Quick Guide to Car Calculations
These are very simple guides to converting data
Disclaimer: In no way am I a mechanic, an engineer, or a professional. These figures should be taken with a grain of salt. In other words, don't take my advice for granted.
According to Austin Broadhead, a way to convert crank horsepower to wheel horsepower is by simply inputting the crank number with a combination of transmission and drivetrain. A 1,000-horsepower, front-wheel-drive manual car should produce 930 to the wheels, while a 1000-hp car with all-wheel drive and an automatic should make 780 to the wheels.
FWD: an automatic, a dual-clutch, and a manual suffer from a 12%, a 9%, and a 7% drivetrain loss, respectively.
RWD: an automatic, a dual-clutch, and a manual suffer from a 17%, a 14%, and a 12% drivetrain loss, respectively.
AWD: an automatic, a dual-clutch, and a manual suffer from a 22%, a 19%, and a 17% drivetrain loss, respectively. (AWD = full-time)
4WD: an automatic, a dual-clutch, and a manual suffer from a 19%, a 16%, and a 14% drivetrain loss, respectively. (4WD = part-time)
For modern-day, turbocharged and twin-turbocharged European cars, I would ignore this advice myself since they're usually underrated in terms of advertised power, with the exception of some entry-level models. A BMW M2 CS and a previous-gen BMW M4 Competition weigh about the same and make about the "same" advertised power, but one is really faster than the other.
Dry Weight to Curb Weight / Add Fluids
Curb weight = dry weight + 50 to 200 kg (110 to 440 lb), in case manufacturer doesn't list such. This varies by engine size, however. The '50 kg' stuff is for economy cars which happen to have 3- and 4-cylinder engines; I wouldn't use that on V8s or V12s.
I would stick with 100 kg for something as medium as a twin-turbocharged V6 or a naturally aspirated V8, up to 200 kg for something as large as a twin-turbocharged V12 or the infamous W16, and around 125-175 kg for everything else in-between.
On rare occasions, manufacturers will list what is called "curb weight," but leave the fuel tank empty. This is very rare and it doesn't happen often. A few sports cars and supercars happen to be noted in this way; it was especially common in the 1980s, 1990s, and 2000s. I would add 75 to 100 kg to the listed "curb weight" in this case scenario.
US to European prices (for American cars)
This is for just in case your favorite American car isn't sold in Europe. Let's compute the conversion for a 6.2-liter sports car, worth $60,000: $60,000*(6.2/4) = €93,000.
If this were about a pony/muscle car, then I would replace the '4' with a '5': €74,400. For a truck or an SUV, I would replace that '4' or '5' with a '6': €62,200 for a 6.2-liter of this kind, worth the same $60,000 in the US.
But also, be careful with this kind of calculation because if it's either supercharged or turbocharged, you may want to add in (more of) or multiply the displacement. A 2.7-liter supercharger added to a 6.2 engine translates to an 8.9-liter engine, and a twin-turbo 6.2 is an equivalent to an N/A 9.3-to-12.4-liter engine.
Such a supercharged 6.2-liter sports car, worth $90,000 in America, would cost €200,250 in Europe. As for a muscle car, it would cost less at €160,200. These are accurate pricing figures in my opinion since I have looked up the prices inside of magazine tests as well as advertisements for imported (as well as exported) American performance cars over the last few years.
European to US prices (for European cars)
This one is kind of tricky. Germany, for example, has its own "mainstream" level BMWs and Mercedes-Benzes that it refuses to sell in the rest of the world, especially America; VW Group tends to overlap VWs, Skodas, SEATs, and lower-end Audis with each other in the European market.
The most realistic way to convert, in my opinion, would be to use only the 2.0- to 3.0-liter automobiles. For a 3.0-liter crossover worth 50,000 euros, try 50000*(3.0/3). For a 3.0-liter sedan or wagon worth the same price, try 50000*(3.0/2.5).
Supercars and grand tourers are a bit trickier, since they tend to have 4.0- to 6.0-liter engines, but nowadays some even have 3.0-liter engines. I wouldn't advise putting displacement into factor in this case. But for naturally aspirated supercars (especially past 5.0L), try multiplying by 1.125. For turbocharged cars (usually under 4.0L), try multiplying by 1.375. Most grand tourers would be OK with being multiplied or divided by 1.25 for conversion.
A 100,000-euro, 4.4-liter grand tourer is practically worth $80,000-$125,000 in the U.S. depending on the performance level and brand/model prestige.