Pushing peak power at the top end

[RugbyBro]

So something I've always wondered is what would stop S55 from being able to produce a power curve like this. Essentially a power curve that keeps building instead of staying flat for nearly 2k revs (starting at around 5500). S55 has an insanely strong midrange, which seems to account for the majority of power gains for tuned engines on OE turbos based on the dynos I've seen. And to be clear, I'm suggesting only tuning the top end and leaving everything else the same.

Curious as to what the prevailing thoughts are on this - is it the small turbos/turbines, heat soak, etc. I have my own ideas, but I want to enter this conversation with a fresh mind.

And please excuse the ultra janky MS Paint botch-job below, it's only there to contextualize my question and not an accurate representation of what a real power curve would look like

[Kilabyte]

It's the tiny turbos running out of steam up top. It's also why this thing with a tune pulls so hard in the middle.

It's a lovely painting btw, thinking about framing it

[RugbyBro]

Originally Posted by Kilabyte

It's the tiny turbos running out of steam up top. It's also why this thing with a tune pulls so hard in the middle.

It's a lovely painting btw, thinking about framing it

Yeah that's kind of what I've always thought. Most of the dyno'd tunes I've seen trend back toward the 450hp as they approach 7k.

I wonder if there are any similar ultra quick spool upgraded turbos or maybe even an upgraded compressor kit/build for the OE turbos that can handle that top end push. I know some of the upgraded turbos (VTT, Pure, Etc.) can do that with ease, but to me it would be a waste to buy one of those solely to push power a bit beyond the 5.5k mark.

And yes I do requests for my art

[TractionControlDelete]

Theoretically you could simulate a curve like this by reducing torque in lower gears for it feels like higher speeds are building power. I read about BM3 doing something like that. Think that might do it for you?

[ntg44]

You need bigger turbos with the torque capped throughout the midrange. But it's an expensive way to make the car only marginally faster. It doesn't make sense in most cases not to get the most out of the midrange because the top end is the same whether or not you bring up the mid-range or not.

The closest way to get to that curve economically is a BM3 stage 2 tune with 20% torque reduction in all gears. It'll keep the mid range close to stock while keeping the top end gains the tune provides. But once again, you're only limiting the acceleration potential by doing that. I can see it being useful as a road course tune though. It's just the trade off for having responsive turbos rather than the 4000+ RPM hit that turbo cars from the 90s had. In the end, the responsive turbos with fat midranges are still faster until far beyond jail speeds than the laggy top end builds. Area under the curve so to speak.

[SYT_Shadow]

Bm3 with the limiter kind of does that. I'd like to see a bigger turbo build that has moderate midrange increases and a large top end gain. But then you're adding lag to the engine and it won't be that much faster.

I also really dislike how tunes wind up stock over 7k rpm because the turbos have run out of steam

[RugbyBro]

Originally Posted by F82KPowers

Theoretically you could simulate a curve like this by reducing torque in lower gears for it feels like higher speeds are building power. I read about BM3 doing something like that. Think that might do it for you?

Yup I have looked at doing torque by gear before, but those all stay flat then taper off toward redline. I'm just curious if you could take a stock map and only build more power after 5.5k without staying flat

Originally Posted by ntg44

I can see it being useful as a road course tune though. It's just the trade off for having responsive turbos rather than the 4000+ RPM hit that turbo cars from the 90s had. In the end, the responsive turbos with fat midranges are still faster until far beyond jail speeds than the laggy top end builds. Area under the curve so to speak.

Yup this is purely for feel as I wouldn't care to maximize acceleration potential. I already think stock is ridiculously fast as is, so this is just gravy on top if it could be done. I also agree that it would be a waste of money to buy upgraded turbos just to do this, in my mind it would only be worthwhile if it could be done on stock turbos, or maybe even an upgraded compressor wheel.

Originally Posted by SYT_Shadow

Bm3 with the limiter kind of does that. I'd like to see a bigger turbo build that has moderate midrange increases and a large top end gain. But then you're adding lag to the engine and it won't be that much faster.

I also really dislike how tunes wind up stock over 7k rpm because the turbos have run out of steam

Yup, the idea is really to maintain the impressive throttle response of stock S55, but build a higher peak closer to redline. Heck, I wouldn't mind sacrificing some low end if it meant that top end could be improved. I think that ultimately that's probably the trade off - throttle response (high compression, small turbos) = ton of midrange but lack of potential up top. Still, it won't keep me from asking and hoping one day we can figure it out lol.

