Bigger Engine, Faster Car? Horsepower and Vehicle Speed in Project Zomboid B42

Horsepower 101: How Engines Affect Speed and Acceleration

In Project Zomboid, every vehicle has a fixed engine horsepower (HP) stat that directly influences its performance. This “engine power” determines how fast the car can accelerate and what top speed it can reach. Think of horsepower as the car’s muscle – more HP means the vehicle can potentially move quicker and carry/tow more load. For example, a basic Franklin Valuline van with ₂₆₀ HP struggles to hit 70 mph (taking ₁₇ seconds to reach 60 mph). In contrast, its ambulance variant comes tuned with a monstrous ₄₉₀ HP engine, letting it rocket from 0–60 mph in about 4.6 seconds and push to ₈₅ mph. That’s an insane upgrade – akin to dropping a sports car V8 into a delivery van – resulting in vastly better acceleration and a higher top speed.

However, in vanilla you can’t just swap engines between vehicles. Each car’s HP is fixed by its model and not normally changeable without mods or hacking. So installing a “higher HP engine” in-game isn’t a standard feature (yet). What you can do is find a vehicle that already has a bigger engine or better performance variant. For instance, the Chevalier Nyala police cruiser boasts about 80 more HP than the civilian Nyala sedan, giving it a higher top speed and faster acceleration than the taxi version. Likewise, the Franklin Valuline ambulance mentioned above packs significantly more punch than the regular Valuline vans. Engine power also comes with a trade-off: more HP makes the vehicle louder. High-performance engines create more noise (attracting zombies) unless mitigated by a good muffler. So while a big engine helps you go faster, it also turns your car into a roaring beacon for the undead if you’re not careful.

Below is a comparison of some vehicle engine stats in Project Zomboid (Build 41/42), showing how HP varies by vehicle type and what that means in practice:

Table: Examples of vehicle engine horsepower in PZ and their relative performance. More HP generally means quicker acceleration and higher max speed, at the cost of more noise.

As the table suggests, higher horsepower usually translates to better speed. A sports car like the Cossette can outrun most vehicles thanks to its 570 HP engine, whereas an old van with 260 HP will feel sluggish. In practical terms, if you’re trying to outrun a horde on the highway, grabbing the car with the beefier engine is a smart move. The differences in 0–60 mph times and top speeds between variants (e.g. the Valuline ambulance vs. van) show how much engine upgrades matter in-game.

Build 41 vs. Build 42: What Changed in Vehicle Physics?

Project Zomboid’s Build 42 (B42) introduced some notable changes to vehicle physics and balance. The developers revamped certain mechanics under the hood (no pun intended), aiming for more realism. According to the B42 update notes, the game features “improved vehicle physics” compared to Build 41. But what does that mean for horsepower, speed, and handling?

One immediate change players noticed in B42 is how vehicles handle off-road and towing. In Build 41, driving off-road was possible (though slower than on pavement), and you could tow a disabled car albeit sluggishly. In Build 42, the simulation is less forgiving. Cars now suffer from significantly reduced traction on grass and dirt. If you leave the pavement, you’ll find your speed bleeding off to a crawl on rough terrain. Even with a powerful engine, tires spin and the vehicle struggles to maintain momentum, much like a real car bogging down in mud. Players have reported that in B42, a truck or van that could previously manage a decent clip off-road will gradually slow to a snail’s pace until it’s barely moving at all. This has been dubbed the “ArmA 2 syndrome” by the community – where touching soft ground almost feels like hitting quicksand.

Toward the end of a muddy field, even a 500 horsepower military truck can feel useless. “Vehicles driving offroad… gradually lose speed until they’re barely moving,” notes one survivor.

Towing in B42 is similarly affected. If any of the towed vehicle’s wheels are on grass or dirt, it becomes practically impossible to pull. This is a big shift from B41. For example, one player in B42 tried using a 500 HP armored APC (from a mod) to tow a tiny compact car – and could only manage about 15–20 mph even on a road, despite the huge engine and the “Speed Demon” driving perk. On grass, that setup would likely go nowhere. In short, Build 42’s physics now more heavily factor in friction and weight distribution, so raw horsepower alone won’t overcome a bad towing scenario or rough ground.

On the plus side, these changes make vehicles behave more realistically. Heavier vehicles with strong engines excel at towing on proper roads, where that torque can actually be applied. Lighter vehicles with high horsepower (like the Cossette sports car) can surprisingly tow above their weight on pavement because they have a great power-to-weight ratio – essentially acting like a makeshift tractor for short distances. One community member found the “Chevalier Cossette… is the optimal towing vehicle”, able to pull even large vehicles on-road thanks to its abundance of power and lighter frame. But take that same scenario off-road in B42 and you’re in trouble: “avoid towing other vehicles and leaving the paved roads” warns one mod overview for vehicles. The emphasis now is on using the right tool for the job – a fast car for speed on highways, a heavy truck for hauling on roads – and not expecting one super-engine to brute force every situation.

