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Discussion Starter · #1 ·
There's been a lot of forum discussion about boost lag on the Stelvio 2.0 when the need arises for quick off the line acceleration.

Many of you have determined the Stelvio's boost lag is unacceptable and needs to be "fixed" via installing a GoPedal or some level of tune in an effort to make this characteristic disappear; all with little effect due to the basic engineering limitations of how quickly a turbo can spool up to provide a decent level of boost.

As I've written in other threads, virtually all manufacturers have figured out that boosted 2.0 liter engines are the sweet spot for power, MPGs, and emissions control, and even a taxation sweet spot in the EU where engine displacement determines what you pay.

0.5 liter per cylinder combustion chamber design has been pretty much perfected and works great for the most part. And yet, all boosted 2.0 engines seem to have the same issue with boost lag. (Yep, a couple manufacturers have done some creative things with one small diameter turbo and one large diameter turbo or a combo of supercharger and turbo in Volvo's case.)

Even the 340 HP Twin Turbo V-6 in my '17 Macan S had an initial throttle tip-in flat spot, very similar to what we see in the Stelvio. It is what it is with turbos, even when they're designed by the genius engineers at Porsche.

We need to recognize that automotive turbos spin at 200,000+ rpms at peak boost. I'm sure some engineer out there could tell us the linear relationship between turbo rpm and boost. Lets just recognize that at idle, that turbo impeller on your Stelvio is spinning very slowly and takes about a second or so to spool up.

Still, 122 cubic inches is 122 cubic inches and nothing will wake up that tiny little motor except for boost of some type, either from a turbo or supercharger. Of course, the problem with superchargers is they have a huge parasitic power cost that makes them unsuitable for small displacement engines. You'll see them on big V-8s though since there's enough inherent torque where it doesn't make much difference on Hellcats, etc.

So, what about the boost lag on the Stelvio?

I've been experimenting a bit with throttle tip-in technique and came to the conclusion that I can eliminate the lag by just doing some old school two foot driving; Something I learned back when I had crappy malaise era cars that didn't idle properly.

Left foot on the brake, right foot on the throttle, and bring up the RPMs just enough that you feel movement against brake pressure and let the brake go as you accelerate away. No lag whatsoever.

Using brake torque to bring up RPMs is nothing new or special by any means. Most of you have done similar things with other torque converter equipped cars. It doesn't have to be violent and you don't need a lot of RPMs to build a bit of boost and make the lag go away. It's just something that's really easy to do for those occasions when you have to go NOW.

I would encourage you to practice a bit and find that sweet spot of brake and throttle where you can do it smoothly.

I'd love to hear your results.
 

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2021 Stelvio Ti Lusso Verde Visconti
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In my experience, what we're feeling is turbo spooling up AND programmed in delay in the electronic throttle. Aftermarket pedal boosters can eliminate the electronic throttle lag. Heck, I had a Sprint Booster in my non turbo FIAT 500 to get rid of the electronic throttle lag. In Sport mode on the Sprint Booster, the car did not have any lag between pressing the accelerator and the engine responding and the acceleration(what there was of it) was linear. Made the car a blast to drive. Race mode on the Sprint Booster turned the accelerator into an on/off switch. That was not fun.

One thing that might be a concern with two foot driving, on the FIATs, you could do it only so much before the dash lit up like a Christmas tree with electronic throttle errors. Apparently, the computer thinks you should not be using the brake and accelerator at the same time.
 

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Discussion Starter · #4 ·
I found this was the best solution too. The only downside is everyone thinks I am trying to race them when they hear my engine revving at the stoplight 🤷‍♂️
LOL. When others see us a Stelvio they're already assuming we might be a crazy person so not really a problem, right? 😜
 

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Discussion Starter · #5 ·
In my experience, what we're feeling is turbo spooling up AND programmed in delay in the electronic throttle. Aftermarket pedal boosters can eliminate the electronic throttle lag. Heck, I had a Sprint Booster in my non turbo FIAT 500 to get rid of the electronic throttle lag. In Sport mode on the Sprint Booster, the car did not have any lag between pressing the accelerator and the engine responding and the acceleration(what there was of it) was linear. Made the car a blast to drive. Race mode on the Sprint Booster turned the accelerator into an on/off switch. That was not fun.

One thing that might be a concern with two foot driving, on the FIATs, you could do it only so much before the dash lit up like a Christmas tree with electronic throttle errors. Apparently, the computer thinks you should not be using the brake and accelerator at the same time.
I think we're fine with our very stout ZF tranny. As for the non-turbo 500 with an automatic, I can imagine the population of drivers who brake torque is very small.

Admittedly, I am a big fan of the 500, especially the Abarth company car I had for a few weeks. Best kept secret in the automotive industry.
 

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Discussion Starter · #7 ·
Automatic...please. Mine was a five


Automatic? Please...mine was a five speed. You had to be careful left foot braking or rev matching for downshifts. Too much time on both pedals at once would put you in the penalty box.

View attachment 27711
Ah, that makes a lot more sense. The Fiat heel and toe police were watching you.
 

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I don't think anyone has claimed boost lag. The turbo makes a ton of boost barely off idle. Its actually up top it runs out of boost

The tip in lag is throttle lag.

You can mitigate it by lightly brake boosting while pulling out into traffic or other situations where throttle lag may be a problem.

