What Is A Hot Vee Engine?

Remember how traditional turbocharged V8s would see the turbos placed outside the engine? That makes sense because little has to change in layout compared to a naturally aspirated V8. But in hot V engines, you flip the cylinder banks so that the exhaust ports are on the inside of the valley rather than the outside. That means the turbochargers sit alongside the ports they are fed by, so there's not much space between the cylinder banks anymore. As a result of this and higher temperatures in the region, the intake manifold now becomes two pieces, and each is relocated on the opposite sides of the individual banks, where the turbochargers would have been. The intake manifolds are therefore shielded from excess heat and can be made smaller per side while providing more air volume to the combustion chamber.

Generally, a hot vee engine is cooled through dual air-to-water intercoolers as they are more efficient for their size than a single large air-to-air intercooler. Basically, you get the idea that the hot vee engine was designed to save space, and that's exactly what it does. But there are more benefits.

Ferrari

What Are The Benefits Of A Hot Vee Engine?

Hot vees were designed for a reason, so what are their benefits?

Size

One of the biggest benefits undoubtedly comes in the form of more compact packaging possibilities. As modern cars become ever heavier laden with bulky technology that requires additional sensors and wiring harnesses, the space left in the engine bay for the, uh, engine continues to diminish.

The turbos being placed within the vee frees up some space on the outside of the engine block, space that comes from the turbos and wastegates themselves, and the shorter exhaust manifolds that run directly from the engine to the turbos' exducers, through the downpipes, and into the exhaust. In a cold vee V8 engine, the exhaust gases have to be routed around the steering column and other major components. None of that is required here. Even the piping to the intake manifolds can often be reduced, and two smaller intercoolers versus one top- or front-mounted large one also give you free real estate under the hood.

But in the case of the Ford 'Scorpion' Power Stroke diesel V8, a 6.7-liter behemoth, size wasn't as much of a concern, so what other benefits are there?

BMW

Weight

Fewer components and less piping to run contribute to reducing overall weight and cost, but the bigger benefit is where that weight can be distributed. In the Mercedes-AMG GT, the engine block only begins behind the front axle, making it front-mid-engine. Without a hot vee setup, the exhaust manifolds would have been too bulky. With it, the car takes on better handling characteristics without any additional development on the suspension, tires, or chassis itself.

It must be noted that a hot vee engine is generally taller than a cold vee engine, which makes the center of gravity of the engine itself worse. However, more often than not, the compact width of such a setup, with its shorter hot V lines for intake and exhaust, creates more opportunities for creative engine placement, improving both lateral and longitudinal weight balance overall. Replacing or upgrading the turbos is also usually very easy.

Ferrari

Performance

Yes, turbos – especially those that sit alongside each other – generate A LOT of heat. But that's a good thing for turbos. Not for intakes, no. But for turbos, definitely. The sooner a turbo heats up, the sooner it can perform at its best. That's because hot air is the lifeblood of a turbo: as the air heats up, the pressure of the air drops, thereby increasing its propensity to reach peak velocity. Basically, hot turbos are happy turbos. Of course, it is possible to overheat or overspool a turbo with reckless boost and timing profiles, but that's down to tuning, not the layout.

Heat from the turbos also goes to the catalytic converters, which are conveniently located just behind the exducers, helping to absorb some of that heat energy. The sooner these get hot, the sooner they can do their job too.

Ferrari

The hot vee also places the intake manifolds under the engine, where rising heat cannot reach them, and where individual intakes promise a cooler intake charge and easier troubleshooting of potential boost leaks.

In addition, the firing order of V engines can make controlling the turbo difficult, as the impeller speed is continually changing during engine operation. To get around this, you need a lot of excess piping to try to stabilize the pressure of the air being pumped into the turbos so that it is more predictable and the engine fires cleanly. A hot vee eradicates that need due to the turbos' close proximity to the engine, where it is possible to unlock more acute boost control, simultaneously enhancing efficiency and performance with far less threat of knocking, otherwise known as premature detonation.

Another big benefit is throttle response, as the closer proximity of the turbos to the combustion chamber means they spool quicker when you put your foot on the gas.

Audi

What Are The Drawbacks Of A Hot Vee Engine?

Anything with upside will also have downsides, and while hot-vee engines are all the rage, they also have their own drawbacks.

Size

This is a double-edged sword. While the overall footprint of the engine components has dwindled, the size of the turbos must do the same. That means less turbo lag but also less power. With a cold vee engine, the size of the turbos is dictated by the space in the engine bay. With a hot vee engine, the size of the turbos is defined by how wide or narrow the angle of the vee is and how much space that allows. This is why the Koenigsegg Gemera's engine won't make as much as it does in the Jesko, where there is more space for larger turbos, and also larger downpipes and intakes. The difference in benefits versus drawbacks in these two cars is measured by the other components surrounding these engines, including hybrid systems. That's a story for another day, but the point is that, particularly from an aftermarket tuning perspective, the scope for larger turbos is far smaller with a hot-vee engine.

The SSC Tuatara and the Hoonicorn use cold vee configurations.

Nelson Racing Engines

The cold-vee engine from the SSC Tuatara.

Heat

Yet another double-edged sword. Hot turbos are happy turbos, but a turbo getting too hot is a recipe for disaster. Because the turbos in a hot-vee setup are smaller, extracting power often means higher boost pressures, resulting in them spinning at higher speeds and generating more heat. This is compounded by the turbos being positioned within a confined space where explosions are generating heat rapidly.

Whereas a cold-vee turbo setup exposes the turbos to 'cold' air on three sides, a hot-vee configuration does the opposite, necessitating unique cooling solutions. The AMG GT has done this with cold air flowing through a snorkel that feeds into the vee when driving, and when stationary, flaps close to prevent hot air being pulled back into this area.

Mercedes-Benz

Tuning

This is a small one, but because everything is so close together and so finely controlled, getting a hot vee setup to work can be a challenge when first developing it. The biggest issue is that V engines have a firing order that sometimes messes with the irregular spinning of the impeller, as this is changing its rpm constantly. Getting fuel and air to pulse and mix at the right time is critical, and for those who wish to extract more from their V8 through aftermarket tuning kits, it can sometimes be a bigger risk than it's worth. That being said, this would be true of a cold vee engine too, and overall, the pros are far greater than the cons.

Hoonigan/YouTube

Who Made The First Hot Vee Engine?

As we discussed earlier, Ferrari produced and campaigned the first application of a hot vee engine in racing, but the first production car to feature the concept was the BMW X6 xDrive50i in 2008, with its N63 V8 engine. An evolution of this engine is still used today, and its high-performance counterpart, the S68, has found a home in several fast sedans and SUVs over the years, including the latest X5 M and X6 M.

As a side note, Mercedes-AMG claims that the sports car we mentioned earlier, the AMG GT, was the first production sports car to feature a hot vee engine, and its 4.0-liter twin-turbo V8 is also found in the new Aston Martin DB12. Audi also makes hot vees in the form of the 2.9-liter twin-turbo V6 found in cars like the RS5 Competition and in the 4.0-liter twin-turbo V8 that proliferates the Volkswagen Group in the Audi RS6, the Porsche Cayenne, and the Lamborghini Urus, to mention a few. The McLaren Artura has a hot vee six-cylinder.

Whether it's the BMW hot vee engine, the Mercedes hot V, or the Audi “hot V turbo” engine, all of them use the same principles.

McLaren

Mercedes-AMG

Keyword: What Is A Hot Vee Engine?

Thank Ferrari And Formula 1 For The Hot Vee