Another change from B41 to B42 is how engine load affects fuel consumption and performance. While not immediately visible to players, under-the-hood code adjustments mean things like vehicle mass, drag, and engine RPM have a more dynamic impact. (For instance, an earlier vehicle test build tweaked fuel usage to depend on engine speed, vehicle mass, and quality.) B42’s “improved physics” likely carry forward these refinements, making a fully-loaded truck guzzle more gas and accelerate slower than an empty one, even if the engine’s HP is the same. In B41 these factors existed but B42 balances them further as part of the realism pass.

In summary, Build 42 hasn’t changed the raw horsepower values of engines (your sports car didn’t magically lose or gain HP between versions), but it did change how that power translates to motion in various conditions. High horsepower will still let you go faster, but B42 introduces more situations where other factors limit you: traction, terrain, and weight now play a bigger role. You’ll feel the difference when off-roading or towing – B42 makes you respect the limits of your vehicle, much like real life. As one fan aptly put it, “Once a car touches grass in B42, horsepower doesn’t matter – it’s going to bog down”.

Testing the Limits: Community Findings in B42

Players and modders have been actively testing how far they can push vehicles in Build 42. Here are a few telling examples and experiments that illustrate the impact of engine HP and the B42 physics changes:

1. Ambulance vs. Van Drag Race: A user ran a controlled test comparing a Franklin Valuline 6-seater van (260 HP) and a Valuline ambulance (490 HP) on a straight road. The results were dramatic. The 260 HP van plodded to 60 mph in ₁₇ seconds and eventually topped out around 70 mph. Meanwhile, the ambulance’s 490 HP engine launched it to 60 mph in just ₄.6 seconds, screaming past 80 mph by the time the van hit 60. Clearly, doubling the horsepower more than doubled the performance in this case. (In fact, the ambulance accelerates almost 4× faster, showcasing how engine upgrades in PZ can vastly improve acceleration when weight and gearing aren’t limiting.)

2. Towing Torture Test: In Build 41, towing a heavy vehicle was slow but somewhat manageable on flat ground. In Build 42, players quickly discovered edge cases that break those expectations. One player with a modded LAV-300 APC (≈500 HP) attempted to tow a small compact car. Despite the APC’s immense power, the max speed hit only ₁₈ mph on a road, even with the “Speed Demon” trait giving a top speed boost. The moment they veered off onto grass, the rig almost stalled out entirely. This test showed that beyond engine power, transmission gearing and terrain friction are pivotal – the APC’s engine had the brawn, but the game’s physics in B42 capped the towing speed heavily. (Some suspect the game simulates an implicit drag or brake on the towed car, since in reality a stationary car might have its parking brake on or wheels locked, which PZ doesn’t explicitly model yet.)

3. Sports Car “Tow Truck”: In a more lighthearted experiment, some survivors found that a high-powered Chevalier Cossette (sports car) could function as an emergency tow truck on pavement. The Cossette, with ₅₇₀ HP and a sporty drivetrain, managed to pull a full-size pickup at around 30 mph in Build 41/42, which shocked the player who tried it. The “tow master 3000” as they nicknamed it, performed admirably so long as both vehicles stayed on the road. This is an in-game example of power-to-weight ratio: the Cossette’s powerful engine and relatively low weight gave it enough oomph to drag another vehicle. It’s a vivid demonstration that in PZ a car’s weight class doesn’t always tell the full story – sometimes a muscle car can out-tow a pickup if it has vastly more horsepower and the conditions are ideal. (Of course, don’t expect to tow trailers cross-country with a sports car in B42 – the next bump or patch of grass will ruin your day!)

4. Off-Road Crawl: To assess the new off-road mechanics, players took various vehicles onto grassy fields in Build 42. A common finding was that even robust trucks like the Franklin All-Terrain (470 HP, 4x4 SUV) or heavy “Step Van” (370 HP delivery truck) would gradually slow to 0 if driven across a long stretch of grass. In one case, a player tried reversing and then accelerating forward repeatedly (rocking the vehicle) just to inch across a farm field – a trick akin to what you’d do if stuck in real mud. The consensus is that B42 requires you to stick to roads or risk getting stuck; horsepower can’t save you if your tires can’t grip. This is analogous to real life where a 400 HP sports car is actually worse at driving through a muddy field than a 150 HP tractor with the right tires. 🚜

Overall, community tests confirm that engine HP still provides the raw potential for speed and acceleration, but Build 42’s physics engine introduces more nuance in how that power is applied. A bigger engine will make you faster, but only when other factors aren’t bottlenecking you. It’s a bit like having a racehorse – it can run incredibly fast, but not if you ask it to pull a plow through a swamp. As a survivor in Knox Country, you have to consider the terrain and situation: on a clear highway, floor that 500 HP engine and you’ll zoom past danger; on a muddy backroad, even those 500 horses might as well be stuck in glue.

