New engines, physics that moved, and fixes worth knowing about. Newest first.
Strong engines no longer share one 0-100 time, and the clutch no longer slips the launch away. Anyone signed in can now change the tyres, drive, weight and gearing of the car an engine sits in, and the launch timer reads the quarter mile for everyone.
The clutch is sized to the engine it carries, so a big-torque engine holds its torque and slips far less on the way up through the gears. The clutch also no longer chatters at launch.
Every class has its own tyres now, and weight moves to the rear as the car pulls away: a rear-drive car gains grip, a front-drive car loses some. The V8 7.0L Pushrod in a muscle car runs 0-100 in 4.85 s and the quarter mile in 12.68 s at 193 km/h.
Customize vehicle, under the class picker, is free with an account: tyres from eco to drag slick, front, rear or all-wheel drive, weight, final drive, close, wide or drag gearing with 4 to 10 gears (6 to 18 on a semi) or every ratio by hand, and Eco, Normal or Sport shifting on an automatic or a CVT. Changes are kept for each class in your browser, so they follow you to every engine in that class, and COMPARE ALL CLASSES shows your car beside the stock ones.
The launch timer times the quarter mile with its trap speed, and keeps the top speed of the run.
Spark-ignition piston and radial engines can now run the Atkinson cycle, radial rows can sit in line or staggered, and propellers take up to 12 blades a disc.
Atkinson closes the intake valve late, so the engine expands more than it compresses. Always runs it all the time, like a Prius engine: about 15 % less peak power on a build the builder raises to 13:1, and more on an engine left at its own compression. Light load runs it only while cruising and keeps full power at full throttle, the way Toyota and Mazda petrol cars do. A new fuel use readout in g/kWh shows the difference; compare at the same speed, not the same pedal.
Row offset sets how far round each radial row sits from the one in front. Rows in line look like the Lycoming XR-7755 or the Junkers Jumo 222, and the firing follows the geometry: a twin row of nine in line fires unevenly.
Propellers take 2 to 12 blades, and a contra-rotating pair can have a different count on the rear disc, like the An-70's 8 + 6. Turboprops can now be contra-rotating, Wankel builds can drive a propeller, and every propeller makes a blade tone.
Both engine builders now make turboprops, radials whose whole case spins like a WWI Clerget, and radials with any number of cylinders a row from 3 to 12.
A turboprop turns its propeller through a free power turbine, and a prop lever sets the propeller speed the governor holds. It shows torque, turbine temperature, gas generator speed and prop rpm, and its default is sized like a PT6A-114A: about 500 kW with the prop at 1,900 rpm. It is the first engine where you hear the propeller.
Rotating case: the crankshaft stays still and the cylinders, case and propeller spin round it, with no supercharger. Hold BLIP, or the B key, to cut the spark the way WWI pilots slowed them down.
An even number of cylinders a row fires evenly on 2, 4, 6 or 8 rows. On one row, or an odd number of rows, it cannot: one gap is longer and one shorter, so the engine lopes.
Cars, bikes and trucks can now brake. Hold BRAKE in the drive controls, HOLD BRAKE in the phone dock, or the S key, and the vehicle slows to a stop and stays there.
An automatic or a CVT stopped in D keeps idling instead of stalling, and creeps forward again once you let go.
With the auto-clutch on, a manual stops in gear without stalling too.
Both engine builders now make radials of up to 8 rows, up to 72 cylinders, and up to 3.1 L a cylinder, so a 4-row Wasp Major or a 3 L-a-cylinder Duplex Cyclone fits.
Propeller engines can turn two discs, one behind the other, spinning opposite ways. The pair adds rotating weight; there is no thrust model yet, so it shows no efficiency gain.
The fuel tank size is now a spec row on every engine, from 2 to 2,000 L. A bigger tank fills to the brim; a smaller one keeps what fits. Share links carry it.
A third gearbox for every car and bike: the CVT. It has no gears; its ratio slides, so the engine holds one speed while you speed up. A Pro pick in the Gearbox menu.
