This article is going to address theoretical racing horsepower using a simple formula. This formula for calculating HP uses the quarter mile drag strip as the basis of predicting your theoretical horsepower to produce the MPH you want to achieve within the formula, using a constant of 234 and the gross vehicle weight. The ³ in the formula is for cubed. Most quarter mile racing enthusiasts should think about what mile per hour they would like to achieve within a quarter mile. This will help with designing an engine and drive line to accomplish this goal. Theoretical horsepower is just what it states “Theoretical”. You may get different results at a real race track. Many things affect horsepower results and ET at real race tracks. This formula should get you in the correct direction to achieve the mile per hour goal set.
This formula can also be used to calculate a theoretical race before the actual race. For example your friend states his vehicle will do 100 MPH in the quarter mile. Your vehicle has achieved 110 mile per hour within a quarter mile. Both vehicles are the same year, make and model. Using the theoretical horsepower formula below and entering in MPH and weight of the vehicle allows us to calculate the theoretical horsepower needed to achieve this MPH within a quarter mile.
First locate the gross vehicle weight label on the vehicle or look this information up in a vehicle specifications resource. Most vehicle GVW labels are located on the driver’s door (B) pillar, which is the pillar that the driver’s door latch is located. The pillar where the door hinges and the windshield meets is called an “A” pillar. Once you have the GVW you must add the drivers weight. The GVW weight represents all the fluids and fuel are at correct levels. Another words the fuel tank is full.
Our case study vehicles will be two 2006 Honda Civics’, 2.0 liter i-VTEC 4, 197 factory horsepower, GVW is 4450 lb. The owners of the case study vehicle 1 claims he can achieve 100 MPH in a quarter mile. Case study vehicle two achieves 110 mile per hour in the quarter mile. Using the formula below we will solve for the needed theoretical horsepower of both vehicles:
Theoretical HP = (MPH/234)³ x Weight
Here is the calculations for vehicle number one (100MPH/234) = 0.427350427 this number cube = 0.07804632, this number multiplied by 4450 =347.306 or 347 theoretical horsepower to achieve 100 miles per hour within a quarter mile. Vehicle number two calculations (110MPH/234) = 0.47008547 this number cube =0.103879651 multiplied by 4450 = 462.2644484 or 462 theoretical horsepower. As you can see from the results it would take 115 more theoretical horsepower to have the same vehicle achieve 10 miles per hour faster in the quarter mile. If neither vehicle has been modified to achieve these theoretical horsepower numbers the possibility of achieving the mile per hours stated is low. The vehicle closes to the theoretical horsepower will have a better chance of winning the actual race.
Another formula can be found in an article, “Affects Of Altitude On Horsepower”, can be used for theoretically figuring out the horsepower losses at different elevations you may drive or race at. Remember mathematics is cheaper than purchasing expensive components or the incorrect components to get the performance results you are looking for. Our case study vehicles would need extensive performance modifications to achieve the mile per hour goals of the vehicle owners. Mathematics also teaches “Critical thinking skills”.