Under the Hood: Engine Quality, Scaling, and Modding Impacts

Aside from pure horsepower numbers, there are a few subtler mechanics governing vehicle performance in Project Zomboid. One is engine condition/quality. Each engine part has a quality percentage (visible in the Mechanics UI) that affects how well it runs. Importantly, the game scales effective engine power based on quality – a worn or damaged engine won’t output full horsepower even if it’s rated for, say, 400 HP. In fact, according to players who dug into the Lua code, the game clamps engine output between about 37.5% and 100% based on quality. If your engine falls below ₃₇% condition, it will still deliver around one-third power (it won’t drop to zero, to ensure the car can limp). And if you repair an engine to 100% (or it spawns in excellent shape), you’ll get up to about 62.5% quality worth of power as a bonus factor – effectively the cap for full horsepower output. In simpler terms, an engine at 60+ quality is as good as new in performance, while an engine at 30 quality will severely underperform. This scaling hasn’t fundamentally changed in Build 42 as far as we know – but it’s an important factor when considering performance. A sports car with a busted engine won’t outrun much until you fix it up. Always check that engine condition before assuming your ride will perform as listed in the table above!

Now let’s talk modding. Build 42’s release initially broke a lot of vehicle mods due to code changes and the new experimental modding system. Mod creators had to update their mods to be B42-compatible. The good news is many popular mods quickly got patched or reworked for the new build. These mods often allow players to tinker with engine performance in ways vanilla doesn’t. For example, the Better Car Physics mod overhauls vehicle handling and even allows things like manual gear shifting. The mod’s author notes that if a car accelerates unrealistically fast with his mod, it’s likely because “some mod boosts its engine horsepower” beyond vanilla values. Better Car Physics had to be updated for Build 42 (since B42 integrated the ModOptions library and changed how some files load), but it is now fully compatible. With such a mod, one could edit the engineForce parameter of a vehicle to effectively increase its torque/horsepower output. In fact, modders on Reddit have shared that changing engineForce is the key to editing horsepower – it “will effectively modify the overall power output and change the ‘horsepower’ value in the game”. This opens the door to custom tweaks: want a supercharged family car? You could mod its engineForce (and ideally its maxSpeed setting) to give it a higher top end. Just beware that you’ll need to also account for things like braking force and tire friction, or you might create an uncontrollable rocket that can’t stop.

Another mod, Vehicle Class Overhaul (B42), takes a more balanced approach. It automatically categorizes and adjusts vehicles into three classes – Quiet (stealthy but weak off-road/towing), Strong (towing beasts, but slow and loud), and Fast (high speed and versatile). This mod explicitly boosts the horsepower of heavier vehicles so they can actually fulfill the towing role well, and ensures lighter vehicles aren’t too overpowered. One of its rules: “The heavier the vehicle, the more horsepower it will have” (statically assigned), ensuring trucks feel torquey and sports cars remain in their lane. It also reiterates the trade-off we discussed: “More horsepower == more speed == more noise”. Mods like this aim to make every vehicle type useful by leveraging or tweaking the horsepower mechanics in B42’s new physics system.

For most players, mods aren’t required – you can absolutely enjoy vehicles in vanilla B42 – but it’s good to know they exist. If you find, for instance, that towing is too underpowered or that certain vehicles feel unrealistically weak or strong, the modding community likely has a tweak available. Just remember that any mod altering vehicles will need to be updated for Build 42’s changes; always look for a “[B42]” tag or compatibility notes (as seen with Vehicle Class Overhaul [B42 Compatible] etc.).

Conclusion: Mastering Horsepower in Build 42

In Build 42, horsepower absolutely matters – a bigger engine does mean a faster, quicker car – but only within the bounds of Project Zomboid’s physics. Upgrading from a 260 HP engine to a 500 HP engine (or choosing a car that has one) can be the difference between life and death when outrunning a horde on open roads. You’ll accelerate faster, hit higher top speeds, and be able to haul more weight before slowing down. On the flip side, B42’s more realistic mechanics ensure that raw power isn’t a silver bullet. If you’re bogged down in mud or towing a bus up a hill, even the strongest engine will strain. The key is to play to your vehicle’s strengths: use high-HP sports cars for speedy getaways on highways, use heavy trucks for moving loot or towing on-road, and avoid taking any vehicle (no matter how powerful) into deep mud or dense woodland if you can help it. Keep your engine in good repair to maintain peak performance, and consider picking up the Speed Demon trait for an extra boost (it gives +15% top speed to any vehicle). Finally, don’t hesitate to try mods if you want to fine-tune the experience – the community has provided tools to tweak engine outputs, transmissions, and more to your liking.

Stay safe on the roads of Knox Country, and remember: it’s not just about the horsepower under the hood, but also how (and where) you unleash it. Floor it wisely! 🏎️💨