Unfortunately manual mode does not help

 

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I guess it's all perspective on what you think you are driving. I really don't notice much lag during commute on these cars.. that is not much different from other cars. If I thought I were driving a sports car and want to feel the push off, that may be a different story. Yes I do leave people behind at the light change then I stop at the next light with all the other cars. kinda feel silly cuz i know what they are thinking? 😁
 

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Funny how I just don't have this problem. Not for the last 3 years since I learned how to manipulate the pedal properly.
The lag is much less noticeable at part throttle because you are requesting less power. The only way to get full power quickly off the line is to brake boost. It's similar to saying your vehicle doesn't often engage traction control because you are not pushing it to the limit for it to engage.
 

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The lag is much less noticeable at part throttle because you are requesting less power. The only way to get full power quickly off the line is to brake boost. It's similar to saying your vehicle doesn't often engage traction control because you are not pushing it to the limit for it to engage.
I usually liken it to people who tell me they have no problem managing 450hp in their front wheel drive car because they know how to " manage the throttle"....

...so yeah you have to feather it with those cars or program in boost by gear but you're still traction limited.

...same with throttle lag. You can roll into it so its not as noticeable but that doesn't mean its not there.
 

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Discussion Starter · #15 ·
I don't think anyone has claimed boost lag. The turbo makes a ton of boost barely off idle. Its actually up top it runs out of boost

The tip in lag is throttle lag.

You cam mitigate it by lightly brake boosting while pulling out into traffic or other situations where throttle lag may be a problem.

Unfortunately manual mode does not help

I do recognize the throttle mapping side of the issue. I'm assuming some of the built in delay is a safety thing to help keep people from launching into their garage wall if they accidentally tap the throttle at idle in gear.

It's also one of the reasons many people miss having a cable linkage which went they way of the dinosaur in the mid-2000's. I don't think there are any new vehicles with a cable linkage anymore so we're stuck with whatever programming the OEMs think is correct.

I'm also thinking OEMs do way more torque management than we realize to keep the twisty bits from failing under warranty which is easy to accomplish when they can manipulate the throttle position signal to throttle body mapping.

As for boost at idle, I need to take a look at the performance screen boost gauge tomorrow and play around with it a bit. I'd still argue turbo spool up is a big part of the issue with the dead spot at idle.

Also, from what I understand, the low 5,500 RPM red line is due to to design limitations with the MultiAir system, not any issue with bottom end strength or the turbo itself.
 

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I do recognize the throttle mapping side of the issue. I'm assuming some of the built in delay is a safety thing to help keep people from launching into their garage wall if they accidentally tap the throttle at idle in gear.

It's also one of the reasons many people miss having a cable linkage which went they way of the dinosaur in the mid-2000's. I don't think there are any new vehicles with a cable linkage anymore so we're stuck with whatever programming the OEMs think is correct.

I'm also thinking OEMs do way more torque management than we realize to keep the twisty bits from failing under warranty which is easy to accomplish when they can manipulate the throttle position signal to throttle body mapping.

As for boost at idle, I need to take a look at the performance screen boost gauge tomorrow and play around with it a bit. I'd still argue turbo spool up is a big part of the issue with the dead spot at idle.

Also, from what I understand, the low 5,500 RPM red line is due to to design limitations with the MultiAir system, not any issue with bottom end strength or the turbo itself.

The turbo design is such it will produce a peak of 24psi at redline and thats it. It'll make 31-32psi at 2500rpm though. This assumes pushing it to max wgdc.

Most cars are this way for fuel economy. And yeah agree the multiair is yet another complimentary limitation.

Add 2.5psi to the below graph of boost for actual manifold boost...

Slope World Font Parallel Terrestrial plant

Atmosphere Nature Font Electric blue Space



If we swap the turbo though it looks very different up top...

Slope Font Rectangle Parallel Space
 

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Ya'll certainly know more than me both about how a car functions and about how I drive.

Funny how I put up a thread about one thing like the MAF... People say its cause I drive so hard.

Next thing... You say it's cause I don't.

I wish you would make up your minds.
No, we are just saying your Stelvio doesn't operate differently than everyone else's. In fact, I agree with you there is less lag at part throttle. However, there is also less power. So it's a bit of pick your poison; give up a second or so of no movement before full power kicks in when you floor it or feather the throttle to get the car moving right away and then drop the hammer to get full power. Either way there is a delay to get full power.
 

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Ya'll certainly know more than me both about how a car functions and about how I drive.

Press the pedal less. Little tiny bit of gas... Teeny tiny. Car moves.. then goose it.

Nobody beats me from a light anymore...
🙄

Like i said. Just because you decide to roll into it or wait it out doesn't mean its not there.
 

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Nope, it certainly doesn't operate any differently.

What's the point here?

Having full power from 0 rpm?

See, I could care less about anything other then how fast I begin moving when the time comes I get to start moving. Which when that time comes, I do rapidly, generally fast enough that cars next to me think I am racing them when really... I'm driving how I drive they aren't part of the equation.

Since cleaning my MAF, I have had to readjust how I use the gas and slow down how fast I hit the pedal when behind a car at a stop light. Because I don't have a problem with lag... At all.


The fastest way to launch a car is not to mash the gas. Not in an Alfa.

Use the gas pedal like you would launch a high HP manual transmission car with a progressive pedal push. The lag is almost unoticable if you use the pedal right.
 
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