| Useful Calculations |
| 1/4 Mile Data Normalization Drag strip numbers depend on atmospheric conditions. In order to be able to compare numbers from one outing to the next it is necessary to normalize the ET and MPH to standard conditions. Here are the equations to compensate for temperature and barometric. Weather Normalization ETstd = ETraw * Cet Cet = 0.9986 + 0.0095 * (Baro-29.1) - 0.0002556 * (Temp-35.0) MPHstd = MPHraw * Cmph Cmph = 1.0003525 - 0.00975 * (Baro-29.1) + 0.0002667 * (Temp-35.0) ETstd is normalized ET, ETraw is ET from time slip, Cet is the ET normalization factor, MPHstd is normalized MPH, MPHraw is MPH from time slip, Cmph is the MPH normalization factor, Temp and Baro are temperature and barometric at run time. Though Relative Humidity is not included here, these numbers are better than raw data. Altitude Normalization BHPloss = (Elevation * 0.03) * BHPsealevel / 1000, or 3%HP loss per 1,000' elevation. BHPloss = Brake HP measured at elevation, Elevation = elevation above sea level in feet, BHPsealevel = Break HP measured at sea level |
| HP calculation from 1/4 Mi Data Crank HP can be calculated from 1/4 mile trap speed and vehicle weight. CHP = (MPH / 234)^3 * Weight ET = 1357 / MPH |
| Injector Sizing & Fuel Pressure TPI fuel injectors are rated in lb/hr of steady fuel flow at 43.5psi. In an L98 engine the maximum injector duty cycle is 80%. Required injector size can be estimated from Brake HP (BHP). Assume a Brake Specific Fuel Consumption (BSFC) value of 0.50 for a TPI (the range is 0.45 to 0.50 for normally aspirated engines). Then injector size (Flow Rate) is given by: Flow Rate = (BHP * BSFC) / (8 * 0.8) Maximum fuel flow capacity can be adjusted with fuel pressure as follows: FuelFlow2 = FuelFlow1 * SQRT(Pressure2 / Pressure1). Table A shows full capacity fuel flow at various fuel pressure values. The corresponding BHP values assume BSFC=0.50 (for TPI intake) and 80% fuel injector duty cycle. Table A - Fuel Flow / BHP vs Fuel Pressure [email protected] @ 40psi @ 45psi @48psi @ 50psi @ 55psi @ 60psi Comments 19 lb/hr rated 18.1 / 232 19.2 / 246 19.8 / 254 20.3 / 259 21.2 / 272 22.2 / 284 stock LB9 22 lb/hr rated 21.0 / 268 22.2 / 285 23.0 / 294 23.5 / 300 24.6 / 315 25.7 / 329 stock L98 24 lb/hr rated 22.9 / 293 24.3 / 311 25.1 / 321 25.6 / 327 26.8 / 343 28.0 / 359 30 lb/hr rated 28.6 / 366 30.3 / 388 31.1 / 401 32.0 / 409 33.5 / 429 35.0 / 448 NOTE: Trap Speed BHP calculation for my L98 gave 295HP @48psi w/ stock 22lb/hr injectors; this correlated with dyno pulls showing a max RWHP of 247HP for a 17% drive train loss. |