[TopJimmy]

The trouble is the size of the stock turbos. Their increase comes in for our midrange and that's all. I hear this from 3 major tuners. Even my all-out-race tune falls off after 6500RPM.

Bigger turbos have the power increase later in the midrange up through the top end. Plus Size units have an even later increase and fuller top end.

[Chris@VargasTurboTech]

It's all in the tune. Tuners try to maximize power output, and turbos that are sized for X flow up top will always have more headroom in the lower RPM ranges. A decent tuner can dial in about any hp curve you want by leaving some torque off the table in the middle, but most people do not have that as a goal. Bigger turbos will have a peak output higher in the RPM band at the expense of spooling later and increased lag (time-to-torque).

I do think that if whp goals are achieved with margin left in the system, a powerband that has peak hp higher in the RPM range is more fun (for me) to drive.

In my opinion not enough "drivability" torque curve tune change options are out there, primary reason is that the average dude just looks at dyno's and maybe reads a little too much into them; they're a useful tool but don't show lag. If you know any tuners that are also track racers, they are much more likely to dial in something a little different than the norm.

[TractionControlDelete]

Originally Posted by RugbyBro

Yup I have looked at doing torque by gear before, but those all stay flat then taper off toward redline. I'm just curious if you could take a stock map and only build more power after 5.5k without staying flat

Yup this is purely for feel as I wouldn't care to maximize acceleration potential. I already think stock is ridiculously fast as is, so this is just gravy on top if it could be done. I also agree that it would be a waste of money to buy upgraded turbos just to do this, in my mind it would only be worthwhile if it could be done on stock turbos, or maybe even an upgraded compressor wheel.

Yup, the idea is really to maintain the impressive throttle response of stock S55, but build a higher peak closer to redline. Heck, I wouldn't mind sacrificing some low end if it meant that top end could be improved. I think that ultimately that's probably the trade off - throttle response (high compression, small turbos) = ton of midrange but lack of potential up top. Still, it won't keep me from asking and hoping one day we can figure it out lol.

Look at this video. They run a S55 from a F82 Competition on the dyno to compare it to the M2 Comp. He says that the M4 ZCP is stock and that the power curve is identical to what he's seen on other stock M3/4's. What is interesting is that the power curve actually seems to pick up after 5000rpm as you'd like it to. It's a fun watch overall, but the part I'm talking about is at the 6:00 mark. What do you think?

[TractionControlDelete]

Originally Posted by Chris@VargasTurboTech

It's all in the tune. Tuners try to maximize power output, and turbos that are sized for X flow up top will always have more headroom in the lower RPM ranges. A decent tuner can dial in about any hp curve you want by leaving some torque off the table in the middle, but most people do not have that as a goal. Bigger turbos will have a peak output higher in the RPM band at the expense of spooling later and increased lag (time-to-torque).

I do think that if whp goals are achieved with margin left in the system, a powerband that has peak hp higher in the RPM range is more fun (for me) to drive.

In my opinion not enough "drivability" torque curve tune change options are out there, primary reason is that the average dude just looks at dyno's and maybe reads a little too much into them; they're a useful tool but don't show lag. If you know any tuners that are also track racers, they are much more likely to dial in something a little different than the norm.

Please tell me you have such a tuner in mind, Chris 🙏

[RugbyBro]

Originally Posted by Chris@VargasTurboTech

It's all in the tune. Tuners try to maximize power output, and turbos that are sized for X flow up top will always have more headroom in the lower RPM ranges. A decent tuner can dial in about any hp curve you want by leaving some torque off the table in the middle, but most people do not have that as a goal. Bigger turbos will have a peak output higher in the RPM band at the expense of spooling later and increased lag (time-to-torque).

I do think that if whp goals are achieved with margin left in the system, a powerband that has peak hp higher in the RPM range is more fun (for me) to drive.

In my opinion not enough "drivability" torque curve tune change options are out there, primary reason is that the average dude just looks at dyno's and maybe reads a little too much into them; they're a useful tool but don't show lag. If you know any tuners that are also track racers, they are much more likely to dial in something a little different than the norm.

Oh interesting - have you or anyone else at VTT seen a tuner only tune the top end before on stock turbos? I'm peaked

[RugbyBro]

Originally Posted by F82KPowers

Look at this video. They run a S55 from a F82 Competition on the dyno to compare it to the M2 Comp. He says that the M4 ZCP is stock and that the power curve is identical to what he's seen on other stock M3/4's. What is interesting is that the power curve actually seems to pick up after 5000rpm as you'd like it to. It's a fun watch overall, but the part I'm talking about is at the 6:00 mark. What do you think?

