeling (albeit I was stage 2 in my F80) when I rip into my G80. I recall the days of even being stock on the F80 and running in MDM and having to control it getting squirrely. When it was stage 2, it was a constant fight (fun fight lol) to keep it still. In the G80, in MDM, I have not really broken traction and no feeling of getting squirrely with it. I do miss it, but know it's due to the instant torque the F80 had in comparison to the linear delivery the G80 has.
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