[00:02] old days of sports cars being behind us. And that is especially true of turbocharged cars, which have never been better. All right, obviously just my opinion, but from a driving perspective, turbocharged cars have suffered from
[00:16] three major flaws. A narrow power band, so no bottom-end torque. Turbo lag, so delayed response. And poor throttle control, especially at partial throttle. But recent history reverses pretty much all of these massive wide torque curves,
[00:32] minimal turbo lag, and exceptional throttle control. And what better vehicle to demonstrate how far we've come than the C8 Corvette ZR1 with over come than the C8 Corvette ZR1 with over 800 lb feet of torque from 3,000 to
[00:46] nearly 7,000 RPM, a clever anti-lag system, and beautiful throttle control in a car with 1,064 horsepower. This is made possible thanks to two Borg Warner turbochargers, which Borg Warner claims are the largest
[01:02] passenger car twin turbochargers in the market. So, let's dive into the engineering details, starting with the ZR1's anti-lag strategy. So, as far as reducing turbo lag, Corvette engineers have put in place a very clever anti-lag
[01:16] strategy, and it doesn't even use any fuel. So, keep in mind as we discuss this, the anti-lag has two goals in mind. First, it wants to keep that possible, right? Because once you get back on the throttle, you need to
[01:31] accelerate this wheel. It has inertia, and so it's resisting that. And so, if you can keep that spinning fast, you can get back into boost quicker. Also, they're trying to maintain some boost within that intake. They say as high as
[01:43] about 6 to 7 PSI with this thing typically operating at full boost around 20 PSI. All right, so let's run through an example of how this anti-lag system We're already flooring it. We're going down a straight. We're making peak boost
[01:57] 20 PSI. Our air, of course, is coming in our air filter, passing through the compressor side of our turbocharger, where it then builds up to 20 PSI. This passing through this intercooler, then through the throttle valve, through the
[02:10] intake manifold into our engine, out the exhaust, and then out that turbine. The be open because we're already at peak boost. So, we're bleeding off any excess exhaust through that wastegate and of course keeping this turbocharger spooled
[02:23] up. Then, we're coming up on a corner, so we let off the throttle. What happens? Well, immediately you're going to close your throttle. You're going to gases are now routed through this exhaust turbine, keeping it spooled up,
[02:36] and you're going to cut fuel. So, where does your boost go in this scenario? Well, some of that pressure is going to be bled off with a bypass valve that reroutes to your intake and then just keeps circulating within the compressor
[02:48] side of that turbocharger. You of course will still have some pressure built up throttle valve that's ready and waiting to go for you to get back on the gas. be some air flow going through your engine. And all of that air flow is
[03:02] forced to route through this turbine wheel to help keep it spooled up. So, it maintains inertia, keeps that spinning, and it maintains some boost. And what's crazy about this is that it can actually maintain boost for some time. Now, not
[03:15] 20 PSI, of course, much lower, but it's still in positive boost after 10 seconds of being off throttle. It's hard to think of a track driving scenario where you'd ever be off throttle for that long. But naturally, the question is,
[03:29] does the anti-lag system actually work? All right, so two great pieces of data on this. First, Corvette engineers actually provide a plot of at what RPM, how much time does it take to reach full boost. I'll include the actual plot on
[03:43] But essentially looking at this, you can see that using the anti-lag system versus if you're to just go from absolutely nothing and floor it and wait and see how much time it takes. Well, if you're at 4,000 RPM, that's 1.2 seconds
[03:57] baseline versus using the anti-lag system, it only takes 6 seconds. So, about half the time to reach peak boost if you're in a scenario where you can take advantage of anti-lag. Very cool. Okay, but how about a realworld
[04:12] scenario? So, here I am coming into a corner. You can see I'm at full boost with the boost gauge reading over 20 psi. Once I get on the brakes, boost pressure drops, but never below atmospheric. It maintains positive
[04:26] boost. And as I hit the apex of the corner, it's down to just 2 PSI. But again, there's still momentum in that turbine wheel. So, as I ease back onto the throttle on corner exit, of course, there's no point in flooring it just
[04:39] yet. The boost builds, and by the time I have finally given it full throttle in second gear, you can see boost pressure is already at 14 psi. And just five frames of video later, less than 2/10 of a second, I'm at 21 PSI, full boost. So
[04:56] in this scenario, there's genuinely no perception of turbo lag because as you roll onto the throttle on corner exit, the boost has already come back fully from a throttle standpoint on track. And of course, this is scenario dependent,
[05:11] but there's very minimal difference between this and a naturally aspirated engine. Most people would never notice it was turbocharged by how it drives, except for the fact that it pulls like crazy. Moving on. My personal biggest
[05:23] problem with turbocharged cars is partial throttle response. So, say for example, you're in a turbo car. You give it 50% throttle and eventually somehow "What the heck? I was only asking for half of that. Why am I at peak boost?"