Floor it and the engine sits at its power peak: the 5.0 V8 holds 6,644 to 6,667 rpm all the way up. At 30% pedal it holds 2,350 to 2,400.
A RATIO readout, such as 1.42:1, takes the place of GEAR. The belt never slips, and the ratio spans the same range as the class's first to top gear.
It is slower off the line than the automatic: 0 to 100 km/h in 6.95 s against 6.37 on the V8, 11.04 against 9.62 on the Inline-4 2.0L.
On a bike it is a scooter's: twist and go, a centrifugal clutch that bites as the engine spins up, so it sits at exactly 0 km/h idling in drive. The V-twin does 0 to 100 in 5.73 s.
Both engine builders offer it too.
The gauges now show engine temperature. It climbs from the ambient air as the engine works and holds at 90 °C once the thermostat opens.
Every temperature on the gauges follows the metric / imperial switch: intake, exhaust, intercooler, ambient, jet T4 and the rotary's hottest face.
Switch any piston engine to methanol from its Fuel row (Pro), or build one on it. It burns more than twice the fuel and resists knock: the Inline-4 2.0L makes about 5% more power on it at the same compression, and takes 15:1 without knocking.
At 14:1 the 2.0 on methanol makes about 18% more torque than the stock petrol engine, which knocks at that compression.
Fuel use goes up about 2.1 times by volume, so a tank lasts half as long, and the exhaust runs cooler.
Switching fuel now takes the new fuel's own octane. An engine set up for 98 RON petrol no longer carries 98 onto LPG or methanol.
The builder and the AI builder offer methanol, at 10 to 16:1 compression.
Engines are drawn with the exhaust they run: a header per head, log or equal-length primaries, the crossover and muffler you picked, and smoke from the real tailpipe. Valve covers, oil pan and timing cover are ghosted, so the parts under them stay in view.
Car engines get a belt drive with a water pump and alternator, and the intake runners curve into the head.
The M-14P gathers its exhaust into two collector rings, the R-2800 into six three-into-one stacks.
Smoke comes from diesels only, darkening to charcoal near full rack.
Phones, Chromebooks and slow machines pick a lighter setting on their own: half the smoke, no valve springs. Across everyone, frames over 50 ms are about 30% rarer.
The gauges and readouts can show mph, lb·ft, psi and °F. Switch in Settings, the gear button next to mute. Visitors in the US start on imperial, everyone else on metric.
It converts road speed, torque, pressures, temperatures, fuel volume and flow, vehicle weight and jet thrust. Pressures stay absolute, so manifold pressure reads about 14.5 psi at idle.
Power stays in hp either way. Spec inputs, the builder, the tools and the engine pages stay metric.
Fit a second, wilder cam to any four-stroke piston engine from the Camshaft group and set the rpm where it takes over: the mild cam's low end below, the big cam's top end above. A chip on the gauges shows HIGH CAM or LOW CAM.
High-cam duration runs 230 to 310°, lift 5 to 18 mm, the switch 2,000 to 8,000 rpm. Fitted, it starts 48° longer than the low cam with 1.55 times the lift, switching where the two torque curves cross.
On the Inline-4 2.0L with a mild 240° low cam, switching takes peak power from 99.6 to 141.4 hp, the same peak as the big cam alone, which gives up 13% of the torque below 4,000 rpm.
Switch too late and you feel it: at 5,000 rpm the hand-over leaves a 26% hole in the torque curve.
The intake note hardens by about 5 dB when the high cam comes in, clearest on a loaded pull.
The builder's Breathing step and the AI builder fit it too.
Pick a rotary's ports from its spec panel: side ports idle smooth and quiet at 900 rpm, a bridge port lopes at 1,200, and a peripheral port idles at 2,400 with a race engine's misfiring brap. Rotaries and radials now play the new exhaust sound.
The brap is partial burns and misfires, each played quieter than a full burn. A bridge-ported two-rotor idles with 37% of its burns partial and 29% missed; a street port idles at 900 with a few.
