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
| Flow@43.5psi |
40
psi |
45
psi |
48
psi |
50
psi |
55
psi |
60
psi |
Comments |
| 19
lb/hr |
18.1
/ 232
|
19.2
/ 246
|
19.8
/ 254
|
20.3
/ 259
|
21.2
/ 272
|
22.2
/ 284
|
stock
LB9 |
| 22
lb/hr |
21.0
/ 268
|
22.2
/ 285
|
23.0
/ 294
|
23.5
/ 300
|
24.6
/ 315
|
25.7
/ 329
|
stock
L98 |
| 24
lb/hr |
22.9
/ 293
|
24.3
/ 311
|
25.1
/ 321
|
25.6
/ 327
|
26.8
/ 343
|
28.0
/ 359
|
Ford
SVO |
| 30
lb/hr |
28.6
/ 366 |
30.3
/ 388 |
31.1
/ 401 |
32.0
/ 409 |
33.5
/ 429 |
35.0
/ 448 |
Non-OEM |
|