[05:38] Well, to get a better understanding, we need to discuss electronic wastegates. Okay, so traditionally in turbocharged cars, in order to regulate how much boost they create, they use vacuum actuated wastegates. How does this work?
[05:50] It's very simple. So, here we have our turbocharger. You're going to have your air coming in through the compressor side of that turbo. And some of that air is routed with a vacuum line to your wastegate. Now, once the pressure gets
[06:03] to a certain point, it's going to press this spring in. So, let's say you have a 20 PSI spring. Well, then once your boost pressure is at 20 PSI, it forces that spring in, opening up this wastegate and allowing your exhaust to
[06:16] it's still going to be routing through Some will bypass it, and you'll sit at a perfect 20 psi within your engine. All right. So, the Corvette replaces this
[06:28] vacuum-based actuator with an electronic wastegate. So, instead of this spring you just have an electric motor, and that electric motor can open or close this wastegate whenever it wants at whatever percentage it wants. All right.
[06:41] So, let's walk through the same scenario with both types of technology. So say with our foot we press our accelerator pedal about 50%. So first starting with this vacuum actuator once we've pressed that throttle pedal about 50%. Well our
[06:55] throttle valve is going to open about 50%. From then we're really limited on control right? So our air starts to go in the engine. It starts to then spool up this turbocharger and that starts to create more boost which means you get
[07:08] more power, more exhaust. It spools it up faster and eventually you're at peak boost and you're like what the heck? I only asked for 50%, why is it giving me full boost? Well, this spring is limited in its control, right? Anything below 20
[07:21] PSI and it doesn't care. So, you have really poor partial throttle control versus let's look at what happens if we switch over to an electronic wastegate. We give it 50% throttle. The ECU says, "Hey, we have a torque target. We want
[07:35] half torque based on the position of the accelerator pedal." Well, your electronic wastegate is going to remain closed so that you can rapidly get to that torque target and then it will start leaking air past so that you
[07:47] remain at that perfect 10 psi. So, what happens is your foot is just so much actually what you get because you're going for a torque target rather than going for a throttle position target and not having control over it. Now, there
[08:02] are two major points worth mentioning here. First, electronic wastegates are not that new. However, mass adoption is still relatively recent for this technology. I was surprised to learn that many modern cars still use vacuum
[08:15] actuated wastegates in the 2010s and even the 2020s. For example, when I try turbocharged engine and poor throttle control, I think of the 2.0 L Subaru WRX, a car that was sold as late as 2021, just 4 years ago. I distinctly
[08:32] remember while driving it, if I give it 50% throttle, you wouldn't get half up. And again, that's because vacuum controlling partial throttle, right? This thing only cares if it sees 20 PSI.