Rotary power now matches published figures: the 13B makes 159 hp where it made 179, the 26B 693 where it made 359. The 26B no longer slips its clutch, and the single rotor no longer stalls on launch.
Lift off at full revs and a rotary used to go near silent for about three seconds. Overrun now sits just under a side-port idle.
In the builder, a Ports row on the Character step and a Port Timing section: six sliders for when the intake and exhaust ports open and close and how big each one is. The idle follows the ports you draw. A peripheral port needs at least 0.55 litres per rotor, and the builder says why. The AI builder sets ports too.
Listen in the builder now idles, revs, and plays until the engine is back at idle, so you hear the brap. It used to go straight to 60% throttle.
The M-14P plays its two collector halves, five cylinders and four; the R-2800 its six three-cylinder stacks. Radials are heard from 8 m off the right side, so the near cylinders arrive first.
Every engine now breathes through a throttle plate and an idle air valve into a manifold that takes time to fill. A little pedal gives a little power: at 5% the 5.0 V8 settles near 1,700 rpm, where it used to run to 3,400.
No rotary reaches the limiter at 15% pedal or less; before, every one did. The 26B's idle wander dropped from 112 rpm to 10.
Lift off and the engine drops back to idle sooner: the V8 in 2.9 s where it took 3.8. The Inline-4 2.0L never got back to idle before; it now does in under five seconds.
Manifold pressure at a fixed pedal falls as revs rise, as on a real engine. At quarter pedal the V8 reads 0.84 bar at 30% of redline and 0.48 at 80%, where it sat near 0.37 throughout.
Turbos spool a little quicker and flutter longer after a lift. A supercharger makes no boost at part pedal: its bypass valve opens.
Each position of a radial's throttle lever holds its own rpm against the propeller: 1,257 at 10% lever on the R-2800, 2,649 at full.
Full throttle is untouched: the change moves no engine's peak by more than 1%.
Choose pushrods, one cam per head or two, and two to five valves per cylinder, from the Camshaft group in the spec panel or the builder's Breathing step. The valves, springs, rockers, pushrods and cams are drawn, and they move with the engine.
33 four-stroke presets carry a stock head, 19 of them from the real engine's: the VR6's two cams in one head, the W18's 72 valves, the Vulture's single cam per bank.
Set the Ford 4.6 to three valves and a 6,500 redline, as Ford's three-valve engine, and it makes 302.9 hp against the published 300. Give the LS7 four valves and two cams per head and it goes from 503 to 547 hp.
On a generic engine, swapping to pushrods costs about 17% of its power.
The Detroit 6-71 draws the four exhaust valves per cylinder its uniflow scavenging runs on.
Intake runners meet the head from the side, so they no longer run through the valve gear on V, U and X engines.
Each cylinder's pulse now travels its own pipe to the tailpipe, so the note follows rpm and pipe length instead of a fixed tone. The pipes are yours to change: a cast log or headers, primary length, an H- or X-pipe, and an open, straight-through or chambered muffler.
The rows are in a new Exhaust group in the spec panel and on the builder's Breathing step. Headers need a four-stroke without a turbo; two-strokes get none.
Headers are worth 2 to 3% over a cast log, a crossover about 1% on a dual system. A chambered muffler costs 1 to 1.5% and adds 2.3 to 2.9 psi of back pressure.
At cruise an open pipe is 2 to 3 dB louder and a chambered muffler 3.5 dB quieter. An X-pipe smooths a cross-plane V8's burble. Header length changes the note; it used to make no audible difference.
Loudness holds steadier from idle to redline: within 3 dB on a four, where the old sound swung over 7.
It takes less than half the old sound's processor time, and the builder's Listen button plays it.
Cat's 550 hp truck six, built to the published 137 × 165 bore and stroke and 14.6 litres. Two people asked for a CAT; the lineup had every truck diesel bolted into a pickup. This one ships on the new Semi vehicle class: 30 tonnes, a ten-speed, a 107 km/h governor.