Yeah the stock ZCP tune has a bump around 5.5k to 6.5k before tapering back down to the stock curve through the remainder of the range - that's where the 444 hp is coming from vs the 425 hp on the base tune. Imagine if it didn't dip back to stock, that would be a sweet power curve, could possibly hit 475 at the top

Separate but related, this graph shows what BMW did to neuter S55 for M2C... just chopped off the top end

[RSXDC5]

https://www.bimmermilvs.com

[cobra2814]

Originally Posted by ntg44

You need bigger turbos with the torque capped throughout the midrange. But it's an expensive way to make the car only marginally faster. It doesn't make sense in most cases not to get the most out of the midrange because the top end is the same whether or not you bring up the mid-range or not.

The closest way to get to that curve economically is a BM3 stage 2 tune with 20% torque reduction in all gears. It'll keep the mid range close to stock while keeping the top end gains the tune provides. But once again, you're only limiting the acceleration potential by doing that. I can see it being useful as a road course tune though. It's just the trade off for having responsive turbos rather than the 4000+ RPM hit that turbo cars from the 90s had. In the end, the responsive turbos with fat midranges are still faster until far beyond jail speeds than the laggy top end builds. Area under the curve so to speak.

Wouldn't the boost reduction by gear in the bm3 tunes simply shift the torque curve down, but not change the shape of the curve? If that's the case, the car wouldn't feel stronger on the top end vs midrange - it just wouldn't pull as hard throughout the rev range due to the torque reduction. My understanding is that the torque reduction isn't able to be programmed by rpm, but rather by gear only. Am I missing something? I'm curious about this as I plan to get tuned next summer and I like the idea of more top end power without the midrange just blowing off the tires until I'm going 80mph 😆

[TractionControlDelete]

Originally Posted by RSXDC5

https://www.bimmermilvs.com

Really good point! https://www.***********.com/content....-whp-at-7k-rpm

[ntg44]

Originally Posted by cobra2814

Wouldn't the boost reduction by gear in the bm3 tunes simply shift the torque curve down, but not change the shape of the curve? If that's the case, the car wouldn't feel stronger on the top end vs midrange - it just wouldn't pull as hard throughout the rev range due to the torque reduction. My understanding is that the torque reduction isn't able to be programmed by rpm, but rather by gear only. Am I missing something? I'm curious about this as I plan to get tuned next summer and I like the idea of more top end power without the midrange just blowing off the tires until I'm going 80mph 😆

No, I originally though this too, but it has been discussed in a thread a few years back where it was confirmed how it works.

If you picture the torque curve as a hill (as most are), boost reduction looks like capping torque as if you were to draw a straight line across a dyno sheet cutting off the top of the curve and the horizontal line becomes the curve wherever it is lower than the regular curve. The higher the percentage of reduction, the lower the horizontal line moves on the torque curve. So this keeps the mid range at a plateau while leaving the top end wherever it lies (most likely under the horizontal line). In theory you could put this percentage so low that you would have a nearly flat torque curve, but the car wouldn't be very quick, much slower than stock.

Lowering it enough to be truly max HP at redline would only make sense with larger turbos, but again, you're only holding the engine and turbos back by doing so, and severely overpaying for a minimally faster car that would only show itself above 100 MPH. Like I said in my previous post, maybe as a track tune to keep temps down or for consistent throttle modulation in and out of corners, but that's really it.

[Chris@VargasTurboTech]

You'll pull the whole curve down with enough boost reduction, for the guys running high boost and not running super sticky tires, you'll see a big reduction whole way through, i.e. first gear limited to 16psi, second 20, full boost in third and above... you'll 100% make less power throughout first and second gear, but it isn't "slower" as you set the boost reduction sufficient to be on the threshold of traction... so any more power and you're just spinning (i.e. slower) in those lower gears. If you were only capping boost a couple psi then yes, you'd probably leave top end alone, but I've mostly seen giant wholesale reduction in boost as the car is 100% undrivable at WOT in low gears without drag radials on a prepped track.

[cobra2814]

Thanks guys. I learned something new today!

[RugbyBro]

Originally Posted by F82KPowers

Really good point! https://www.***********.com/content....-whp-at-7k-rpm

Yeah this is actually pretty interesting, basically allowing more air intake at the top end through the valves versus putting on bigger turbos. Wonder if you could just take a stock tune and have a tuner just add that top end using this lift kit.

[Bluer2]

these will give you more top end with the OEM Turbos. Not sure how much it will shift the powerband though.