[08:45] It can't directly control anything below that. So, it's not very good at it. The result is really poor partial throttle control. Electronic wastegates, on the other hand, completely game-changing technology that makes turbo cars so so
[08:59] much better to drive. Okay, second major point. There are workarounds for vacuum actuated systems. You can overcome some of the disadvantages to an extent with solutions like multiport boost control solenoids. That said, there are so many
[09:13] advantages of going electric. Honestly, it's worthy of its own video, but just to cover briefly, you get way better control, way better response as you're springs, which take time to adjust. Instead, you just have an electric motor
[09:27] positioning that wastegate wherever you want. And they're far simpler. Just an electric motor. No vacuum lines and complex routing for four-port boost controllers and all the added potential for leaks. And electronic wastegates
[09:40] result in better efficiency because you can keep the wastegates open at low exhaust. All right, so let's move on to some other neat strategies the Corvette ZR1 implements. The first one discussing turbocharger red line. So at a certain
[09:54] point as that turbocharger spins faster and faster, it just spins so fast that shreds it apart. So, this is the red line for that turbocharger wheel. For line for that turbocharger wheel. For the Corvette, that speed is 143,000 RPM.
[10:10] So, the compressor side, the intake side of that turbocharger, the wheel, the outer edge of that wheel is spinning at 569 m/s over,200 mph. Absolutely ridiculous. Now, one of the ways that you ensure that you never
[10:25] cross red line in development is you will put speed sensors on these turbochargers, see what speed they get to, and ensure that you map your engine line. Now, you can do this and confidently you'll leave about a 7%
[10:39] buffer before you know you say, "Okay, we need to now ease back off. We can't use the turbocharger above that 7% buffer." But the Corvette doesn't just use that speed sensor on the turbo for development. It actually is a part on
[10:51] the car. So the ECU knows the speed of the turbo at any moment. This isn't plenty of cars will just use them in development. And then on production cars, they won't have that speed sensor. But what they say this enables by having
[11:05] that speed sensor is they can run the turbo closer to red line more confidently because they know exactly what speed they're at. So they can leave about a 3% margin to redline rather than about a 7% margin, allowing them to
[11:19] maximize that turbocharger's capability. And finally, we'll touch on one last subject, overboost. Now, something that's often confusing about turbocharged cars is that if you ask the question, how much boost does it make?
[11:31] straightforward answer because the real answer is it depends. So, when the answer is it depends. So, when the Corvette was certified for its 1,064 horsepower, it did so using 20 PSI of boost. Now, you might think, well, that
[11:45] means its peak boost is 20 PSI, but it is not. Actually, that number is closer is not. Actually, that number is closer to about 24 PSI. Now, why is that? Well, how much an engine makes, you have standards as far as what air temperature
[11:58] that should be. So, your air supply should be at about 25° C or you correct should be at about 25° C or you correct for 25° C. So, with that air temperature and 20 PSI of boost, this engine makes 1,64 horsepower. But what about when
[12:12] much hotter than that? Like when I was track testing this at Kota Circuit of the Americas in Austin, Texas, and it was about 100° outside. Well, in order temperatures, of course, cooler air, more dense, more oxygen, more power, the
[12:28] turbocharger can force more air into the engine because it's hotter air, less oxygen. So, it can force more of that hotter air into the engine. you'll pull back your ignition timing so it's not quite so advanced and as a result you're
[12:42] that is associated with those high going to be making that perfect 1064 horsepower, but you're going to get closer than you would if you didn't allow that turbocharger to have that
[12:54] over boost increase how much pressure you have going into the air and then of course delaying your ignition timing and giving you a way to minimize the power hit from high ambient temperatures. So, all of this results in an engine that is
[13:07] exceptional to drive and yet it's turbocharged. If you have not yet watched it, I'd recommend checking out my video on how the rearwheel drive ZR1 manages to be quicker to 60 than the all-wheel drive Corvette. Absolutely
[13:21] nuts. And also my video breaking down the 5.5 L twinturbo V8 that goes inside the ZR1. Also really neat to check out. If you have any questions or comments, feel free to leave them below. Thanks for watching.