Measured 2,537 N·m at 1,200 rpm and 549 hp at 1,600; the rating sheet says 2,516 and 550. At the 2,100 governor it makes 601 where the sheet says 525: the same pump-curve gap the Cummins carries.
The Semi class's clutch went from 2,000 to 2,600 N·m for it. At 2,000 this engine's torque slipped the clutch for good; at 2,600 it locks, and the smaller diesels and a petrol V8 still launch.
The builder takes a sentence. Describe the engine you want and the AI builds it within the simulator's limits, shows a card of what changed, and puts it on the bench when you press Run.
Keep asking in the same conversation. Each reply says what changed, or that nothing did.
Ask past a spec limit and a change is refused with the reason; a new engine is built at the limit.
Conversations are saved and listed in the sidebar, so you can come back to a build.
The step-by-step builder is still there.
You can set the parts a tuner changes first from the spec panel: runner length and plenum volume, a camshaft by duration, lobe separation and lift, a spark advance curve, the mixture, and a carburettor in place of injection.
Beside the cam you see its overlap, the angle where the intake valve closes, and the dynamic compression ratio the knock model reads. A longer cam moves power up the rev range and gives away the bottom end.
A bigger plenum fills slower when you stab the throttle, and the dyno curve stays put. On the 5.0 V8 the manifold fills in under a fifth of a second with the stock plenum and takes over a second with the largest.
Run rich of stoichiometric for the most power. Fuel use bottoms out lean, near λ 1.1.
A carburettor meters fuel through a fixed main jet. Jet it small and the engine runs lean near redline on the road, which the dyno misses because it runs without the fuel system. A cold engine starts on the choke.
In the builder you set the intake and the cam on a new Breathing step, and the mixture and carburettor on the Fuel step.
Both F1 engines fire at 14 degrees before top dead centre at their 4,000 rpm idle and reach full advance by 6,000, so they stop knocking on a launch. The CA2006's full advance moved from 20 to 19 degrees, and all nine points of Cosworth's published curve land within 5%.
Start from nothing. Pick a shape, size it, choose the fuel, the induction and what it drives, name it, and finish on the bench with the engine running. Twelve shapes, from a single to a W16, a radial, a rotary or a turbojet.
Measured peak power and torque update on the step you are standing on, so you see what a bigger bore or a turbo buys.
A Listen button revs the draft as it stands. Add a bank and hear it.
Finish drops you on the bench with a card: the name, the spec strip, the dyno figures. The whole build sits in the URL, so you can send it to someone.
Rotaries now take a turbo or a supercharger, in the builder and from the spec panel on the bench.
The engine picker and the roster page both end with a Build-your-own card.
Compression ratio, displacement, bore and stroke, horsepower from torque, and dyno correction, each on its own page with the maths written out. Four of the five carry the roster as a reference table.
On those four, the result points at the closest engine in the lineup, one click from running it.
The Cosworth CA2006 V8 and the Renault RS25 V10, both at 19,250 rpm. Three people asked for a high-revving F1 engine. Reaching 19,250 took new friction and knock physics, and every engine now runs on them.
Against a published nine-point power curve the CA2006 lands within 2% at the peak, with eight of nine points inside 5%. The RS25 makes 902 hp against Renault's "about 900".
Friction now scales with mean piston speed, and the knock threshold rises with rpm, so a short-stroke engine revs where a long-stroke one detonates.
The spec editor now goes to 20,000 rpm, and an open-wheeler vehicle class carries downforce. The F1 cars used to run out of grip at 194 and 224 km/h in fourth. They now run out of drag at 301 and 326 in seventh.
Both presets fire at 20 degrees before top dead centre. 25 makes more top-end power and detonated on every launch.
The four-cylinder turbo diesel from the 2000s Chevrolet S10, built to its published 93 × 103 bore and stroke and 17.8:1 compression. Four people asked for a turbo four-cylinder diesel; the lineup had none.
