Hi guys.
How is efficiency measured? I am talking race efficient.
From what I understand having two cars with same amount of HP, only difference was one car was more % efficient than the other, so obviosuly it was faster.
So pretty much all modifications that are used to get the most out of the engine's HP (stall,gear,suspension etc.)
I was reading an article about this long time ago, and I cannot find it. I'm nowhere near advanced tech, but I know some of You guys are maybe You can help explain, how can I measure car efficiency?

Thanks!

 

technically speaking, efficiency is how much hp a car makes compared to how much gas it uses. most of the other heat is lost to friction and heat of the combustion process. effciency % = energy put out / energy put in


both of those cars have the same hp rating, but efficiency doesnt tell us which one is faster. if you have 2 cars that make 100 hp, but one of the car uses twice as much gas, it doesnt matter(as far as "fast-ness" goes). they both still make 100 hp.

EDIT- and check out www.howstuffworks.com for the math side of cars, specifically the Bugatti Veyron W16.

 

You probably should separate engine efficiency from vehicle efficiencies. There's a lot that goes into each.

Engine: One way to compare is BSFC or Brake Specific Fuel Consumption, which is usually expressed as "pounds of fuel per horsepower per hour" or (lb/hp/hr). A value of .300 would be very good, and .600 wouldn't.

Example: Assume a Nextel Cup engine running flat out @ Daytona with a 425 hp plate engine. If the engine has a BSFC of .400 and the cars are averaging 180 mph, the car is getting about 6.5 miles per gallon. If the BSFC was 5% better or .380, the car would be getting 6.8 mpg. Assuming about 12 usable gallons @ Daytona, that's at least one more lap before fuel is needed.

FWIW, Cup plate engines probably have BSFCs a lot lower than this example.

Another comparison on plate engines might be BSAC or "Brake Specific Air Consumption". If we assume that the restricter plates are identical, and allow only so much airflow, the engine getting the most flywheel HP has the best BSAC. That's not quite true, but it's fairly accurate, I believe.

Vehicle efficiencies. The most obvious is driveline efficiency. The difference between a 12% loss of power from engine to the wheels and a 7% loss is huge for closely contested racing. Every 1% on a Cup plate car is about 4+ HP. 5% is over 20 HP, which is a lot on a plate engine.

I suspect that a lot of design/testing/development goes on in Cup drivelines. Perhaps even little things like smaller contact areas on rear gears because of the low hp on plate engines. Coatings like DLC and the superfinishing that preceeds that may be used. It is probably safe to assume that this kind of thing is used in most series where the money to do it is available.