Torque is in by 1,800 rpm and the governor ends it at 4,200. Measured 328 N·m at 1,800 and 132 hp at 3,600; the brochure says 333 and 130.
The real engine carries a 52 mm turbo. Fitted here, its wastegate runs out of travel above 3,600 rpm and boost climbs to the redline, so it ships on a 60 mm wheel. The spec panel says so.
Four presets on three new block shapes: the Bugatti Type 45 U-16 on two crankshafts, the Rolls-Royce Vulture X-24 with four banks on one crank, the Napier Sabre H-24 with two cranks phased 180°, and a Harley Evolution 1340 whose two cylinders fire 315° and 405° apart.
The Harley is the first engine here with an uneven firing order. You can hear it: 22.5 and 17.5 ms between fires at 3,000 rpm, the potato-potato idle.
The Sabre fires twelve cylinder pairs at once, one on each crank. The Type 45 runs on the alcohol-benzol the real car used and knocks at full throttle. The panel prints the margin.
Three new layout chips on the roster page: U, X and H.
Fixed: the Ford 4.6 V8 had its cylinders on the wrong exhaust pipes, so one bank went silent for a whole revolution. Start it and listen to the cross-plane burble.
A hydrodynamic torque converter with a lockup clutch and a shift scheduler, on published ratio sets: a 4L80-E for the muscle class, a ZF 8HP for the exotics, an RX-8 Sport AT for the rotaries. Pick P, R, N or D and drive.
A converter automatic never disconnects the engine, so an upshift is the oncoming clutch pulling engine speed down rather than a cut. Wide-open upshifts no longer flare into the rev limiter, and 0-100 km/h on the 5.0 V8 came down from 6.85 to 6.41 s.
The same flare was landing in the event log as ignition-off entries that never happened.
Rotaries can have one too: the RX-7 and the RX-8 both shipped automatics.
Chevrolet's 7.0-litre LS7, built to its published bore, stroke and 11.0:1 compression. Seven litres on two valves and one cam, spinning to 7,000.
The first engine here that takes a supercharger and refuses a turbo: a wastegate creeps past its knock ceiling where a blower lands on it. Real LS7 builds go the same way round.
The piston-speed lint stopped condemning engines people have built: the F20C, the Ferrari F136F and this one run past the old flat threshold.
Shrinking a quad-turbo W16 in the spec editor kept all four turbos on a fraction of the displacement. At one cylinder the collective housing was 2.4 times too wide and peak power read 31 hp where a single turbo made 64.
On a small engine the turbo assemblies no longer overlap: the spacing comes from the size of the housings themselves.
Free Roam lasted one edit, and the dyno showed numbers the car could not make. One player found both.
Touching any slider on a Free Roam engine dropped it back to the stock bounds: the QSK60 went from 60.4 to 34.4 litres on one nudge, with no warning and no undo.
The model sized injectors from displacement alone, so a boosted engine ran out of fuel under its own throttle while the dyno, which runs on unlimited fuel, showed the full curve. The YZ250 was down 65%, the Audi five 52%, the turbo six 24%. Each shaft engine now makes its dyno figure within 0.1%.
A power stroke every revolution, port timing in place of valves, and three engines to hear it on: a YZ250-geometry motocross single, a Saab 93 triple, and the Detroit Diesel 6-71.
Port timing is editable, and the spec panel shows the trapped compression ratio it produces. A two-stroke starts compressing when the exhaust port shuts, later than the bottom of the stroke.
The roster gained a cycle filter, so you can list the two-strokes on their own.
The 6-71 is the engine the Roots blower is named after, and the same blower model scavenges it.
Two narrow-angle W engines on a shared bank-geometry module: twelve cylinders in four banks, and sixteen in a quad-turbo 8.0.
The Viper's 8.4 V10, Audi's 2.5 TFSI five, Ford's 7.3 Power Stroke and the Cummins QSK60. All four are built to published geometry and land within 5% of their rated output.
A 60-litre mining engine cannot share a spec editor with a road car, so those engines get a second bounds tier: 200 mm bores, 18 cylinders, 1,200 rpm floors. The panel says Free Roam when you are in it.
The engine list is now a real index: filter by family, layout, cycle, induction and fuel, with the filter carried in the URL so a list is something you can send someone.
Each engine gets a schematic drawn from its own bore, stroke, bank angle and cylinder count.
Each card carries measured peak power and torque, re-measured on every build.
Fourteen presets are built to a real engine's published bore, stroke and compression: the 2JZ-GTE, the Hellcat 6.2, a Bullet 500, the VR6, the K20, the Viper V10. Each one now says so, and says which figures agree.
An engine that shares a layout and nothing else says that instead, so a claim means the same thing wherever you repeat it.
The sim now hands the renderer a fresh pose every frame instead of one sampled at panel rate, and extrapolates crank and propeller angles across the remainder of the fixed physics step. Idle crank jitter dropped from 6.6% to 1.1%.
Meshes share their materials instead of rebuilding them per engine, and the data panels update at 15 Hz: the numbers stay readable and the frames go to the engine.
A 500 cc Bullet thumper and a Honda GX160 utility single, with the vehicle classes they needed to have something to pull.
Pages below the landing shipped their markup without the stylesheet that styles them. On a slow connection an article sat unstyled for over ten seconds; each page now carries its own stylesheet in the head.
Fit a blower to any piston engine with the knock margin to take one. Two machines with different curves: a centrifugal builds head with tip speed squared, a Roots runs flat from off idle.
Drive power comes off brake torque, and the mesh brightens the belt with it: the one parasitic loss the simulator draws.
You can hear the difference: four lobes at 2.5:1 is a 1 kHz moan, ten vanes at 7:1 is a 7 kHz shriek. Both fall away when you lift.
The Hellcat 6.2 is the first factory-blown preset.
Your browser keeps your spec edits and restores them when you come back to the same engine. A shared link wins over a stored build, and picking a different engine starts clean.
The sweep now scales its step to hold 12 degrees of crank per substep, and waits for boost to settle before it samples. Turbo engines had been reading up to 41% under their real output through the spool.
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Fit one to any piston engine with the compression to take it. The refusal is half the feature, and it is why the turbo engines here run 8.5 to 9.5:1.
A wastegate that creeps, a blow-off valve you can hear, a surge line that rises with tip speed, and a turbine housing that glows with inlet temperature.
The whistle sweeps up through the audible window as the rotor spools, the way blade-pass frequency does.
Fitting one re-plumbs the engine: the air filter moves to the compressor mouth and a boosted V8 gets one exhaust exit instead of two.
A check listed engine types instead of asking what an engine can do, and that hid the gauges, the dyno and the P-V trace from a whole engine family.
An M-14P nine and an R-2800 eighteen, on a master-rod and link-rod linkage: each link cylinder solves its own stroke and its own compression ratio, and the spec panel shows the spread.
A reduction gear and a fixed-pitch propeller give the throttle something to work against on an engine with no gearbox.
Both run 130-octane avgas, which is why they make their rated power.
Silence on overrun, a rotor drawn to the wrong shape, and a dyno that lagged behind the engine.
One to four rotors off a 654 cc chamber, in the 13B, 20B and 26B shapes, on a 1,080-degree eccentric-shaft cycle with three chambers per rotor and no pistons.
Six more engines, and wider piston spec bounds, so the editor stops fencing you in halfway through a build.
A proper engine selection flow in place of a dropdown, and controls you can drive with a thumb.
A realism pass that shipped as one release: a live P-V trace, engineering lint in the spec editor, shareable build URLs, audio driven per fire rather than by a volume knob, and a clutch, gearbox and vehicle to load the engine.
A J85, a FADEC J85 and a JetCat P300, with wet starts, torching, a fuel cock separate from ignition, and a compressor map you can watch the engine walk across.
Piston engines solved cycle by cycle from their own geometry, three fuel types, and an event-driven audio worklet that gets its pitch from the firing rate rather than a tone generator.